Citation
Hydrology of Green Swamp area in Central Florida ( FGS: Report of investigations 42 )

Material Information

Title:
Hydrology of Green Swamp area in Central Florida ( FGS: Report of investigations 42 )
Series Title:
( FGS: Report of investigations 42 )
Creator:
Pride, R. W
Meyer, F W
Cherry, R. N ( Rodney N. ), 1928-
Geological Survey (U.S.)
Place of Publication:
Tallahassee
Publisher:
Florida Geological Survey
Publication Date:
Language:
English
Physical Description:
xi, 137 p. : ill. ; 23 cm.

Subjects

Subjects / Keywords:
Hydrology -- Florida -- Green Swamp ( lcsh )
Swamps -- Florida ( lcsh )
Green Swamp ( flgeo )
Central Florida ( flgeo )
Swamps ( jstor )
Creeks ( jstor )
Rain ( jstor )

Notes

Bibliography:
Bibliography : p. 131-134.
Statement of Responsibility:
by R. W. Pride, F. W. Meyer, and R. N. Cherry, prepared by the United States Geological Survey in cooperation with the Florida Geological Survey, the Florida Division of Water Resources and Conservation, and the Southwest Florida Water Management District

Record Information

Source Institution:
University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier:
030429617 ( aleph )
03536171 ( oclc )
AES0060 ( notis )

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Full Text





FLORIDA STATE BOARD

OF

CONSERVATION






HAYDON BURNS
Governor


TOM ADAMS
Secretary of State




BROWARD WILLIAMS
Treasurer




FLOYD T. CHRISTIAN
Superintendent of Public Instruction


EARL FAIRCLOTH
Attorney General




FRED O. DICKINSON, JR.
Comptroller




DOYLE CONNER
Commissioner of Agriculture


W. RANDOLPH HODGES
Director






LETTER OF TRANSMITTAL


lorida geological Survey

tCaLlahassee

February 4, 1966

Honorable Haydon Burns, Chairman
Florida State Board of Conservation
Tallahassee, Florida


Dear Governor Burns:
For many years, it has been thought that much of the recharge
of water to Florida's prolific artesian aquifer occurred in the Green
Swamp area. For this reason, it was believed that a detailed geo-
logic and hydrologic study of the area would be helpful and neces-
sary. I am pleased to report to you that a study, "Hydrology of
Green Swamp Area in Central Florida," prepared by R. W. Pride,
F. W. Meyer, and R. N. Cherry, of the U. S. Geological Survey, in
cooperation with the Division of Geology of the State Board of
Conservation, will be published as Florida Geological Survey Re-
port of Investigations No. 42.
This report provides all of the data necessary for the wise utili-
zation, and perhaps for the preservation, of parts of the Green
Swamp area. It will also assist in the planning for the Four-
Rivers area to alleviate floods and to conserve our water and land.

Respectfully yours,
Robert O. Vernon
Director and State Gcologist





















































Completed manuscript received
September 9, 1965

Published for the Florida Geological Survey
By the E. O. Painter Printing Company
DeLand, Florida

iv







CONTENTS

Preface -_.---_ ... ------------.-...-..--..._--..-----..-.. ..- ---- XI
Abstract ______ 1
Introduction -----.........--..__-_ -__-____-_-___---- 3
Purpose and scope ........---- ____ .._--- ------ ---- 4
Previous investigations -----------___ ----.-- ..__ -----4 4
Methods of investigation _----------------- --------- 5
Geography _........_.--------...------.. --- 19
Location ---__ ---------_-----_--...--.---_------. ------ --- 19
Topography __.-_...----------------- ----------- 20
Drainage ___-. ..------------------------.------...-------- --_--__ 21
Culture and development ---.........-----_----.......--- 22
Climate -_.. ... .. .. ....._______-------------------------- 23
Precipitation -__ ---_____ ---_-----_--------.--- 23
Temperature _------------ 24
Environmental factors affecting the quality of water ----.--- ------ 26
Geology _.----_----_-__-______ ------------------.------ ____ -------_---- 27
Formations --__--- ..------ ___---------------- 28
Undifferentiated plastic deposits .-----.------.-----------_ ------28
Undifferentiated clay ___---------------------------------- --. 30
Suwannee Limestone .---._------- -.---_.____-- 30
Ocala Group ..--------... ......--------------- 31
Crystal River Formation -----------------.--_---_-.--- 31
Williston Formation ------------------------ -- ---_ 31
Inglis Formation __...-.------------__ _--.--- 31
Avon Park Limestone _....---------- ---------.. ------- .. 31
Structure .. ----_...- ----- -........ .... --_ 32
Hydrology ....- _____ --------___----- -------- -- -- 33
Withlacoochee River basin ......--------___---.--.--- 33
Description of basin -- ----------------------- ------- 33
Streamflow ----...-----__ ...-- ------------------- 35
Chemical characteristics of surface water __------------------------- 41
Oklawaha River basin .--_----------- -----.----------- 44
Description of basin ---------------- _-------------------------------__ -- 44-
Streamflow _____--- ------ 47
Chemical characteristics of surface water _------------ ---- 49
Hillsborough River basin ____ ------------- 49
Relation to Green Swamp area 49
Streamflow -----------52
Chemical characteristics of surface water ---52
Kissimmee River basin 53
Relation to Green Swamp area --_____ ---- -_-_-..---------- 53
Streamflow -- -------------- 53
Chemical characteristics of surface water ------ 54
Peace River basin ---------------55
Relation to Green Swamp area ---- -- 55
Streamflow --------- -- 56
Diversions and interconnections of basins ----- --56
Effects of man-made changes ---------- 53






Ground-water accretions to streamflow in Horse and
Pony Creek basins _.. --- -....----__ .._ ....... ..------------------. ---.. 61
Aquifers ---........ -- -----------_. .--------- ...........----------- ..----. 64
Nonartesian aquifer .-__ ........--------------------- -- 69
Description of the aquifer ..--.. .. .-...........---- ---- -----------. --.... ---. 69
Recharge and discharge ....-------...-.-------------------. 69
Hydraulics of the nonartesian aquifer ------.. ........-.------------. 76
Chemical characteristics of nonartesian ground water ------- 78
Secondary artesian aquifer .....------.-....- ------------.. -- 78
Relation to Green Swamp area ..........-----.--------------- 78
Floridan aquifer ....-............... ----------- ------ 79
Description of the aquifer ----...---------------------------- 79
Recharge and discharge .---------------------------- 79
Hydraulics of the Floridan aquifer ................----.--------------. 82
Chemical quality of water in the Floridan aquifer ..----....--...---- 87
Hydrochemistry of the Floridan aquifer in central Florida .---. 89
Analysis of the hydrologic system .. .--.-..------ -------.---.- --------. 92
Rainfall, runoff, and water loss --...-..---- ----.. -. -----------------------.. 92
Water-budget studies .......----------------------.--.--------- 99
Evaporation and water budget of Lake Helene ...---....--...-.-----------.. 101
Comparison of eastern and western basins ...-... .... .--------- ----.. 105
Outflow from Green Swamp area ....................------------- .---. 109
Evaluation of proposed plan of water control __...----.--.--- ------ ----. 119
Reduction of flood peaks in the Hillsborough River ....--.....-...---------... 119
Reduction of flood peaks in the Withlacoochee River ...........---------.. 122
Effect of water impoundment in Green Swamp Reservoir on
ground-water levels ....------...---.- ------------------------------- 125
Effect of water impoundment in Southeastern Conservation
Area on ground-water levels ...... ..... ..--------------------- 126
Significance of the hydrology of the area .--....------ -- ..--------- 127
References -. -----------------------------------..---. 131
Glossary ------- -.------------------- --------- ----- 134



ILLUSTRATIONS

Figure Page
1 Ma.p of Florida showing location of Green Swamp area ------ -- 3
1 Map showing data-collection points in Green Swamp area .. In pocket
3 Diagram showing the well-numbering system used in Florida ..----. 6
4 Map showing topography of central Florida and its relation to
Green Swamp area -- ------ -------- In pocket
5 Map showing surface-water drainage features of Green Swamp
area ___-- --- In pocket
6 Graphs showing annual and mean monthly rainfall of Green
Swamp area ----- _.. 25
7 Relation of annual water loss to temperature in humid areas _..- 26
8 Generalized geologic cross sections along lines A-A', B-B' and
C-C' _--- ----- ---- --- In pocket
9 Map showing contours on top of the Avon Park Limestone __ In pocket
10 Flow-duration curves for Withlacoochee River basin, 1931-62 -..----. 37






11 Map showing results of low-flow investigation of Withlacoochee
River, May 23-25, 1961 -...-.- ..- ... --..-.--- .... ----.--------- In pocket
12 Graphs showing annual and mean monthly discharge of With-
lacoochee River at Trilby ._-.. -_.-____ ...-..-...... ...--------. ---------- 40
13 Relation of mineral content to discharge at gaging stations in
Withlacoochee River basin ..--..- ----..-..-....-------------------- 42
14 Flow diagram of the upper Oklawaha River ___--------.__.------------. 45
15 Flow-duration curve for Big Creek near Clermont, 1931-62 .--..-..-----. 50
16 Relation of mineral content to discharge at gaging stations in
upper Palatlakaha Creek basin .........---...............------- -------------.......51
17 Relation of mineral content to discharge, Hillsborough River
near Zephyrhills ---..---.._. ............--- -- --------.-----------------------. 53
18 Relation of mineral content to discharge, Horse Creek at Davenport 54
19 Double-mass curves of measured runoff versus computed run-
off, Withlacoochee River and Palatlakaha Creek basins .--.------- --60
20 Graphs of monthly rainfall and runoff for July 1960 to June
1962 and estimated base flows for November 1960 to June 1962,
Horse Creek at Davenport _____ ... --. ......-- ...-..-----.. --------------- 62
21 Graphs of monthly rainfall and runoff for uly 1960 to June 1962
and estimated base flows for November 1960 to June 1962,
Pony Creek near Polk City .-...---.-.---....----...----.---- ---------- 63
22 Flow-duration curves for Horse Creek at Davenport and Pony
Creek near Polk City, 1960-62 ------..........---......------.....---...---....-.----. 66
23 Hydrographs of long-term records of ground-water levels near
the Green Swamp area --...-----.................-------....------....--- In pocket
24 Hydrographs of water levels and rainfall at wells in the Green
Swamp' area, 1959 --...----. ---..-.....-------------..... --..-.....--- .------- 71
25 Hydrographs of water levels in wells (805-155-1, 2, and 3)
near Lakeland .............__.--------------------........-------.. --- In pocket
26 Hydrographs of water levels in wells (808-155-1, 2) 4 miles
north of Lakeland and in a well (815-157-2) 12 miles north
of Lakeland _-...---..... .....------ --___ ...---........------ --------- 72
27 Hydrographs of water levels in wells (810-144-1, 2; 813-149-1,
2; 813-150-2; 814-143-1, 2; 815-149-3) in south-central Green
Swamp and in wells (815-134-1, 2; 815-139-2, 3) about 9 miles
north of Haines City ..............----..----..... _.. ....-----..... .....-----.. 73
28 Hydrographs of water levels in wells (821-202-3; 822-149-1, 2;
832-154-1, 2) in north-central Green Swamp; in a well (826-
211-1) 5 miles north of Dade City; in wells (822-138-1, 2) 17
miles north of Haines City; and in a well (833-137-2) 7 miles
east of Clermont ..------. --____. -----__.. __ ___ --___ -__--- ... 74
29 Hydrographs of water levels in wells 810-144-1, 2 and of Lake
Lowery and Lake Mattie .......----....-.....- ---------.... .. ..__ .. ... 75
30 Graphical determination of specific yield --_ ---_.-..---- 77
31 Map of Green Swamp area showing depths to the top of the
Floridan aquifer .------ ..--.... .----- --------.--..-....... In pocket
32 Map of Green Swamp area showing the limestone formations
that comprise the top of the Floridan aquifer and contours on
its upper surface .----- ----------------------................. In pocket
33 Map of Florida showing contours on the piezometric surface of
the Floridan aquifer, 1961 ---...................-----------------...... .. In pocket






34 Map showing major surface drainage areas and their ground-
water contributing areas in the Floridan aquifer ........_--_ In pocket
35 Map of the Green Swamp area showing contours on the piezo-
metric surface of the Floridan aquifer during a wet period, No-
vember 1959 -- -- .....___-------_ _.._ ___ In pocket
36 Map of the Green Swamp area showing contours on the piezo-
metric surface of the Floridan aquifer during a dry period,
May 1962 -____- -_------ --...-.-- ----. ... In pocket
37 Map showing decline in piezometric surface of the Floridan
aquifer, November 1959 to May 1962 -__---_ -----......------...... --.......... In pocket
38 Graphs showing the relations between coefficient of transmissi-
bility and depth of penetration in the Floridan aquifer _-__..... .. 84
39 Graphs of pumping test at a well (814-139-5) about 9 miles
north of Haines City ------------------------- -------- -----...-..... 86
40 Map showing environment affecting pumping test at a well
(814-139-5) about 9 miles north of Haines City -.--------___ .... 87
41 Hardness of water in the Floridan aquifer in Green Swamp area --- 88
42 Iron content of water in the Floridan aquifer in Green Swamp
area ___- -__-----.---.--..... -- -------...--....... --.--.....-....-- 89
43 Map of central Florida showing the percentage of calcium
carbonate saturation of water in the Floridan aquifer ---......---......... -91
44 Vertical distribution of chloride content of water in wells
across central Florida ..--. ..------........ .---.... ----.........----.-.......-----. 93
45 Map of central Florida showing mineral content of water in
the Floridan aquifer -_-...--............-- -------........... ... .. ... .... 94
46 Relation of effective annual rainfall and annual water loss,
Withlacoochee River at Trilby, 1931-61 .--------------------_ ...----..... 96
47 Relation of effective annual rainfall and annual runoff, With-
lacoochee River at Trilby, 1931-61 ................---- ... ---------------------. 97
48 Relation of effective annual rainfall and annual water loss,
Palatlakaha Creek above Mascotte, 1946-61 .........-----.-----....- ----._ --. 98
49 Relation of effective annual rainfall and annual runoff, Palat-
lakaha Creek above Mascotte, 1946-61 ___.---___--...-_---..-....---.-.. 99
50 Map of Lake Helene showing depth contours and locations of
data-collection equipment ------- ---------- ------- --...-........... 103
51 Hydrograph of daily stage for Lake Helene, 1961-62 --.-..........-........... 104
52 Hydrographs of streamflow from eastern and western basins in
Green Swamp area, 1959-61 __------------------ --.................... In pocket
53 Sketch showing analysis of a flow section -__-----...---------... -- .....-_. 114
54 Map showing plan of proposed improvements in Green Swamp
area in Four Rivers basins ---------_____ ------------..................... In pocket
55 Hydrographs of mean daily discharge for three Hillsborough
River gaging stations, flood of March 1960 ----------------------.......-.......... 120
56 Hydrographs of computed mean daily stage of Hillsborough
River at 22nd Street, Tampa, flood of March 1960 ---.----- --------........... 121
57 Relation between basin runoff and drainage area for Withla-
coochee River, March 16 to April 20, 1960 ..___.-- ---------------------........... 123
58 Relation between peak discharge and drainage area for Withla-
coochee River, flood of March 1960 ---- .----------------------------.-----......... 124






TABLES
Table Page
1 Surface-water data-collection points in Green Swamp area
and vicinity ... _..... _.........._...------.......------ ........... .. ----_. 7--------7
2 Ground-water data-collection points in Green Swamp area and
vicinity ...--.... .. ......-- ....... --------- -- ...........---....---..... 12
3 Test-well data in Green Swamp area and vicinity ----. --------_ 16
4 Geologic formations and their water-bearing characteristics
in Green Swamp area and vicinity ---- -------- -- ------ 29
5 Streamflow data for Withlacoochee River basin gaging stations
in Green Swamp area .-............-- .......-..... .....--- --- --------------- 36
6 Streamflow data for Palatlakaha Creek basin gaging stations
in Green Swamp area ...............------..... __-------------------..----. 48
7 Monthly water budgets for Horse Creek and Pony Creek
basins, 1960-62 .--. .------------------___ -- 65
8 Hydrologic analyses of disturbed sand samples from a test hole
in Lake Parker near Lakeland --.._-....- -------------.......... ------ 67
9 Hydrologic analyses of core samples from a well (805-154-8)
near Lakeland -----. _---------- __ ------------- 68
10 Pumping test data (Floridan aquifer) ------------------------- 83
11 Estimates of transmissibility ____ ----------------- --------- 85
12 Monthly water budget for Lake Helene near Polk City, 1962 ------ 106
13 Ground-water outflow from the Floridan aquifer for eastern
and western basins _------------------- ___---- 110
14 Comparison of budget factors for eastern and western basins ------ 111
15 Surface-water outflow from Green Swamp area, July 1958
to June 1962 ___.---------------__.-----------. 112
16 Ground-water outflow from the Polk piezometric high in Green
Swamp area _--- ------------------------- 116
17 Ground-water outflow from Green Swamp area ------ _----------_ 117
18 Summary of water-budget factors in Green Swamp area, 1959-
61 ... ------------.-. ...... .--------.- 118







PREFACE


This report was prepared by the Water Resources Division of
the U. S. Geological Survey in Cooperation with the Florida
Geological Survey, the Florida Division of Water Resources and
Conservation, and the Southwest Florida Water Management
District.
The authors wish to express their appreciation for the
cooperation of the many residents and public officials for
information given during the well inventory and reconnaissance
of the area. Special acknowledgement is due the Florida State
Road Department, the Florida Forest Service, and property owners
who granted permission to drill test wells. The following agencies
made financial contributions for the collecting of data used in this
report: Hillsborough County, Marion County, Pasco County, Polk
County, Sumter County, Lake Apopka Recreation and Water
Conservation Control Authority, Oklawaha Basin Recreation and
Water Conservation and Control Authority, and Tsala Apopka
Basin Recreation and Water Conservation Control Authority.
The calcium carbonate equilibrium study of ground water of
central Florida was based on data collected and analysed in
cooperation with William Back, Geologist, Water Resources
Division, Arlington, Virginia, as part of an investigation of ground
water along the Atlantic seaboard. Contributions to the knowledge
of the geohydrology in the Withlacoochee-Hillsborough overflow
area were made by Z. S. Altschuler, Geologist, Geologic Division,
Washington, D. C. Assistance in the interpretation of electric and
drillers' logs was rendered by C. R. Sproul, Geologist, Florida
Geological Survey.
The work on this project was done under the supervision of
the Florida Water Resources Division Council comprised of A. O.
Patterson, district engineer of the Branch of Surface Water, M. I.
Rorabaugh, succeeded by C. S. Conover, district engineers of the
Branch of Ground Water, and J. W. Geurin, district chemist,
succeeded by K. A. MacKichan, district engineer, of the Branch of
Quality of Water.








HYDROLOGY OF GREEN SWAMP AREA IN
CENTRAL FLORIDA
By
R. W. Pride, F. W. Meyer, and R. N. Cherry


ABSTRACT

Green Swamp is an area of about 870 square miles of swampy
flatlands and sandy ridges near the center of the Florida Peninsula.
The elevation of the land surface ranges from about 200 feet above
mean sea level in the eastern part to about 75 feet in the western
part. The Withlacoochee River drains two-thirds of the area. The
Little Withlacoochee River, the headwaters of the Oklawaha River,
the Hillsborough River, the headwaters of the Kissimmee River,
and the headwaters of Peace River drain the remaining area. The
surface is mantled with a varying thickness of sand and clay which
comprises the nonartesian aquifer. Porous marine limestones
comprising the Floridan aquifer underlie and drain the subsurface.
The Floridan aquifer crops out in the western part of the area and
occurs at depths ranging from 50 to more than 200 feet in the
eastern part. The mineral content of both surface and ground
water does not impair the usability of the water for most purposes.
However, surface water is generally highly colored and acidic, and
ground water is hard and generally contains objectionable amounts
of iron.
Hydrologic data were collected during the period, July 1, 1958,
to June 30, 1962, for making quantitative and qualitative analyses
of the hydrologic budget and for determining the significance of
the hydrology of the Green Swamp area with respect to central
Florida.
Extremely high and unusually low annual rainfalls were
recorded during the period of investigation. The factors of the
water budget for each of the 3 complete years of record, 1959-1961,
show that average rainfall on the area ranged from 70.9 to 34.7
inches; surface runoff ranged from 31.1 to 2.3 inches; ground-water
outflow ranged from 1.8 to 2.2 inches; and water derived from
change in storage ranged from insignificant amounts in 1959 and
1960 to about 4.3 inches in 1961. Evapotranspiration losses, which
were the residuals in the water-budget equation, ranged from 39.1






FLORIDA GEOLOGICAL SURVEY


to 34.5 inches. Surface runoff varied through a wide range from
wet to dry years, while ground-water outflow varied little. The
data show that the annual losses by evapotranspiration varied
little from wet to dry years. Evaporation losses from Lake Helene
amounted to 53.1 inches during 1962.
Comparison of water-budget factors for the eastern and western
parts of the area shows that higher rates of ground-water recharge
to the Floridan aquifer occur in the eastern part.
The amount of annual runoff from the total area has not
significantly changed in recent years. However, the distribution
of the runoff has been changed by drainage canals that divert
some of the flow from the upper Oklawaha River into the
Withlacoochee River.
Impoundment of water in Green Swamp would provide some
flood protection for the lower Hillsborough River and the lower
Withlacoochee River basins. Impoundment of the total discharge
from Green Swamp to the Hillsborough River during the March
1960 flood would have reduced the flood crest at 22nd Street, Tampa,
by about 1 foot. Impoundment of the March 1960 flood discharge
in reservoirs proposed for the Green Swamp area (Corps of
Engineers, 1961) would have reduced the flood crest of the
Withlacoochee River at the Trilby gaging station by about 4 feet
and at the Croom gaging station by about 1.7 feet.
Impoundment of water in Green Swamp Reservoir would have
little effect on ground-water outflow from the total Green Swamp
area because of increased seepage rates beneath the levee, increased
evaporation losses, and because the aquifer under present conditions
is essentially full. Impoundment of water in the Southeastern
Conservation Area (Johnson, 1961) would increase the seepage
rates during dry periods by about 60 percent. Impoundment of
water will become more significant relative to ground-water
recharge as pumpage from the Floridan aquifer increases.
High piezometric levels in the southeastern part of the Green
Swamp area are caused partly by a relatively slow rate of
ground-water outflow due to sand-filled fractures, caverns, and
sinkholes in the Floridan aquifer.
Mineral content and calcium carbonate saturation studies show
that generally the water in the Floridan aquifer in central Florida
is low in mineral content and undersaturated.
Interpretation of quantitative and qualitative data indicate
that recharge to the Floridan aquifer in the Green Swamp area is
about the same as that in other parts of central Florida.






REPORT OF INVESTIGATIONS NO. 42


INTRODUCTION

To satisfy the demands of a rapidly increasing population, many
acres of land in Florida are converted each year to residential and
industrial uses. Urbanization of these areas and the demand for
increasing the food supply thus require that man search for new
areas to develop for agricultural uses. This search, in many
instances, has led to the development of marginal lands.
The Green Swamp area, shown in figure 1, in central Florida
is an area where man is developing agricultural land from marginal
land. The present efforts for its development are similar to the
early efforts for developing the Everglades in that many miles of
canals and ditches have been constructed to improve the drainage.


.Figure 1. Map of Florida showing location of Green Swamp area.





FLORIDA GEOLOGICAL SURVEY


PURPOSE AND SCOPE

Lest the early mistakes of the Everglades be repeated, the
Florida Division of Water Resources and Conservation considered
that an appraisal of the physical and hydrologic features of the
Green Swamp area was needed for future guidance in planning
water-resource policy. Lack of factual hydrologic information has
contributed to the controversy on whether the area should be
utilized for flood control and water conservation or for agriculture.
This investigation provides factual information on the hydrology
of the area for determining the feasibility of either choice of
utilization.
The hydrology of the Green Swamp area was investigated by
the U. S. Geological Survey in cooperation with the Florida
Geological Survey, the Florida Division of Water Resources and
Conservation, and the Southwest Florida Water Management
District. The investigation covered a 4-year period beginning July
1, 1958. A Comprehensive Report on Four River Basins, Florida,
was prepared by the Corps of Engineers in 1961.
The following factual data, used to appraise the hydrologic
significance of the area, were collected during the investigation;
the amount of rainfall on the area; the pattern of surface-water
drainage; the effects of improved drainage channels and man-made
diversions; the amount and direction of surface-water runoff; the
amount and direction of ground-water outflow; the amount of
evaporation losses from an open water surface; the interrelationship
of rainfall, surface water, and ground water; and the chemical and
physical characteristics of water in relation to the hydrologic
environment.
A comprehensive appraisal of the hydrology of the Green
Swamp area and its significance to central Florida have been made
on the basis of the findings of this investigation. The report does
not recommend any plan of development or utilization of the water
resources of the area. An appraisal was made, however, of the
hydrologic effectiveness of a plan of water control and water
conservation proposed by the U. S. Corps of Engineers (1961).

PREVIOUS INVESTIGATIONS

Only cursory investigations of the water resources and geology
of the Green Swamp area were made prior to this investigation.
Few long-term records of streamflow, ground-water levels, and






REPORT OF INVESTIGATIONS NO. 42


chemical quality had been collected in the vicinity as part of the
statewide data-collection programs.
Many of the physical and hydrologic features of the area are
,iven in an interim report by Pride, Meyer, and Cherry (1961).
General descriptions of the geology of the region have been
,iven by Cooke (1945), Vernon (1951), White (1958), and Stewart
:1959). Stringfield (1936) defined and described the principal
artesian aquifer of Florida.
Analyses of water from surface and ground sources in the
vicinity of the Green Swamp area are given in reports by Collins
and Howard (1928) and Black and Brown (1951).


METHODS OF INVESTIGATION

Most of the data for the investigation were collected during
the 4-year period from July 1958 to June 1962 and covered a wide
range of hydrologic conditions.
The investigation of the water resources of the Green Swamp
area involves studies of water in three main physical environments:
(1) precipitation, which occurs as rainfall; (2) surface water, which
occurs on the surface of the ground; and (3) ground water, which
occurs beneath the surface of the ground.
Waters in these environments are interrelated. Thus, it was
necessary to study the whole process or system, rather than any
part, to understand and to evaluate the water resources of the area.
The methods of studying water in each environment are
different. Some characteristics of water in the three environments
may be measured directly; some may be evaluated by analysis of
representative samples from which results may be inferred; and
some characteristics and quantities must be determined indirectly.
For instance, the chemical characteristics of the water at a
particular place can be used as an indication of the environment
through which the water has passed. The surface materials in the
Green Swamp area are relatively insoluble and the surface waters
are therefore low in mineral content. The rock below the surface
materials is relatively soluble and the contained water is
considerably more mineralized. Mineralized streamflow in areas
such as the Green Swamp, where industrial and municipal disposals
into streams are minor, indicates ground-water inflow into streams.
Therefore, the chemistry of the water can be used as a tool to give
more complete evaluation of the hydrology of the area.





6 FLORIDA GEOLOGICAL SURVEY

Daily records of rainfall were collected at 24 stations located as
shown in the figures on pages 2 and 5. Some of these records
are from U. S. Weather Bureau long-term stations. Short-term
rainfall records were collected at stream or well data-collection
stations during part of the investigation using standard 8-inch
gages with tipping-bucket attachments to the water-stage
recorders.
Surface-water characteristics of the area were determined by
collecting stage, streamflow, and chemical-quality data at gaging
stations and at miscellaneous sites; by making field and aerial
reconnaissance of the area; and by studying maps and aerial
photographs.
All surface-water data-collection stations are presented in table
1 and located in figure 2 and in the figure on page 5. The grid
coordinate number shown in column 2 of table 1 is based on the


Figure 3. Diagram showing the well-numbering system used in Florida.








REPORT OF INVESTIGATIONS NO. 42 7


TABLE 1. Surface-water data-collection points in Green Swamp area and
vicinity.

Type of record: A, Standard chemical analysis; D, Discharge and stage;
E, Evaporation; K, Conductivity; S. Stage.

Frequency of record: d, Daily; p, periodic (monthly to bimonthly
intervals); r, Continuous; w. Weekly; (9), Total number of analyses of
samples or measurements of streamflow.


Grid co-
Station ordinate
No. on No. on
fig. 5 fig. 2


2



3



4

5



6

7



8


9


10

11


12


13


14


15


807-140


815-140



826-144



826-144

825-147



827-145

828-147



829-144


832-145


836-146

835-149


837-151


832-187

834-135


843-141


Location
(in downstream order)


ST. JOHNS RIVER BASIN
Lake Lowery near Haines
City

Green Swamp Run near
Loughman


Big Creek near Clermont



Bear Branch near Clermont

Little Creek at Cooper's
Ranch near Clermont


Little Creek near Clermont

Lake Glona Outlet near
Clermont


Lake Louisa near Clermont


Lake Minnehaha at Clermont


Lake Apshawa near Minneola

Palatlakaha Creek at Cherry
Lake Outlet near Groveland

Palatlakaha Creek near
Mascotte

Johns Lake at Oakland

Lake Apopka at Winter
Garden

Apopka-Beauclair Canal
near Astatula


Drainage
area
sq. mi.


33


68



1.9


10


15


8.4


Type and
frequency
of record


Sd
A(3)
Dr

A(1)
Dp (27)
Dr
A(11)
Dp(27)
A(1)

Dr
A(3)
Dp(34)
A(6)

Dp(8)
Dd

Sd
A(1)
Sr
A(2)
Sw


Dr


Dr

Sw


Sr


Dr


Period of record


June 1960 to June
1962
1959-62

March 1961 to June
1962
1959
1945-47. 1952-56
July 1958 to June
1962
1956-61
1958-61
1960

June 1960 to June
1962
1959-61
1945-60
1956-59

1959-60
April 1961 to June
1962

March 1957 to June
1962
1959

June 1945 to June
1962
1956, 1961
April 1953 to June
1962

March 1957 to June
1962

May 1945 to March
1956
September 1959 to
June 1962

September 1942 to
June 1962

July 1958 to June
1962










FLORIDA GEOLOGICAL SURVEY


TABLE 1. (Continued)


24


25

26






28


29


30







31

32


802-139


806-142



804-143


805-144


801-142

804-145


803-144


801-144


802-153


801-154




811-209

810-211

808-209


Grid co-
Station ordinate
No. on No. on
fig. 5 fig. 2



16 829-132

17 823-131

1 815-132


19 810-135




20 806-131


Lake Marion near Haines
City

PEACE RIVER BASIN

Lake Hamilton at Lake
Hamilton

Gum Lake marsh outlet at
Lake Alfred


Lake Rochelle near Lake
Alfred

Lake Alfred at Lake Alfred


Lake Otis at Winter Haven

Lake Mariana near
Auburndale

Lake Hartridge at Winter
Haven

Lake Howard at Winter
Haven

Lake Parker at Lakeland

Crystal Lake at Lakeland

HILLSBOROUGH RIVER
BASIN

Hillsborough River at State
Highway 39

Crystal Springs near
Zephyrhils
Blackwater Creek near
Knights


Drainage
area
sq. mi.






30.3





22.8


Location
(in downstream order)


KISSIMMEE RIVER BASIN

Lake Butler at Windermere

Cypress Creek near Vineland

Reedy Creek near Loughman


Horse Creek at Davenport


Type and
frequency
of record Period of record




Sw, Sd January 1933 to June
1962

Dr August 1945 to June
1962

Dr October 1939 to
September 1959
A (1) 1959

Dr June 1960 to June
1962
A (10) 1959-61
Kr July to November
1960

Sd February 1958 to
June 1962



Sw June 1945 to June
1962

Dd October 1960 to June
1962
A(2) 1960, 1961

Sd March 1946 to June
1962
Sd March 1961 to June
1962

Sr August 1954 to June
1962

Sw February 1946 to
June 1962

Sw February 1946 to
June 1962

Sr April 1945 to June
1962
Sw, Sr 1949-54, July 1954 to
June 1962
Sr, Sp 1951-52, 1954-57
A(1) 1959




A(1) 1959


Dp (227) 1933-62
A(3) 1959
Dr January 1951 to
June 1962








REPORT OF INVESTIGATIONS NO. 42 9


TABLE 1. (Continued)


Grid co-
Station ordinate Drainage Type and
No. on No. on Location area frequency
fig. 5 fig. 2 (in downstream order) sq. mi. of record Period of record


808-214





809-142

807-147

804-147


815-146

818-148

821-149


810-148




815-148




809-148

810-149
818-155
819-155

819-200


818-203


818-203

816-205


817-206 Withlacoochee River near
Richland


Dd
A(55)


Hillsborough River near
Zephyrhills


WITHLACOOCHEE
RIVER BASIN

Swamp at Holiday Manor
near Haines City
Lake Juliana near Polk City

Lake Mattie near Polk City


Swamp near Polk City

Withlacoochee River at Van
Fleet Road, near Eva
Withlacoochee River near Eva


Lake Helene near Polk City




Pony Creek near Polk City




Little Lake Agnes near
Polk City
Lake Agnes at Polk City
Grass Creek near Rock R:dge
Withlacoochee River near
Rock Ridge
Withlacoochee River near
Cumpressco

Withlacoochee River upstream
from Gator Creek

Gator Creek at mouth

Withlacoochee-Hillsborough
overflow near Richland


November 1939 to
June 1962
1956-62




1959
December 1961 to
June 1962
June 1960 to
December 1961
1960-62
1959

1959
July 1958 to June
1962
1958-61
April 1961 to
December 1962
December 1961 to
December 1962
1962
June 1960 to June
1962
1960-61
July to November
1960

1959
1961-62
1959

1959


1961


1961

1961

1930-31
July 1958 to June
1962
1959-60


A(1)
Sd

Sd, Sw
A(3)
A(1),

A (1)

Dr

A(14)
Sr
Er
A(2)
Dr
A(9)
Kr


A(1)
Sp
A(1)

A(1)

D(2),
A(1)

D(2),
A(1)
D(2),
A(1)

Dd
Dp, Dr

A(4)

D(2),
A 2)


1959-61







10 FLORIDA GEOLOGICAL SURVEY

TABLE 1. (Continued)


Grid co-
Station ordinate
No. on No. on
fir- 5 fig. 2

40 821-207



41 822-211


824-209


826-209


826-201

827-203

821-202

S 828-208

828-209

42 828-210


829-154
829-158

829-200


Location
(in downstream order)

Withlacoochee R'ver near
Dade City


Pasco Packing Co. canal
at Dade City

Hamilton Lake Outlet near
Dade City

Withlacoochee River near
Lacoochee

Gator Hole Slough near
Bay Lake
Gator Hole Slough near
Clay Sink
Swamp near Cumpressco
Weaver Hole Slough at
Lacoochee
Withlacoochee River at
Lacoochee

Withlacoochee River at
Trilby


Bay Lake near Bay Lake
Bayroot Slough near Bay
Lake
Little Withlacoochee River


near Clay Sink
43 834-209 Little Withlacoochee River
at Rerdell


44 835-213 Withlacoochee River at
Croom


Drainage
area
sq. mi.


390


Type and
frequency
of record


Dd.Dp
(29)
A(12)

Dp(48)
A(5)

D (2),
A(1)

D(2),
A(4)

A(1)

A(1)
A(1)

A(1)

A(1)

Dr
A(9)

A(1)

A(1)

A(2)

Dr

A(9)

Dr

A(8)


Period of record



1930-33; 1958-62
1958-61

1957-62
1959-61


1961


1959-61

1959

1959
1959

1959

1959

1928-29; February
1930 to June 1962
1959-61

1959

1959

1959

July 1958 to June
1962
1959-61

October 1939 to
June 1962
1959-61


well-numbering system shown in figure
and stage at 24 sites and of stage of 20
near the area of investigation.


3. Records of streamflow
lakes were collected in or


Information on the quality of surface water was obtained during
high, intermediate, and low flows to determine the general chemical

characteristics and the extremes in quality characteristics during
the period of study. These data were supplemented with a series of
reconnaissances over the entire area generally within a period of






REPORT OF INVESTIGATIONS NO. 42


1 to 3 days. The data were used to determine the quality of water
prevalent in the area at a given time and to help determine the
interrelations between surface water and ground water.
Ground-water characteristics were determined by collecting
data concerning water levels, surface and subsurface geology, and
water chemistry from an inventory of existing wells in the Green
Swamp area and vicinity (fig. 2). Information on the depth of the
well, the amount of casing, and the depth to static water level was
recorded for more than 600 wells. Most of the inventoried wells
penetrated the Floridan aquifer. The approximate elevation of land
surface above mean sea level was determined at each well by use
of either altimeter, topographic maps, or spirit level. These data
were supplemented by selected data collected prior to this
investigation and by test drilling to provide better coverage of
the area.
The well-numbering system that is derived from latitude and
longitude coordinates is based on a state-wide grid of 1-minute
parallels of latitude and 1-minute meridians of longitude, shown in
figure 3.
Instruments were used to record continuously the water-level
fluctuations in the various aquifers. These data were supplemented
by periodic determinations of water levels and chemical character-
istics of water in selected wells in order to evaluate areas of
recharge and discharge for the aquifers.
The wells in which continuous and selected periodic water-level
data, and quality-of-water data were collected, are presented in
table 2.
During the periods October to December 1959 and May to June
1962, water-level measurements were made to prepare piezometric
maps which show the direction of water movement in the Floridan
aquifer. Hydraulic gradients scaled from these maps were used to
infer rates of water movement.
To obtain general information on the occurrence of artesian
and nonartesian ground water in the Green Swamp area, 26 test
wells were drilled at 16 different sites. At 9 of these sites a pair
of wells were drilled (one into the Floridan aquifer and one into
the nonartesian aquifer). A summary of test-well data is presented
in table 3. During the drilling, samples of rock cuttings were
collected. The lithology of the various formations and significant
changes in water levels were recordered in the well log.
Examination of rock cuttings of selected wells were supplemented






12 FLORIDA GEOLOGICAL SURVEY


TABLE 2. Ground-water data-collection points in Green Swamp area and
vicinity.

Well number: See figure 3 for explanation of well-numbering system.
County: He, Hernando; Hi, Hillsborough; La, Lake; Or, Orange; Pa,
Pasco; Po, Polk; Su, Sumter.
Aquifer (s) : F, Floridan; H, secondary artesian; N, nonartesian.
Type and frequency of record: A, standard chemical analysis; B, spectro-
graphic analysis; K, partial chemical analysis; S, water level; T, tritium
determination; (3) number of analyses; p, periodic; r, continuous.


Type and
frequency
Well number i County Aquifer of record Period of record

800-153-1 Po F, H Sp December 1954 to May 1962
801-207-1 Hi F A(1) May 1962
802-135-1 Po F Sp November 1957 to February 1960
802-157-12 Po F A(l) March 1962
803-147-4 Po F A (1) March 1962
803-204-1 Hi F Sp May 1958 to May 1962
804-207-1 Hi F Sp November 1956 to May 1962
805-155-1 Po N Sr August 1955 to February 1960
Sp February 1960 to June 1962
805-155-2 Po F Sr March 1956 to February 1960
Sp February 1960 to June 1962
A (1) November 1959
805-155-3 Po H Sr February 1956 to February 1960
Sp February 1960 to June 1962
806-137-6 Po F A (1) March 1962
806-140-2 Po F A(1) November 1959
806-135-3 Po F Sp July 1954 to February 1960
806-156-1 i Po N Sp August 1955 to June 1962
806-156-2 Po F Sp January 1956 to June 1962
807-202-1 Po F A(1) November 1959
808-139-1 Po N A(1) February 1962
808-143-1 Po F A (1) February 1962
808-147-1 Po F A(1) February 1962
808-153-1 Po F Sp January 1958 to May 1962
A (1) November 1959
808-155-1 Po F Sp June 1955 to March 1956
Sr March 1956 to June 1962
A (1) November 1959
808-155-2 Po N Sp June 1955 to June 1962
809-154-4 Po F A(1) February 1962
809-158-1 Po H A(1) February 1962
810-136-1 Po F Sr 1946 to June 1962
(P-44)







REPORT OF INVESTIGATIONS No. 42 13


TABLE 2. (Continued)


Type and
frequency
Well number County Aquifer of record Period of record


810-136-2 Po N Sr 1948 to June 1962
(P-47)
810-144-1 Po F Sp July 1959 to October 1960
Sr October 1960 to June 1962
A(21), July 1959 to April 1962
K(5),
T(4),
B(4)

810-144-2 Po N Sr October 1960 to June 1962
A(3), July 1959 to November 1961
K(2)

810-149-1 Po F A(2) November 1959 to March 1962
810-149-2 Po F Sp January 1955 to May 1962
810-151-2 Po F Sp February 1960 to May 1962
810-207-1 Pa F Sp June 1960 to May 1962
813-147-1 Po F A(1) February 1962
813-149-1 Po F Sr March 1959 to June 1962
A(6) April 1959 to March 1962

813-149-2 Po N Sr April 1959 to June 1962
813-150-2 Po N Sr October 1960 to June 1962
813-201-1 Po F Sp August 1959 to June 1962
A(2) November 1959 to March 1962

814-143-1 Po F Sr October 1960 to June 1962
814-143-2 Po N Sr October 1960 to June 1962
814-148-1 Po F Sp October 1955 to July 1957
Sr July 1957 to April 1959

814-210-1 Pa F A(1) March 1962
814-210-2 Pa F A(1) March 1962
815-134-1 Po F Sp August 1960 to October 1960
Sr October 1960 to June 1962
A(1) March 1962

815-134-2 Po N Sp August 1960 to October 1960
Sr October 1960 to June 1962

815-139-1 Po F A(1) June 1959
815-139-2 Po F Sp August 1960 to October 1960
Sr October 1960 to June 1962

815-139-3 Po N Sr October 1960 to June 1962
815-149-3 Po F Sp July 1960 to November 1960
Sr November 1960 to June 1962
A(1) April 1961
815-157-2 Po F Sp March 1956 to May 1958
Sr May 1958 to June 1962
A (1) November 1959

815-203-1 Po F A(1) February 1962
816-202-1 Po F A(2) May 1951 to-March 1962
816-202-2 Po F A(1) May 1961







14 FLORIDA GEOLOGICAL SURVEY


TABLE 2. (Continued)



Type and
frequency
Well number County Aquifer of record Period of record


816-206-1 Pa F Sp July 1959 to June 1962
A(2) November 1959 to March 1962
816-211-1 Pa F Sp 1936 to August 1951
Sr August 1951 to March 1962

817-149-1 Po F A(1) February 1962
817-150-1 Po F Sp July 1959 to June 1962
818-155-3 Po F A(1) November 1959

818-156-2 Po F A(1) February 1962
818-209-1 Pa F Sp October 1959 to June 1962
818-209-2 Pa F A (1) February 1962
819-140-1 Po F Sp May 1959 to June 1962
A(1) May 1959

849-147-1 Po F A (1) November 1959
819-151-1 Po F Sp October 1955 to June 1962
819-211-2 Pa F Sp December 1959 to June 1962
821-158-2 Su F Sp October 1959 to June 1962
821-202-1 Su F A(1) May 1959
821-202-3 Su F Sr March 1959 to June 1962
A(2) May 1959 to November 1959
821-207-1 Pa F October 1959 to June 1962
821-203-2 Pa F A(1) February 1962
821-210-1 Pa F A(1) November 1959
821-211-1 Pa F A(1) March 1962
822-138-1 Or F Sr February 1959 to June 1962
A(1) March 1962

822-138-2 Or N Sr April 1959 to June 1962
822-149-1 La F Sr February 1959 to March 1962
A(8) April 1959 to March 1962

822-149-2 La N Sr April 1959 to June 1962
822-149-3 La F A(1) February 1962
822-210-1 Pa F Sp October 1959 to June 1962
822-211-1 Pa F A(1) February 1959
824-142-1 La F Sp December 1959 to June 1962
824-206-1 Pa F Sp November 1958 to June 1962
824-211-1 Pa F Sp December 1959 to June 1962
824-211-2 Pa F A(1) February 1962
825-151-1 La F Sp Ocober 1959 to June 1962
826-208-1 Pa F Sp November 1958 to June 1962
826-211-1 Pa F Sp October 1959 to February 1960
Sr February 1960 to June 1962







REPORT OF INVESTIGATIONS NO. 42 15


TABLE 2. (Continued)



Type and
frequency
Well number County Aquifer of record Period of record

827-144-1 La F A(1) February 1962
827-149-1 Po N A(1) February 1962
827-154-1 La N A(1) February 1962
827-158-1 Su F Sp July 1959 to June 1962
A(1) July 1959
827-210-1 Pa F Sp 1936-50 (U.S. Corps of Engineers)
Sp October 1959.to July 1961
827-210-2 Pa F Sp August 1961 to June 1962
828-154-1 La F Sp November 1959 to June 1962
828-203-1 He F A(2) July 1959 to November 1959
828-204-1 Pa N A(1) February 1962
828-209-1 Pa F A(1) February 1962
829-146-2 La F Sp October 1959 to June 1962
829-202-1 Su F Sp December 1959 to June 1962
829-206-1 He F Sp May 1959 to June 1962
A(3) May 1959 to November 1959
830-157-1 Su F Sp May 1959 to June 1962
A (3) May 1959 to November 1959
820-210-2 He F A(1) November 1959
832-154-1 La F Sr February 1959 to June 1962
A(9) April 1959 to March 1962
832-154-2 La N Sr February 1959 to June 1962
832-154-3 La N A(3) May 1959 to November 1959
832-204-1 Su F A (1) February 1962
833-137-2 Or F Sr March 1960 to June 1962
833-144-1 La F Sp November 1959 to June 1962
833-144-2 La F A(1) March 1962
833-151-1 La F Sp November 1959 to June 1962
833-151-5 La F A(1) March 1962
833-209-1 He F A(1) February 1962
834-159-1 Su F Sp November 1959 to June 1962
836-202-1 Su F A (1) March 1962
836-202-2 Su F A(1) February 1962
836-208-2 Su F A (1) February 1962
838-159-2 Su F A (1) November 1959
841-156-1 La F Sp March 1961 to June 1962













TABLE 8 Test-well data in Green Swamp area and vicinity
(Aquifer: F, Floridan; N, Nonartesian)

Casing Open hole
Total depth
below land Depth below Range
surface Diameter land surface Diameter in depth
Well number Date drilled (feet) (inches) (feet) (inches) (feet) Aquifer Remarks

Lake County

822-149-1 February 1950 95 0 50 5% 50- 95 F
July 1959 192 6 100 5/ 05-192 F Deepened for geologic control.
Added easing.
822-149.2 February 1959 28 0 18 65% 18. 23 N Gravel packed (limestone pebbles).
882-154.1 February 1950 78 53 G63- 73 F
July 1959 100 0 63 2 78-160 F Deepened for geologic control.
882.154.2 February 1959 22 0 10 5% 16- 22 N Gravel packed (limestone peebles).

Orange County

822-188.1 February 1959 114 6 108 5% 103-114 F
October 1960 818 5% 114-818 F Deepened for geologic control.
822-188-2 February.1959 80 6 1 1 5 8- 80 N Gravel packed (limestone pebbles).

Pasco County

816-206-1 July 1959 200 8 41 2%/ 41-200 F





TABLE 3. (Continued)

Casing Open hole
Total depth
below land Depth below Range
surface Diameter land surface Diameter in depth
Well number Date drilled (feet) (inches) (feet) (ihches) (feet) Aquifer Remarks

Polk County


810-144-1 July 1959 249 6 101 51/ 101-249 F
October 1960 425 5% 249-425 F Deepened for geologic control.
810-144-2 October 1960 9 6 6 5% N Finished with 8-foot section of no.
10 slot steel screen
818-149-1 February 1959 90 6 78 51 78- 90 F
July 1959 217 5 90-217 F Deepened for geologic control.

818-149-2 February 1950 27 6 20 5% 20. 27 N Gravel packed (limestone pebbles).
818-150-1 July 1960 205 6 100 5% 100-205 F
818-150-2 July 1960 28 6 17 5% 17- 28 N
818-201-1 July 1959 255 8 40 2% 40-255 F
814-148-1 July 1960 285 6 80 5% 80-285 F
814-148-2 August 1960 18 6 15 5% 15- 18 N
815-184-1 August 1960 250 6 85 5% 83-250 F
815-184-2 August 1960 82 6 29 5%1 .... N Finished with 8-foot section of no.
10 slot steel screen

815-189-2 August 1960 458 6 858 5% 858-458 F
815-189-8 August 1960 02 6 89 5%1 N Finished with 8-foot section of no.
10 slot steel screen.

815-157-2 July 1959 168 8 52 2% 110-168 F Existing U. S. Geological Survey
well deepened for geologic control.


0


0







0
~Z
rj

z
P3


















TABLE 3. (Continued)

Casing Open hole
To'l depth
below land Depth below Range
surface Diameter land surface D'nm-"tr in depth
Well number Date drilled (feet) (inches) (feet) (.nch-a) (feet) Aquifer Remarks

Sumter County

821-158-1 July 1050 53 3 53 21/. 0 F Chert at 58 feet impenetrable. Well
destroyed.
821-158-2 July 1959 40 3 49 21/ 0 F Chert at 49 feet impenetrable. Uot-
tom of casing blasted open for
use as observation well.
821-202-8 February 1959 20 6 20 5/ 20- 29 F
July 1959 148 2% 20-143 F Deepened for geologic control.
821-202-4 February 1959 12 6 5 5% 5- 12 F Gravel packed (limestone pebbles).
827-158-1 July 1059 175 3 09 2% 99-175 F





REPORT OF INVESTIGATIONS No. 42


by interpretation of electric and gamma-ray logs of some wells and
geologists' and drillers' logs of wells which are on file with the
Florida Geological Survey.

GEOGRAPHY

One of the most prominent topographic features in the central
part of the Florida Peninsula is Green Swamp which is an
extensive area of flatland and swampland at a relatively high
elevation. Five major drainage systems originate in or near the
Green Swamp area and flow in several directions to the sea. The
area contains the headwaters of the Oklawaha River, which flows
generally northward to become the largest tributary of the St.
Johns River; the Kissimmee and Peace Rivers that flow southward;
the Hillsborough River that flows southwestward; and the Withla-
coochee River that flows northwestward.

LOCATION

The Green Swamp area is in central Florida (see fig. 1) west
of and adjacent to a high sandy ridge that forms the major axis
of the peninsula. For this study the boundaries of the area were
established arbitrarily and the Green Swamp area should not be
confused with a small drainage basin that is generally known as
Green Swamp Run in the headwaters of the Big Creek watershed
in southern Lake County and northeastern Polk County. The
boundaries of the Green Swamp area, as designated for this
investigation, have been extended to encompass a much larger
area. The project area includes the southern parts of Lake and
Sumter counties, the northern part of Polk County, and the
eastern parts of Pasco and Hernando counties (see fig. 2).
The eastern boundary of the Green Swamp area is U. S.
Highway 27, from Clermont south-southeastward to Haines City.
The southern and southwestern boundaries of the area generally
coincide with the divides separating drainage northward to the
Big Creek and Withlacoochee River basins from drainage south-
ward to the Peace and Hillsborough River basins. These boundaries
follow a meandering line westward from Haines City to a point
two miles north of Lakeland and then northwestward to Dade City.
The western boundary of the area is U. S. Highway 301 northward
from Dade City to St. Catherine. The northern boundary extends
from St. Catherine eastward along the Little Withlacoochee River





FLORIDA GEOLOGICAL SURVEY


basin divide to State Highway 50 and along State Highway 50
eastward to Clermont. The boundaries described enclose an area
of 870 square miles.



TOPOGRAPHY

The Green Swamp area is in the Central Highlands topographic
region as defined by Cooke (1945). The area is bordered on the
eastern side by the Lake Wales Ridge, on the southern side by the
northern termini of the Winter Haven and Lakeland Ridges, and
on the western side by the Brooksville Ridge (White, 1958, pp.
9-11). Figure 4 shows the locations of these ridges.
Although the area is designated the Green Swamp, it is not a
continuous expanse of swamp but is a composite of many swamps
that are distributed fairly uniformly within the area. Interspersed
among the swamps are low ridges, hills, and flatlands. Several
large and many small lakes of sinkhole origin rim the southeastern
and northeastern parts of the area. The elevation of the land
surface ranges from about 200 feet above mean sea level (msl)
in the eastern part to about 75 feet in the river valleys in the
western part.
Prominent topographic features affecting the drainage of the
eastern part of the area are the alternating low ridges and swales
that trend generally north-northwestward from the southern
boundary to the Polk-Lake County line. The ridges parallel the
major axis of the Florida Peninsula and their configuration suggests
that they were formed by subsidence and erosion along fractures
and joints. Aerial photographs of the area between U. S. Highway
27 and the Seaboard Air Line Railroad show five of these long
narrow ridges with intervening swales.
In the western part of the Green Swamp area there is little
evidence of the elongated ridges, and the main land-surface features
are large swamps, flatlands, and rolling hills. There are many
small swamps in patches and strips generally less than half a mile
wide. Most of these swamps support good growths of cypress
trees while in the uplands pine and scrub oak trees grow
abundantly. The largest continuous. expanse of swampland lies
within the valley of the Withlacoochee River and is more than a
mile wide at places. Limestone is exposed in the western part of
the Green Swamp area.





REPORT OF INVESTIGATIONS NO. 42


DRAINAGE

The drainage system of the Green Swamp area and vicinity is
shown on the map in figure 5. The headwaters of four stream
systems within the Green Swamp area, listed in order of their
proportion of the area drained, are: Withlacoochee River, Little
Withlacoochee River, Oklawaha River, and Hillsborough River.
Other streams that head near the boundaries of the Green Swamp
area are: Reedy, Davenport, and Horse creeks in the Kissimmee
River basin; Peace Creek drainage canal and Saddle Creek in the
Peace River basin; Fox Branch in the Hillsborough River basin;
and Jumper Creek Canal and a major canal that head northwest
of Mascotte in the Withlacoochee River basin. Of the total area
of 870 square miles, 710 square miles are drained by the
Withlacoochee River and its tributaries.
The surface drainage of the Green Swamp area is poor because
of the flat topography and lack of well developed stream channels.
Following heavy rainfall, water stands in large shallow sheets over
much of the area.
Boundaries of the elongated north-south drainage basins, in
the eastern part of the Green Swamp area, are formed by low
ridges. The valleys between the ridges are not deeply incised but
their effectiveness as drainage channels has been improved by
many miles of canals and ditches. Some parallel drainage basins
are interconnected in several places by gaps or saddles through
the ridges. Through these gaps water may flow at times from one
stream valley into another. The amount and direction of flow
depend on the relative elevation of water levels in the adjoining
basins and the hydraulic conveyance of the connecting channels.
The canals and ditches, for the most part, have been dug to
follow the natural drainage courses through the shallow swamps.
However, in some places, probably to provide firm footing for the
excavation equipment and to avoid clearing through the dense
growth of cypress trees, the ditches have been dug along the edges
of the large swamps rather than through the interior. Also, to
provide better alignment in some places, the ditches have been cut
through ridges to connect the adjacent swamps. These shortcuts
have bypassed the circuitous natural drainage routes and have
straightened and shortened the courses of the waterways.
Surface drainage from most of the Green Swamp area is
generally toward the north and west. However, the headwaters of
the Peace River basin originate along the southern boundaries of





FLORIDA GEOLOGICAL SURVEY


the area and the flow is generally southward. Along the eastern
boundary of the area, drainage is toward the east and southeast
into the Kissimmee River basin. Other drainage from the Green
Swamp area is toward the southwest into the Hillsborough River
via a natural channel in eastern Pasco County.
The subsurface drainage of the Green Swamp area is generally
poor. Ground-water levels in the interior of the area remain near
the surface most of the time, consequently the aquifers provide
little opportunity to store water from heavy rainfall. Ground-water
levels fluctuate through a greater range in the ridges that form the
eastern, southern, and western boundaries. The wide range of
fluctuation indicates better subsurface drainage and greater storage
capacity along the boundaries than in the interior.
Subsurface drainage is through both the Floridan and the
nonartesian aquifers but most is via the Floridan aquifer. Water
percolates downward from the overlying nonartesian aquifer to the
Floridan aquifer or enters exposed portions of the Floridan aquifer.
Movement of ground water in the Floridan aquifer is generally
outward in all directions from the southeastern part of the area.
However, the areas contributing to the aquifer (p. 80) show that
the predominant directions of ground-water movement are east and
west. The ground-water divides in the aquifer shift slightly in
response to demands in each contributing area. Most of the surface
area that potentially would contribute recharge to the Floridan
aquifer in Green Swamp lies within the Withlacoochee River basin.
The distribution of ground-water outflow originating in each
surface basin is shown in the tables on pages 116 and 117.

CULTURE AND DEVELOPMENT

The Green Swamp area is sparsely populated except for a few
small towns and communities on the ridges along the border and
along State Highway 33.
Most of the land is in large tracts owned by private individuals
or corporations. The only large tract of public land in the area is
the Withlacoochee State Forest, part of which is within the
boundaries of the Green Swamp area in Sumter, Hernando, and
Pasco counties.
The principal industry is agriculture. Much of the upland area
has been cleared and planted in citrus groves. Other upland areas
have been cleared and are used for cattle raising. Very little of
the land is cultivated. The low swampland is unsuitable for






REPORT OF INVESTIGATIONS NO. 42


agriculture because of poor drainage. In spite of the many miles of
ditches, drainage is still inadequate. Even in the cleared areas that
are suitable for agriculture, few attempts have been made to
reclaim the many small, round, cypress swamps that dot the area.
Cypress lumbering was once an important industry in the
western part of the area, particularly in the Withlacoochee River
Swamp where there were extensive stands of trees. The first access
roads to penetrate the interior of the swamp were trails and tram
roads built for cypress lumbering. Timber and pulpwood are now
produced from the pine flatwoods interspersed among the swamps.
There is some development of the mineral resources of the area
for the commercial market. Extensive phosphate deposits in Polk
County lie just south of the Green Swamp area. Some phosphate
is mined within the area but the amount is only a small percentage
of that produced in southern Polk and eastern Hillsborough
counties. Limerock, used in road construction and agriculture, is
mined in the northwestern part of the area. Deposits of sand,
suitable for building uses, are mined in many places in the eastern
part of the area.

CLIMATE

The location of the Green Swamp area, well south in the
Temperate Zone, and its proximity to large bodies of warm water
produce a warm humid climate. Precipitation and temperature, the
principal climatic elements that influence the hydrology of the
Green Swamp area, are described separately.

PRECIPITATION

The study of precipitation in central Florida can be restricted
to rainfall only, because snow and hail are virtually unknown. The
normal or long-term average annual rainfall of the Green Swamp
area is 52.7 inches. This normal is computed by the Thiessen
method of weighting long-term rainfall records at each of the
following U. S. Weather Bureau stations in or near the project area:
Clermont 6 miles south, Lake Alfred Experiment Station, Lakeland,
and St. Leo (figs. 2 and 5).
The average rainfall for the station at St. Leo, west of the area,
is slightly higher than that for the other three stations which are
located farther inland. The average rainfall at the four stations
ranges from a minimum of 50.1 inches at the Clermont station to





FLORIDA GEOLOGICAL SURVEY


a maximum of 56.4 inches at the St. Leo station. In view of the
small deviation of these extreme values from the mean, the
weighted average rainfall of 52.7 inches for the area of
investigation appears to be reasonably accurate.
The amount of rainfall on the area varies seasonally. About
60 percent of the annual total rainfall occurs during the wet season
from June through September. In the spring and early summer,
local thunderstorms of high intensity and short duration sweep
over the area. Showers occur almost daily, or perhaps several times
a day, during June and July. Heavier and more prolonged rainfalls
occur generally in August and September and are often intensified
by tropical storms that occasionally reach hurricane proportions.
On the other hand, there are periods of a month or more with little
or no rainfall. Periods of below average rainfall usually occur
during the winter season from November to February.
During wet years the annual rainfall is about twice that of dry
years. The annual and the mean monthly rainfalls for the years
1931-1961 are shown by bar graphs in figure 6. The maximum
annual rainfall during this 31-year period was 70.9 inches in 1959
and the minimum was 34.7 inches in 1961. Both occurred during the
period of the investigation. It is a fortunate circumstance that the
full range of hydrologic conditions was experienced during the
investigation.


TEMPERATURE

A knowledge of temperature variations in central Florida is
pertinent to a study of its water resources because of the dominant
influence of temperature on rates of water losses by evaporation
and transpiration.
The mean monthly temperature in the Green Swamp area ranges
from 610 F. for January to 82' F. for August. The lowest
temperature recorded during the 69-year period of record at the
Clermont station was 180 F. and the highest was 104 F. Daily
temperatures recorded at the U. S. Weather Bureau stations show
that all parts of the area have essentially the same temperature,
ranging no more than 2 to 30 F.
Killing frosts occur infrequently in this area, and damage to
vegetation, although severe from the standpoint of agriculture,
seldom is great enough to affect the hydrologic factors pertinent
to water supplies.








REPORT OF INVESTIGATIONS NO. 42


tr) Lr 0 L r) ~
-n n 0 Un 0 -
CALENDAR YEAR
CALENDAR YEAR


Rainfall of Green Swamp area
computed from U. S. Weather
Bureau records at four stations,
weighted by Thiessen method
as follows:

Station Percentage
Clermont 6S 37
Lake Alfred Exp. Sta. 22
Lakeland II
St. Leo 30
100


Based on records 1931-61

IJ FI I I IMI JIJ J AIS O N D
MONTH
Figure 6. Graphs showing annual and mean monthly rainfall of Green Swamp
area.

Water loss from a drainage basin is the difference between the
average rainfall over the basin and the runoff from the basin for a
given period (Williams, 1940, p. 3). In humid regions, where there
is sufficient water to satisfy the demands of vegetation, the mean
annual water loss is principally a function of temperature
(Langbein, 1949, p. 7). The relation between mean annual


9

8




6




4

3
9- --






FLORIDA GEOLOGICAL SURVEY


temperature and mean annual water loss under such conditions
is shown in figure 7, which is taken from U. S. Geological Survey
Circular 52. For the Green Swamp area where the mean annual
temperature is 72' F., the annual water loss would be 48 inches
according to this figure.

ENVIRONMENTAL FACTORS AFFECTING THE
QUALITY OF WATER

The quality of water in the Green Swamp area reflects the
solubility of the material which the water contacts and its biologic
environment, both of which are natural influences. Surface water
is usually lower in mineral content than ground water because of
low solubility of materials on the surface of the ground and short
time of contact of water with the materials.
The quality of the surface water (lakes, streams, and swamps)
depends mostly on the composition of the precipitation and the


10 20


30 40


50 E0


Natural water loss, in inches
Figure 7. Relation of annual water loss to temperature in humid areas.


80




70

u-
o

0 60

0.
E
50
a5



40




30
30


Polatlakaho Creek above Mascotte
I I I /
Withlacoochee River at Trilby-.













SComputed annual water loss
at two gaging stations in
Green Swamp area.

(After Longbein, W. B., and
others, 1949)
______ _____ I






REPORT OF INVESTIGATIONS NO. 42


biologic environment. Generally, the mineral content of water in
streams varies inversely with discharge. Surface waters are
usually highly colored and acidic. Sodium and chloride, although
in very low concentrations, are the principal dissolved mineral
constituents and may be present as a result of wind and rain-borne
salts from the ocean.
The quality of ground water in the Green Swamp area generally
meets the requirements for most municipal, industrial, domestic,
and agricultural uses. Ground water of lowest mineral content
occurs along the eastern and western boundaries of the area and
is lowest near the lakes. Ground water of highest mineral content
occurs in the central part of the Green Swamp. The principal
dissolved mineral constituents are calcium and bicarbonate which
are products of limestone solution. Relatively high concentrations
of calcium in the water cause hardness which is probably the most
objectionable characteristic of the ground water in the Green
Swamp area.

GEOLOGY'

Topographically, the surface of the Green Swamp area
resembles a basin, or trough, opening to the north. However,
geologically, the Green Swamp is part of an eroded, faulted
anticline. The oldest formations are exposed along the axis of the
anticline and eroded remnants of younger formations rim the flanks
and present a basin-like feature.
The Green Swamp area is underlain by several hundred feet of
limestone and dolomite that have been periodically exposed to
solution-weathering and erosion. The surface is mantled with a
varying thickness of plastic material (sand and clay) that was
deposited in fluctuating shallow seas. No attempt has been made
to differentiate the formations within the plastic material because
of its complexity and the lack of data.
The upper part of the elastic sediments, composed of clayey
sands, forms a distinct hydrologic unit, commonly referred to as
the nonartesian aquifer. The basal portion of the plastic sediments,
composed mostly of clay and some interbedded limestone
(secondary artesian aquifer), is less permeable than the overlying,

1The classification and nomenclature of the rock units conform to the usage
of the Florida Geological Survey and also with those of the U. S. Geological
Survey, except for the Fort Preston Formation (?), the Tampa Formation,
and the Ocala Group and its subdivisions.





FLORIDA GEOLOGICAL SURVEY


clayey sands or the underlying porous limestone. The solution-
riddled limestone formations, which underlie the clay deposits,
comprise the Floridan aquifer, the principal source of artesian
ground water in the State. Where present, the clay forms an
aquiclude which retards the rate of water movement between the
aquifers.
The principal artesian aquifer was first described by Stringfield
(1936) and later named the Floridan aquifer by Parker (1955).
According to Parker, the Floridan aquifer includes those limestone
formations ranging in age from the middle Eocene (Lake City
Limestone) to perhaps early and middle Miocene (Hawthorn
Formation). In the Green Swamp area the following formations
comprise the Floridan aquifer (from youngest to oldest); the
Suwanee Limestone; the Ocala Group which includes the Crystal
River, Williston, and Inglis Formations; and the Avon Park
Limestone. The base of the aquifer is considered to be near the
base of the Avon Park limestone at the first occurrence of gypsum
because the presence of gypsum probably indicates poor circulation
of ground water.

FORMATIONS

The formations that underlie the Green Swamp area are
presented in table 4. Generalized geologic cross sections, shown in
figure 8 were prepared based on data from wells located along lines
A-A', B-B' and C-C'.

UNDIFFERENTIATED CLASTIC DEPOSITS

Undifferentiated plastic deposits, ranging from late Miocene to
Recent in age, underlie the Green Swamp area except in the western
part where Tertiary limestones are exposed at the surface. The
deposits consist primarily of clayey sand or sandy clay. The
following lithologic sequence (from youngest to oldest) is indicated:
(1) fine quartz sand surficiall sand) with varying amounts of clay
and organic material; (2) variegated (red-orange-tan) fine to
coarse quartz sand with little clay; (3) white fine to very coarse
quartz sand with varying amounts of white-green kaolinitic or
montmorillonitic clay; and (4) white silty quartz sand with varying
amounts of mica flakes.
Generally, the deposits range from 100 to 200 feet in thickness
beneath the ridges that rim the Green Swamp area; however, they
are thin or absent in the western part and tend to become more




TABLE 4. Geologic formations and their water-bearing characteristics in Green Swamp area and vicinity.


System Series


Recent
Quaternary


Pliocene


Pleistocene



Upper


Miocene Middle



Lower


Oligocene


Eocene


Upper


Middle


Formation
(after F.G.S.)


Recent
Deposits


Terrace
Sands


Citronelle
Formation


Fort Preston
Formation (7)


Hawthorn
Formation


Tampa
Formation


Suwannee
Limestone

Crystal
River
Formation

0 Williston
g Formation

S Inglis
Formation


Formations
used in this
report







Undifferentiated
Clastic
Deposits


Undifferentiated
Clay




Suwannee
Limestone


Crystal River
Formation


Williston
Formation


Inglis
Formation


Avon Park Avon Park
Limestone Limestone


Approximate
range of
thickness
(feet)







0-200


0- 60


0- 80


0-120


0- 40


0- 50


800-1,000


Lithology





Light-colored clayey
sands grading
into sandy clays


Dark-colored phos-
phatic clay with
limestone lenses



Hard, white-yellow
limestone


Soft, gray,
limestone


Hard, tan
limestone


Hard, tan
limestone

Soft to hard,
white-brown,
dolomitic lime-
stone


Water-bearing
Aquifer characteristics


Non-
artesian


Secondary
artesian


Floridan


Generally poor source in the cen-
tral part of the area. A fair
source in the ridge areas.


Generally very poor except in
the Lakeland area where iriter-
bedded limestones are a fair
source.


Generally good to excellent. The
best source is the dolomitic
Avon Park Limestone. Evapo-
rite (selenite) deposits near
the base of the Avon Park
Limestone is considered to be
the base of the aquifer.


Tertiary


------





FLORIDA GEOLOGICAL SURVEY


clayey where they thin over the crest of the anticline (fig. 8, A-A').
The deposits appear to increase in coarseness from the interior of
the Green Swamp area eastward to the Lake Wales Ridge. Much
of these deposits occur as cavity fill in the underlying limestones
especially in the ridge areas.
The undifferentiated plastic deposits form the nonartesian
aquifer in the area. Generally, the deposits in the western part
of the Green Swamp area are thin or absent, low in permeability
and porosity; and therefore, they are of minor significance as an
aquifer.

UNDIFFERENTIATED CLAY

Undifferentiated clays of Miocene age underlie most of the area,
except in the western part, and contain varying amounts of quartz,
phosphatic sand, and interbedded limestone. The following
general lithologic sequence (from younger to older) is indicated:
(1) light gray-tan-blue-green, montmorillonitic clay with varying
amounts of quartz, phosphatic sand, and interbedded limestone;
(2) dark gray-green-blue phosphatic, silty clay with varying
amounts of quartz pebbles, silt and mica flakes.
The light-colored clay with interbedded limestone is part of the
Hawthorn Formation of early and middle Miocene age. Generally,
its occurrence is limited to the southeastern part of the Green
Swamp area. It thickens eastward and southward and forms a
secondary artesian aquifer which is a significant source of artesian
water outside of the Green Swamp area. The dark, silty clay is
probably equivalent to the Tampa Formation of early Miocene age
(Carr, 1959). Generally, its occurrence is limited to the eastern
part of the Green Swamp area where it forms an aquiclude.

SUWANNEE LIMESTONE

The Suwannee Limestone (Cooke and Mansfield, 1936) of
Oligocene age is a white dense fossiliferous limestone. It is present
in the southern and western parts of the Green Swamp area and
crops out along the Withlacoochee River near Polk-Sumter-Pasco
County line. The formation thickens southward in Polk and
Hillsborough counties and westward in Pasco County. Many of the
springs along the upper Hillsborough River flow from exposures
of Suwannee Limestone. The Suwannee Limestone overlies the
Crystal River Formation and it is overlain by either undifferen-
tiated clay or undifferentiated plastic deposits.





REPORT OF INVESTIGATIONS NO. 42


OCALA GROUP

The Ocala Group (Puri, 1957) includes three limestone
formations of late Eocene age. The subdivisions of the Ocala Group
(from youngest to oldest) are the Crystal River, the Williston,
and the Inglis Formations.

CRYSTAL RIVER FORMATION

The Crystal River Formation is primarily a coquina of large
foraminifers and crops out in an area extending from northern
Polk County through the southern end of Sumter County and into
eastern Hernando County. It ranges from 50 to 120 feet in
thickness, except in the eastern part of the area where it is absent.
In the central part of the area, the formation contains many
sand-filled cavities.

WILLISTON FORMATION

The Williston Formation is a tan-cream, medium to hard
limestone containing abundant micro-fossils. The formation is
slightly coarser than the underlying Inglis Formation but generally
finer than the overlying Crystal River Formation. In most of the
area, the Williston Formation ranges from 20 to 40 feet in thickness.
It is thin or absent along the eastern boundary of the area.

INGLIS FORMATION

The Inglis Formation is generally a white-tan, hard, fossil-
iferous limestone. The texture of the formation appears to be finer
than that of the Crystal River and Williston Formations. In most
of the area, the Inglis Formation is about 50 feet thick. It is thin
or absent along the eastern boundary of the Green Swamp area.

AVON PARK LIMESTONE

The Avon Park Limestone (Applin and Applin, 1944) of late
middle Eocene age was the deepest formation penetrated by test
drilling. The formation is nearest the surface on an upthrown
fault block along the eastern side of the area (fig. 8, A-A'). The
formation is found at considerable depth in the area south and
southwest of Green Swamp. The top of the formation is





FLORIDA GEOLOGICAL SURVEY


characterized by a distinct color change from tan to brown
limestone and by abundant cone-shaped foraminifers. The formation
is a brown, dolomitic, porous limestone. Selenite (gypsum) near
the base of the formation probably forms the bottom of the
Floridan aquifer. The Avon Park Limestone is highly permeable
and is the main source of water for most of the high-capacity wells
in the area. Figure 9 shows the configuration of the top of the
Avon Park Limestone. The map shows the northwest-southwest
trend of the faulted anticline.


STRUCTURE

The Peninsular arch (Applin, 1951), a buried anticlinal structure
of Paleozoic sediments, trends generally north-northwestward and
its main axis is located east of the Green Swamp area. A flexure,
developed on the western flank of the Peninsular arch in the
Tertiary limestones, is called the Ocala Uplift. The Green Swamp
area is located at the southern end of the Ocala Uplift (figs. 8
and 9).
Vernon (1951) dated the Ocala Uplift as post-Oligocene in age.
Faults in the Green Swamp area complicate the definition of the
geology and the hydrology. The main area of faulting occurs
along the Lake Wales Ridge. Faulting in this area was described
by Vernon (1951, p. 56) and named The Kissimmee Faulted Flexure.
The cross sections in figure 8 show vertical displacement along
fault zones.
The faults are probably post-Oligocene. Subsequent movement
along fault zones may have occurred over a long period of time,
the later movements being associated primarily with subsidence
and sinkhole collapse along the solution-widened zones.
Figure 9 shows a structural map based on the top of the Avon
Park Limestone. The contour lines generally define the shape of
the anticline with associated faults. The linearity of ridges on the
anticline suggests that other faults exist in the area.
Faulting probably could affect the hydrology of the Green
Swamp in the following ways:
(1) Joints or faults within the Floridan aquifer, widened by
solution, could cause zones of high permeability, or could cause
zones of low permeability when filled with plastic materials.
(2) Displacement along the faults could position formations
of different lithology (hence permeability) one against the other,






REPORT OF INVESTIGATIONS No. 42


breaking the hydraulic continuity and producing barriers that
retard water movement.
(3) Faults cutting confining beds could increase ground-water
circulation between aquifers.

HYDROLOGY

The water supply of the earth, whether it is on the surface or
below the ground, has its origin in precipitation. Of the
precipitation that reaches the ground, part is returned to the
atmosphere by evapotranspiration; part remains above ground and
is stored temporarily in lakes, ponds, and swamps, or moves to
the sea as streamflow; and part percolates into the ground, some
to replenish the soil moisture and some to enter the zone of
saturation and recharge the ground-water aquifers. Ground water
moves in the aquifers under the influence of gravity, towards areas
of discharge such as streams, lakes, springs, wells and the oceans.

WITHLACOOCHEE RIVER BASIN

DESCRIPTION OF BASIN

The'Withlacoochee River drains 82 percent of the Green Swamp
area. The total drainage area at stations 42 and 43 at the western
boundary is 740 square miles, all of which is within the project
area except for 45 square miles of lakes and hills west of U. S.
Highway 301 and south of U. S. Highway 98 near Dade City.
Most of the general topographic and drainage features of the
Green Swamp area, described in preceding sections of this report,
apply to the Withlacoochee River basin in particular. The following
description of the basin refers specifically to this stream system.
The Withlacoochee River heads in a group of lakes and swamps
in the north-central part of Polk County in the vicinity of Polk
City and the town of Lake Alfred (see fig. 5). Lakes Van and
Juliana, the uppermost of these headwater lakes, drain into Lake
Mattie. Surface drainage from Lake Mattie spills through a wide
shallow marsh along the northeastern shoreline and flows
northward through a series of interconnected shallow swamps and
ditches to the northern boundary of Polk County. This is generally
considered to be the major headwater channel of the Withlacoochee
River. Other headwater tributaries originate in the marshes
between Lakes Mattie and Lowery and flow generally northward
between the confining ridges. These channels join near the





FLORIDA GEOLOGICAL SURVEY


northern boundary of Polk County and flow westward to form the
Withlacoochee River.
West of State Highway 33 the tributaries of the Withlacoochee
River are not confined by the ridges that are prominent in the area
east of the highway. These tributaries have developed basins that
are generally more fan-shaped than those in the eastern part.
Pony Creek, which flows northwestward, is the first of the large
tributaries entering the Withlacoochee River west of the Seaboard
Air Line Railroad. Pony Creek heads in a swamp east of Lake
Helene near Polk City. Lake Helene has no surface outlet except
at extremely high stages when it overflows into the Pony Creek
basin.
Grass Creek, the next large tributary, empties into the
Withlacoochee River about one mile downstream from Pony Creek.
Grass Creek heads in a group of small lakes in the vicinity of Polk
City. the largest of which is Lake Agnes. The outlet from Lake
Agnes is a ditch leading from the northern end of the lake and
connecting with the network of canals and ditches that carry the
water northwestward through the swamp. Several other tributaries
flow into Grass Creek as it crosses the swamp.
Gator Creek empties into the Withlacoochee River at the
Polk-Pasco County line. This is the largest tributary upstream
from the diffluence of the Withlacoochee River to the Hillsborough
River. Gator Creek heads in several small swamps northeast of
Lakeland and flows northwestward through a network of swamp
channel and ditches.
From the point of diffluence to the Hillsborough River, the
channel of the Withlacoochee River turns abruptly to the north and
continues northwestward to the western boundary of the Green
Swamp area at U S. Highway 301.
About 14 miles downstream from the point of diffluence, a major
canal draining several lakes and swamps east of Dade City empties
into the river from the west. This canal also carries the drainage
from an area of hills and lakes west of Dade City and the effluent
from citrus concentrate plants at Dade City.
One of the larger tributaries entering the Withlacoochee River
from the east is formed by the confluence of Devils Creek and
Gator Hole Slough. Devils Creek heads in a swamp about 21/
miles east of the Sumter-Pasco County line. At high stages some
water from the Withlacoochee River moves through a gap in a low
ridge into Devils Creek. This water returns to the Withlacoochee
River farther downstream.






REPORT OF INVESTIGATIONS NO. 42


Gator Hole Slough heads just east of the Seaboard Air Line
Railroad and flows westward through an unimproved swamp
channel, entering the eastern boundary of the Withlacoochee State
Forest about 3 miles west of the railroad. It continues within the
boundaries of the Forest to its confluence with Devils Creek which
empties into the Withlacoochee River 21/ miles farther west.
The Little Withlacoochee River, the largest tributary of the
Withlacoochee River, heads near State Highway 33 in Lake County
and flows westerly. Bay Root Slough is the headwater tributary
of the Little Withlacoochee River. This stream carries the drainage
from several lakes and swamps east of the Seaboard Air Line
Railroad and flows northwestward to the Lake-Sumter County line
at the eastern boundary of the Withlacoochee State Forest. The
river channel within the Forest is wide and shallow and contains
dense growths of cypress trees. The channel has been allowed to
remain in its natural swampy condition to store as much water as
possible, rather than to remove the water by improved drainage,
as a precautionary measure against fire damages to the valuable
cypress and pine trees in the Forest. The Little Withlacoochee
River emerges from the Forest near the Sumter-Hernando County
line, where it is joined on the north by a major canal. This canal
drains a swampy area between the Forest and State Highway 50.
The river continues westward through the swamp to the crossing
of State Highway 50 where it turns and flows northwestward
toward U. S. Highway 301. Another canal joins the river about a
quarter of a mile upstream from U. S. Highway 301. This canal
heads near Webster, flows southward about 11 miles, then turns
westward to Big Gant Lake and then to the Little Withlacoochee
River. The Little Withlacoochee River continues westward and
empties into the Withlacoochee River 3 miles downstream from
U. S. Highway 301.
STREAMFLOW

Streamflow data for gaging stations in the Withlacoochee River
basin during the data-collection phase of the investigation are
summarized in table 5.
Flow-duration curves for five gaging stations in the Withla-
coochee River basin are given in figure 10. Records for only the
Trilby gaging station are continuous for the 311/2-year period,
1931-62. The curves for the other four stations in the basin have
been adjusted from their individual short-term records to the
31/-year base period.









TABla1 5. Streamflow data for Withlacoocheo River basin gaging stations in Green Swamp area
(see figure 5 for station locations)


Drainage Discharge in chf
Station area Calendar Runoff
number Station (yd.ml.) year Maximum Minimum Mean in Inches


80 Withlacoochee River near Eva




38 Pony Creek near Polk City


80 Withlacoochee-Hillsborough
overflow near Richland



40 Withlacoochee River
near Dade CAty


41 Pasco Packing Co. canal
at Dade City
42 Withlacoochee R:ver
at Trilby




48 Little Withlacoochee R:ver
at Rerdell


"1158
10560
1000
1001
"1062
"1960
1061
"1962
"1958
1059
1060
1980O
1001
"1062
1959
1960
1060
n1002
1961
"1962
1957-02

1058
1969
1960
1061
"1902
1981-01
n1968
1950
1060
1961
"1962


"86
2,160
107

284
6,8



1,880
20

2,740
5,000
302

e75.6

2,600
2,960
0,920
872
8,840

1,940
8,400
106


240
288
12.2


.55


l1i44
11140
.82


'.58
0
"4.07

48
109
158
28
26
8.6
2.9
80
8.8
0
0


884
1,157
115
406

842
824
9.18


25.07
24.41
1.27


.79






E'


d80.45
d81.80
d2.70



28.98
27.48
.77


nRecords for part of year.
'Partly estimated.
aMaxfmum or minimum measured; probably not the extreme.
dAdjusted for diversion to Hillsborough River basin.







REPORT -OF INVESTIGATIONS NO. 42


GAGING STATION

--(---- Withlocoochee River near Eva

- Withlocoochee Hiilsborough Overflow
near Richlond

- -Withlocoochee River near Dade City

- Withlocoochee River at Trilby

-...Little Withlocoochee River of Rerdell

te Curve for station 42 computed from
records for 31 /2 -year base period, 1931-
Curves for all other stations adjusted from
the short-term period, 1958-62, to the
31 1/2-year base period.


001 05 2 0 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 995 993 9999
PERCENT OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED.
Figure 10. Flow-duration curves for Withlacoochee River basin, 1931-62.





FLORIDA GEOLOGICAL SURVEY


The flow-duration curves indicate the percentage of time that
specified discharges were equaled or exceeded during the period
of record. These may be considered probability curves used to
estimate the percent of time a specified discharge will be equaled
or exceeded in the future. The use of flow-duration curves to
indicate the future pattern of flow from a basin is valid only if the
climatic conditions remain the same and the amount and
distribution of runoff from the basin is not significantly changed
by man.
The flow-duration curve for Withlacoochee River at Trilby
(station 42) may be only an approximate representation of duration
of future low flows because of the progressive increases in
ground-water inflow by pumpage above the gaging station.
However, the flow-duration curves for the other four stations
shown in figure 10 may be considered probability curves and used
to estimate the percent of time that a specified discharge will be
equaled or exceeded in the future.
During a period of extremely low flow on May 23-25, 1961,
streamflow was measured and water samples for chemical analysis
were collected at several sites on the Withlacoochee River. The
results of this low-flow investigation are shown on the map in
figure 11.
The base flow of the Withlacoochee River near Dade City
(station 40) represents the natural drainage from 390 square miles
because no surface flow is diverted to the Hillsborough River basin
through the overflow channel, C-9. Since about 1941 or 1942, the
effluent from citrus processing plants at Dade City has been drained
into the Withlacoochee River by way of the Pasco Packing Company
canal. The water used by these plants is pumped from deep wells.
Measurements at station 41 of the effluent from the Pasco Packing
Company canal during 1958-62, ranged from 5 cfs, when the plant
was at minimum operation, to about 76 cfs at peak operation during
the citrus packing season. Inflow to the river from this plant and
others at Dade City produces higher discharge below station 40
east of Dade City than would be derived from the natural yield of
the basin. During dry periods, the effluent at Dade City greatly
exceeds the base flow of the Withlacoochee River (see fig. 11).
The drainage area above Trilby (station 42) comprises
two-thirds of the Green Swamp area and the record collected at this
station is a good index of the long-term variations of surface runoff
from the entire area except at low flow.





REPORT OF INVESTIGATIONS No. 42


The discharge at the Trilby gaging station does not represent
the natural runoff from the Withlacoochee River basin because of
the high-water flow diverted from the basin to the Hillsborough
River by the Withlacoochee-Hilisborough overflow channel (C-9)
and the effluent into the river from the citrus concentrate plants
at Dade City. When the Withlacoochee River reaches a stage of
about 78.5 feet above msl at the overflow channel, part of its flow
is diverted into the Hillsborough River. At high stages more than
a fourth of the flow from the upper Withlacoochee River is diverted
through this channel. Computations of basin runoff for either the
Withlacoochee or the Hillsborough Rivers must be adjusted for the
amount of discharge from one basin to the other. Percentagewise,
the plant effluent into the basin is small except when the discharge
in the Withlacoochee River is extremely low and the plant is at peak
operation.
The annual and mean monthly discharges at the Trilby gaging
station are shown by the bar graphs in figure 12. The general
relation between rainfall and streamflow is evident from figures 6
and 12. During the wet years of 1959 and 1960, annual rainfall over
the Green Swamp area was 70.9 inches and 69.5 inches, respectively.
The annual mean discharge at the Trilby gaging station was 1,157
cfs for 1959 and 1,209 cfs for 1960. The higher runoff for 1960 was
probably the result of a carry-over from the high rainfall of 1959.
The maximum discharge of record at the Trilby station was
8,840 cfs on June 21, 1934. Flood-frequency studies by Pride (1958)
indicate that the recurrence interval of a flood at this magnitude
is more than 100 years. The peak discharge of the flood of March
1960 was 6,920 cfs and was the third highest flood of record. The
recurrence interval of a flood of this magnitude is about 40 years.
The drought of 1954-56 was the most severe dry period of
record, considering its 3-year duration and yearly deficiencies.
Annual rainfall on the basin above the Trilby station for 1954-56
was 39.9, 40.2, and 46.2 inches per year, respectively. The prolonged
period of low rainfall resulted in low discharges at the Trilby
station during each of the 3 years. The lowest annual mean
discharge at the Trilby station was 75.4 cfs for 1932, a year in
which the total rainfall amounted to 39.6 inches. The total annual
rainfall on the basin in 1961 amounted to only 35.2 inches and was
the minimum for any year of record. Effluent from citrus
concentrate plants, derived from ground-water sources, accounted
for the higher annual mean discharges for 1954-56 and 1961 than
that for 1932.






FLORIDA GEOLOGICAL SURVEY


CALENDAR YEAR
CALENDAR YEAR


5000

Based on records
1928-29, 1930-62

94000 --------- | --
W



4 000

U.



z 2o00





1000


MONTH
Figure 12. Graphs showing annual and mean monthly discharge of
Withlacoochee River at Trilby.






REPORT OF INVESTIGATIONS NO. 42


The graph of mean monthly discharge for the Withlacoochee
River at Trilby (fig. 12) shows that runoff from the basin is lowest
for the months of November through June. The season of highest
runoff is the 4-month period, July through October. During these
months, 58 percent of the runoff from the basin occurs.

CHEMICAL CHARACTERISTICS OF SURFACE WATER

Waters of the Withlacoochee River in the eastern part of the
Green Swamp area are very low in mineral content (figure 13
a, b) acidic, and usually highly colored. Chloride is the principal
dissolved mineral constituent. The low mineral content is due to the
insolubility of the surface sands. The acidic condition of the water
in the southern area is probably due to decomposition of organic
matter and subsequent release of carbon dioxide and humic acids to
the water. The pH of surface water in this area ranged from 4.0
to 5.9 units. The presence of chloride as the principal dissolved
mineral constituent may be due to rain and wind-borne salt from
the coastal area. The chloride concentration is usually less than
12 ppm. High color is caused by organic matter in the water. The
color ranged from 90 to 600 units and was higher than 250 units
most of the time.
The chemical characteristics of water in the Withlacoochee
River near Eva (station 36) indicate no inflows from the Floridan
aquifer to the stream. Between Eva and Dade City (station 40)
the mineral content is higher during periods of low flow but is
essentially the same as that above Eva during periods of high flow.
The highest mineral content observed in this reach of the river
was 302 ppm (see fig. 11). This high mineral content was present
in the river just above the mouth of Gator Creek and is about the
same as the mineral content of the water from the Floridan aquifer
in this area. The hardness of the water at this point was 254 ppm
and the color, 15 units. The principal dissolved mineral constituents
were calcium and bicarbonate.
During periods of low flow, the chemical characteristics of the
water in the Withlacoochee River between Dade City (station 40)
and Trilby (station 42) are similar to those of the water from the
Pasco Packing Company Canal at Dade City. The source of water
in this canal is from wells penetrating the Floridan aquifer. The
mineral content of water in the canal ranged from 182 to 190 ppm.
The color of water in the canal is low (usually less than 10 units),
and the principal dissolved mineral constituents are calcium and


























510 -








96 1195 61) 958 -61)
0 20 40 0 20 40 0 0 40 60 80

(o) (b) (I)
Pony Cremk Withlocooce River Wllhlocoche River
neor Polk City near Evo near Dode City


I)0 2 4 I 19- 140 1
0 20 40 60 S0 100 120 140 160


MINERAL CONTENT, IN PARTS PER MILLION
(d)


Wlthlaeochle River
at Trllby


Withlocoochee River
)a Croom


\








\


S \ "


959-01)
20 40 60 60 100 i20 140 160 IO 2


Figure 13. Relation of mineral content to discharge at gaging stations in the
Withlacoochee River basin.


Ig

0

0


-i0


-~--------- --~-~I-u~--~-Ulla~u*arsarrpa


20 40 60 80 100 120 1400 10 180 200 220 240

(f)
Little Wlthlacoochd River
at Rerdell


SO
100|T
aol





REPORT OF INVESTIGATIONS NO. 42


bicarbonate. Additional ground-water inflow in this reach of the
river is indicated. The chemical characteristics of this inflow
indicate that it was derived from the Floridan aquifer.
Gator Hole Slough, a tributary to the Withlacoochee River
downstream from Dade City, was sampled at high flow. The water
was low in mineral content and contained sodium and chloride as
the principal dissolved mineral constituents. The color was 180
units.
Data were collected during the period of low flow (May 23-25,
1961) to determine the quantity and mineral content of the
ground-water inflow in the reach of the Withlacoochee River
between the stations near Lacoochee and Trilby (see fig. 11). The
mineral content of the ground-water inflow from the Floridan
aquifer into this reach of the Withlacoochee River was computed
using the load equation (Hem, 1959):
QIC, + Q2C2 Q3C3
where, Q is the discharge in cfs
C is the mineral content in ppm
QiCi is the instantaneous load near Lacoochee
Q2C2 is the instantaneous load between data-
Collection stations
QsC3 is the instantaneous load at Trilby
The inflow (Q2) was determined to be 12.2 cfs by subtracting the
discharge near Lacoochee from that at Trilby. The mineral content
(C2) of the inflow was then computed to be 260 ppm which is
approximately equal to that of water in the Floridan aquifer in
this area.
The mineral content of water in the Withlacoochee River at
Croom (station 44) was less than that at Trilby (station 42) or
that at Rerdell (station 43). The difference between the sum of
the discharges at Trilby and Rerdell and that at Croom on May 25,
1961, was 38.9 cfs (see fig. 11). Based on the load equation, the
mineral content of the inflows between the stations would be 148
ppm. Similar computations of data during other periods show
the mineral content of the ground-water inflows in this area to
range from 148 to 174 ppm. The computed mineral content indicates
that the inflow between stations was probably a composite of
surface water and ground-water inflows.
The mineral content of the water in the Little Withlacoochee
River is shown in figure 13f. The color was usually above 100 units
during periods of high flow. The principal mineral constituents
during periods of low flow were calcium-and bicarbonate, the water





FLORIDA GEOLOGICAL SURVEY


was very hard (204 ppm), and the color was low (15 units). These
overall chemical characteristics during low flow indicate inflow
from the Floridan aquifer. The mineral content of water of the
Withlacoochee River at Croom (station 44) varied from 176 ppm
during low flow to 45 ppm during a period of high flow (fig. 13e).
The color ranged from 10 units at low flow to 120 units at high flow.
The water was soft (34 ppm) during high flow and hard (144 ppm)
during low flow.
Data collected at Lake Helene during April 1962 show that the
water was low in mineral content (51 ppm); the temperature
ranged from 760F. at the surface to 680F. at the deepest point in
the lake (25 feet); dissolved oxygen ranged from 7.5 ppm at the
top to 3.8 ppm at the bottom; and the pH ranged from 6.0 units at
the top to 5.3 units at the bottom.
The waters of Lake Mattie and Little Lake Agnes were low in
mineral content and slightly colored. These lakes are similar in
chemical characteristics to those of Lake Helene. The mineral
content of water in the three lakes is about the same as that of
water in the nonartesian aquifer.

OKLAWAHA RIVER BASIN

DESCRIPTION OF BASIN

Palatlakaha Creek is the major headwater stream of the
Oklawaha River. Figure 14 shows a flow diagram of the upper
Oklawaha River system and the names of the various segments of
the water course.
Lake Lowery, the largest of a group of lakes located near Haines
City is the headwaters of the Palatlakaha Creek basin. Most of
the drainage from Lake Lowery is to the north into Green Swamp
Run through a culvert in the old Haines City-Polk City road. At
extremely high lake stages the road is inundated.
The Palatlakaha Creek basin is confined by parallel sand ridges
that extend from Lake Lowery northward almost to Lake Louisa.
Between Lake Lowery and the Polk-Lake County line the drainage
course is called Green Swamp Run. The stream channels in this
water course are not deeply incised, and drainage is through wide
shallow swamps.
Big and Little creeks drain the basin between the Polk-Lake
County line and Lake Louisa. Big Creek is a continuation of
Green Swamp Run. The stream channels for both Big and Little






REPORT OF INVESTIGATIONS No. 42 45

creeks have more definitely incised valleys and the flood plain
swamps are not as.wide.as those for Green Swamp Run.
The Big Creek basin is confined along its eastern boundary by
the Lake Wales Ridge. However, along the boundary between Big


Lake Lowery (head of basin)

Green Swamp Run

Big Creek Little Creek

Lake Louisa Lake Nellie ---Lake Glona

Lake Minnehaha

Lake Minneolo
LaPalatlakaha Creek
Cherry Lake connects these lakes.

Lake Lucy
Le Johns Lake
Lake Emma
Lake Apopka
Palatlakaha Creek
and many small lakes Apopkd-Beaucla
t +
Lake Harris Lake Beauclair

Dead River Lake Dora

Lake Eustis --- Dora Canal

Haines Creek Lake Yale

Lake Griffin Lake Yale Canal

Oklawaha River

St. Johns River


ir Canal


Figure 14. Flow diagram of the upper Oklawaha River.






FLORIDA GEOLOGICAL SURVEY


and Little creeks, the ridge is broken by swamps in several places
and the two basins are interconnected. Big Creek, including Green
Swamp Run, drains an area of about 70 square miles. The basin,
from Haines City to Lake Louisa, is about 25 miles long and from
2 to 4 miles wide. The swamp channel ranges in elevation from
about 130 feet near Lake Lowery to about 100 feet near Lake
Louisa.
Little Creek drains an area in Lake County west of Big Creek
and empties into Lake Louisa. The western boundary of the Little
Creek basin is fairly well defined by low ridges. However, in a few
places the ridges are broken by saddles. The exchange of surface
drainage between Little Creek and the Withlacoochee River
through the saddles in the western boundary appears to be
negligible.
The southern boundary of the Little Creek basin is not well
defined. The probable boundary is along an old road that extends
from State Highway 33 to U. S. Highway 27 about a mile or two
north of the Lake-Polk County line. Much of the drainage from
the area that was formerly drained by Little Creek has been
diverted into the Withlacoochee River by interceptor canals. These
canals are located near the Polk-Lake County line. However, some
water from its former basin still drains into Little Creek through
natural swamp channels that were not closed when the interceptor
canals were dug. The present (1962) drainage area for Little
Creek, as outlined in figure 5, is about 15 square miles during dry
periods. During wet periods, water flows into the basin through the
openings in the road along the southern boundary of Lake County.
Lake Louisa is the uppermost of a chain of large lakes in the
upper Palatlakaha Creek system. Lake Minnehaha, Lake Minneola,
and Cherry Lake are next in order below Lake Louisa. These lakes
are connected by the wide, deep channel of Palatlakaha Creek. In
addition to draining these lakes, Palatlakaha Creek also drains an
area of smaller lakes and upland marshes westward to State
Highway 33. This area affords storage facilities for large quantities
of water.
During the latter part of 1956, an earthen dam with two radial
gates was built at the outlet of Cherry Lake to maintain the stages
of the waterway and lakes upstream during prolonged periods of
dry weather. The water surface from the upper pool at this dam
to Lake Louisa is essentially level except during periods of high
discharge. During the maximum discharge period in 1960, the
stage of Lake Louisa was about 1.6 feet higher than that of the





REPORT OF INVESTIGATIONS No. 42


upper pool at Cherry Lake outlet. The fall between Lakes Louisa
and Minnehaha was 0.4 foot during this period.
The channel below Cherry Lake has been improved by a canal
leading into Lake Lucy and Lake Emma. Palatlakaha Creek follows
a more definite channel with steep gradient from Lake Emma to
its mouth at Lake Harris. The fall in this reach is about 32 feet
in 12 miles.


STREAMFLOW

Streamflow data. for gaging stations in the Palatlakaha Creek
basin during the data-collection phase of the investigation are
summarized in table 6.
The flow-duration curve for Big Creek near Clermont (station
3), adjusted from the short-term period to the 311/-year period,
1931-62, is shown in figure 15. Long-term records for the
Withlacoochee River at Trilby (station 42) were used for the
adjustment because discharges at other long-term downstream
stations on the Oklawaha River are partly regulated by
water-control structures.
Streamflow of the headwaters of the Palatlakaha Creek
upstream from Lake Louisa is unregulated. Since 1956, the flow
below Lake Louisa has been regulated by a water-control structure
at the outlet of Cherry Lake. During periods of low rainfall, most
of the drainage from the 160-square mile basin above Cherry Lake
Outlet is stored in the chain of large lakes and marshes between
Lake Louisa and Cherry Lake.
Comparison of peak discharges during floods in March 1960
and September 1960 in Big Creek, Little Creek, and the upper
Withlacoochee River shows the effect of the interconnections
between the Little Creek and the Withlacoochee River basins. The
peak discharge for the March 1960 flood in Big Creek at station 3
was 628 cfs. The discharge in Little Creek measured at station 6
near the peak of this flood was 801 cfs. The higher discharge from
the smaller drainage area of Little Creek indicates that most of the
flow was draining from the Withlacoochee basin into Little Creek
through saddles in the drainage divide.
The peak discharge during the flood of September 1960 for Big
Creek at station 3 was 691 cfs. The concurrent flood peak for Little
Creek at station 5 was 400 cfs. The flood peak for Withlacoochee
River near Eva (station 36) was 2,160 cfs in March 1960 and 1,290














TABLE 6. Streamflow


data for Palatlakaha Creek basin stations In Green Swamp area
(see figure 5 for station locations)


Station
Number


Station


2 Green Swamp Run near
Loughman
8 Big Creek near Clermont




5 Little Creek at Coopers
Ranch near Clermont
6 Little Creek near Clermont


7 Lake Glona Outlet near
Clermont
11 Palatlakaha Creek at Cherry
Lake Outlet near Groveland



12 Palatlakaha Creek near
Mascotte


Drainage
area
(eq. ml.)


33

68




10

15


8.4

160




180


Calendar
year


"1059
"1061.62
A1058
1059
1060
1961
"1962
1961
"1062
A1068
n1958
1959
1960
"1060.62

1058
1959
1960
1961
"1062
1945.56


Maximum


"'54


288
691
64

18


"f210
"801
110

804
370
584
162

458


Discharge in efu

Minimum


0
0
,4
18
22
.1
0

0
0

'"8.92
0
0

0
11
36
0
0
.2


nRecords for part of year.
!'Maximum or minimum measured; probably
"Estimated.


not the extreme.


Runoff
in inches


Mean


112
142
12.2

1.27


'58
'51



78.4
224
251
28.7
..--


I

S3
L'


22.87
28.89
2.42










6.65
18.98
21.40
2.00


_____~_II____~ ____ ___ _________ __ _I __ ___~I_____


_~


_C~C_






REPORT OF INVESTIGATIONS NO. 42


cfs in September 1960. Little Creek serves as an outlet for much of
the flood drainage from the upper Withlacoochee River basin.

CHEMICAL CHARACTERISTICS OF SURFACE WATER

Waters of Big and Little Creeks have chemical characteristics
similar to those of the Withlacoochee River upstream from State
Highway 33 in that they have very low mineral content and are
highly colored. Figure 16a shows that the mineral content of
water in Big Creek ranges from 19 to 61 ppm. Figure 16b shows
that the mineral content of water in Little Creek ranges from 18
to 31 ppm. Color of water in Big Creek ranges from 65 to 240
units and that of Little Creek ranges from 150 to 300 units. Both
streams usually contain sodium and chloride as their principal
dissolved mineral constituents.
Waters of the two streams differ in chemical characteristics in
that water of Big Creek is more mineralized, usually less colored,
and the pH is higher than that of Little Creek. The higher mineral
content of water in Big Creek is due mostly to higher concentrations
of calcium and bicarbonate.


HILLSBOROUGH RIVER BASIN

RELATION TO GREEN SWAMP AREA

The Withlacoochee-Hillsborough overflow channel (C-9, fig. 5),
previously described with the Withlacoochee River basin, is one of
the major drainage outlets from Green Swamp during high flows
and is generally considered to be the head of the Hillsborough River.
The overflow channel as it leaves the Withlacoochee River is about
a mile wide. The road fill and bridge of U. S. Highway 98 crosses
the channel about 1 mile downstream from the Withlacoochee
River. The entire flow is confined by the road fill to the bridge
opening which is 200 feet wide.
White (1958, p.19-24) presents evidence to support an
assumption that the Withlacoochee-Hillsborough overflow channel
was formerly the main channel of the Hillsborough River and that
the Withlacoochee River was once the headwaters of the
Hillsborough River. Field studies made in the area in 1962 by
Altschuler and Meyer indicate that the Withlacoochee-Hillsborough
River overflow was formed prior to natural divergence of the






50 FLORIDA GEOLOGICAL SURVEY

headwaters of the Hillsborough River to the Withlacoochee River
and that the divergence may be related to uplift in the area.
From the bridge on U. S. Highway 98, the Hillsborough River
flows generally southwestward through Pasco and Hillsborough
counties and empties into Hillsborough Bay 531/2 miles downstream.



\\_






soI



S40


a. T2Z __- -

CUP
us


__ _
---- --















from the short-term period,
198--62, to o/-ye-ar
base period
Si I i I



11













PERCENT OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED
Figure 15. Flow-duration curve for Big Creek near Clermont, 1931-62.


.99





REPORT OF INVESTIGATIONS No. 42


W
Ui


(L
L- 10


m 5


z
u r



0




(1956-61) 956-61)


.1 -*
20 30 40 50 60 70 10 O2 30 40

MINERAL CONTENT, IN PARTS PER MILLION

(a) (b)
Big Creek Little Creek
near Clermont near Clermont
Figure 16. Relation of mineral content to discharge at gaging stations in
upper Palatlakaha Creek basin.





FLORIDA GEOLOGICAL SURVEY


The lower 15 to 18 miles of the river passes through the City of
Tampa. The city water supply is a reservoir created by a dam in
the river 10.2 miles upstream from the mouth. Tampa is vulnerable
to damages from floods in the Hillsborough River because of
extensive development of property in the flood plain.

STREAMFLOW

A summary of streamflow data for the gaging station on
Withlacoochee-Hillsborough overflow (station 39) is shown in table
5. The flow-duration curve is shown in figure 10. No flow occurs
in the channel at this point about 65 per cent of the time.
Crystal Springs flows into the Hillsborough River in southern
Pasco County near the Pasco-Hillsborough County line. The average
flow of Crystal Springs (station 31) is 62 cfs, ranging from 20.3
cfs to 147 cfs. Downstream from Crystal Springs the base flow of
Hillsborough River is well sustained. The flow of Hillsborough
River near Zephyrhills (station 33), which includes flow from
Blackwater Creek, is reported to be 71 cfs or more for 90 percent
of the time (Menke, 1961, p. 29).

CHEMICAL CHARACTERISTICS OF SURFACE WATER

The chemical characteristics of water of the Hillsborough River
upstream from Crystal Springs are similar to those of the
Withlacoochee River between Eva and Dade City although the
mineral content is somewhat higher.
The water of the Hillsborough River at the Withlacoochee-
Hillsborough overflow contained calcium and bicarbonate as the
principal dissolved mineral constituents. The water contained
color that ranged from 80 to 150 units. The mineral content ranged
from 41 to 121 ppm.
The water of Crystal Springs had a mineral content of about
170 ppm, was clear, and contained calcium and bicarbonate as the
principal dissolved minerals. The water was hard and alkaline.
During the periods of low flow, the chemical characteristics of
the water of the Hillsborough River near Zephyrhills (below
Crystal Springs) are essentially the same as those of water of
Crystal Springs. Figure 17 shows the relation of the mineral
content to discharge. During periods of high flow the mineral
content of water is low. A more detailed discussion of the chemical
character of the water of the Hillsborough River is given in a
report by Menke (1961, p. 28-36).






REPORT OF INVESTIGATIONS NO. 42


5000


IL


0 0
=o
a z
2 (0



IJ
oCw
0-U_
af


Iu --


iOo
100
*
*


*

100 -- -
(1956 62)
50 ____


40 60 80 100 120 140 I1
MINERAL CONTENT, IN
PARTS PER MILLION


;0 180


200


i Figure 17. Relation of mineral content to discharge, Hillsborough River near
Zephyrhills.

KISSIMMEE RIVER BASIN

RELATION TO GREEN SWAMP AREA

The eastern boundary of the Green Swamp area is U. S.
Highway 27 atop the Lake Wales Ridge. This is generally the
surface drainage divide between Palatlakaha Creek in the St. Johns
River basin and headwater tributaries of the Kissimmee River.
The surface drainage from only 5 square miles of the Green
Swamp area flows eastward into the Kissimmee River basin.
Piezometric maps in figures 35 and 36 indicate ground-water move-
ment eastward from the Green Swamp area into the Kissimmee
River basin.

STREAMFLOW

Horse Creek is one of the Kissimmee River tributaries adjacent
to Green Swamp. Streamflow records of Horse Creek at Davenport
(station 19) were collected to study the base flow that is derived






FLORIDA GEOLOGICAL SURVEY


from ground water. The drainage area at the gaging station is
22.8 square miles. The maximum discharge during 2 years of data
collection was 358 cfs and the minimum was 0.5 cfs. Runoff
characteristics of the Horse Creek basin are compared with those
of the Pony Creek basin in a following section of this report.

CHEMICAL CHARACTERISTICS OF SURFACE WATER

Data concerning the chemical characteristics of water in the
Kissimmee River basin were collected from Horse Creek and Reedy
Creek.
Water of Horse Creek is more mineralized than water in the
upper Withlacoochee River. Figure 18 shows the general relation
of mineral content to discharge. The mineral content from July to
November 1960 ranged from 22 to 64 ppm (from daily conductivity
records). Calcium and bicarbonate were the principal dissolved
mineral constituents. The surface materials in the Horse Creek
basin are sands and clays, which are essentially insoluble in water,
and therefore the calcium bicarbonate type water in Horse Creek
is probably due to seepage from the Floridan aquifer. The following


m z
30
i w
zM

W
e_,

U) LL


10


,o
20


Figure 18. Relation of


30 40 50 60
MINERAL CONTENT, IN
PARTS PER MILLION
mineral content to discharge,
Davenport.


Horse Creek at






REPORT OF INVESTIGATIONS NO. 42


equations were used to determine the approximate amount of
seepage from the aquifer:
Q1 + Q2 = Q
33Q1 + 167Q2 = CQ
where, Q1 is the component of discharge from nonartesian
aquifer and from direct runoff
Qs is the component of discharge from Floridan
aquifer
Q is total discharge of Horse Creek
C is mineral content of water of Horse Creek
33 is average mineral content of ppm of typical water
from nonartesian and from direct runoff
167 is average mineral content in ppm of typical water
from the Floridan aquifer.
Based on the computation, seepage from the Floridan aquifer
averaged about 6 cfs for the 4 complete months of daily conductivity
records.
Color of water in Horse Creek ranged from 60 to 160 units and
the pH ranged from 6.4 to 7.4 units.
Mineral content of water from Reedy Creek during a wet period
in 1959 was 33 ppm, the color 80 units, and the pH 6.0 units.


PEACE RIVER BASIN

RELATION TO GREEN SWAMP AREA

The Peace River basin lies immediately to the south of the
designated boundary for the Green Swamp area. Before construc-
tion of levees, highway and railroad fills, ditches and other drainage
improvements, Lake Lowery and the surrounding marsh apparently
drained southward into Peace River as well as northward to the
Palatlakaha Creek and the Withlacoochee River basins. Under
present conditions, the surface runoff from only 7 square miles of
the Green Swamp area drains southward into the Peace River basin.
This small area includes Gum Lake and its marsh outlet and Lake
Alfred. The headwaters of the Peace River basin lie immediately
south of the highest artesian water levels in the southeastern
part of the Green Swamp area. Piezometric maps in figures 35 and
36 indicate ground-water movement southward to the Peace River
basin.





FLORIDA GEOLOGICAL SURVEY


STREAMFLOW

During the flood of September 1960, caused by Hurricane Donna,
Lake Lowery reached a maximum stage of 133.32 feet above mean
sea level. During this flood, a road fill between a marsh in the
Withlacoochee River headwaters and Gum Lake marsh washed out
and an undetermined amount of water flowed southward into the
Peace River basin through an opening 12 feet wide (C-4, fig. 5).
The flow at Gum Lake marsh outlet (station 22) includes the
drainage from 4.2 square miles in the Gum Lake basin plus that
diverted from the Withlacoochee River basin through opening C-4.
During the flood of September 1960, the peak discharge was not
determined but most of this flood discharge was from the
Withlacoochee River basin. The 3' x 8' box culvert and a section
of the highway at the gaging station were overtopped. The flood
peak reached a stage of 132.0 feet above mean sea level, as
determined from high water marks at the gage. During periods
of low rainfall there is no flow in this channel. For the period May
1961 to June 1962, the channel was dry. The average discharge at
station 22 was 0.55 cfs in 1961. There was no flow from Lake Alfred
during the period April 1961 to June 1962. The total surface
outflow from the Green Swamp area to the Peace River basin is
negligible except during flood periods.

DIVERSIONS AND INTERCONNECTION OF BASINS

Although surface drainage from the Green Swamp area follows
rather definite routes and although the drainage divides are
generally determined by the topographic features, there are several
places where the basins are interconnected and water is diverted
from one basin to another. Some of these points of diversion have
been mentioned under the foregoing discussion of the individual
drainage basins. The hydrologic importance of these intercon-
nections, which are integral parts of the drainage systems, is
shown in the following discussion.
The arrows on the map in figure 5 locate and show the direction
of flow through many of the saddles in the drainage divides. The
interconnections that are shown on the map are the most important
ones disclosed by the investigation, but they by no means include
all such points in the small subbasins where there are no definite
drainage divides.
One of the major diversionary channels is the Withlacoochee-
Hillsborough overflow in southeastern Pasco County (C-9, fig. 5).






REPORT OF INVESTIGATIONS NO. 42


This diversion was discussed in detail under sections describing
the Withlacoochee River and Hillsborough River basins.
Other major interconnections of basins are near the Polk-Lake
County line (C-3) in the eastern part of the Green Swamp area.
The sand ridges in this area are dismembered by a transverse
network of swamps that connect the Withlacoochee River and Little
Creek basins. The alignment of the swamps and the relative widths
of the flood plains shown on aerial photographs indicate that, in
the former natural state, water carried to this area from the south
was discharged by either of three different routes-Big Creek,
Little Creek, or Withlacoochee River. The evidence indicates that
most of the drainage from the southeastern area ran off via Big
and Little creeks.
Beginning about 1948 and continuing progressively each year,
extensive land reclamation by property owners has considerably
altered the pattern of drainage in the eastern area. These physical
changes, which were made for the development of the area,
apparently changed the proportion of the water that drained by
the three routes. Based entirely on the present pattern of drainage
canals and without any factual data on the streamflow from the
upper basins prior to the development of the area, it appears that
the most significant change has been a decrease in the area drained
by Little Creek and an increase in the area drained by the
Withlacoochee River.
Major canals near the Polk-Lake County line were dug about
1948 and 1949 and appear to have intercepted the greater part
of the flow from an area of about 60 square miles that was formerly
the headwaters of the Little Creek basin. This area is roughly 18
miles long and 3 to 4 miles wide. It extends from the present
southern divide of the Little Creek basin southward almost to the
town of Lake Alfred. The greater part of the water from this area
now drains to the Withlacoochee River. However, as discussed in
the description of the Palatlakaha Creek basin, some flow still
enters the Little Creek basin from its former headwaters. The
changes in the drainage system predate streamflow records in the
headwater basins. Therefore, the change in proportion of drainage
between the two basins and the increased effectiveness of the
drainage system may be inferred only on the basis of long-term
streamflow records at downstream gaging stations. The runoff
under present conditions, as compared with the runoff that occurred
during the earlier years, is discussed under the heading "Effects
of Man-Made Changes" in the following section.





FLORIDA GEOLOGICAL SURVEY


A levee now fills a saddle in the drainage divide between Green
Swamp Run and the Withlacoochee River in northeastern Polk
County south of the Polk-Lake County line (fig. 5). Prior to the
construction of the levee (about 1956 or 1957), drainage from Green
Swamp Run divided into flow westward into the Little Creek basin
(now the Withlacoochee River basin) and flow northward into Big
Creek basin.
Lake Lowery and swamps in the upper Withlacoochee River
basin are connected by a natural saddle (C-1) in the confining ridge
northwest of the lake. This saddle is 200 to 300 feet wide and is
one point at which flow may be diverted between the Palatlakaha
Creek and Withlacoochee River basins. At high stages the two
basins are interconnected at this point. Apparently water may flow
through this saddle in either direction, depending on the
distribution of rainfall and the relative water levels in the basins.
There are four interconnections (C-2) between Big and Little
creeks. These openings, all in Lake County, are small and their
net exchange of water is probably negligible in comparison with the
total flow from the basin.
Other places, shown on the map in figure 5, where basins are
interconnected are: (C-4) between the Withlacoochee River
headwaters and Peace River headwaters; (C-5, C-6, C-7) between
Lake Mattie, Withlacoochee River, and Pony Creek; and (C-8)
between the Withlacoochee River and Devils Creek. Many of these
interconnections act as equalizing channels through which water
may flow in either direction, depending on relative water levels in
connected basins.

EFFECTS OF MAN-MADE CHANGES

Many of the physical changes that have been made on the land
surface through man's efforts have already been described. The
most extensive developments of the area have occurred in recent
years, but the first changes in the hydrologic characteristics
undoubtedly occurred several years ago when logging trails and
tramroads were built and much of the native timber was cleared
from the area. The early developments of the area cannot be
evaluated as they predate the period of data collection, but they
probably had only minor effects on the hydrology.
Changes in the drainage characteristics of the Green Swamp
area can be detected by comparing the hydrologic data for years
before drainage developments with the data collected since major






REPORT OF INVESTIGATIONS No. 42


developments have been made. Long-term records of rainfall and
streamflow in the upper Palatlakaha Creek (stations 11 and 12)
and Withlacoochee River (station 42) have been used to detect
changes or trends in the pattern of discharge from the upper
Palatlakaha Creek basin since 1946.
Double-mass curves of cumulative measured runoff and
cumulative computed runoff have been plotted to provide a means
of examining the records of streamflow from the area of
investigation to detect changes that may have occurred (Searcy
and Hardison, 1960). The variables used in preparing the curves
shown in figure 19 are the values of cumulative computed runoff,
taken from the precipitation-runoff relations in the figures on
pages 97 and 99 and cumulative measured runoff at each of the
two gaging stations.
The rainfall pattern is not affected by the progressive changes
in the drainage system in the Green Swamp area. The theoretical
or computed runoff based on rainfall is taken from an average curve
for several years of record. Any change in slope in the double-mass
curves of figure 19 would reflect progressive man-made changes in
runoff.
Figure 19a is the double-mass curve for the Withlacoochee
River basin above the Trilby gaging station. Straight lines are
drawn to average several points that show definite trends. These
lines change in slope between 1942 and 1943, between 1945 and
1946, and between 1953 and 1954. The two changes in slope in the
1940's indicate changes in the runoff pattern but the authors have
no knowledge of the causes of such changes. Minor deviations of
the plotted yearly values of runoff are probably caused by variations
of rainfall distribution and intensity during the year and are not
necessarily indications of changes in the long-term trends. Yearly
values of runoff for 1954-61 define an average line with less slope
than that for any previous period. This change in slope indicates
that a higher rate of runoff from the basin occurred during 1954-61
than that indicated from the same rainfall pattern of previous
years.
Figure 19b is the double-mass curve for the upper Palatlakaha
Creek basin. The figures of annual runoff were adjusted for changes
in storage in lakes. For the period 1946-49, the curve takes the
general direction .as shown by the straight line. However, after
1949, a definite break occurs in the slope of the average line
indicating, less runoff from the area.







60 FLORIDA GEOLOGICAL SURVEY


Figure 19c has been plotted to show the cumulative runoff from
the combined Withlacoochee River and Palatlakaha Creek basins.
The average line defining this curve has the same slope for the
entire period, 1946-61. This indicates that there has been no
significant change in runoff from the combined basins.






300~ ---- --- --- ---- ------ ---- _-- ---- ---
35C



300 1,960


250

S' 1955


1950

c 0I 5 10945

(o) Withlacoochee River
100 1940\ oft Trilby, 1931-61

- O t 1935 0'
50- ----- --- --- --- --- ___ ___ ___

193

0- 0 50 100 150 200 250 300 350 400 450


zuu I-------- i ---
(b) Palatlakaha Creek above
Mascotte, 1946-61
150



100 19 60



50 195 1955 -


519046
S 50 100 150 200


Cumulative


measured runoff, in inches


Figure 19. Double-mass curves of measured runoff versus computed runoff,
Withlacoochee River and Palatlakaha Creek basins.






REPORT OF INVESTIGATIONS No. 42


The explanation for the significant decrease in runoff from the
Palatlakaha Creek basin is a decrease in the size of the drainage
area. Such a change in the headwaters of Little Creek, a tributary
to Palatlakaha Creek, occurred during the period 1948-49 and has
been discussed earlier in this report. This change has resulted in
the diversion of part of the flow from the Little Creek basin into
the Withlacoochee River basin. The gain to the Withlacoochee
River basin is not as obvious as the loss from the Palatlakaha
Creek basin because of the difference in size of the drainage basins.

GROUND-WATER ACCRETIONS TO STREAMFLOW IN
HORSE AND PONY CREEK BASINS

Stream flow consists of direct surface runoff and ground-water
runoff or base flow. Surface runoff is rainfall that drains directly
into the stream channel during and after a storm. Ground-water
runoff is rainfall that infiltrates to the ground and then discharges
into a stream channel. In well-drained basins surface runoff ceases a
few days after the occurrence of rainfall, and streamflow is then
derived entirely from ground-water runoff. Surface contributions
to streamflow continue for longer periods in basins containing
lakes, swamps, or other surface storage features.
Daily streamflow records were collected for the period June
1960 to June 1962 for Horse Creek at Davenport (station 19) and
Pony Creek near Polk City (station 38). The runoff of these two
streams probably represents the maximum variation in runoff of
streams in the Green Swamp area. Horse Creek and Pony Creek
basins have generally similar characteristics of geology and rainfall,
but the two basins are situated differently with respect to the
piezometric high. The basin slope of Horse Creek is higher than
that of Pony Creek. Pony Creek basin above gaging station 38 is
entirely atop the piezometric high. Horse Creek above gaging
station 19 lies adjacent to the southeastern boundary of the Green
Swamp area (fig. 5) and downslope from the piezometric high
(fig. 35) in an area of artesian flow as indicated by hydrographs in
figure 23.
Graphs of monthly rainfall and runoff in inches for the Horse
and Pony creeks basins for July 1960 to June 1962 are shown in
figures 20 and 21. Base flows, expressed in inches of runoff from
the two basins, were estimated for the low runoff period from
November 1960 to June 1962. Base-flow recession curves were
developed and used as a partial basis for separation of the






FLORIDA GEOLOGICAL SURVEY


14.6 14.5"

,1--0-g-


Totals for 1961:

inches
Rainfall 37.2
Runoff 6.41
Base flow 4.90


4








2








JAso ND J FM AIJ M J A S N DJ F M A M
1960 1961 1962
Figure 20. Graphs of monthly rainfall and runoff for July 1960 to June 196i
and estimated base flows for November 1960 to June 1962, Horse Creek al
Davenport.






REPORT OF INVESTIGATIONS NO. 42


14.6"

142"
tI a n


Totals for 1961:

inches

Rainfall 38.4
Runoff .79
7 Base flow .39















4 9




o
















JIA S 0 NID J -F MIAIMIJ JIAISIO0N D N F MIAIMIJ
1960 1961 1962


Figure 21. Graphs of monthly rainfall and runoff for July 1960 to June 1962
and estimated base flows for November 1960 to June 1962, Pony Creek near
Polk City.


IU


a,
-o

-2
09_
E
w
4-5
to


I





FLORIDA GEOLOGICAL SURVEY


streamflow into the two component, base flow and direct runoff. The
methods of separating streamflow into its components of base flow
and direct runoff are hypothetical and the results are generally
subject to some limitations. During months of high runoff, July to
October 1960, streamflow was mostly from direct runoff and base
flows could not be estimated with any degree of reliability.
Monthly values of rainfall and runoff for Horse Creek and Pony
Creek are summarized in table 7. Direct runoff was computed as
the difference between total runoff and base flow. For the months
of July, August, and September 1960, the average rainfall on the
Horse Creek basin was 38.8 inches and the runoff was 13.0 inches.
For the same period, the rainfall on the Pony Creek basin was 32.1
inches and the runoff was 19.4 inches. The greater runoff from
Pony Creek resulted from less rainfall than that which occurred
in the Horse Creek basin. This was probably caused by high
ground-water levels in the Pony Creek basin and lack of storage
capacity in the nonartesian aquifer as indicated by comparison of
the hydrographs of wells in the basins (see fig. 23, well 810-136-2;
and fig. 27, well 813-149-2).
Comparison of the data for the year 1961 for the two stations
in table 7 shows that Horse Creek received 37.2 inches of rainfall
and Pony Creek received 38.4 inches. However, the runoff from
the Horse Creek basin was 6.41 inches as compared to 0.79 inch
from Pony Creek. The base flow or ground-water runoff for Horse
Creek was 4.90 inches which was 76 percent of the total runoff.
The base flow of Pony Creek was 0.40 inch which was 51 percent
of the total runoff. Most of the additional runoff for Horse Creek
in 1961 was probably gained by ground-water inflow. Base flow of
the stream was sustained even during prolonged periods of little
rainfall. On the other hand, Pony Creek basin is on top of the
piezometric high and the stream received no ground-water flow
during prolonged periods of low rainfall in 1961 and 1962.
Flow-duration curves based on the 2 years of record for Horse
Creek and Pony Creek are shown in figure 22. A comparison of the
runoff characteristics for the two basins may be made from these
curves. The curves have not been adjusted to a long-term base
period, and therefore should not be used to estimate future
long-term patterns.

AQUIFERS
Aquifers are classified as either nonartesian or artesian.
Nonartesian aquifers are unconfined, and their water surface (the




TABLE 7. Monthly water budgets for Horse Creek and Pony Creek basins, 1960-62


Horse Creek at Davenport (Station 19)


Pony Creek near Polk City (Station 88)


Base flow Base flow

Month 0 'o r -
S *- Direct r. Direct
S .. Runoff runoff Runoff runoff
(nches) (inc hes) (inc) hes) (inches) ( he) (ich) nches) ( hes)

.1960
July 14.6 8.98 14.2 5.71 -
August 9.7 2.86 3.3 5.14
September 14.6 6.16 14.6 8.52 -
October 3.1 2.64 1.6 1.26 -
November .0 1.01 .06 .95 94 .0 .24 .05 .19 79
December 1.1 .84 .10 .74 88 2.0 .11 .03 .08 78

1961
January 1.9 1.01 .20 .81 80 1.7 .07 .01 .06 86
February 2.0 .91 .17 .74 81 2.4 .08 .02 .06 75
March 2.0 .55 .04 .51 93 2.9 .10 .05 .05 60
April .7 .88 .05 .88 87 1.0 .09 .05 .04 44
May 2.8 .30 .07 .23 77 8.4 .002 .00 .002 100
June 5.6 .18 .05 .13 72 6.8 .13 .08 .05 88
July 6.0 .53 .11 .42 79 8.8 .01 .001 .009 90
August 9.4 1.15 .67 .48 42 9.2 .20 .13 .07 85
September 1.7 .80 .11 .69 86 1.6 .11 .06 .06 54
October 1.7 .28 .02 .21 91 2.8 .00 .00 .00
November .9 .18 .01 .17 94 1.6 .00 .00 .00
December 2.5 .19 .01 .18 95 2.7 .00 .00 .00

Year 37.2 30.8 6.41 1.51 4.90 76 38.4 37.6 .79 .39 .40 51

1962
January 1.2 .32 .03 .29 91 1.6 .03 .01 .02 67
February .7 .18 .01 .17 94 .6 .01 .00 .01 100
March 8.3 .22 .03 .19 86 3.8 .04 .02 .02 60
April 1.5 .17 .02 .16 88 2.1 .02 .00 .02 100
May 1.3 .03 .00 .03 100 5.2 .01 .008 .002 20
June 6.9 .38 .14 .24 63 8.4 .37 .22 .15 41






66 FLORIDA GEOLOGICAL SURVEY

water table) is free to rise and fall. Artesian aquifers are saturated,
confined or semi-confined, and their water surface is not free to
rise and fall. The water in an artesian aquifer is under pressure
(greater than atmospheric) which causes it to rise above the top
of the aquifer. The level to which water will rise in tightly cased
wells, penetrating an artesian aquifer, is called the piezometric
surface.








I ,
^rrz: ~ ~ ~ --- -_-::_:--z= ::


i \
tL




M. _
.. .---.-- ---- -- --- -


i -_ -

r T ri'~~'^ ~~~ ~ ~ -
S|Horse Creek at Davenport


j Pony Creek near Polk City _____

c Qo8|-- --- - --
4 ___- -----
C 51 -- - -- -- --


0 OS 005 2 a5 I Z S 10 20 30 40 50 60 T 80 90 95 98 99 995 999 99.91
PERCENT OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED
Figure 22. Flow-duration curves for Horse Creek at Davenport and Pony
Creek near Polk City, 1960-62.






REPORT OF INVESTIGATIONS NO. 42


The principal importance of an aquifer is its ability to transmit
and store water. The coefficients of permeability (P) and
transmissibility (T) are measures of the capacity of an aquifer to
transmit water. Permeability is usually determined by laboratory
measurements of a minute part of the aquifer, whereas transmissi-
bility usually determined in the field by aquifer tests, represents
the average permeability for a localized area of the aquifer.
The coefficient of storage (S) is a measure of the capacity of
an aquifer to store water. The coefficient of storage for artesian
aquifers is usually determined by pumping tests and may range
from about 0.00001 to 0.001. The coefficient of storage for
nonartesian aquifers can be determined by pumping tests or
laboratory methods and may range from about 0.05 to 0.30 and, for
all practical purposes, equals the specific yield.
Coefficients of permeability were determined by laboratory
analysis for samples from the nonartesian and artesian (Floridan)
aquifers in the Green Swamp area (see tables 8 and 9). Aquifer
tests were made at selected sites and the data were analyzed to
determine coefficients of transmissibility using (1) the type curve



TABLE 8. Hydrologic analyses of disturbed sand samples from a test hole in
Lake Parker near Lakeland

(Analyses by U. S. Geological Survey Hydrologic Laboratory, Denver,
Colorado.)

Depth below Specific Coefficient
Sample lake bottom Porosity yield of permeability
number (feet) (percent) (percent) (gpd/ft2)

1 6-7 37.1 36.3 75
2 11-12 34.0 33.4 40
3 15-16 35.0 34.6 50
4 20-23 32.7 32.1 80
5 24-26 34.2 34.0 20
6 27-28 35.2 38.4 60
7 35-37 36.9 35.8 90
8 44-45 36.2 34.5 150
9 50 32.2 31.0 95
10 55-56 39.7 37.3 180
11 60 44.8 43.9 110
12 70 45.4 41.7 115
13 73-77 43.2 39.0 40









TABLE 0, Hfydrologic analyses of core samples from a well (805-154-8) near Lakeland
(Analytse by U. S. Geological Survey Hydrologic Laboratory, Denver, Colorado.)

Formation: AP, Avon Park Limestone; CR, Crystal River; I, Inglis; LC, Lake City Limestone; 0, Oldsmar Limestone;
S, Suwannee Limestone; W, Williston,
Specific yield: The pore space that drains by gravity.
Coefficient of permeability: Gallons per day at 00 F through cross section of 1 square foot under unit hydrologic
gradient.


Lithology

Limestone, tan, fragmental, very
soft
Limestone, cream, chalky, coquina,
soft
Limestone, tan, granular, hard

Limestone, cream, granular, hard

Limestone, tan-gray, very dolo-
mitic, very hard
Limestone, brown, very dolomitic,
very porous
Limestone, white, very chalky,
very soft
Limestone, cream, chalky, soft
with gypsum inclusions
Limestone, tan, very dolomitic, hard

Limestone, gray-brown, very dolo-
mitic, with gypsum and anhy-
drite inclusion


(percent)
Porosity

31.5

43.8

26.8

44.1

18.3

30.3

41.3

35.1

19.6

15.4


Specific
yield
(percent)

14.0

15.5

3.0

23.2

10.8

10.0

12.2

21.6

8.8

.2


Coefficient of
permeability (gpd/ftt

Horizontal Vertical

0,1 0.03

1. .0


Sample
number

1

4

5

7

9

11

14

16

17

19


Depth below
land surface
(feet)

71,8 to
72,4
209 to
260.5
282.2 to
282.5
317.5 to
817.9
447.5 to
447.9
519.5 to
510.8
1,001.9 to
1,002.5
1,169.5 to
1,169.9
1,886.8 to
1,886.6
1,476.8 to
1,477.8


1Sample fractured at end of test. Permeability may be too high.


.0006

11

121

10

.004

.02


.0001

12

.4

15

.0003

.02


Formation

S

CR

W

I

AP

AP

AP

LC

LC

0





REPORT OF INVESTIGATIONS No. 42


of the nonequilibrium formula (Theis, 1935), (2) the family of
leaky aquifer curves (Cooper, 1963), or (3) a modified
nonequilibrium formula (Jacob, 1950).
Semi-confining beds that impede the movement of ground water
comprise what is commonly called an aquiclude. Ground water will
move through an aquiclude under hydrostatic pressure. For
instance, when the water table is higher than the piezometric
surface of an artesian aquifer, the potential leakage is downward
(recharge to the artesian aquifer) and vice versa. The rate at
which ground water moves through the aquiclude depends on the
vertical permeability and the hydraulic gradient across the
aquiclude.
The aquifers of the Green Swamp area are discussed in order
of occurrence from land surface downward: (1) the nonartesian
aquifer; (2) the secondary artesian aquifer; and (3) the Floridan
aquifer.


NONARTESIAN AQUIFER

DESCRIPTION OF THE AQUIFER

The nonartesian aquifer is composed of undifferentiated plastic
deposits (table 4) which consist of fine-to-coarse-grained quartz
sand with varying amounts of kaolinitic clay.
On the eastern side of the Green Swamp area (see fig. 8, A-A'),
the aquifer ranges from about 50 to more than 100 feet in thickness.
The permeability and specific yield is higher in the vicinity of the
ridges than in the central and western areas. A relatively thin
aquiclude, consisting of clay, forms the base of the aquifer.
On the western side of the Green Swamp area, the aquifer
ranges in thickness from 0 to about 50 feet. An aquiclude consisting
of sandy clay which thickens eastward and grades into the sand of
the nonartesian aquifer forms the base.

RECHARGE AND DISCHARGE

Ground water in the nonartesian aquifer is recharged primarily
by local rainfall. It is discharged by (1) evapotranspiration, (2)
flow into streams and lakes, (3) downward leakage into the Floridan
aquifer, and (4) outflow to areas of lower head outside of the Green
Swamp area.





FLORIDA GEOLOGICAL SURVEY


Most of the nonartesian ground water in the Green Swamp area
is discharged by evapotranspiration because the water table is
relatively close to the surface and surface drainage is poor.
Evapotranspiration losses are least in the sandy ridge areas that
rim the Green Swamp because the water table is farther beneath
the ground than in the interior.
Ground water percolates downward from the nonartesian aquifer
to recharge the underlying Floridan aquifer because the water table
is usually at a higher elevation than the piezometric surface
as shown by the hydrographs in figures 23-29 and the aquiclude
(undifferentiated clay) between the aquifers is relatively thin (see
fig. 8) and permeable. The coincidence of areas of high water table
and of high piezometric head is evidence of leakage. The amount
of ground water that percolates downward is equal to the net
outflow of artesian water from the underlying Floridan aquifer.
The quantity of ground water leaving the Polk piezometric high
in the Green Swamp area, hence leakage from the nonartesian
aquifer, is presented in the table on page 116.
Nonartesian ground water moves laterally to contribute to the
surface runoff from the area. The direction of movement is
generally governed by the topography. Therefore, ground-water
divides in the nonartesian aquifer closely coincide with surface
drainage divides shown in figure 5 except along the eastern
boundary of the area where some nonartesian ground water flows
laterally beneath the Lake Wales Ridge eastward to the Kissimmee
River basin. The quantity of nonartesian ground water leaving the
Green Swamp area by lateral seepage beneath the ridge was
estimated to be insignificant in the water-budget analysis.
Fluctuations of the water table were recorded in several shallow
wells and water-table lakes in and near the southern and eastern
parts of the area, shown in figures 23-29. No data were obtained in
the western part because the nonartesian aquifer is thin or absent.
The hydrographs of wells in the nonartesian aquifer are presented
with hydrographs of wells in the secondary artesian or Floridan
aquifers to show the hydraulic relation between aquifers and the
potential movement of water in a vertical direction.
No long-term records of water-table fluctuations are available
within the Green Swamp area. However, records of water levels
in a well located southeast of the Green Swamp area (810-136-2)
show that the highest and lowest water levels since 1948 occurred
during the period of investigation.






REPORT OF INVESTIGATIONS NO. 42


S Floridaon aquifer)
A 1 832-154-1


3-
4 832-154-2'-
(5Nonortesion pquifer)
3 mile
Ronf ol at well 832-54-1,2
3 --------------- --- ---


s soult


h of Mascotte

t-[.i


103
S i 102
101
100
99

o


813-149-2 (Non.oresan oquifer) 131



S4 ----------------- 813-149-1 ----- 128 -
(Floridon aquifer) 27
2.5 miles north of Polk City _





.... r- I ^ I .~929



821-202-3 (Floridon aquifer in unconfined area) 9

9 rules east of Dode Cty
Rtifoll at well 821-202-3
a: Q-








.I 2 I


JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC
1959
Figure 24. Hydrographs of water levels and rainfall at wells in the Green
Swamp area, 1959.

Water levels in most wells in the Green Swamp area show rises
in response to local daily rainfalls. Only wells 810-136-2 and
815-139-3, located in the sandy ridges east of the Green Swamp

area, show no response to local daily rainfall. Apparently, this is
due to the high retention of the thick section of sand through which
the water must percolate to reach the water table.
Hydrographs of water levels in wells located in the central
part of the Green Swamp area (figs. 27 and 28; wells 813-149-2,
i 3 129-- -- -- -





























813-150-2, 814-143-2, 822-149-2, 832-154-2) show that the water
table declined less than 5 feet from a wet to a dry period (1959-62).


near the surface and the aquifer afforded little capacity to store
21-5-,84132 2-4-,82142 hwta h ae
talr elndls hn5fe rmawtt r eid(996)
Durin th e er f15 n 90 h ae aleAine
nEa

n Ina


",,


2"


























, Well 8081551
1 Floridon aquifer
ie6 -

116
*_j"6 ---

S114
J 10 Well.815-157-2
S, Floridan aquifer


A


A^


I FA NDIFMAMJ O MAMJF FM J D F JMA
04 LJJF' MAMJJASOND AMJASOND JFMAMJJAS ONDDJPMAMJJASONDJFMAMJ'J ASOND J__MAMJJASONDJFMAMJJASONDJ FAMJSJON


1960


Figure 26. Hydrographs of water levels in Wells (808-155-1, 2) 4 miles north
of Lakeland and in a well (815-157-2) 12 miles north of Lakeland.


I-



i


1962


'4

6 ,
2
8 -





16 ""
I-



Ui
18
U.
20
-J
22 U
I-r



4

6*







REPORT OF INVESTIGATIONS NO. 42 73


136 Well 810-144-2 2
134 Nonortesion oquifer \

1324 1 _
132


Well 810-144-1 8
28 Floridon aquifer _

126 12
212

132 Well 813-149-2 0
NoX13 esian oqu~

_-_A\ -, /-
128 --4
Well 813-149-1 4
1 Floridon aquifer

124 ____
28 Well 813-150-2
S12 Nonoaresion aqu'fer 2
LU 126 r
N/ ^X ^ ./ -4 c
LJ -6.-
124 F--r"dan\aqifer/ 14
122 -j
1 4
> 32 Well 814-143-24
S130 Nonortesion oquifer
Well 814-143- -6 6
S 12 | Floridn oquifer -
LU
126 ___ __-\/ ,-.
S10
S124__
S94 Well 815-134-2
92 Nonodresion oquifer ._12 _"
a Well 815-134-1
19- Floidan aquifer -14
S90 ------

88 -16
130 Well 815-139-3 60
28 Nonarlesion oquifer 3b i _______
Well 815-139-2 -62
126 Floridon oquifer

24 -64
\ -66
122 6______
68
120 ________ _________ _______ __
1. 70
118 ________ ________ _____1- ______
126 Well 815-149-3 -- 6
124 Floridian aquifer I V t\ I A 6

122 8..... I ..... .......
1959 ,960 1961 1962
Figure 273: Hydrographs of water levels in wells (810-144-1, 2; 813-149-1,-2;
813-150-2; 814-143-1, 2; 815-149-3) in south-central Green Swamp and in wells
(815-134-1; 2; 815-139-2, 3) about 9 miles 'north of Haines City.








FLORIDA GEOLOGICAL SURVEY


116 We 822-138-2 2

-4
2114 o__i__ aqifer /

.12._ \ -

110
Well 822-138-1 -8
SFloridom oaqfer



114 r ^ ^ Well 822-149-2 0
S /\. l N-c oesiaon aogfer


Wel 822-149-1 -4
Q Flidn aquife V
6 Well 826-211-1
74 Fldn aqifer 6

72' -










62 4-- --






mFbaQgifer A


Wel832-454-2 -4
9pNofrticn aqufer
88
Well 833-137-2 34
86 PEndcn aquifer __
36
84-
\38
82 -4 0

-4
80

78 _______ _______ 42

76
S 4(


859 860 861


162


LL

r=
=D
o
z

CO

ni
Q




LLI


LLJ
-i
-
3





LUJ
03:
LL-


_I
LU
>
LU


[I


Figure 28. Hydrographs of water levels in wells (821-202-3; 822-149-1, 2;
832-154-1, 2) in north-central Green Swamp; in a well (826-211-1) 5 miles
north of Dade City; in wells (822-138-1, 2) 17 miles north of Haines City;
and in a well (833-137-2) 7 miles east of Clermont.






REPORT OF INVESTIGATIONS NO. 42


v^^, /<-4


-6
130
30 .:
--8

128 Well 810-144-1
c Floridan aquifer -10

S126
12
r 124
S136
Lake Mottie

134


132
Lake Lowery
130


128 I I
J FMAMJ JASONDJ FMAMJ JASON D J FMAMJ ASOND
1960 1961 1962
Figure 29. Hydrographs of water levels in wells 810-144-1, 2 and of Lake
Lowery and Lake Mattie.
additional rainfall. Therefore, the runoff was high. Although the
hydraulic gradient between the water table and the piezometric
surface indicated that water moved downward most of the time, a
reversal in direction was noted for dry periods.
Hydrographs of water levels in wells in the southwestern part
of the Green Swamp area (fig. 25, well 805-155-1 and fig, 26, well
808-155-2) show that the water table fluctuated between 5 and 10
feet during the period 1959-62. The water table remained near the
surface during the wet years of 1959 and 1960, and the aquifer
afforded little capacity for storing: rainfall. During the dry years
of 1961 and 1962, the water table was progressively lowered by
pumping from the Floridan aquifer south of the Green Swamp.





FLORIDA GEOLOGICAL SURVEY


The area of greatest decline was in the vicinity of well 808-155-2
where the secondary artesian aquifer is absent. Large fluctuationF
of the water table in this area indicate good recharge to the
Floridan aquifer and good hydraulic connection between the
aquifers.
Hydrographs of water levels in wells east of the Green Swamp
area (figs. 23, 27, and 28, wells 810-136-2, 815-134-2, 815-139-3, and
822-138-2) show that the water table fluctuated between 5 and 10
feet during the period 1959-62. The water table occurs at depths
ranging from about 2 feet to more than 70 feet below land surface.
The area has a potentially large capacity to store rainfall. Water
moves downward from the nonartesian aquifer to the Floridan
aquifer in the Lake Wales Ridge and moves upward in the valleys
of Davenport and Reedy creeks. The best hydraulic connection
between aquifers in the eastern part of the Green Swamp area
probably occurs beneath the Lake Wales Ridge. This is indicated
by almost identical fluctuations of water levels in wells 815-139-2,
-3 (fig. 27).
Water levels in wells and sinkhole lakes, located in the
southeastern part of the Green Swamp area, fluctuated about 5
feet (fig. 29). During wet periods, the water level is near or above
land surface and water is stored in lakes and swamps. During dry
periods, water levels decline due to lack of recharge and to pumping.
Water levels in the nonartesian aquifer are generally higher than
the piezometric surface indicating recharge to the Floridan aquifer.

HYDRAULICS OF THE NONARTESIAN AQUIFER

Permeability of a 3-foot section of the nonartesian aquifer
was determined in a well (810-144-2) in southeastern Green
Swamp and in a well (815-134-2) 5 miles east of Green Swamp by
using the slug test method (Ferris, 1962). The field coefficients of
permeability for the wells were determined to be about 50 gallons
per day per square foot (gpd/ft2) and about 40 gpd/ft2,
respectively. The results of laboratory tests of disturbed sand
samples collected from a test hole in the bottom of Lake Parker
near Lakeland (Stewart, 1959) ranged from 20 to 180 gpd/ft2
(table 8). The permeability of the aquifer is probably lower in the
interior of the Green Swamp area than in the surrounding ridges
because of greater clay content.
The specific yield of the nonartesian aquifer was determined
using a graphical analysis of rainfall and water-table fluctuations







REPORT OF INVESTIGATIONS No. 42


.n wells located generally along the eastern and southern bounda-
ries and in the interior. Continuous records of water-level fluctua-
tions and rainfall were collected at each well site. The data were an-
alyzed to select short periods during which all of the rainfall was
assumed to reach the water table. One or two-day periods were se-
lected when (1) antecedent conditions compensated for moisture
requirements of the unsaturated material above the water table;
(2) the water table was far enough below the ground to store all
the rainfall and none left as runoff; and (3) the rainfall was of
short duration, high intensity, and widespread. The rise in the wa-
ter table is directly proportional to the depth of rainfall. The spe-
cific yield of the aquifer therefore is inversely proportional to the
ratio of rise in the water table in inches to the depth of rainfall in
inches.

EASTERN-SOUTHERN RIDGE AREA


Well 810-144-2 (Nonortesion aquifer)
(010


5 Average slope=
5 4.5
Specific yield 22.2 %


0 --
0 5 10 15 20
RISE IN WATER LEVEL IN INCHES
INTERIOR OF THE

Well 813-149-2 (Nonartesion aquifer)



S5
SAverage slope =-
Specific yield 12 5% --


0 5 10 15- 20
RISE IN WATER LEVEL IN INCHES


Well 822-138-2(Nonarlesion aquifer)
10




z 4.7
4 1'. Average slope=
a: o ^ Specific yield 47%
0 5 10 15 20
RISE IN WATER LEVEL IN INCHES
GREEN SWAMP AREA


Well 832-154-2 (Nonortesian

10
2:


z
J 5-

vi
'2


aquifer)


Average slope 10
Specific yield IB% __ .--
0'


0 5 10 15 21
RISE IN WATER LEVEL IN INCHES


WESTERN AREA

Well 821-202-3 (Unconfined Floridan aquifer)

EXPLANATION
Plots of change in water level ofter selected
5Average lope periods of rainfall recorded at same well.
Average slope =-
Specific yield 14.3% _, ----- Line represents the overage change in water level.

S..._.----. -- Specific yield = average slope X 100
0 5 10 1 20
RISE IN WATER LEVEL IN INCHES

SFigure 30. Graphical determination of specific yield.






FLORIDA GEOLOGICAL SURVEY


The specific yield of the sand comprising the nonartesian aquifer
ranged from 31.0 to 43.9 percent by laboratory analysis (table 8)
and from 12.5 to 47 percent by analysis of water-level fluctuations
caused by local rainfall, shown in figure 30.
The highest values (22.2 and 47 percent) are considered to be
representative of the aquifer in the sandy ridges that surround
the eastern and southern part of the Green Swamp area. The lower
values (12.5 and 18 percent) are considered to be representative
for the clayey sands in the central portion of the area.

CHEMICAL CHARACTERISTICS OF NONARTESIAN GROUND WATER

Water in the nonartesian aquifer in the eastern part of the
Green Swamp area is less mineralized than that in the Floridan
aquifer. The mineral content of water from the shallow wells in
this area, ranging from 30 to 50 ppm, is due to the low solubility
of the sand and clay which comprise the aquifer. The principal
dissolved mineral constituents are sodium and chloride. The iron
content ranged from 0.19 to 4.0 ppm. The 4.0 ppm in water from
well 808-139-1 was the highest found in the Green Swamp area.
The color of water from wells in the area was less than 15 units
which is lower than that of surface water.
In the western part of the area, the nonartesian aquifer is
almost nonexistent. The chemical characteristics of water in most
shallow wells and in the Floridan aquifer are similar.

SECONDARY ARTESIAN AQUIFER

RELATION TO GREEN SWAMP AREA

The secondary artesian aquifer is composed of interbedded
limestone in the undifferentiated clay (table 4). About 36 feet of
the aquifer is present in well 810-144-1 in the southern part of the
Green Swamp area. The aquifer thickens southward from the
southern boundary of the area and is an important source of
artesian water in southern Polk County. The aquifer pinches out
northward and is absent in most of the Green Swamp area.
The aquifer is recharged by downward percolation of water from
the overlying nonartesian aquifer and discharges principally by.
downward leakage to the Floridan aquifer.
Fluctuations of the piezometric surface of the secondary
artesian aquifer were recorded in well 805-155-3 (fig. 25) and the





REPORT OF INVESTIGATIONS NO. 42


surface is between the water. table of the nonartesian aquifer and
the piezometric surface of the Floridan aquifer. The clay beds
separating the aquifers are leaky as indicated by the conformance
of the fluctuations of the piezometric surfaces.

FLORIDAN AQUIFER

DESCRIPTION OF THE AQUIFER

The Floridan aquifer is the principal source of artesian ground
water in Florida. In the Green Swamp area, the aquifer is exposed
at the surface in the western and northwestern parts and occurs
at depths ranging from 50 to more than 200 feet below land surface
in the eastern part, shown in figure 31.
The Floridan aquifer is composed of marine limestones that have
been exposed to erosion and solution weathering. The formations
that comprise the aquifer in the Green Swamp area range in age
from middle Eocene to Oligocene (table 4). The Geologic cross
sections (fig. 8) show the limestone aquifer and the position of the
overlying plastic material.
The top of the aquifer is highest (90 to 100 feet above msl) in
the west-central part of the area as shown in figure 32. The base
of the aquifer was determined by the first major occurrence of
gypsum. Apparently, the gypsum fills the pores in the lower part
of the Avon Park Limestone. The existing data indicate that the
aquifer is about 1,000 feet thick in the central part of the area.
The transmissibility of the Floridan aquifer will vary depending
primarily on the occurrence of solution features such as caverns,
cavities, and pipes. The presence of dolomite in the limestone is an
indication of solution activity. Dolomite zones and cavities
generally occur in the Inglis Formation and the Avon Park
Limestone which are highly permeable. Logs of numerous wells in
the Green Swamp area indicate that a large percentage of the
cavities in the aquifer contain sand which reduces the transmissi-
bility. The low yields of some wells in the Lake Wales Ridge area
are attributed to sand-filled and clay-filled caverns.

RECHARGE AND DISCHARGE

The Floridan aquifer in the Green Swamp area is recharged by
rainfall that percolates downward from the surface of the ground
either through the nonartesian aquifer and aquiclude or directly





FLORIDA GEOLOGICAL SURVEY


into the Floridan aquifer in outcrop areas. Water is discharged
from the aquifer by (1) outflow to areas of lower piezometric head,
(2) seepage and spring flow into the streams, (3) upward leakage
to the nonartesian aquifer in areas of artesian flow, (4)
evapotranspiration, or (5) pumpage.
Piezometric maps of the area were made from water-level
measurements in about four hundred wells. These maps were
analyzed to determine areas of recharge and discharge and the
direction and rate of ground-water movement.
The first piezometric map of peninsular Florida was prepared
by Stringfield (1936) and the latest, figure 33, was prepared by
Healy (1961).
Ground water moves from high head to low head in a direction
perpendicular to the contour lines. Piezometric mounds, referred
to as "highs," usually indicate areas of recharge to the aquifer.
Piezometric depressions or troughs, referred to as "lows," usually
indicate areas of discharge from the aquifer. Recharge and
discharge may take place anywhere from the high to the low
where geologic and hydrologic conditions are favorable. Therefore,
there is no one point of recharge nor one point of discharge. The
difference in head between contour lines divided by the distance
between them is the hydraulic gradient of the piezometric surface.
The hydraulic gradient varies because of (1) unequal amounts of
recharge or discharge, (2) differences in permeability within the
aquifer, (3) differences in thickness of the aquifer, or (4) boundary
conditions within the aquifer.
Ground water in the central part of the Florida Peninsula moves
outward in all directions from an elongated piezometric high that
extends approximately from central Lake County to southern
Highlands County, generally referred to as the "Polk high," and
from a smaller piezometric high in Pasco County, commonly
referred to as the "Pasco high." The Green Swamp area occupies
a relatively small part of the Polk high. The top of the Polk high
occurs within the southeastern part of the Green Swamp area.
Ground-water drainage areas in the Floridan aquifer do not
coincide with the surface-water drainage areas in the Green Swamp,
shown in figure 34. The ground-water divides in the aquifer shift
slightly in response to recharge and discharge. Therefore, the
positions of the divides as shown in figure 34 were considered to be
average for determining the size of the ground-water drainage
areas that contribute outflow from the Green Swamp area toward
the major surface drainage areas. Water in the Floridan aquifer






REPORT OF INVESTIGATIONS NO. 42


moves generally from the southeastern part of the Green Swamp
area eastward toward the Kissimmee River Basin; westward toward
the Hillsborough and Withlacoochee River basins; southward
toward the Peace and Alafia River basins; and northward toward
the St. Johns River basin.
Figures 35 and 36 show the shape of the piezometric surface of
the Floridan aquifer in the Green Swamp area and vicinity during
a wet period (November 1959) and during a dry period (May 1962).
Analysis of the maps shows the direction of movement of ground
water did not change appreciably from wet to dry periods but the
elevations of the piezometric surface declined. The decline was
greatest along the southern and western borders and least in the
interior of the Green Swamp area. Lows or troughs in the
piezometric surface indicate that ground water discharges into
Withlacoochee River through a spring at the mouth of Gator Creek
and downstream from Dade City; into Hillsborough River at Crystal
Springs; into Blackwater Creek; into Davenport and Reedy Creeks;
and into Horse Creek. Closed depressions, such as those in the
vicinity of Lakeland, indicate the effects of pumping.
Natural hydraulic gradients, indicated by the spacing of the
contour lines in figures 35 and 36, are steep toward the Hillsborough
River on the western side of Green Swamp and toward Reedy,
Davenport, and Horse Creeks on the eastern side. The base flow
of Hillsborough River below Crystal Springs is sustained by more
than 50 cfs of ground-water inflow from the Floridan aquifer. The
base flows of streams on the eastern side of the area are sustained
by relatively small amounts of ground-water inflow from the
Floridan aquifer. Obviously then, the steep gradient toward the
east is caused by some factor other than a high rate of
ground-water discharge. The geology along the eastern side of the
Green Swamp area (see fig. 8, A-A') suggests that the steep
eastward gradient is due to a barrier, or constriction in the aquifer,
that was formed by natural grouting (sink-hole collapse and
cavity-fill) along the fractures and joints in the limestone. Thus,
the barrier effect decreases the ground-water outflow and a piezo-
metric high is formed along the eastern side.
Figure 37 shows the decline in the piezometric surface from the
wet period (1959-60) to the dry period (1962). Water levels
declined least in the interior of the Green Swamp, in the
Hillsborough River basin, and in the Kissimmee River basin
(Davenport, Horse, and Reedy-creeks). Water levels declined most
along the southern (near Lakeland), western (near Dade City),





FLORIDA GEOLOGICAL SURVEY


and northeastern boundaries. Water levels declined about 5 feet in
discharge areas (Hillsborough and Kissimmee River basins)
because the ground-water discharge is relatively uniform regardless
of seasonal variations in rainfall. Water levels declined less than 5
feet in the interior of the Green Swamp because there was little
local pumpage and the rainfall during the dry period was about
enough to balance the outflow; therefore, the aquifer remained
relatively full.
The area surrounding the Green Swamp is more populated and
developed and increased pumping during the dry period (1962)
caused a greater decline in piezometric levels than would have
occurred under natural conditions. If there had been no appreciable
increase in pumping, the map could be used to detect areal changes
in the hydraulic characteristics of the aquifer, particularly changes
in permeability.
The northernmost extent of an area of heavy pumping for
mining, industrial, municipal, and irrigational supplies is in the
vicinity of Lakeland where the water levels declined about 20 feet.
The drawdown is confined to the southern boundary of Green
Swamp, suggesting that the area of the sinkhole-riddled ridges
around southern Green Swamp is a recharge area. Water levels
declined between 10 and 20 feet on the western side of Green
Swamp in the vicinity of Dade City. This is considered to be an
area of high permeability and good recharge. Water levels declined
about 10 feet in the northeastern area which is also considered to
be an area of high permeability and good recharge.
The general conclusion is that increase in discharge (natural
or pumping) does not appreciably increase the lateral movement
of ground water from the interior of Green Swamp but does affect
the border areas.

HYDRAULICS OF THE FLORIDAN AQUIFER

Coefficients of horizontal and vertical permeability were
determined for selected core samples of the limestones that
comprise the Floridan aquifer. The samples were obtained from
well 805-154-8, located just north of Lake Parker. The laboratory
determinations are presented in table 9. The permeability values
ranged from 0.0001 to 19 gpd/ft2. The specific yields ranged from
0.2 to 23.2 percent. However, the specific yield determined in the
laboratory represents that of the rock sample and not of the aquifer
as confined.







REPORT OF INVESTIGATIONS NO. 42 83


Pumping tests were conducted in Green Swamp area and
vicinity to determine coefficients of transmissibility (T) and storage
(S) for the Floridan aquifer. The results of the tests are presented
in table 10. Values of T ranged from about 20,000 gpd/ft to about
700,000 gpd/ft. The storage coefficients ranged from 0.013 to 0.0018
which means that for 1 foot change in head of the piezometric



TABLE 10. Pumping test data (Floridan aquifer)


Aquifer Average field
Coefficient Coefficient penetration coefficient of
transmissibility Coefficient of leakage (nearest permeability
Well number gpd/ft) of storage (gpd/ft2/ft) ten feet) (gpd/ft2)

(a) Determined by one or more observation wells

807-154-4 "5r720,000 "0.0036 1,130 637
808-153-2 520.000 .0057 510 1,020
814-139-5 b'C680,000 .0018 .... 350 1,940
814-139-5 b'cl,150,000 .012 0.042 350 3,280
816-135-2 120,000 .011 ._- 360 333
821-202-1 c22,000 .003 .022 130 169
828-154-2 293,000 .013 .036 260 1,130

(b) Determined by observations in the pumped well

807-154-4 I*'1,150,000 1. 1,130 1,020
810-144-1 110,000 340 324
813-149-1 40,000 .. 140 286
813-201-1 62,000 ... .... 240 258
814-139-5 c120,000 350 340
814-143-1 77,000 200 385
814-134-1 37,000 _160 231
815-149-3 29,000 170 171
815-157-2 84,000 .... 130- 646
816-206-1 150,000 _. 180 833
821-202-1 c22,000 _130 169
822-138-1 26,000 230 113
822-149-1 32.000 130 246
826-211-1 300.000 190 -1,580
827-158-1 57,000 160 356
832-154-1 28,000 100 280


aAverage of two tests.
bDetermined to be invalid.
CAnalysed by Theis (1935)


See pumping test analysis section.
type curve and semilog method (Jacob, 1950).






84 FLORIDA GEOLOGICAL SURVEY

surface, the aquifer releases or takes into storage 0.013 to 0.0013
foot of water per square foot of surface area of the aquifer.
A comparison of the results of laboratory tests with pumping
tests indicate that the permeability of the Floridan aquifer is
largely dependent upon the presence of solution holes (caverns,
pipes, etc.) which, of course, are not represented in the small core
samples.


Davenport- Horse Creek area
-Eastern area
----*-- -*-- Northwestern area
a-- --- --- Southwestern area
----x---- x-- Dode City area


1 r I1 111 i iI I I i II
t---

-A
/ /


S--/ / /
I: -






SI I

0,000 100,000 1,000,000
COEFFICIENT OF TRANSMISSIBILITY
(gpd/ft)
Figure 38. Graphs showing the relations between coefficient of transmissibility
and depth of penetration in the Floridan aquifer.


The values of T for the pumping tests in table 10 were plotted
against depth of aquifer penetration, as shown in figure 38. The
wide range in values of T are caused by unequal penetration and by
areal and vertical variations in permeability. Areal analysis of
the data indicate that generally the eastern side (Davenport-
Horse Creek area) of the Green Swamp area has a low value of T
and the western side (Dade City) has a high value of T. Therefore.
the test data were evaluated by location and depth of penetration.






REPORT OF INVESTIGATIONS No. 42


The average field coefficients of permeability (Pf) table 10) were
averaged for each area and then multiplied by the approximate
thickness of the aquifer (1,000 feet) to estimate the coefficient of
transmissibility (Te) for each representative area. The data were
analyzed for (1) the Davenport-Horse Creek area east of the Lake
Wales Ridge; (2) the eastern area, which includes the general area
between State Highway 33 and U.S. Highway 27; (3) the
northwestern area, which includes the area west of State Highway
33 and north of the Withlacoochee River; (4) the southwestern
area, which includes the area west of State Highway 33 and south
of the Withlacoochee River; and (5) the Dade City area west of the
Withlacoochee River. The results of the computations (expressed
to the nearest hundred thousand gpd/ft) are presented in table 11.
Computations of ground-water movement into or out of the area
used in the water-budget analysis were based on the estimated
coefficients of transmissibility shown in table 11.

TABLE 11. Estimates of transmissibility
T,,
Area (gpd/ft)

1. Davenport-Horse Creek 200,000
2. Eastern 300,000
3. Northwestern 500,000
4. Southwestern 600,000
5. Dade City 1,200,000

Barrier boundaries caused variations in the values of T in the
vicinity of the Lake Wales Ridge. Observation wells 815-139-2 and
815-140-1 were used to observe the effects of drawdown and
recovery caused by pumping well 814-139-5. Water level measure-
ments were also made in the pumped well. The data were analyzed
by the Theis method (1935), the family of leaky aquifer curves by
Cooper (1936), and the Jacob method (1950). The data defined
three curves, figure 39, with T values of 680,000 gpd/ft and
1,150,000 gpd/ft, for the observation wells and 120,000 gpd/ft for
the pumped well. The wide variation in T probably indicates that
the basic assumptions prerequisite for the analysis of the data do
not apply and is probably caused by heterogeneity of the aquifer
and existence of a barrier boundary. The test site is in a faulted
area (see fig. 8, C-C'). Figure 40 shows the location of the wells
with respect to sand-filled fractures in the underlying lime-
stone along the Lake Wales Ridge. The variation in T values
is probably caused by sand-filled fractures which act as barriers






FLORIDA GEOLOGICAL SURVEY


OIf
01 Usi-n-
10-6

a Using


10-5
Time(minutes) / Distance (feet)
Theis method (1935) and Cooper method (1963)


I I lilt II I 1 11











T= 120,000 gpd/ft
Q= 1,600 g.pm.



S I l ill I 1 1I


I0
TIME, IN MINUTES
b. Using Jacob method (1950) and pumped well.


100 2C(


Figure 39. Graphs of pumping test at a well (814-139-5)
of Haines City.


about 9 miles north


289
I.--
LI

29-
S2

o

^ 301



311L






REPORT OF INVESTIGATIONS No. 42 87


81040' 8139
28'160+g 1 EXPLANATION
Pumpf% well
Observation well
Well

n +5 Lower number is the elevation of the
zn top of the Florldon aquifer, in feet,
0 referred to mean sea level.
M -/00--
SR 5 Contour represents the approximate
o elevation of the top of the Floridon
Aquifer, in feet, referred to mean
-3 419 sea level. Contour interval 100 feet
Land surface contour, In feet, above
meon sea level. Contour interval 25 foee

2 Sand filled fractures
3 Note: structure not shown
lo0 39 I mile

Figure 40. Map showing environment affecting pumping test at a well
(814-139-5) about 9 miles north of Haines City.


between the pumped well and the two observation wells. The
barriers decrease the drawdown in the observation wells giving
erroneously high values of T. Probably the best value of T was
obtained from data from the pumped well which is comparable to
the results of a nearby test (see table 10, well 816-135-2).

CHEMICAL QUALITY OF WATER IN THE FLORIDAN AQUIFER

The quality of water in the Green Swamp area is good. The
total mineral content is generally less than 350 ppm. Water
containing a mineral content of less than 500 ppm is usable for most
purposes. The water of the Floridan aquifer is more mineralized
(100-400 ppm) than surface water or water from the nonartesian
aquifer (20-50 ppm). The higher mineral content is caused by
contact of water with materials that are more soluble. About 75
percent (by weight) of the mineral constituents dissolved in water
of the Floridan aquifer are calcium and bicarbonate that cause the
water to be hard and alkaline. Hardness, illustrated in figure 41,
is one of the more undesirable characteristics. The water ranges
from moderately hard in the eastern part of Green Swamp to very
hard in the western part.
Figure 42 shows the iron content of water in the Floridan
aquifer in the Green Swamp area. The highest concentrations of






FLORIDA GEOLOGICAL SURVEY


iron are found in the west-central part of the area. Iron greater
than 0.20 ppm generally should be removed for most uses.
Other dissolved mineral constituents, including silica, potassium,
sulfate, and chloride, occur in concentrations generally less thail
10 ppm. Fluoride and nitrate are usually present in concentrations
less than 1.0 ppm. The water is clear (color less than 5 units), the
temperature ranges from 74 to 780F., and the pH ranges from 6.8
to 8.6 units.
Water from a well (830-210-2) near the northwestern boundary
had a sulfate concentration of 101 ppm. The high sulfate
concentration is due to contact of water with gypsum. Samples of


Figure 41. Hardness of water in the Floridan aquifer in the Green Swaml
area.




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STATE OF FLORIDA STATE BOARD OF CONSERVATION DIVISION OF GEOLOGY FLORIDA GEOLOGICAL SURVEY Robert O. Vernon, Director REPORT OF INVESTIGATIONS NO. 42 HYDROLOGY OF GREEN SWAMP AREA IN CENTRAL FLORIDA By R. W. Pride, F. W. Meyer, and R. N. Cherry Prepared by the UNITED STATES GEOLOGICAL SURVEY in cooperation with the FLORIDA GEOLOGICAL SURVEY, the FLORIDA DIVISION OF WATER RESOURCES AND CONSERVATION, and the SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT TALLAHASSEE 1966

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FLORIDA STATE BOARD OF CONSERVATION HAYDON BURNS Governor TOM ADAMS EARL FAIRCLOTH Secretary of State Attorney General BROWARD WILLIAMS FRED O. DICKINSON, JR. Treasurer Comptroller FLOYD T. CHRISTIAN DOYLE CONNER Superintendent of Public Instruction Commissioner of Agriculture W. RANDOLPH HODGES Director ii

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LETTER OF TRANSMITTAL §fiorda jeoloqical Survey tCalalhassee February 4, 1966 Honorable Haydon Burns, Chairman Florida State Board of Conservation Tallahassee, Florida Dear Governor Burns: For many years, it has been thought that much of the recharge of water to Florida's prolific artesian aquifer occurred in the Green Swamp area. For this reason, it was believed that a detailed geologic and hydrologic study of the area would be helpful and necessary. I am pleased to report to you that a study, "Hydrology of Green Swamp Area in Central Florida," prepared by R. W. Pride, F. W. Meyer, and R. N. Cherry, of the U. S. Geological Survey, in cooperation with the Division of Geology of the State Board of Conservation, will be published as Florida Geological Survey Report of Investigations No. 42. This report provides all of the data necessary for the wise utilization, and perhaps for the preservation, of parts of the Green Swamp area. It will also assist in the planning for the FourRivers area to alleviate floods and to conserve our water and land. Respectfully yours, Robert O. Vernon Director and State Geologist S111

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Completed manuscript received September 9, 1965 Published for the Florida Geological Survey By the E. O. Painter Printing Company DeLand, Florida iv

PAGE 5

CONTENTS Preface -_.---_ ... ------------.-...-..--..._--..-----..-.. ..----XI Abstract ______ _ _ 1 Introduction -----.........--..-_--__--________.--3 Purpose and scope ........---____ .._----------4 Previous investigations -----------___ ----.-..__ .-----4 4 Methods of investigation _------------------------5 Geography _........_.--------...------.. --19 Location ---__ ---------_-----_--...--.---_------. -------19 Topography __.-_...--------------------------20 Drainage ___-. ..------------------------.------...---------_--__ 21 Culture and development ---.........-----_----.......--22 Climate -_.. ... .. .. ....._______-------------------------23 Precipitation -__ ----_____ ---_-----_--------.--23 Temperature _ -_-----------24 Environmental factors affecting the quality of water ----.-------26 Geology _--_-__.-______ ------...--------____-----------___--------27 Formations -__ -..... -------_.. _----------..28 Undifferentiated clastic deposits ..-----.------.-----------_ ------28 Undifferentiated clay ___---------------------------------30 Suwannee Limestone .---.---_--__-----...-----30 Ocala Group ..--------... ......---------------31 Crystal River Formation -----------------.--_---_-.--31 Williston Formation ------------------------------------.--_ 31 Inglis Formation __----.-----__----_---------31 Avon Park Limestone _....------------------.. ------.. 31 Structure .. ----_...-----........ .... --_ 32 Hydrology _____...._____ __---_-------------------33 Withlacoochee River basin ......--------___---.--.--33 Description of basin -----------------------------33 Streamflow ----.__-..---. _ -----.----------.--.-35 Chemical characteristics of surface water __------------------------41 Oklawaha River basin .--_---------------.----------44 Description of basin ---------------_-------------------------------__ -44Streamflow _____-------47 Chemical characteristics of surface water _-------------49 Hillsborough River basin ____-----------49 Relation to Green Swamp area 49 Streamflow _ -----------52 Chemical characteristics of surface water ----52 Kissimmee River basin -53 Relation to Green Swamp area --_____ -----_-_-..---------53 Streamflow --------------53 Chemical characteristics of surface water-------------54 Peace River basin ---------------55 Relation to Green Swamp area ----55 Streamflow ---------56 Diversions and interconnections of basins 56 Effects of man-made changes ----------53 v

PAGE 6

Ground-water accretions to streamflow in Horse and Pony Creek basins _.. -_ --....----__ .._ ....... ..------------------.. ---.. 61 Aquifers .---........ ------------_. ..--------...........----------..----. 64 Nonartesian aquifer .-__ .........-----------------------. 69 Description of the aquifer ..--.. .. .-...........-----------------. --.... ---. 69 Recharge and discharge ....-------...-.-------------------. 69 Hydraulics of the nonartesian aquifer ------.. ........-.------------. 76 Chemical characteristics of nonartesian ground water ------78 Secondary artesian aquifer .....------.-....------------.. --78 Relation to Green Swamp area ..........-----.---------------78 Floridan aquifer ....-............... ---------------79 Description of the aquifer ----...---------------------------79 Recharge and discharge .---------------------------79 Hydraulics of the Floridan aquifer ................----.--------------. 82 Chemical quality of water in the Floridan aquifer ..----....--...---87 Hydrochemistry of the Floridan aquifer in central Florida .---. 89 Analysis of the hydrologic system .. .--._-.. .--.------.-------------. 92 Rainfall, runoff, and water loss --...-..-------.. -. -----------------------.. 92 Water-budget studies .......----------------------.--.--------99 Evaporation and water budget of Lake Helene ...---....--...-.-----------.. 101 Comparison of eastern and western basins ...-... .... .------------.. 105 Outflow from Green Swamp area ....................------------.---. -109 Evaluation of proposed plan of water control __...----.--.--------.----. 119 Reduction of flood peaks in the Hillsborough River ....--.....-...---------... 119 Reduction of flood peaks in the Withlacoochee River ...........---------.. 122 Effect of water impoundment in Green Swamp Reservoir on ground-water levels ....------...---.------------------------------125 Effect of water impoundment in Southeastern Conservation Area on ground-water levels ...... ..... ..--------------------126 Significance of the hydrology of the area _ .--....------..--------.127 References -. -----------------------------------..---. 131 Glossary .------.-.------------------------------134 ILLUSTRATIONS Figure Page 1 Ma.p of Florida showing location of Green Swamp area ------3 1 Map showing data-collection points in Green Swamp area .. In pocket 3 Diagram showing the well-numbering system used in Florida ..----. 6 4 Map showing topography of central Florida and its relation to Green Swamp area _ -------___-------... _. In pocket 5 Map showing surface-water drainage features of Green Swamp area ___---In pocket 6 Graphs showing annual and mean monthly rainfall of Green Swamp area ----_.. 25 7 Relation of annual water loss to temperature in humid areas _...26 8 Generalized geologic cross sections along lines A-A', B-B' and C-C' _ _-----------In pocket 9 Map showing contours on top of the Avon Park Limestone __ In pocket 10 Flow-duration curves for Withlacoochee River basin, 1931-62 -..----. 37 vi

PAGE 7

11 Map showing results of low-flow investigation of Withlacoochee River, May 23-25, 1961 -...-...... --..-.--.... ----.--------In pocket 12 Graphs showing annual and mean monthly discharge of Withlacoochee River at Trilby ._-.. -_.-____ ...-..-...... ...--------. ---------40 13 Relation of mineral content to discharge at gaging stations in Withlacoochee River basin ..--..----..-..-....-------------------42 14 Flow diagram of the upper Oklawaha River .___--------.__.------------. 45 15 Flow-duration curve for Big Creek near Clermont, 1931-62 .--..-..-----. 50 16 Relation of mineral content to discharge at gaging stations in upper Palatlakaha Creek basin .........---...............-------------------.......51 17 Relation of mineral content to discharge, Hillsborough River near Zephyrhills ---..---.._. ............-----------.-----------------------. .53 18 Relation of mineral content to discharge, Horse Creek at Davenport 54 19 Double-mass curves of measured runoff versus computed runoff, Withlacoochee River and Palatlakaha Creek basins .--.--------60 20 Graphs of monthly rainfall and runoff for July 1960 to June 1962 and estimated base flows for November 1960 to June 1962, Horse Creek at Davenport _____ ... --. ......-...-..-----.. --------------62 21 Graphs of monthly rainfall and runoff for uly 1960 to June 1962 and estimated base flows for November 1960 to June 1962, Pony Creek near Polk City .-...---.-.---....----...----.------------.63 22 Flow-duration curves for Horse Creek at Davenport and Pony Creek near Polk City, 1960-62 .------..........---......------.....---...---....-.----. 66 23 Hydrographs of long-term records of ground-water levels near the Green Swamp area --...-----.................-------....------....--In pocket 24 Hydrographs of water levels and rainfall at wells in the Green Swamp' area, 1959 --...----. ---..-.....-------------..... --..-.....--..------71 25 Hydrographs of water levels in wells (805-155-1, 2, and 3) near Lakeland .............__.--------------------........-------.. --..In pocket 26 Hydrographs of water levels in wells (808-155-1, 2) 4 miles north of Lakeland and in a well (815-157-2) 12 miles north of Lakeland _-...---..... .....-------___ ...---...... -.-------------72 27 Hydrographs of water levels in wells (810-144-1, 2; 813-149-1, 2; 813-150-2; 814-143-1, 2; 815-149-3) in south-central Green Swamp and in wells (815-134-1, 2; 815-139-2, 3) about 9 miles north of Haines City ..............----..----..... _.. ....-----..... .....-----.. 73 28 Hydrographs of water levels in wells (821-202-3; 822-149-1, 2; 832-154-1, 2) in north-central Green Swamp; in a well (826211-1) 5 miles north of Dade City; in wells (822-138-1, 2) 17 miles north of Haines City; and in a well (833-137-2) 7 miles east of Clermont ..-----. --____-. -----__.. __ ___ --___ -__---... 74 29 Hydrographs of water levels in wells 810-144-1, 2 and of Lake Lowery and Lake Mattie .......----....-.....---------.... .. ..__ .. ... 75 30 Graphical determination of specific yield --_ ---_.-..---77 31 Map of Green Swamp area showing depths to the top of the Floridan aquifer .-----..--.... ..------------.--..-....... In pocket 32 Map of Green Swamp area showing the limestone formations that comprise the top of the Floridan aquifer and contours on its upper surface -.--------------------------................. In pocket 33 Map of Florida showing contours on the piezometric surface of the Floridan aquifer, 1961 ---...................-----------------...... .. In pocket vii

PAGE 8

34 Map showing major surface drainage areas and their groundwater contributing areas in the Floridan aquifer ........_--_ .In pocket 35 Map of the Green Swamp area showing contours on the piezometric surface of the Floridan aquifer during a wet period, November 1959 .--.....___-------_ _.._ ___ _ In pocket 36 Map of the Green Swamp area showing contours on the piezometric surface of the Floridan aquifer during a dry period, May 1962 -____--___ _--------------.._ .In pocket 37 Map showing decline in piezometric surface of the Floridan aquifer, November 1959 to May 1962 -__---_ -----......------...... --.......... In pocket 38 Graphs showing the relations between coefficient of transmissibility and depth of penetration in the Floridan aquifer _-__..... .. 84 39 Graphs of pumping test at a well (814-139-5) about 9 miles north of Haines City ------------------------------------...-..... 86 40 Map showing environment affecting pumping test at a well (814-139-5) about 9 miles north of Haines City ----------____ ... 87 41 Hardness of water in the Floridan aquifer in Green Swamp area --88 42 Iron content of water in the Floridan aquifer in Green Swamp area _ ___-__-----.---.--..... --------...--....... --.--.....-....-.89 43 Map of central Florida showing the percentage of calcium carbonate saturation of water in the Floridan aquifer ---......---......... -91 44 Vertical distribution of chloride content of water in wells across central Florida ..--. -..--.--............----.........----.........----.----. 93 45 Map of central Florida showing mineral content of water in the Floridan aquifer -_-...--............--------........... ... .. ... .... 94 46 Relation of effective annual rainfall and annual water loss, Withlacoochee River at Trilby, 1931-61 .--------------------_ --...----..... .96 47 Relation of effective annual rainfall and annual runoff, Withlacoochee River at Trilby, 1931-61 ................---... _ _ ---------------------. .97 48 Relation of effective annual rainfall and annual water loss, Palatlakaha Creek above Mascotte, 1946-61 .........-----.-----....----._ --. 98 49 Relation of effective annual rainfall and annual runoff, Palatlakaha Creek above Mascotte, 1946-61 ___.---___--...-_---..-....---.-.. 99 50 Map of Lake Helene showing depth contours and locations of data-collection equipment -__.-.----.------. ---.--.------................... 103 51 Hydrograph of daily stage for Lake Helene, 1961-62 --.-..........-........... 104 52 Hydrographs of streamflow from eastern and western basins in Green Swamp area, 1959-61 __-------------------.................... In pocket 53 Sketch showing analysis of a flow section -__-----...-----------... ....._.. 114 54 Map showing plan of proposed improvements in Green Swamp area in Four Rivers basins ---------__ ---------------..................... In pocket 55 Hydrographs of mean daily discharge for three Hillsborough River gaging stations, flood of March 1960 ----------------------.......-.......... 120 56 Hydrographs of computed mean daily stage of Hillsborough River at 22nd Street, Tampa, flood of March 1960 ---.------------........... 121 57 Relation between basin runoff and drainage area for Withlacoochee River, March 16 to April 20, 1960 ..___.----------------------........... 123 58 Relation between peak discharge and drainage area for Withlacoochee River, flood of March 1960 ---.---------------------------.-----.......... 124 viii

PAGE 9

TABLES Table Page 1 Surface-water data-collection points in Green Swamp area and vicinity ... _ _..... ._.........._...------.......-----........... .. -----_ 7-------7 2 Ground-water data-collection points in Green Swamp area and vicinity ...---.... .... _ .....---______ ....... .. .--..........----. .....12 3 Test-well data in Green Swamp area and vicinity ----. --------_ -16 4 Geologic formations and their water-bearing characteristics in Green Swamp area and vicinity -------------------29 5 Streamflow data for Withlacoochee River basin gaging stations in Green Swamp area .-............-.......-..... .....------------------36 6 Streamflow data for Palatlakaha Creek basin gaging stations in Green Swamp area ...............------..... __-------------------..----. 48 7 Monthly water budgets for Horse Creek and Pony Creek basins, 1960-62 .--. -.------------------___ .-65 8 Hydrologic analyses of disturbed sand samples from a test hole in Lake Parker near Lakeland --. ---........-------.. -----...... ....---. 67 9 Hydrologic analyses of core samples from a well (805-154-8) near Lakeland -----. _---------__ ------------68 10 Pumping test data (Floridan aquifer) ------------------------83 11 Estimates of transmissibility ____ ------------------------85 12 Monthly water budget for Lake Helene near Polk City, 1962 -----106 13 Ground-water outflow from the Floridan aquifer for eastern and western basins -_------------------___----_ 110 14 Comparison of budget factors for eastern and western basins -----111 15 Surface-water outflow from Green Swamp area, July 1958 to June 1962 ___.---------------__.-----------. 112 16 Ground-water outflow from the Polk piezometric high in Green Swamp area _--_ ------------------------116 17 Ground-water outflow from Green Swamp area -----_----------_ _ 117 18 Summary of water-budget factors in Green Swamp area, 195961 -----.---------------------------------118 ix

PAGE 10

PREFACE This report was prepared by the Water Resources Division of the U. S. Geological Survey in Cooperation with the Florida Geological Survey, the Florida Division of Water Resources and Conservation, and the Southwest Florida Water Management District. The authors wish to express their appreciation for the cooperation of the many residents and public officials for information given during the well inventory and reconnaissance of the area. Special acknowledgement is due the Florida State Road Department, the Florida Forest Service, and property owners who granted permission to drill test wells. The following agencies made financial contributions for the collecting of data used in this report: Hillsborough County, Marion County, Pasco County, Polk County, Sumter County, Lake Apopka Recreation and Water Conservation Control Authority, Oklawaha Basin Recreation and Water Conservation and Control Authority, and Tsala Apopka Basin Recreation and Water Conservation Control Authority. The calcium carbonate equilibrium study of ground water of central Florida was based on data collected and analysed in cooperation with William Back, Geologist, Water Resources Division, Arlington, Virginia, as part of an investigation of ground water along the Atlantic seaboard. Contributions to the knowledge of the geohydrology in the Withlacoochee-Hillsborough overflow area were made by Z. S. Altschuler, Geologist, Geologic Division, Washington, D. C. Assistance in the interpretation of electric and drillers' logs was rendered by C. R. Sproul, Geologist, Florida Geological Survey. The work on this project was done under the supervision of the Florida Water Resources Division Council comprised of A. O. Patterson, district engineer of the Branch of Surface Water, M. I. Rorabaugh, succeeded by C. S. Conover, district engineers of the Branch of Ground Water, and J. W. Geurin, district chemist, succeeded by K. A. MacKichan, district engineer, of the Branch of Quality of Water. xi

PAGE 11

HYDROLOGY OF GREEN SWAMP AREA IN CENTRAL FLORIDA By R. W. Pride, F. W. Meyer, and R. N. Cherry ABSTRACT Green Swamp is an area of about 870 square miles of swampy flatlands and sandy ridges near the center of the Florida Peninsula. The elevation of the land surface ranges from about 200 feet above mean sea level in the eastern part to about 75 feet in the western part. The Withlacoochee River drains two-thirds of the area. The Little Withlacoochee River, the headwaters of the Oklawaha River, the Hillsborough River, the headwaters of the Kissimmee River, and the headwaters of Peace River drain the remaining area. The surface is mantled with a varying thickness of sand and clay which comprises the nonartesian aquifer. Porous marine limestones comprising the Floridan aquifer underlie and drain the subsurface. The Floridan aquifer crops out in the western part of the area and occurs at depths ranging from 50 to more than 200 feet in the eastern part. The mineral content of both surface and ground water does not impair the usability of the water for most purposes. However, surface water is generally highly colored and acidic, and ground water is hard and generally contains objectionable amounts of iron. Hydrologic data were collected during the period, July 1, 1958, to June 30, 1962, for making quantitative and qualitative analyses of the hydrologic budget and for determining the significance of the hydrology of the Green Swamp area with respect to central Florida. Extremely high and unusually low annual rainfalls were recorded during the period of investigation. The factors of the water budget for each of the 3 complete years of record, 1959-1961, show that average rainfall on the area ranged from 70.9 to 34.7 inches; surface runoff ranged from 31.1 to 2.3 inches; ground-water outflow ranged from 1.8 to 2.2 inches; and water derived from change in storage ranged from insignificant amounts in 1959 and 1960 to about 4.3 inches in 1961. Evapotranspiration losses, which were the residuals in the water-budget equation, ranged from 39.1 1

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2 FLORIDA GEOLOGICAL SURVEY to 34.5 inches. Surface runoff varied through a wide range from wet to dry years, while ground-water outflow varied little. The data show that the annual losses by evapotranspiration varied little from wet to dry years. Evaporation losses from Lake Helene amounted to 53.1 inches during 1962. Comparison of water-budget factors for the eastern and western parts of the area shows that higher rates of ground-water recharge to the Floridan aquifer occur in the eastern part. The amount of annual runoff from the total area has not significantly changed in recent years. However, the distribution of the runoff has been changed by drainage canals that divert some of the flow from the upper Oklawaha River into the Withlacoochee River. Impoundment of water in Green Swamp would provide some flood protection for the lower Hillsborough River and the lower Withlacoochee River basins. Impoundment of the total discharge from Green Swamp to the Hillsborough River during the March 1960 flood would have reduced the flood crest at 22nd Street, Tampa, by about 1 foot. Impoundment of the March 1960 flood discharge in reservoirs proposed for the Green Swamp area (Corps of Engineers, 1961) would have reduced the flood crest of the Withlacoochee River at the Trilby gaging station by about 4 feet and at the Croom gaging station by about 1.7 feet. Impoundment of water in Green Swamp Reservoir would have little effect on ground-water outflow from the total Green Swamp area because of increased seepage rates beneath the levee, increased evaporation losses, and because the aquifer under present conditions is essentially full. Impoundment of water in the Southeastern Conservation Area (Johnson, 1961) would increase the seepage rates during dry periods by about 60 percent. Impoundment of water will become more significant relative to ground-water recharge as pumpage from the Floridan aquifer increases. High piezometric levels in the southeastern part of the Green Swamp area are caused partly by a relatively slow rate of ground-water outflow due to sand-filled fractures, caverns, and sinkholes in the Floridan aquifer. Mineral content and calcium carbonate saturation studies show that generally the water in the Floridan aquifer in central Florida is low in mineral content and undersaturated. Interpretation of quantitative and qualitative data indicate that recharge to the Floridan aquifer in the Green Swamp area is about the same as that in other parts of central Florida.

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REPORT OF INVESTIGATIONS No. 42 3 INTRODUCTION To satisfy the demands of a rapidly increasing population, many acres of land in Florida are converted each year to residential and industrial uses. Urbanization of these areas and the demand for increasing the food supply thus require that man search for new areas to develop for agricultural uses. This search, in many instances, has led to the development of marginal lands. The Green Swamp area, shown in figure 1, in central Florida is an area where man is developing agricultural land from marginal land. The present efforts for its development are similar to the early efforts for developing the Everglades in that many miles of canals and ditches have been constructed to improve the drainage. ALABAMA( GEORGIA Green Swomp ooo * -"0 .Figure 1. Map of Florida showing location of Green Swamp area.

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4 FLORIDA GEOLOGICAL SURVEY PURPOSE AND SCOPE Lest the early mistakes of the Everglades be repeated, the Florida Division of Water Resources and Conservation considered that an appraisal of the physical and hydrologic features of the Green Swamp area was needed for future guidance in planning water-resource policy. Lack of factual hydrologic information has contributed to the controversy on whether the area should be utilized for flood control and water conservation or for agriculture. This investigation provides factual information on the hydrology of the area for determining the feasibility of either choice of utilization. The hydrology of the Green Swamp area was investigated by the U. S. Geological Survey in cooperation with the Florida Geological Survey, the Florida Division of Water Resources and Conservation, and the Southwest Florida Water Management District. The investigation covered a 4-year period beginning July 1, 1958. A Comprehensive Report on Four River Basins, Florida, was prepared by the Corps of Engineers in 1961. The following factual data, used to appraise the hydrologic significance of the area, were collected during the investigation; the amount of rainfall on the area; the pattern of surface-water drainage; the effects of improved drainage channels and man-made diversions; the amount and direction of surface-water runoff; the amount and direction of ground-water outflow; the amount of evaporation losses from an open water surface; the interrelationship of rainfall, surface water, and ground water; and the chemical and physical characteristics of water in relation to the hydrologic environment. A comprehensive appraisal of the hydrology of the Green Swamp area and its significance to central Florida have been made on the basis of the findings of this investigation. The report does not recommend any plan of development or utilization of the water resources of the area. An appraisal was made, however, of the hydrologic effectiveness of a plan of water control and water conservation proposed by the U. S. Corps of Engineers (1961). PREVIOUS INVESTIGATIONS Only cursory investigations of the water resources and geology of the Green Swamp area were made prior to this investigation. Few long-term records of streamflow, ground-water levels, and

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REPORT OF INVESTIGATIONS NO. 42 5 chemical quality had been collected in the vicinity as part of the lstatewide data-collection programs. Many of the physical and hydrologic features of the area are ,iven in an interim report by Pride, Meyer, and Cherry (1961). General descriptions of the geology of the region have been ,iven by Cooke (1945), Vernon (1951), White (1958), and Stewart :1959). Stringfield (1936) defined and described the principal irtesian aquifer of Florida. Analyses of water from surface and ground sources in the vicinity of the Green Swamp area are given in reports by Collins and Howard (1928) and Black and Brown (1951). METHODS OF INVESTIGATION Most of the data for the investigation were collected during the 4-year period from July 1958 to June 1962 and covered a wide range of hydrologic conditions. The investigation of the water resources of the Green Swamp area involves studies of water in three main physical environments: (1) precipitation, which occurs as rainfall; (2) surface water, which occurs on the surface of the ground; and (3) ground water, which occurs beneath the surface of the ground. Waters in these environments are interrelated. Thus, it was necessary to study the whole process or system, rather than any part, to understand and to evaluate the water resources of the area. The methods of studying water in each environment are lifferent. Some characteristics of water in the three environments may be measured directly; some may be evaluated by analysis of representative samples from which results may be inferred; and some characteristics and quantities must be determined indirectly. For instance, the chemical characteristics of the water at a articular place can be used as an indication of the environment through which the water has passed. The surface materials in the Green Swamp area are relatively insoluble and the surface waters are therefore low in mineral content. The rock below the surface materials is relatively soluble and the contained water is considerably more mineralized. Mineralized streamflow in areas such as the Green Swamp, where industrial and municipal disposals into streams are minor, indicates ground-water inflow into streams. Therefore, the chemistry of the water can be used as a tool to give amore complete evaluation of the hydrology of the area.

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6 FLORIDA GEOLOGICAL SURVEY Daily records of rainfall were collected at 24 stations located as shown in the figures on pages 2 and 5. Some of these records are from U. S. Weather Bureau long-term stations. Short-term rainfall records were collected at stream or well data-collection stations during part of the investigation using standard 8-inch gages with tipping-bucket attachments to the water-stage recorders. Surface-water characteristics of the area were determined by collecting stage, streamflow, and chemical-quality data at gaging stations and at miscellaneous sites; by making field and aerial reconnaissance of the area; and by studying maps and aerial photographs. All surface-water data-collection stations are presented in table 1 and located in figure 2 and in the figure on page 5. The grid coordinate number shown in column 2 of table 1 is based on the O *qre of lomnudwe I " of the Greennich. Englani, proe me on odn 1e Ge__ I EO R IA A .... ---C I 1*he.ee n Nauga= 4-' 827-131-3 30 --r he---m" beth '-tn' * be Wl l quronl north -Fis of »e 2827r pamirol of Uhfude and Mgl al e 8g "' nwridion of koatud| i ou ,s u d i Fi_ re m9 83 D a r a-nr Figure 3. Diagram showing the well-numbering system used in Florida.

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REPORT OF INVESTIGATIONS NO. 42 7 TABLE 1. Surface-water data-collection points in Green Swamp area and vicinity. Type of record: A, Standard chemical analysis; D, Discharge and stage; E, Evaporation; K, Conductivity; S. Stage. Frequency of record: d, Daily; p, periodic (monthly to bimonthly intervals); r, Continuous; w. Weekly; (9), Total number of analyses of samples or measurements of streamflow. Grid coStation ordinate Drainage Type and No. on No. on Location area frequency fig. 5 fig. 2 (in downstream order) sq. mi. of record Period of record ST. JOHNS RIVER BASIN 1 807-140 Lake Lowery near Haines City Sd June 1960 to June 1962 A (3) 1959-62 2 815-140 Green Swamp Run near Loughman 38 Dr March 1961to June 1962 A(1) 1959 3 826-144 Big Creek near Clermont 68 Dp (27) 1945-47. 1952-56 Dr July 1958 to June 1962 A (11) 1956-61 4 826-144 Bear Branch near Clermont 1.9 Dp (27) 1958-61 A(1) 1960 5 825-147 Little Creek at Cooper's Ranch near Clermont 10 Dr June 1960 to June 1962 A (3) 1959-61 6 827-145 Little Creek near Clermont 15 Dp (34) 1945-60 A (6) 1956-59 7 828-147 Lake Glona Outlet near Clermont 8.4 Dp (8) 1959-60 April 1961 to June Dd 1962 8 829-144 Lake Louisa near Clermont --Sd March 1957 to June 1962 A (1) 1959 9 832-145 Lake Minnehaha at Clermont -Sr June 1945 to June 1962 A(2) 1956. 1961 10 836-146 Lake Apshawa near Minneola -Sw April 1953 to June 1962 11 835-149 Palatlakaha Creek at Cherry Lake Outlet near Groveland 160 Dr March 1957 to June 1962 12 837-151 Palatlakaha Creek near Mascotte 180 Dr May 1945 to March 1956 13 832-137 Johns Lake at Oakland Sw September 1959 to June 1962 14 834-135 Lake Apopka at Winter Garden Sr September 1942 to June 1962 15 843-141 Apopka-Beauclair Canal near Astatula 180 Dr July 1958 to June 1962

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8 FLORIDA GEOLOGICAL SURVEY TABLE 1. (Continued) Grid coStation ordinate Drainage Type and No. on No. on Location area frequency fig. 5 fig. 2 (in downstream order) sq. mi. of record Period of record KISSIMMEE RIVER BASIN 16 829-132 Lake Butler at Windermere -Sw, Sd January 1933 to June 1962 17 823-131 Cypress Creek near Vineland 30.3 Dr August 1945 to June 1962 1 815-132 Reedy Creek near Loughman Dr October 1939 to September 1959 A (1) 1959 19 810-135 Horse Creek at Davenport 22.8 Dr June 1960 to June 1962 A (10) 1959-61 Kr July to November 1960 20 806-131 Lake Marion near Haines City -Sd February 1958 to June 1962 PEACE RIVER BASIN 1 I 802-139 Lake Hamilton at Lake Hamilton Sw June 1945 to June 1962 22 806-142 Gum Lake marsh outlet at Lake Alfred 4.2 Dd October 1960 to June 1962 A(2) 1960, 1961 23 804-143 Lake Rochelle near Lake Alfred Sd March 1946 to June 1962 24 805-144 Lake Alfred at Lake Alfred Sd March 1961 to June 1962 25 801-142 Lake Otis at Winter Haven Sr August 1954 to June 1962 26 804-145 Lake Mariana near Auburndale _ Sw February 1946 to June 1962 27 803-144 Lake Hartridge at Winter Haven Sw February 1946 to June 1962 28 801-144 Lake Howard at Winter Haven Sr April 1945 to June 1962 29 802-155 Lake Parker at Lakeland Sw, Sr 1949-54, July 1954 to June 1962 30 i 801-154 Crystal Lake at Lakeland Sr, Sp 1951-52, 1954-57 A (1) 1959 HILLSBOROUGH RIVER BASIN 811-209 Hillsborough River at State Highway 39 -A(1) 1959 31 810-211 Crystal Springs near Zephyrhills Dp (227) 1933-62 A(3) 1959 32 808-209 Blackwater Creek near Knights 110 Dr January 1951 to June 1962

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REPORT OF INVESTIGATIONS NO. 42 9 TABLE 1. (Continued) Grid coStation ordinate Drainage Type and No. on No. on Location .area frequency fig. 5 fig. 2 (in downstream order) sq. mi. of record Period of record 33 808-214 Hillsborough River near Zephyrhills 220 Dd November 1939 to June 1962 A (55) 1956-62 WITHLACOOCHEE RIVER BASIN 809-142 Swamp at Holiday Manor near Haines City A (1) 1959 34 807-147 Lake Juliana near Polk City ---Sd December 1961 to June 1962 35 804-147 Lake Mattie near Polk City Sd, Sw June 1960 to December 1961 A (3) 1960-62 815-146 Swamp near Polk City A(1) 1959 818-148 Withlacoochee River at Van Fleet Road, near Eva A(1) 1959 36 821-149 Withlacoochee River near Eva 130 Dr July 1958 to June 1962 A(14) 1958-61 37 810-148 Lake Helene near Polk City Sr April 1961 to December 1962 Er December 1961 to December 1962 A(2) 1962 38 815-148 Pony Creek near Polk City 9.5 Dr June 1960 to June 1962 A(9) 1960-61 Kr July to November 1960 809-148 Little Lake Agnes near Polk City A (1) 1959 810-149 Lake Agnes at Polk City Sp 1961-62 818-155 Grass Creek near Rock R:dge -A(1) 1959 -819-155 Withlacoochee River near Rock Ridge A (1) 1959 819-200 Withlacoochee River near Cumpressco D (2), A(1) 1961 818-203 Withlacoochee River upstreamfrom Gator Creek D (2), A(1) 1961 -818-203 Gator Creek at mouth D(2), A(1) 1961 39 816-205 Withlacoochee-Hillsborough overflow near Richland Dd 1930-31 Dp, Dr July 1958 to June 1962 A(4) 1959-60 -817-206 Withlacoochee River near Richland D(2), At2) 1959-61 ______________ ___________.

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10 FLORIDA GEOLOGICAL SURVEY TABLE 1. (Continued) Grid coStation Iordinate Drainage Type and No. on No. on Location area frequency fi.5 fig. 2 (in downstream order) sq. mi. of record Period of record 40 821-207 Withlacoochee River near Dade City 390 Dd.Dp (29) 1930-33; 1958-62 A (12) 1958-61 41 822-211 Pasco Packing Co. canal at Dade City -Dp (48) 1957-62 A(5) 1959-61 824-209 Hamilton Lake Outlet near Dade City D (2), A(1) 1961 826-209 Withlacoochee River near Lacoochee D (2), A(4) 1959-61 826-201 Gator Hole Slough near Bay Lake A (1) 1959 827-203 Gator Hole Slough near Clay Sink --A(1) 1959 821-202 Swamp near Cumpressco -A(1) 1959 828-208 Weaver Hole Slough at Lacoochee A (1) 1959 828-209 Withlacoochee River at Lacoochee -A(1) 1959 42 828-210 Withlacoochee River at Trilby 580 Dr 1928-29; February 1930 to June 1962 A (9) 1959-61 829-154 Bay Lake near Bay Lake A(1) 1959 829-158 Bayroot Slough near Bay Lake A(1) 1959 829-200 Little Withlacoochee River near Clay Sink -A(2) 1959 43 834-209 Little Withlacoochee River at Rerdell 160 Dr July 1958 to June 1962 A (9) 1959-61 44 835-213 Withlacoochee River at Croom 880 Dr October 1939 to June 1962 A (8) 1959-61 well-numbering system shown in figure 3. Records of streamflow and stage at 24 sites and of stage of 20 lakes were collected in or near the area of investigation. Information on the quality of surface water was obtained during high, intermediate, and low flows to determine the general chemical characteristics and the extremes in quality characteristics during the period of study. These data were supplemented with a series of reconnaissances over the entire area generally within a period of

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REPORT OF INVESTIGATIONS NO. 42 11 1 to 3 days. The data were used to determine the quality of water prevalent in the area at a given time and to help determine the interrelations between surface water and ground water. Ground-water characteristics were determined by collecting data concerning water levels, surface and subsurface geology, and water chemistry from an inventory of existing wells in the Green Swamp area and vicinity (fig. 2). Information on the depth of the well, the amount of casing, and the depth to static water level was recorded for more than 600 wells. Most of the inventoried wells penetrated the Floridan aquifer. The approximate elevation of land surface above mean sea level was determined at each well by use of either altimeter, topographic maps, or spirit level. These data were supplemented by selected data collected prior to this investigation and by test drilling to provide better coverage of the area. The well-numbering system that is derived from latitude and longitude coordinates is based on a state-wide grid of 1-minute parallels of latitude and 1-minute meridians of longitude, shown in figure 3. Instruments were used to record continuously the water-level fluctuations in the various aquifers. These data were supplemented by periodic determinations of water levels and chemical characteristics of water in selected wells in order to evaluate areas of recharge and discharge for the aquifers. The wells in which continuous and selected periodic water-level data, and quality-of-water data were collected, are presented in table 2. During the periods October to December 1959 and May to June 1962, water-level measurements were made to prepare piezometric maps which show the direction of water movement in the Floridan aquifer. Hydraulic gradients scaled from these maps were used to infer rates of water movement. To obtain general information on the occurrence of artesian and nonartesian ground water in the Green Swamp area, 26 test wells were drilled at 16 different sites. At 9 of these sites a pair of wells were drilled (one into the Floridan aquifer and one into the nonartesian aquifer). A summary of test-well data is presented in table 3. During the drilling, samples of rock cuttings were collected. The lithology of the various formations and significant changes in water levels were recordered in the well log. Examination of rock cuttings of selected wells were supplemented

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12 FLORIDA GEOLOGICAL SURVEY TABLE 2. Ground-water data-collection points in Green Swamp area and vicinity. Well number: See figure 3 for explanation of well-numbering system. County: He, Hernando; Hi, Hillsborough; La, Lake; Or, Orange; Pa, Pasco; Po, Polk; Su, Sumter. Aquifer (s) : F, Floridan; H, secondary artesian; N, nonartesian. Type and frequency of record: A, standard chemical analysis; B, spectrographic analysis; K, partial chemical analysis; S, water level; T, tritium determination; (3) number of analyses; p, periodic; r, continuous. Type and frequency Well number I County Aquifer of record Period of record 800-153-1 Po F, H Sp December 1954 to May 1962 801-207-1 Hi F A(1) May 1962 802-135-1 Po F Sp November 1957 to February 1960 802-157-12 Po F A(l) March 1962 803-147-4 Po F A (1) March 1962 803-204-1 Hi F Sp May 1958 to May 1962 804-207-1 Hi F Sp November 1956 to May 1962 805-155-1 Po N Sr August 1955 to February 1960 Sp February 1960 to June 1962 805-155-2 Po F Sr March 1956 to February 1960 Sp February 1960 to June 1962 A (1) November 1959 805-155-3 Po H Sr February 1956 to February 1960 Sp February 1960 to June 1962 806-137-6 Po F A (1) March 1962 806-140-2 Po F A(1) November 1959 806-135-3 Po F Sp July 1954 to February 1960 806-156-1 i Po N Sp August 1955 to June 1962 806-156-2 Po F Sp January 1956 to June 1962 807-202-1 Po F A(1) November 1959 808-139-1 Po N A(1) February 1962 808-143-1 Po F A (1) February 1962 808-147-1 Po F A(1) February 1962 808-153-1 Po F Sp January 1958 to May 1962 A (1) November 1959 808-155-1 Po F Sp June 1955 to March 1956 Sr March 1956 to June 1962 A (1) November 1959 808-155-2 Po N Sp June 1955 to June 1962 809-154-4 Po F A(1) February 1962 809-158-1 Po H A (1) February 1962 810-136-1 Po F Sr 1946 to June 1962 (P-44)

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REPORT OF INVESTIGATIONS No. 42 13 TABLE 2. (Continued) Type and frequency Well number County Aquifer of record Period of record 810-136-2 Po N Sr 1948 to June 1962 (P-47) 810-144-1 Po F Sp July 1959 to October 1960 Sr October 1960 to June 1962 A(21), July 1959 to April 1962 K(5), T(4), B(4) 810-144-2 Po N Sr October 1960 to June 1962 A(3), July 1959 to November 1961 K(2) 810-149-1 Po F A(2) November 1959 to March 1962 810-149-2 Po F Sp January 1955 to May 1962 810-151-2 Po F Sp February 1960 to May 1962 810-207-1 Pa F Sp June 1960 to May 1962 813-147-1 Po F A(1) February 1962 813-149-1 Po F Sr March 1959 to June 1962 A(6) April 1959 to March 1962 813-149-2 Po N Sr April 1959 to June 1962 813-150-2 Po N Sr October 1960 to June 1962 813-201-1 Po F Sp August 1959 to June 1962 A(2) November 1959 to March 1962 814-143-1 Po F Sr October 1960 to June 1962 814-143-2 Po N Sr October 1960 to June 1962 814-148-1 Po F Sp October 1955 to July 1957 Sr July 1957 to April 1959 814-210-1 Pa F A(1) March 1962 814-210-2 Pa F A(1) March 1962 815-134-1 Po F Sp August 1960 to October 1960 Sr October 1960 to June 1962 A(1) March 1962 815-134-2 Po N Sp August 1960 to October 1960 Sr October 1960 to June 1962 815-139-1 Po F A(1) June 1959 815-139-2 Po F Sp August 1960 to October 1960 Sr October 1960 to June 1962 815-139-3 Po N Sr October 1960 to June 1962 815-149-3 Po F Sp July 1960 to November 1960 Sr November 1960 to June 1962 A(1) April 1961 815-157-2 Po F Sp March 1956 to May 1958 Sr May 1958 to June 1962 A (1) November 1959 815-203-1 Po F A(1) February 1962 816-202-1 Po F A(2) May 1951 to-March 1962. 816-202-2 Po F A (1) May 1961

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14 FLORIDA GEOLOGICAL SURVEY TABLE 2. (Continued) Type and frequency Well number County Aquifer of record Period of record 816-206-1 Pa F Sp July 1959 to June 1962 A(2) November 1959 to March 1962 816-211-1 Pa F Sp 1936 to August 1951 Sr August 1951 to March 1962 817-149-1 Po F A(1) February 1962 817-150-1 Po F Sp July 1959 to June 1962 818-155-3 Po F A(1) November 1959 818-156-2 Po F A () February 1962 818-209-1 Pa F Sp October 1959 to June 1962 818-209-2 Pa F A (1) February 1962 819-140-1 Po F Sp May 1959 to June 1962 A(1) May 1959 849-147-1 Po F A (1) November 1959 819-151-1 Po F Sp October 1955 to June 1962 819-211-2 Pa F Sp December 1959 to June 1962 821-158-2 Su F Sp October 1959 to June 1962 821-202-1 Su F A(1) May 1959 821-202-3 Su F Sr March 1959 to June 1962 A(2) May 1959 to November 1959 821-207-1 Pa F October 1959 to June 1962 821-203-2 Pa F A(1) February 1962 821-210-1 Pa F A(1) November 1959 821-211-1 Pa F A(1) March 1962 822-138-1 Or F Sr February 1959 to June 1962 A(1) March 1962 822-138-2 Or N Sr April 1959 to June 1962 822-149-1 La F Sr February 1959 to March 1962 A(8) April 1959 to March 1962 822-149-2 La N Sr April 1959 to June 1962 822-149-3 La F A(1) February 1962 822-210-1 Pa F Sp October 1959 to June 1962 822-211-1 Pa F A(1) February 1959 824-142-1 La F Sp December 1959 to June 1962 824-206-1 Pa F Sp November 1958 to June 1962 824-211-1 Pa F Sp December 1959 to June 1962 824-211-2 Pa F A(1) February 1962 825-151-1 La F Sp Ocober 1959 to June 1962 826-208-1 Pa F Sp November 1958 to June 1962 826-211-1 Pa F Sp October 1959 to February 1960 Sr February 1960 to June 1962

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REPORT OF INVESTIGATIONS NO. 42 15 TABLE 2. (Continued) Type and frequency Well number County Aquifer of record Period of record 827-144-1 La F A(1) February 1962 827-149-1 Po N A(1) February 1962 827-154-1 La N A(1) February 1962 827-158-1 Su F Sp July 1959 to June 1962 A(1) July 1959 827-210-1 Pa F Sp 1936-50 (U.S. Corps of Engineers) Sp October 1959.to July 1961 827-210-2 Pa F Sp August 1961 to June 1962 828-154-1 La F Sp November 1959 to June 1962 828-203-1 He F A(2) July 1959 to November 1959 828-204-1 Pa N A(1) February 1962 828-209-1 Pa F A(1) February 1962 829-146-2 La F Sp October 1959 to June 1962 829-202-1 Su F Sp December 1959 to June 1962 829-206-1 He F Sp May 1959 to June 1962 A(3) May 1959 to November 1959 830-157-1 Su F Sp May 1959 to June 1962 A (3) May 1959 to November 1959 820-210-2 He F A(1) November 1959 832-154-1 La F Sr February 1959 to June 1962 A(9) April 1959 to March 1962 832-154-2 La N Sr February 1959 to June 1962 832-154-3 La N A(3) May 1959 to November 1959 832-204-1 Su F A (1) February 1962 833-137-2 Or F Sr March 1960 to June 1962 833-144-1 La F Sp November 1959 to June 1962 833-144-2 La F A(1) March 1962 833-151-1 La F Sp November 1959 to June 1962 833-151-5 La F A(1) March 1962 833-209-1 He F A(1) February 1962 834-159-1 Su F Sp November 1959 to June 1962 836-202-1 Su F A (1) March 1962 836-202-2 Su F A(1) February 1962 836-208-2 Su F A (1) February 1962 838-159-2 Su F A (1) November 1959 841-156-1 La F Sp March 1961 to June 1962

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TABLE 8 .Test-well data in Green Swamp area and vicinity (Aquifer: F, Floridan; N, Nonartesian) Casing Open hole Total depth below land Depth below Range surface Diameter land surface Diameter in depth Well number Date drilled (feet) (inches) (feet) (inches) (feet) Aquifer Remarks Lake County 822-149-1 February 1050 95 0 50 %/ 59. 95 F July 1959 192 6 100 5/ 05-192 F Deepened for geologic control. Added easing. 822-149.2 February 1959 28 0 18 65% 18. 23 N Gravel packed (limestone pebbles). 882-154.1 February 1950 78 5VI G373 F July 1959 100 0 63 2 78-160 F Deepened for geologic control. 882.154.2 February 1959 22 6 10 5% 1622 N Gravel packed (limestone peebles). Orange County 822-188.1 February 1959 114 6 108 5' 103-114 F October 1960 818 5% 114-818 F Deepened for geologic control. 822-188-2 February.1959 80 6 13 5% 1380 N Gravel packed (limestone pebbles). Pasco County 816-206-1 July 1959 200 8 41 2%/ 41-200 F

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TABLE 3. (Continued) Casing Open hole Total depth below land Depth below Range surface Diameter land surface Diameter in depth Well number Date drilled (feet) (inches) (feet) (ihches) (feet) Aquifer Remarks Polk County 810-144-1 July 1959 249 6 101 51/ 101-249 F October 1960 425 5% 249-425 F Deepened for geologic control. 810-144-2 October 1960 9 6 6 5% .N Finished with 8-foot section of no. 10 slot steel screen 818-149-1 February 1959 90 6 /78 5 7890 FI July 1959 217 6 90-217 F Deepened for geologic control. 818-149-2 February 1950 27 6 20 5% 20. 27 N Gravel packed (limestone pebbles). 818-150-1 July 1960 205 6 100 5% 106-205 F 818-150-2 July 1960 28 6 17 5% 1728 N 818-201-1 July 1959 255 8 40 2% 40-255 F 814-148-1 July 1960 285 6 80 5%/ 80-285 F 814-148-2 August 1960 18 6 15 5% 1518 N 815-184-1 August 1960 250 6 85 5% 83-250 F 815-184-2 August 1960 82 6 29 51% .... N Finished with 8-foot section of no. N 10 slot steel screen 815-189-2 August 1960 458 6 858 5% 858-458 F 815-189-8 August 1960 02 6 89 5%1 -N Finished with 8-foot section of no. 10 slot steel screen. 815-157-2 July 1959 168 8 52 2% 110-168 F Existing U. S. Geological Survey well deepened for geologic control.

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00 TABLE 3. (Continued) Casing Open hole To'l depth below land Depth below Range surface Diameter land surface D'nm-"tr in depth Well number Date drilled (feet) (Inches) (feet) (.nch-a) (feet) Aquifer Remarks Sumter County 821-158-1 July 1050 53 3 58 21/. 0 F Chert at 58 feet impenetrable. Well destroyed, 821-158-2 July 1959 40 3 49 21/1 0 F Chert at 49 feet impenetrable. Bottom of casing blasted open for use as observation well. 821-202-8 February 1959 20 6 20 51 2029 F July 1959 148 2 V 29-143 F Deepened for geologic control. 821-202-4 February 1959 12 6 5 5%/ 512 F Gravel packed (limestone pebbles). 827-158-1 July 1059 175 3 09 2/ 90-175 F

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REPORT OF INVESTIGATIONS No. 42 19 by interpretation of electric and gamma-ray logs of some wells and geologists' and drillers' logs of wells which are on file with the Florida Geological Survey. GEOGRAPHY One of the most prominent topographic features in the central part of the Florida Peninsula is Green Swamp which is an extensive area of flatland and swampland at a relatively high elevation. Five major drainage systems originate in or near the Green Swamp area and flow in several directions to the sea. The area contains the headwaters of the Oklawaha River, which flows generally northward to become the largest tributary of the St. Johns River; the Kissimmee and Peace Rivers that flow southward; the Hillsborough River that flows southwestward; and the Withlacoochee River that flows northwestward. LOCATION The Green Swamp area is in central Florida (see fig. 1) west of and adjacent to a high sandy ridge that forms the major axis of the peninsula. For this study the boundaries of the area were established arbitrarily and the Green Swamp area should not be confused with a small drainage basin that is generally known as Green Swamp Run in the headwaters of the Big Creek watershed in southern Lake County and northeastern Polk County. The boundaries of the Green Swamp area, as designated for this investigation, have been extended to encompass a much larger area. The project area includes the southern parts of Lake and Sumter counties, the northern part of Polk County, and the eastern parts of Pasco and Hernando counties (see fig. 2). The eastern boundary of the Green Swamp area is U. S. Highway 27, from Clermont south-southeastward to Haines City. The southern and southwestern boundaries of the area generally coincide with the divides separating drainage northward to the Big Creek and Withlacoochee River basins from drainage southward to the Peace and Hillsborough River basins. These boundaries follow a meandering line westward from Haines City to a point two miles north of Lakeland and then northwestward to Dade City. The western boundary of the area is U. S. Highway 301 northward from Dade City to St. Catherine. The northern boundary extends from St. Catherine eastward along the Little Withlacoochee River

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20 FLORIDA GEOLOGICAL SURVEY basin divide to State Highway 50 and along State Highway 50 eastward to Clermont. The boundaries described enclose an area of 870 square miles. TOPOGRAPHY The Green Swamp area is in the Central Highlands topographic region as defined by Cooke (1945). The area is bordered on the eastern side by the Lake Wales Ridge, on the southern side by the northern termini of the Winter Haven and Lakeland Ridges, and on the western side by the Brooksville Ridge (White, 1958, pp. 9-11). Figure 4 shows the locations of these ridges. Although the area is designated the Green Swamp, it is not a continuous expanse of swamp but is a composite of many swamps that are distributed fairly uniformly within the area. Interspersed among the swamps are low ridges, hills, and flatlands. Several large and many small lakes of sinkhole origin rim the southeastern and northeastern parts of the area. The elevation of the land surface ranges from about 200 feet above mean sea level (msl) in the eastern part to about 75 feet in the river valleys in the western part. Prominent topographic features affecting the drainage of the eastern part of the area are the alternating low ridges and swales that trend generally north-northwestward from the southern boundary to the Polk-Lake County line. The ridges parallel the major axis of the Florida Peninsula and their configuration suggests that they were formed by subsidence and erosion along fractures and joints. Aerial photographs of the area between U. S. Highway 27 and the Seaboard Air Line Railroad show five of these long narrow ridges with intervening swales. In the western part of the Green Swamp area there is little evidence of the elongated ridges, and the main land-surface features are large swamps, flatlands, and rolling hills. There are many small swamps in patches and strips generally less than half a mile wide. Most of these swamps support good growths of cypress trees while in the uplands pine and scrub oak trees grow abundantly. The largest continuous. expanse of swampland lies within the valley of the Withlacoochee River and is more than a mile wide at places. Limestone is exposed in the western part of the Green Swamp area.

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REPORT OF INVESTIGATIONS NO. 42 21 DRAINAGE The drainage system of the Green Swamp area and vicinity is shown on the map in figure 5. The headwaters of four stream systems within the Green Swamp area, listed in order of their proportion of the area drained, are: Withlacoochee River, Little Withlacoochee River, Oklawaha River, and Hillsborough River. Other streams that head near the boundaries of the Green Swamp area are: Reedy, Davenport, and Horse creeks in the Kissimmee River basin; Peace Creek drainage canal and Saddle Creek in the Peace River basin; Fox Branch in the Hillsborough River basin; and Jumper Creek Canal and a major canal that head northwest of Mascotte in the Withlacoochee River basin. Of the total area of 870 square miles, 710 square miles are drained by the Withlacoochee River and its tributaries. The surface drainage of the Green Swamp area is poor because of the flat topography and lack of well developed stream channels. Following heavy rainfall, water stands in large shallow sheets over much of the area. Boundaries of the elongated north-south drainage basins, in the eastern part of the Green Swamp area, are formed by low ridges. The valleys between the ridges are not deeply incised but their effectiveness as drainage channels has been improved by many miles of canals and ditches. Some parallel drainage basins are interconnected in several places by gaps or saddles through the ridges. Through these gaps water may flow at times from one stream valley into another. The amount and direction of flow depend on the relative elevation of water levels in the adjoining basins and the hydraulic conveyance of the connecting channels. The canals and ditches, for the most part, have been dug to follow the natural drainage courses through the shallow swamps. However, in some places, probably to provide firm footing for the excavation equipment and to avoid clearing through the dense growth of cypress trees, the ditches have been dug along the edges of the large swamps rather than through the interior. Also, to provide better alignment in some places, the ditches have been cut through ridges to connect the adjacent swamps. These shortcuts have bypassed the circuitous natural drainage routes and have straightened and shortened the courses of the waterways. Surface drainage from most of the Green Swamp area is generally toward the north and west. However, the headwaters of the Peace River basin originate along the southern boundaries of

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92 FLORIDA GEOLOGICAL SURVEY the area and the flow is generally southward. Along the eastern boundary of the area, drainage is toward the east and southeast into the Kissimmee River basin. Other drainage from the Green Swamp area is toward the southwest into the Hillsborough River via a natural channel in eastern Pasco County. The subsurface drainage of the Green Swamp area is generally poor. Ground-water levels in the interior of the area remain near the surface most of the time, consequently the aquifers provide little opportunity to store water from heavy rainfall. Ground-water levels fluctuate through a greater range in the ridges that form the eastern, southern, and western boundaries. The wide range of fluctuation indicates better subsurface drainage and greater storage capacity along the boundaries than in the interior. Subsurface drainage is through both the Floridan and the nonartesian aquifers but most is via the Floridan aquifer. Water percolates downward from the overlying nonartesian aquifer to the Floridan aquifer or enters exposed portions of the Floridan aquifer. Movement of ground water in the Floridan aquifer is generally outward in all directions from the southeastern part of the area. However, the areas contributing to the aquifer (p. 80) show that the predominant directions of ground-water movement are east and west. The ground-water divides in the aquifer shift slightly in response to demands in each contributing area. Most of the surface area that potentially would contribute recharge to the Floridan aquifer in Green Swamp lies within the Withlacoochee River basin. The distribution of ground-water outflow originating in each surface basin is shown in the tables on pages 116 and 117. CULTURE AND DEVELOPMENT The Green Swamp area is sparsely populated except for a few small towns and communities on the ridges along the border and along State Highway 33. Most of the land is in large tracts owned by private individuals or corporations. The only large tract of public land in the area is the Withlacoochee State Forest, part of which is within the boundaries of the Green Swamp area in Sumter, Hernando, and Pasco counties. The principal industry is agriculture. Much of the upland area has been cleared and planted in citrus groves. Other upland areas have been cleared and are used for cattle raising. Very little of the land is cultivated. The low swampland is unsuitable for

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REPORT OF INVESTIGATIONS NO. 42 23 agriculture because of poor drainage. In spite of the many miles of ditches, drainage is still inadequate. Even in the cleared areas that are suitable for agriculture, few attempts have been made to reclaim the many small, round, cypress swamps that dot the area. Cypress lumbering was once an important industry in the western part of the area, particularly in the Withlacoochee River Swamp where there were extensive stands of trees. The first access roads to penetrate the interior of the swamp were trails and tram roads built for cypress lumbering. Timber and pulpwood are now produced from the pine flatwoods interspersed among the swamps. There is some development of the mineral resources of the area for the commercial market. Extensive phosphate deposits in Polk County lie just south of the Green Swamp area. Some phosphate is mined within the area but the amount is only a small percentage of that produced in southern Polk and eastern Hillsborough counties. Limerock, used in road construction and agriculture, is mined in the northwestern part of the area. Deposits of sand, suitable for building uses, are mined in many places in the eastern part of the area. CLIMATE The location of the Green Swamp area, well south in the Temperate Zone, and its proximity to large bodies of warm water produce a warm humid climate. Precipitation and temperature, the principal climatic elements that influence the hydrology of the Green Swamp area, are described separately. PRECIPITATION The study of precipitation in central Florida can be restricted to rainfall only, because snow and hail are virtually unknown. The normal or long-term average annual rainfall of the Green Swamp area is 52.7 inches. This normal is computed by the Thiessen method of weighting long-term rainfall records at each of the following U. S. Weather Bureau stations in or near the project area: Clermont 6 miles south, Lake Alfred Experiment Station, Lakeland, and St. Leo (figs. 2 and 5). The average rainfall for the station at St. Leo, west of the area, is slightly higher than that for the other three stations which are located farther inland. The average rainfall at the four stations ranges from a minimum of 50.1 inches at the Clermont station to

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24 FLORIDA GEOLOGICAL SURVEY a maximum of 56.4 inches at the St. Leo station. In view of the small deviation of these extreme values from the mean, the weighted average rainfall of 52.7 inches for the area of investigation appears to be reasonably accurate. The amount of rainfall on the area varies seasonally. About 60 percent of the annual total rainfall occurs during the wet season from June through September. In the spring and early summer, local thunderstorms of high intensity and short duration sweep over the area. Showers occur almost daily, or perhaps several times a day, during June and July. Heavier and more prolonged rainfalls occur generally in August and September and are often intensified by tropical storms that occasionally reach hurricane proportions. On the other hand, there are periods of a month or more with little or no rainfall. Periods of below average rainfall usually occur during the winter season from November to February. During wet years the annual rainfall is about twice that of dry years. The annual and the mean monthly rainfalls for the years 1931-1961 are shown by bar graphs in figure 6. The maximum annual rainfall during this 31-year period was 70.9 inches in 1959 and the minimum was 34.7 inches in 1961. Both occurred during the period of the investigation. It is a fortunate circumstance that the full range of hydrologic conditions was experienced during the investigation. TEMPERATURE A knowledge of temperature variations in central Florida is pertinent to a study of its water resources because of the dominant influence of temperature on rates of water losses by evaporation and transpiration. The mean monthly temperature in the Green Swamp area ranges from 610 F. for January to 82' F. for August. The lowest temperature recorded during the 69-year period of record at the Clermont station was 180 F. and the highest was 104° F. Daily temperatures recorded at the U. S. Weather Bureau stations show that all parts of the area have essentially the same temperature, ranging no more than 2 to 30 F. Killing frosts occur infrequently in this area, and damage to vegetation, although severe from the standpoint of agriculture, seldom is great enough to affect the hydrologic factors pertinent to water supplies.

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REPORT OF INVESTIGATIONS NO. 42 25 80 70 S31year average, S 52.7 inches 60 z 20 0 CALENDAR YEAR 910----------------W) 8------------f Rainfall of Green Swamp area Z 71 -computed from U.S. Weather z I 1 Bureau records at four stations, S6 weighted by Thiessen method 44 as follows: -Station Percentage >j , Clermont 6S 37 Lake Alfred Exp. Sta. 22 O 3-Lakeland II O St. Leo 30 1 100 Based on records 1931-61 J F)MIIAIMIoj |A sloIrN D MONTH Figure 6. Graphs showing annual and mean monthly rainfall of Green Swamp area. Water loss from a drainage basin is the difference between the average rainfall over the basin and the runoff from the basin for a given period (Williams, 1940, p. 3). In humid regions, where there is sufficient water to satisfy the demands of vegetation, the mean annual water loss is principally a function of temperature (Langbein, 1949, p. 7). The relation between mean annual

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26 FLORIDA GEOLOGICAL SURVEY temperature and mean annual water loss under such conditions is shown in figure 7, which is taken from U. S. Geological Survey Circular 52. For the Green Swamp area where the mean annual temperature is 72' F., the annual water loss would be 48 inches according to this figure. ENVIRONMENTAL FACTORS AFFECTING THE QUALITY OF WATER The quality of water in the Green Swamp area reflects the solubility of the material which the water contacts and its biologic environment, both of which are natural influences. Surface water is usually lower in mineral content than ground water because of low solubility of materials on the surface of the ground and short time of contact of water with the materials. The quality of the surface water (lakes, streams, and swamps) depends mostly on the composition of the precipitation and the 80 Palatlakaho Creek above Mascotte I I I / Withlacoochee River at Trilby-. 70 S60 E 50 a / Computed annual water loss Sat two gaging stations in S40 Green Swamp area. (After Longbein, W.B., and others, 1949) 30 I 0 10 20 30 40 50 E0 Natural water loss, in inches Figure 7. Relation of annual water loss to temperature in humid areas.

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REPORT OF INVESTIGATIONS NO. 42 27 biologic environment. Generally, the mineral content of water in streams varies inversely with discharge. Surface waters are usually highly colored and acidic. Sodium and chloride, although in very low concentrations, are the principal dissolved mineral constituents and may be present as a result of wind and rain-borne salts from the ocean. The quality of ground water in the Green Swamp area generally meets the requirements for most municipal, industrial, domestic, and agricultural uses. Ground water of lowest mineral content occurs along the eastern and western boundaries of the area and is lowest near the lakes. Ground water of highest mineral content occurs in the central part of the Green Swamp. The principal dissolved mineral constituents are calcium and bicarbonate which are products of limestone solution. Relatively high concentrations of calcium in the water cause hardness which is probably the most objectionable characteristic of the ground water in the Green Swamp area. GEOLOGY' Topographically, the surface of the Green Swamp area resembles a basin, or trough, opening to the north. However, geologically, the Green Swamp is part of an eroded, faulted anticline. The oldest formations are exposed along the axis of the anticline and eroded remnants of younger formations rim the flanks and present a basin-like feature. The Green Swamp area is underlain by several hundred feet of limestone and dolomite that have been periodically exposed to solution-weathering and erosion. The surface is mantled with a varying thickness of clastic material (sand and clay) that was deposited in fluctuating shallow seas. No attempt has been made to differentiate the formations within the clastic material because of its complexity and the lack of data. The upper part of the elastic sediments, composed of clayey sands, forms a distinct hydrologic unit, commonly referred to as the nonartesian aquifer. The basal portion of the clastic sediments, composed mostly of clay and some interbedded limestone (secondary artesian aquifer), is less permeable than the overlying, 1The classification and nomenclature of the rock units conform to the usage of the Florida Geological Survey and also with those of the U. S. Geological Survey, except for the Fort Preston Formation (?), the Tampa Formation, and the Qcala Group and its subdivisions.

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28 FLORIDA GEOLOGICAL SURVEY clayey sands or the underlying porous limestone. The solutionriddled limestone formations, which underlie the clay deposits, comprise the Floridan aquifer, the principal source of artesian ground water in the State. Where present, the clay forms an aquiclude which retards the rate of water movement between the aquifers. The principal artesian aquifer was first described by Stringfield (1936) and later named the Floridan aquifer by Parker (1955). According to Parker, the Floridan aquifer includes those limestone formations ranging in age from the middle Eocene (Lake City Limestone) to perhaps early and middle Miocene (Hawthorn Formation). In the Green Swamp area the following formations comprise the Floridan aquifer (from youngest to oldest); the Suwanee Limestone; the Ocala Group which includes the Crystal River, Williston, and Inglis Formations; and the Avon Park Limestone. The base of the aquifer is considered to be near the base of the Avon Park limestone at the first occurrence of gypsum because the presence of gypsum probably indicates poor circulation of ground water. FORMATIONS The formations that underlie the Green Swamp area are presented in table 4. Generalized geologic cross sections, shown in figure 8 were prepared based on data from wells located along lines A-A', B-B' and C-C'. UNDIFFERENTIATED CLASTIC DEPOSITS Undifferentiated clastic deposits, ranging from late Miocene to Recent in age, underlie the Green Swamp area except in the western part where Tertiary limestones are exposed at the surface. The deposits consist primarily of clayey sand or sandy clay. The following lithologic sequence (from youngest to oldest) is indicated: (1) fine quartz sand (surficial sand) with varying amounts of clay and organic material; (2) variegated (red-orange-tan) fine to coarse quartz sand with little clay; (3) white fine to very coarse quartz sand with varying amounts of white-green kaolinitic or montmorillonitic clay; and (4) white silty quartz sand with varying amounts of mica flakes. Generally, the deposits range from 100 to 200 feet in thickness beneath the ridges that rim the Green Swamp area; however, they are thin or absent in the western part and tend to become more

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TABLE 4. Geologic formations and their water-bearing characteristics in Green Swamp area and vicinity. Approximate Formations range of Formation used in this thickness Water-bearing System Series (after F.G.S.) report (feet) Lithology Aquifer characteristics Recent Recent Deposits Quaternary ____ Terrace Light-colored clayey Generally poor source in the cenliocene Sa sands grading Nontral part of the area. A fair an Undifferentiated 0-200 into sandy clays artesian source in the ridge areas. Clastic Citronelle Deposits Pleistocene Formation Fort Preston Upper Formation (?) Hawthorn Miocene Middle Formation Generally very poor except in Undifferentiated Dark-colored phos. Secondary the Lakeland area where interClay 060 phatic clay with artesian bedded limestones are a fair Tampa limestone lenses source. Lower Formation Suwannee Suwannee Hard, white-yellow Tertiary Oligocene Limestone Limestone 080 limestone Z Crystal Crystal River Soft, gray, River Formation 0-120 limestone SFormation _Generally good to excellent. The E best source is the dolomitic Upper Williston Williston Hard, tan Avon Park Limestone. EvapoUppe Formation Formation 040 limestone Floridan rite (selenite) deposits near a the base of the Avon Park Eocene U Limestone is considered to be Inglis Inglis Hard, tan the base of the aquifer. Formation Formation 050 limestone Avon Park Avon Park Soft to hard, Middle Limestone Limestone 800-1,000 white-brown, * dolomitic limestone

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30 FLORIDA GEOLOGICAL SURVEY clayey where they thin over the crest of the anticline (fig. 8, A-A'). The deposits appear to increase in coarseness from the interior of the Green Swamp area eastward to the Lake Wales Ridge. Much of these deposits occur as cavity fill in the underlying limestones especially in the ridge areas. The undifferentiated clastic deposits form the nonartesian aquifer in the area. Generally, the deposits in the western part of the Green Swamp area are thin or absent, low in permeability and porosity; and therefore, they are of minor significance as an aquifer. UNDIFFERENTIATED CLAY Undifferentiated clays of Miocene age underlie most of the area, except in the western part, and contain varying amounts of quartz, phosphatic sand, and interbedded limestone. The following general lithologic sequence (from younger to older) is indicated: (1) light gray-tan-blue-green, montmorillonitic clay with varying amounts of quartz, phosphatic sand, and interbedded limestone; (2) dark gray-green-blue phosphatic, silty clay with varying amounts of quartz pebbles, silt and mica flakes. The light-colored clay with interbedded limestone is part of the Hawthorn Formation of early and middle Miocene age. Generally, its occurrence is limited to the southeastern part of the Green Swamp area. It thickens eastward and southward and forms a secondary artesian aquifer which is a significant source of artesian water outside of the Green Swamp area. The dark, silty clay is probably equivalent to the Tampa Formation of early Miocene age (Carr, 1959). Generally, its occurrence is limited to the eastern part of the Green Swamp area where it forms an aquiclude. SUWANNEE LIMESTONE The Suwannee Limestone (Cooke and Mansfield, 1936) of Oligocene age is a white dense fossiliferous limestone. It is present in the southern and western parts of the Green Swamp area and crops out along the Withlacoochee River near Polk-Sumter-Pasco County line. The formation thickens southward in Polk and Hillsborough counties and westward in Pasco County. Many of the springs along the upper Hillsborough River flow from exposures of Suwannee Limestone. The Suwannee Limestone overlies the Crystal River Formation and it is overlain by either undifferentiated clay or undifferentiated clastic deposits.

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REPORT OF INVESTIGATIONS NO. 42 31 OCALA GROUP The Ocala Group (Puri, 1957) includes three limestone formations of late Eocene age. The subdivisions of the Ocala Group (from youngest to oldest) are the Crystal River, the Williston, and the Inglis Formations. CRYSTAL RIVER FORMATION The Crystal River Formation is primarily a coquina of large foraminifers and crops out in an area extending from northern Polk County through the southern end of Sumter County and into eastern Hernando County. It ranges from 50 to 120 feet in thickness, except in the eastern part of the area where it is absent. In the central part of the area, the formation contains many sand-filled cavities. WILLISTON FORMATION The Williston Formation is a tan-cream, medium to hard limestone containing abundant micro-fossils. The formation is slightly coarser than the underlying Inglis Formation but generally finer than the overlying Crystal River Formation. In most of the area, the Williston Formation ranges from 20 to 40 feet in thickness. It is thin or absent along the eastern boundary of the area. INGLIS FORMATION The Inglis Formation is generally a white-tan, hard, fossiliferous limestone. The texture of the formation appears to be finer than that of the Crystal River and Williston Formations. In most of the area, the Inglis Formation is about 50 feet thick. It is thin or absent along the eastern boundary of the Green Swamp area. AVON PARK LIMESTONE The Avon Park Limestone (Applin and Applin, 1944) of late middle Eocene age was the deepest formation penetrated by test drilling. The formation is nearest the surface on an upthrown fault block along the eastern side of the area (fig. 8, A-A'). The formation is found at considerable depth in the area south and southwest of Green Swamp. The top of the formation is

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32 FLORIDA GEOLOGICAL SURVEY characterized by a distinct color change from tan to brown limestone and by abundant cone-shaped foraminifers. The formation is a brown, dolomitic, porous limestone. Selenite (gypsum) near the base of the formation probably forms the bottom of the Floridan aquifer. The Avon Park Limestone is highly permeable and is the main source of water for most of the high-capacity wells in the area. Figure 9 shows the configuration of the top of the Avon Park Limestone. The map shows the northwest-southwest trend of the faulted anticline. STRUCTURE The Peninsular arch (Applin, 1951), a buried anticlinal structure of Paleozoic sediments, trends generally north-northwestward and its main axis is located east of the Green Swamp area. A flexure, developed on the western flank of the Peninsular arch in the Tertiary limestones, is called the Ocala Uplift. The Green Swamp area is located at the southern end of the Ocala Uplift (figs. 8 and 9). Vernon (1951) dated the Ocala Uplift as post-Oligocene in age. Faults in the Green Swamp area complicate the definition of the geology and the hydrology. The main area of faulting occurs along the Lake Wales Ridge. Faulting in this area was described by Vernon (1951, p. 56) and named The Kissimmee Faulted Flexure. The cross sections in figure 8 show vertical displacement along fault zones. The faults are probably post-Oligocene. Subsequent movement along fault zones may have occurred over a long period of time, the later movements being associated primarily with subsidence and sinkhole collapse along the solution-widened zones. Figure 9 shows a structural map based on the top of the Avon Park Limestone. The contour lines generally define the shape of the anticline with associated faults. The linearity of ridges on the anticline suggests that other faults exist in the area. Faulting probably could affect the hydrology of the Green Swamp in the following ways: (1) Joints or faults within the Floridan aquifer, widened by solution, could cause zones of high permeability, or could cause zones of low permeability when filled with clastic materials. (2) Displacement along the faults could position formations of different lithology (hence permeability) one against the other,

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REPORT OF INVESTIGATIONS No. 42 33 breaking the hydraulic continuity and producing barriers that retard water movement. (3) Faults cutting confining beds could increase ground-water circulation between aquifers. HYDROLOGY The water supply of the earth, whether it is on the surface or below the ground, has its origin in precipitation. Of the precipitation that reaches the ground, part is returned to the atmosphere by evapotranspiration; part remains above ground and is stored temporarily in lakes, ponds, and swamps, or moves to the sea as streamflow; and part percolates into the ground, some to replenish the soil moisture and some to enter the zone of saturation and recharge the ground-water aquifers. Ground water moves in the aquifers under the influence of gravity, towards areas of discharge such as streams, lakes, springs, wells and the oceans. WITHLACOOCHEE RIVER BASIN DESCRIPTION OF BASIN TheWithlacoochee River drains 82 percent of the Green Swamp area. The total drainage area at stations 42 and 43 at the western boundary is 740 square miles, all of which is within the project area except for 45 square miles of lakes and hills west of U. S. Highway 301 and south of U. S. Highway 98 near Dade City. Most of the general topographic and drainage features of the Green Swamp area, described in preceding sections of this report, apply to the Withlacoochee River basin in particular. The following description of the basin refers specifically to this stream system. The Withlacoochee River heads in a group of lakes and swamps in the north-central part of Polk County in the vicinity of Polk City and the town of Lake Alfred (see fig. 5). Lakes Van and Juliana, the uppermost of these headwater lakes, drain into Lake Mattie. Surface drainage from Lake Mattie spills through a wide shallow marsh along the northeastern shoreline and flows northward through a series of interconnected shallow swamps and ditches to the northern boundary of Polk County. This is generally considered to be the major headwater channel of the Withlacoochee River. Other headwater tributaries originate in the marshes between Lakes Mattie and Lowery and flow generally northward between the confining ridges. These -channels join near the

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34 FLORIDA GEOLOGICAL SURVEY northern boundary of Polk County and flow westward to form the Withlacoochee River. West of State Highway 33 the tributaries of the Withlacoochee River are not confined by the ridges that are prominent in the area east of the highway. These tributaries have developed basins that are generally more fan-shaped than those in the eastern part. Pony Creek, which flows northwestward, is the first of the large tributaries entering the Withlacoochee River west of the Seaboard Air Line Railroad. Pony Creek heads in a swamp east of Lake Helene near Polk City. Lake Helene has no surface outlet except at extremely high stages when it overflows into the Pony Creek basin. Grass Creek, the next large tributary, empties into the Withlacoochee River about one mile downstream from Pony Creek. Grass Creek heads in a group of small lakes in the vicinity of Polk City. the largest of which is Lake Agnes. The outlet from Lake Agnes is a ditch leading from the northern end of the lake and connecting with the network of canals and ditches that carry the water northwestward through the swamp. Several other tributaries flow into Grass Creek as it crosses the swamp. Gator Creek empties into the Withlacoochee River at the Polk-Pasco County line. This is the largest tributary upstream from the diffluence of the Withlacoochee River to the Hillsborough River. Gator Creek heads in several small swamps northeast of Lakeland and flows northwestward through a network of swamp channel and ditches. From the point of diffluence to the Hillsborough River, the channel of the Withlacoochee River turns abruptly to the north and continues northwestward to the western boundary of the Green Swamp area at U .S. Highway 301. About 14 miles downstream from the point of diffluence, a major canal draining several lakes and swamps east of Dade City empties into the river from the west. This canal also carries the drainage from an area of hills and lakes west of Dade City and the effluent from citrus concentrate plants at Dade City. One of the larger tributaries entering the Withlacoochee River from the east is formed by the confluence of Devils Creek and Gator Hole Slough. Devils Creek heads in a swamp about 21/ miles east of the Sumter-Pasco County line. At high stages some water from the Withlacoochee River moves through a gap in a low ridge into Devils Creek. This water returns to the Withlacoochee River farther downstream.

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REPORT OF INVESTIGATIONS NO. 42 35 Gator Hole Slough heads just east of the Seaboard Air Line Railroad and flows westward through an unimproved swamp channel, entering the eastern boundary of the Withlacoochee State Forest about 3 miles west of the railroad. It continues within the boundaries of the Forest to its confluence with Devils Creek which empties into the Withlacoochee River 21/ miles farther west. The Little Withlacoochee River, the largest tributary of the Withlacoochee River, heads near State Highway 33 in Lake County and flows westerly. Bay Root Slough is the headwater tributary of the Little Withlacoochee River. This stream carries the drainage from several lakes and swamps east of the Seaboard Air Line Railroad and flows northwestward to the Lake-Sumter County line at the eastern boundary of the Withlacoochee State Forest. The river channel within the Forest is wide and shallow and contains dense growths of cypress trees. The channel has been allowed to remain in its natural swampy condition to store as much water as possible, rather than to remove the water by improved drainage, as a precautionary measure against fire damages to the valuable cypress and pine trees in the Forest. The Little Withlacoochee River emerges from the Forest near the Sumter-Hernando County line, where it is joined on the north by a major canal. This canal drains a swampy area between the Forest and State Highway 50. The river continues westward through the swamp to the crossing of State Highway 50 where it turns and flows northwestward toward U. S. Highway 301. Another canal joins the river about a quarter of a mile upstream from U. S. Highway 301. This canal heads near Webster, flows southward about 11 miles, then turns westward to Big Gant Lake and then to the Little Withlacoochee River. The Little Withlacoochee River continues westward and empties into the Withlacoochee River 3 miles downstream from U. S. Highway 301. STREAMFLOW Streamflow data for gaging stations in the Withlacoochee River basin during the data-collection phase of the investigation are summarized in table 5. Flow-duration curves for five gaging stations in the Withlacoochee River basin are given in figure 10. Records for only the Trilby gaging station are continuous for the 311/2-year period, 1931-62. The curves for the other four stations in the basin have been adjusted from their individual short-term records to the 31/-year base period.

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TAB~I 5, Strueamflow cdata for Withlacoocheo River basin gaging stations in Green Swamp area (see figure 5 for station locations) Drainawe Discharge in chf Station area Calendar Runoff number Station (yd.mli) year Maximum Minimum Mean in Inches 80 Withlacoochee River near Eva 180 "1958 0. 1050 830 14 240 2:07 1000 2,100 0.5 288 24.41 1001 107 0 12.2 1.27 "1062 .... 0 ........ 88 Pony Creek near Polk City 0.5 "1060 284 ... 1061 6.8 0 .55 .79 "1062 .... 0 80 Withlacoochee-Hillsborough .... 1058 .... .... overflow near Richland 1050 .... 0 1144... 1960 1,880 0 11140 .... 1001 20 0 .82 .... "1062 .... 0 .. .. 40 Withlacoochee River 1950 2,740 .. ........ near Dade CAty 1080 5,000 ............ 1961 802 e.8 "1002 .... 0 .... 41 Pasco Packing Co. canal .... 1057-02 e75,6 P4.07.. at Dade City 42 Withlacoochee R:ver 580 1058 2,600 48 864 .... at Trilby 1099 2,960 109 1,157 d80.45 1060 0,920 158 d. 81.80 1061 872 28 1165 2.70 "1062 .... 26 1981-61 8,840 8.6 406 . 48 Little Withlacoochee R:ver 160 "1058 .. 2.0 . at Rerdell 1050 1,940 80 842 28.8 1060 8,400 8.8 824 27.48 1961 106 0 9.12 .77 "1062 .... 0 ........ nRecords for part of year. 'Partly estimated, aMaxfmum or minimum measured; probably not the extreme. dAdjusted for diversion to Hillsborough River basin.

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REPORT -OF INVESTIGATIONS NO. 42 37 BPOO GAGING STATION P ---( -Withlocoochee River neor Eva 4000-Withlocoochee -Hiltsborough Overflow neor Richlond 3p00 ---C-----°2-Withlocoochee River near Dode City S---Withlocoochee River at Trilby -Little Withlocoochee River of Rerdell 1,00 Note -Curve for station 42 computed from 800 -records for 31 /2year base period, 1931-62 Curves for all other stations adjusted from 60 the short-term period, 1958-62, to the S\ 31 1/2-year base period. -\ 20 0 ------T -" ' ---------0\ 4--_ 0 1 0 I2 OS I 2 5 1 o 30 40 50 60 70 80 90 95 98 9 9-5 993 99 PERGENT.OF TIME INDICATED DISGHARGE WAS EQUALED OR EXGEEDED. Fiure 10. -duration rves for Withlacochee River basin 191-62. W -________ _ __ 01 __ -_ § ~ ~ ~ ~ ~ -__ __ -_4 _ _V ----_---4 --_ _ _ -__ -^ _ _ _ -_ _ ^ _ -_ _ ---.-------_ -^ .-----Id , __ _ _ _ __ _ __ _ _ _ _ _ * __ _ __ _ _ __ __ QE G N l --_ -----_ _ -_ _ --L.^ --t---------EEDE Fiu e ---Flo-------ur es f r ---\-^ -h e R--------3 -6

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38 FLORIDA GEOLOGICAL SURVEY The flow-duration curves indicate the percentage of time that specified discharges were equaled or exceeded during the period of record. These may be considered probability curves used to estimate the percent of time a specified discharge will be equaled or exceeded in the future. The use of flow-duration curves to indicate the future pattern of flow from a basin is valid only if the climatic conditions remain the same and the amount and distribution of runoff from the basin is not significantly changed by man. The flow-duration curve for Withlacoochee River at Trilby (station 42) may be only an approximate representation of duration of future low flows because of the progressive increases in ground-water inflow by pumpage above the gaging station. However, the flow-duration curves for the other four stations shown in figure 10 may be considered probability curves and used to estimate the percent of time that a specified discharge will be equaled or exceeded in the future. During a period of extremely low flow on May 23-25, 1961, streamflow was measured and water samples for chemical analysis were collected at several sites on the Withlacoochee River. The results of this low-flow investigation are shown on the map in figure 11. The base flow of the Withlacoochee River near Dade City (station 40) represents the natural drainage from 390 square miles because no surface flow is diverted to the Hillsborough River basin through the overflow channel, C-9. Since about 1941 or 1942, the effluent from citrus processing plants at Dade City has been drained into the Withlacoochee River by way of the Pasco Packing Company canal. The water used by these plants is pumped from deep wells. Measurements at station 41 of the effluent from the Pasco Packing Company canal during 1958-62, ranged from 5 cfs, when the plant was at minimum operation, to about 76 cfs at peak operation during the citrus packing season. Inflow to the river from this plant and others at Dade City produces higher discharge below station 40 east of Dade City than would be derived from the natural yield of the basin. During dry periods, the effluent at Dade City greatly exceeds the base flow of the Withlacoochee River (see fig. 11). The drainage area above Trilby (station 42) comprises two-thirds of the Green Swamp area and the record collected at this station is a good index of the long-term variations of surface runoff from the entire area except at low flow.

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REPORT OF INVESTIGATIONS NO. 42 39 The discharge at the Trilby gaging station does not represent the natural runoff from the Withlacoochee River basin because of the high-water flow diverted from the basin to the Hillsborough River by the Withlacoochee-Hilisborough overflow channel (C-9) and the effluent into the river from the citrus concentrate plants at Dade City. When the Withlacoochee River reaches a stage of about 78.5 feet above msl at the overflow channel, part of its flow is diverted into the Hillsborough River. At high stages more than a fourth of the flow from the upper Withlacoochee River is diverted through this channel. Computations of basin runoff for either the Withlacoochee or the Hillsborough Rivers must be adjusted for the amount of discharge from one basin to the other. Percentagewise, the plant effluent into the basin is small except when the discharge in the Withlacoochee River is extremely low and the plant is at peak operation. The annual and mean monthly discharges at the Trilby gaging station are shown by the bar graphs in figure 12. The general relation between rainfall and streamflow is evident from figures 6 and 12. During the wet years of 1959 and 1960, annual rainfall over the Green Swamp area was 70.9 inches and 69.5 inches, respectively. The annual mean discharge at the Trilby gaging station was 1,157 cfs for 1959 and 1,209 cfs for 1960. The higher runoff for 1960 was probably the result of a carry-over from the high rainfall of 1959. The maximum discharge of record at the Trilby station was 8,840 cfs on June 21, 1934. Flood-frequency studies by Pride (1958) indicate that the recurrence interval of a flood at this magnitude is more than 100 years. The peak discharge of the flood of March 1960 was 6,920 cfs and was the third highest flood of record. The recurrence interval of a flood of this magnitude is about 40 years. The drought of 1954-56 was the most severe dry period of record, considering its 3-year duration and yearly deficiencies. Annual rainfall on the basin above the Trilby station for 1954-56 was 39.9, 40.2, and 46.2 inches per year, respectively. The prolonged period of low rainfall resulted in low discharges at the Trilby station during each of the 3 years. The lowest annual mean discharge at the Trilby station was 75.4 cfs for 1932, a year in which the total rainfall amounted to 39.6 inches. The total annual rainfall on the basin in 1961 amounted to only 35.2 inches and was the minimum for any year of record. Effluent from citrus concentrate plants, derived from ground-water sources, accounted for the higher annual mean discharges for 1954-56 and 1961 than that for 1932.

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40 FLORIDA GEOLOGICAL SURVEY 1200 1100 IOO 00 to In -406 cftT average, ao -0 0CALENDAR YEAR 5000 Based on records 1928-29, 1930-62 C: MAXIMUM W MONTH Withlacoochee River at Trilby.

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REPORT OF INVESTIGATIONS No. 42 41 The graph of mean monthly discharge for the Withlacoochee River at Trilby (fig. 12) shows that runoff from the basin is lowest for the months of November through June. The season of highest runoff is the 4-month period, July through October. During these months, 58 percent of the runoff from the basin occurs. CHEMICAL CHARACTERISTICS OF SURFACE WATER Waters of the Withlacoochee River in the eastern part of the Green Swamp area are very low in mineral content (figure 13 a, b) acidic, and usually highly colored. Chloride is the principal dissolved mineral constituent. The low mineral content is due to the insolubility of the surface sands. The acidic condition of the water in the southern area is probably due to decomposition of organic matter and subsequent release of carbon dioxide and humic acids to the water. The pH of surface water in this area ranged from 4.0 to 5.9 units. The presence of chloride as the principal dissolved mineral constituent may be due to rain and wind-borne salt from the coastal area. The chloride concentration is usually less than 12 ppm. High color is caused by organic matter in the water. The color ranged from 90 to 600 units and was higher than 250 units most of the time. The chemical characteristics of water in the Withlacoochee River near Eva (station 36) indicate no inflows from the Floridan aquifer to the stream. Between Eva and Dade City (station 40) the mineral content is higher during periods of low flow but is essentially the same as that above Eva during periods of high flow. The highest mineral content observed in this reach of the river was 302 ppm (see fig. 11). This high mineral content was present in the river just above the mouth of Gator Creek and is about the same as the mineral content of the water from the Floridan aquifer in this area. The hardness of the water at this point was 254 ppm and the color, 15 units. The principal dissolved mineral constituents were calcium and bicarbonate. During periods of low flow, the chemical characteristics of the water in the Withlacoochee River between Dade City (station 40) and Trilby (station 42) are similar to those of the water from the Pasco Packing Company Canal at Dade City. The source of water in this canal is from wells penetrating the Floridan aquifer. The mineral content of water in the canal ranged from 182 to 190 ppm. The color of water in the canal is low (usually less than 10 units), and the principal dissolved mineral constituents are calcium and

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A. 6000 5000 -----..----------.. 5000 --_r-9-1) 1-95 61) 59(1951---61 " .I I 0 -.8-----„-----------_-_--_------0 20 40 0 20 40 60 0 20 40 60 80 0 20 40 60 8 100 I 10 10 160 160200 20 40 60 BO 100 120 140 160 20 40 60 80 100 120 140 160 180 200220 240 MINERAL CONTENT, IN PARTS PER MILLION (o) (b) (c) (d) (1) (f) Pony Crmk Withlococh River Wllhlocooch River Wtlhlcoochoe River Withlocoochee River Little Withlacoodwe River near Polk City neor Evo near Dode City at Trilby at Croom at Rerdell Figure 13. Relation of mineral content to discharge at gaging stations in the Withlacoochee River basin.

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REPORT OF INVESTIGATIONS NO. 42 43 bicarbonate. Additional ground-water inflow in this reach of the river is indicated. The chemical characteristics of this inflow indicate that it was derived from the Floridan aquifer. Gator Hole Slough, a tributary to the Withlacoochee River downstream from Dade City, was sampled at high flow. The water was low in mineral content and contained sodium and chloride as the principal dissolved mineral constituents. The color was 180 units. Data were collected during the period of low flow (May 23-25, 1961) to determine the quantity and mineral content of the ground-water inflow in the reach of the Withlacoochee River between the stations near Lacoochee and Trilby (see fig. 11). The mineral content of the ground-water inflow from the Floridan aquifer into this reach of the Withlacoochee River was computed using the load equation (Hem, 1959): QIC, + Q2C2 -Q3C3 where, Q is the discharge in cfs C is the mineral content in ppm QiCi is the instantaneous load near Lacoochee Q2C2 is the instantaneous load between dataCollection stations QsC3 is the instantaneous load at Trilby The inflow (Qs) was determined to be 12.2 cfs by subtracting the discharge near Lacoochee from that at Trilby. The mineral content (C2) of the inflow was then computed to be 260 ppm which is approximately equal to that of water in the Floridan aquifer in this area. The mineral content of water in the Withlacoochee River at Croom (station 44) was less than that at Trilby (station 42) or that at Rerdell (station 43). The difference between the sum of the discharges at Trilby and Rerdell and that at Croom on May 25, 1961, was 38.9 cfs (see fig. 11). Based on the load equation, the mineral content of the inflows between the stations would be 148 ppm. Similar computations of data during other periods show the mineral content of the ground-water inflows in this area to range from 148 to 174 ppm. The computed mineral content indicates that the inflow between stations was probably a composite of surface water and ground-water inflows. The mineral content of the water in the Little Withlacoochee River is shown in figure 13f. The color was usually above 100 units during periods of high flow. The principal mineral constituents during periods of low flow were calcium-and bicarbonate, the water

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44 FLORIDA GEOLOGICAL SURVEY was very hard (204 ppm), and the color was low (15 units). These overall chemical characteristics during low flow indicate inflow from the Floridan aquifer. The mineral content of water of the Withlacoochee River at Croom (station 44) varied from 176 ppm during low flow to 45 ppm during a period of high flow (fig. 13e). The color ranged from 10 units at low flow to 120 units at high flow. The water was soft (34 ppm) during high flow and hard (144 ppm) during low flow. Data collected at Lake Helene during April 1962 show that the water was low in mineral content (51 ppm); the temperature ranged from 760F. at the surface to 680F. at the deepest point in the lake (25 feet); dissolved oxygen ranged from 7.5 ppm at the top to 3.8 ppm at the bottom; and the pH ranged from 6.0 units at the top to 5.3 units at the bottom. The waters of Lake Mattie and Little Lake Agnes were low in mineral content and slightly colored. These lakes are similar in chemical characteristics to those of Lake Helene. The mineral content of water in the three lakes is about the same as that of water in the nonartesian aquifer. OKLAWAHA RIVER BASIN DESCRIPTION OF BASIN Palatlakaha Creek is the major headwater stream of the Oklawaha River. Figure 14 shows a flow diagram of the upper Oklawaha River system and the names of the various segments of the water course. Lake Lowery, the largest of a group of lakes located near Haines City is the headwaters of the Palatlakaha Creek basin. Most of the drainage from Lake Lowery is to the north into Green Swamp Run through a culvert in the old Haines City-Polk City road. At extremely high lake stages the road is inundated. The Palatlakaha Creek basin is confined by parallel sand ridges that extend from Lake Lowery northward almost to Lake Louisa. Between Lake Lowery and the Polk-Lake County line the drainage course is called Green Swamp Run. The stream channels in this water course are not deeply incised, and drainage is through wide shallow swamps. Big and Little creeks drain the basin between the Polk-Lake County line and Lake Louisa. Big Creek is a continuation of Green Swamp Run. The stream channels for both Big and Little

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REPORT OF INVESTIGATIONS NO. 42 45 creeks have more definitely incised valleys and the flood plain swamps are not as.wide.as those for Green Swamp Run. The Big Creek basin is confined along its eastern boundary by the Lake Wales Ridge. However, along the boundary between Big Lake Lowery (head of basin) Green Swamp Run Big Creek Little Creek Lake Louisa -Lake Nellie --Lake Glona Lake Minnehaha Lake Minneolo LaPalatlakaha Creek Cherry Lake connects these lakes. Lake Lucy Le Johns Lake Lake Emma $ Lake Apopka Palatlakaha Creek and many small lakes Apopkd-Beauclair Canal t + Lake Harris Lake Beauclair Dead River Lake Dora Lake Eustis --Dora Canal Haines Creek Lake Yale Lake Griffin -Lake Yale Canal Oklawaha River St. Johns River Figure 14. Flow diagram of the upper Oklawaha River.

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46 FLORIDA GEOLOGICAL SURVEY and Little creeks, the ridge is broken by swamps in several places and the two basins are interconnected. Big Creek, including Green Swamp Run, drains an area of about 70 square miles. The basin, from Haines City to Lake Louisa, is about 25 miles long and from 2 to 4 miles wide. The swamp channel ranges in elevation from about 130 feet near Lake Lowery to about 100 feet near Lake Louisa. Little Creek drains an area in Lake County west of Big Creek and empties into Lake Louisa. The western boundary of the Little Creek basin is fairly well defined by low ridges. However, in a few places the ridges are broken by saddles. The exchange of surface drainage between Little Creek and the Withlacoochee River through the saddles in the western boundary appears to be negligible. The southern boundary of the Little Creek basin is not well defined. The probable boundary is along an old road that extends from State Highway 33 to U. S. Highway 27 about a mile or two north of the Lake-Polk County line. Much of the drainage from the area that was formerly drained by Little Creek has been diverted into the Withlacoochee River by interceptor canals. These canals are located near the Polk-Lake County line. However, some water from its former basin still drains into Little Creek through natural swamp channels that were not closed when the interceptor canals were dug. The present (1962) drainage area for Little Creek, as outlined in figure 5, is about 15 square miles during dry periods. During wet periods, water flows into the basin through the openings in the road along the southern boundary of Lake County. Lake Louisa is the uppermost of a chain of large lakes in the upper Palatlakaha Creek system. Lake Minnehaha, Lake Minneola, and Cherry Lake are next in order below Lake Louisa. These lakes are connected by the wide, deep channel of Palatlakaha Creek. In addition to draining these lakes, Palatlakaha Creek also drains an area of smaller lakes and upland marshes westward to State Highway 33. This area affords storage facilities for large quantities of water. During the latter part of 1956, an earthen dam with two radial gates was built at the outlet of Cherry Lake to maintain the stages of the waterway and lakes upstream during prolonged periods of dry weather. The water surface from the upper pool at this dam to Lake Louisa is essentially level except during periods of high discharge. During the maximum discharge period in 1960, the stage of Lake Louisa was about 1.6 feet higher than that of the

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REPORT OF INVESTIGATIONS NO. 42 47 upper pool at Cherry Lake outlet. The fall between Lakes Louisa and Minnehaha was 0.4 foot during this period. The channel below Cherry Lake has been improved by a canal leading into Lake Lucy and Lake Emma. Palatlakaha Creek follows a more definite channel with steep gradient from Lake Emma to its mouth at Lake Harris. The fall in this reach is about 32 feet in 12 miles. STREAMFLOW Streamflow data. for gaging stations in the Palatlakaha Creek basin during the data-collection phase of the investigation are summarized in table 6. The flow-duration curve for Big Creek near Clermont (station 3), adjusted from the short-term period to the 311/-year period, 1931-62, is shown in figure 15. Long-term records for the Withlacoochee River at Trilby (station 42) were used for the adjustment because discharges at other long-term downstream stations on the Oklawaha River are partly regulated by water-control structures. Streamflow of the headwaters of the Palatlakaha Creek upstream from Lake Louisa is unregulated. Since 1956, the flow below Lake Louisa has been regulated by a water-control structure at the outlet of Cherry Lake. During periods of low rainfall, most of the drainage from the 160-square mile basin above Cherry Lake Outlet is stored in the chain of large lakes and marshes between Lake Louisa and Cherry Lake. Comparison of peak discharges during floods in March 1960 and September 1960 in Big Creek, Little Creek, and the upper Withlacoochee River shows the effect of the interconnections between the Little Creek and the Withlacoochee River basins. The peak discharge for the March 1960 flood in Big Creek at station 3 was 628 cfs. The discharge in Little Creek measured at station 6 near the peak of this flood was 801 cfs. The higher discharge from the smaller drainage area of Little Creek indicates that most of the flow was draining from the Withlacoochee basin into Little Creek through saddles in the drainage divide. The peak discharge during the flood of September 1960 for Big Creek at station 3 was 691 cfs. The concurrent flood peak for Little Creek at station 5 was 400 cfs. The flood peak for Withlacoochee River near Eva (station 36) was 2,160 cfs in March 1960 and 1,290

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00 TABLE 6. Streamflow data for Palatlakaha Creek basin stations in Green Swamp area (see figure 5 for station locations) Drainage Discharge in cfe Station area Calendar Runoff Number Station (eq. ml.) year Maximum Minimum Mean in inches 2 Green Swamp Run near 33 109590 '4 0 ........ Loughman "1061.2 .... 0 ........ S8 Bi Creek near Clermont 68 "1058 .... .4 1959 288 18 112 22.87 1060 691 22 142 28.89 1961 64 .1 12.2 2.42 "1962 .... 0 .... 5 Little Creek at Coopers 10 1961 18 0 1.27 Ranch near Clermont "1062 .... 0 ... 6 Little Creek near Clermont 15 n1958 .... i.65 .... 1959 " 210 "'8.92 58 1060 "801 0 51 .... 7 Lake Glona Outlet near 8.4 "1060-62 110 0 Clermont 11 Palatlakaha Creek at Cherry 160 1958 804 0 78.4 6.06 Lake Outlet near Groveland 1959 370 11 224 18.98 1960 584 36 251 21.40 1961 162 0 28.7 2.00 "1962 ..0 12 Palatlakaha Creek near 180 1945.56 458 .2 Mascotte "Records for part of year. !'Maximum or minimum measured: probably not the extreme. "Estimated.

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REPORT OF INVESTIGATIONS NO. 42 49 cfs in September 1960. Little Creek serves as an outlet for much of the flood drainage from the upper Withlacoochee River basin. CHEMICAL CHARACTERISTICS OF SURFACE WATER Waters of Big and Little Creeks have chemical characteristics similar to those of the Withlacoochee River upstream from State Highway 33 in that they have very low mineral content and are highly colored. Figure 16a shows that the mineral content of water in Big Creek ranges from 19 to 61 ppm. Figure 16b shows that the mineral content of water in Little Creek ranges from 18 to 31 ppm. Color of water in Big Creek ranges from 65 to 240 units and that of Little Creek ranges from 150 to 300 units. Both streams usually contain sodium and chloride as their principal dissolved mineral constituents. Waters of the two streams differ in chemical characteristics in that water of Big Creek is more mineralized, usually less colored, and the pH is higher than that of Little Creek. The higher mineral content of water in Big Creek is due mostly to higher concentrations of calcium and bicarbonate. HILLSBOROUGH RIVER BASIN RELATION TO GREEN SWAMP AREA The Withlacoochee-Hillsborough overflow channel (C-9, fig. 5), previously described with the Withlacoochee River basin, is one of the major drainage outlets from Green Swamp during high flows and is generally considered to be the head of the Hillsborough River. The overflow channel as it leaves the Withlacoochee River is about a mile wide. The road fill and bridge of U. S. Highway 98 crosses the channel about 1 mile downstream from the Withlacoochee River. The entire flow is confined by the road fill to the bridge opening which is 200 feet wide. White (1958, p.19-24) presents evidence to support an assumption that the Withlacoochee-Hillsborough overflow channel was formerly the main channel of the Hillsborough River and that the Withlacoochee River was once the headwaters of the Hillsborough River. Field studies made in the area in 1962 by Altschuler and Meyer indicate that the Withlacoochee-Hillsborough River overflow was formed prior to natural divergence of the

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50 FLORIDA GEOLOGICAL SURVEY headwaters of the Hillsborough River to the Withlacoochee River and that the divergence may be related to uplift in the area. From the bridge on U. S. Highway 98, the Hillsborough River flows generally southwestward through Pasco and Hillsborough counties and empties into Hillsborough Bay 531/2 miles downstream. sIFF ------------------"° --\ -------CC ,co _ 5C 40 C-I i I Not -Curve has been adjusted from the short-term period, 1958-62, to t/2 -year SF hobase period ----^.-.6 __ __ S.1L 5------Figure 15. Flow-duration curve for Big Creek near Clermont, 1931-62.

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REPORT OF INVESTIGATIONS NO. 42 51 1000 500 Z 1000 U n 50 w .1 * 0 0 w LUi (L iit Fiur 106. --------Reatono-mne-cn---t----geatggig -ttinsi L 10 m 5 o z w LJ ar S .5 (1956-61) [1956-61) 20 30 40 50 60 70 10 20 30 40 MINERAL CONTENT, IN PARTS PER MILLION (a) (b) Big Creek Little Creek near Clermont near Clermont Figure 16. Relation of mineral content to discharge atgaging stations in upper Palatlakaha Creek basin.

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52 FLORIDA GEOLOGICAL SURVEY The lower 15 to 18 miles of the river passes through the City of Tampa. The city water supply is a reservoir created by a dam in the river 10.2 miles upstream from the mouth. Tampa is vulnerable to damages from floods in the Hillsborough River because of extensive development of property in the flood plain. STREAMFLOW A summary of streamflow data for the gaging station on Withlacoochee-Hillsborough overflow (station 39) is shown in table 5. The flow-duration curve is shown in figure 10. No flow occurs in the channel at this point about 65 per cent of the time. Crystal Springs flows into the Hillsborough River in southern Pasco County near the Pasco-Hillsborough County line. The average flow of Crystal Springs (station 31) is 62 cfs, ranging from 20.3 cfs to 147 cfs. Downstream from Crystal Springs the base flow of Hillsborough River is well sustained. The flow of Hillsborough River near Zephyrhills (station 33), which includes flow from Blackwater Creek, is reported to be 71 cfs or more for 90 percent of the time (Menke, 1961, p. 29). CHEMICAL CHARACTERISTICS OF SURFACE WATER The chemical characteristics of water of the Hillsborough River upstream from Crystal Springs are similar to those of the Withlacoochee River between Eva and Dade City although the mineral content is somewhat higher. The water of the Hillsborough River at the WithlacoocheeHillsborough overflow contained calcium and bicarbonate as the principal dissolved mineral constituents. The water contained color that ranged from 80 to 150 units. The mineral content ranged from 41 to 121 ppm. The water of Crystal Springs had a mineral content of about 170 ppm, was clear, and contained calcium and bicarbonate as the principal dissolved minerals. The water was hard and alkaline. During the periods of low flow, the chemical characteristics of the water of the Hillsborough River near Zephyrhills (below Crystal Springs) are essentially the same as those of water of Crystal Springs. Figure 17 shows the relation of the mineral content to discharge. During periods of high flow the mineral content of water is low. A more detailed discussion of the chemical character of the water of the Hillsborough River is given in a report by Menke (1961, p. 28-36).

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REPORT OF INVESTIGATIONS NO. 42 53 5000 * 0 1000 ,oo* Ma * z u 500l** o , LL * &.4 0 100 o(1956 -62) 50 ____ 40 60 80 100 120 140 160 180 200 MINERAL CONTENT, IN PARTS PER MILLION Figure 17. Relation of mineral content to discharge, Hillsborough River near Zephyrhills. KISSIMMEE RIVER BASIN RELATION TO GREEN SWAMP AREA The eastern boundary of the Green Swamp area is U. S. Highway 27 atop the Lake Wales Ridge. This is generally the surface drainage divide between Palatlakaha Creek in the St. Johns River basin and headwater tributaries of the Kissimmee River. The surface drainage from only 5 square miles of the Green Swamp area flows eastward into the Kissimmee River basin. Piezometric maps in figures 35 and 36 indicate ground-water movement eastward from the Green Swamp area into the Kissimmee River basin. STREAMFLOW Horse Creek is one of the Kissimmee River tributaries adjacent to Green Swamp. Streamflow records of Horse Creek at Davenport (station 19) were collected to study the base flow that is derived

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54 FLORIDA GEOLOGICAL SURVEY from ground water. The drainage area at the gaging station is 22.8 square miles. The maximum discharge during 2 years of data collection was 358 cfs and the minimum was 0.5 cfs. Runoff characteristics of the Horse Creek basin are compared with those of the Pony Creek basin in a following section of this report. CHEMICAL CHARACTERISTICS OF SURFACE WATER Data concerning the chemical characteristics of water in the Kissimmee River basin were collected from Horse Creek and Reedy Creek. Water of Horse Creek is more mineralized than water in the upper Withlacoochee River. Figure 18 shows the general relation of mineral content to discharge. The mineral content from July to November 1960 ranged from 22 to 64 ppm (from daily conductivity records). Calcium and bicarbonate were the principal dissolved mineral constituents. The surface materials in the Horse Creek basin are sands and clays, which are essentially insoluble in water, and therefore the calcium bicarbonate type water in Horse Creek is probably due to seepage from the Floridan aquifer. The following 1000 500 *\ m z o0 M • eS00 50 * U) LL (1959 -61) 10 20 30 40 50 60 70 MINERAL CONTENT, IN PARTS PER MILLION Figure 18. Relation of mineral content to discharge, Horse Creek at Davenport.

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REPORT OF INVESTIGATIONS No. 42 55 equations were used to determine the approximate amount of seepage from the aquifer: Q1 + Q2 = Q 33Q1 + 167Q2 = CQ where, Q, is the component of discharge from nonartesian aquifer and from direct runoff Qs is the component of discharge from Floridan aquifer Q is total discharge of Horse Creek C is mineral content of water of Horse Creek 33 is average mineral content of ppm of typical water from nonartesian and from direct runoff 167 is average mineral content in ppm of typical water from the Floridan aquifer. Based on the computation, seepage from the Floridan aquifer averaged about 6 cfs for the 4 complete months of daily conductivity records. Color of water in Horse Creek ranged from 60 to 160 units and the pH ranged from 6.4 to 7.4 units. Mineral content of water from Reedy Creek during a wet period in 1959 was 33 ppm, the color 80 units, and the pH 6.0 units. PEACE RIVER BASIN RELATION TO GREEN SWAMP AREA The Peace River basin lies immediately to the south of the designated boundary for the Green Swamp area. Before construction of levees, highway and railroad fills, ditches and other drainage improvements, Lake Lowery and the surrounding marsh apparently drained southward into Peace River as well as northward to the Palatlakaha Creek and the Withlacoochee River basins. Under present conditions, the surface runoff from only 7 square miles of the Green Swamp area drains southward into the Peace River basin. This small area includes Gum Lake and its marsh outlet and Lake Alfred. The headwaters of the Peace River basin lie immediately south of the highest artesian water levels in the southeastern part of the Green Swamp area. Piezometric maps in figures 35 and 36 indicate ground-water movement southward to the Peace River basin.

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56 FLORIDA GEOLOGICAL SURVEY STREAMFLOW During the flood of September 1960, caused by Hurricane Donna, Lake Lowery reached a maximum stage of 133.32 feet above mean sea level. During this flood, a road fill between a marsh in the Withlacoochee River headwaters and Gum Lake marsh washed out and an undetermined amount of water flowed southward into the Peace River basin through an opening 12 feet wide (C-4, fig. 5). The flow at Gum Lake marsh outlet (station 22) includes the drainage from 4.2 square miles in the Gum Lake basin plus that diverted from the Withlacoochee River basin through opening C-4. During the flood of September 1960, the peak discharge was not determined but most of this flood discharge was from the Withlacoochee River basin. The 3' x 8' box culvert and a section of the highway at the gaging station were overtopped. The flood peak reached a stage of 132.0 feet above mean sea level, as determined from high water marks at the gage. During periods of low rainfall there is no flow in this channel. For the period May 1961 to June 1962, the channel was dry. The average discharge at station 22 was 0.55 cfs in 1961. There was no flow from Lake Alfred during the period April 1961 to June 1962. The total surface outflow from the Green Swamp area to the Peace River basin is negligible except during flood periods. DIVERSIONS AND INTERCONNECTION OF BASINS Although surface drainage from the Green Swamp area follows rather definite routes and although the drainage divides are generally determined by the topographic features, there are several places where the basins are interconnected and water is diverted from one basin to another. Some of these points of diversion have been mentioned under the foregoing discussion of the individual drainage basins. The hydrologic importance of these interconnections, which are integral parts of the drainage systems, is shown in the following discussion. The arrows on the map in figure 5 locate and show the direction of flow through many of the saddles in the drainage divides. The interconnections that are shown on the map are the most important ones disclosed by the investigation, but they by no means include all such points in the small subbasins where there are no definite drainage divides. One of the major diversionary channels is the WithlacoocheeHillsborough overflow in southeastern Pasco County (C-9, fig. 5).

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REPORT OF INVESTIGATIONS NO. 42 57 This diversion was discussed in detail under sections describing the Withlacoochee River and Hillsborough River basins. Other major interconnections of basins are near the Polk-Lake County line (C-3) in the eastern part of the Green Swamp area. The sand ridges in this area are dismembered by a transverse network of swamps that connect the Withlacoochee River and Little Creek basins. The alignment of the swamps and the relative widths of the flood plains shown on aerial photographs indicate that, in the former natural state, water carried to this area from the south was discharged by either of three different routes-Big Creek, Little Creek, or Withlacoochee River. The evidence indicates that most of the drainage from the southeastern area ran off via Big and Little creeks. Beginning about 1948 and continuing progressively each year, extensive land reclamation by property owners has considerably altered the pattern of drainage in the eastern area. These physical changes, which were made for the development of the area, apparently changed the proportion of the water that drained by the three routes. Based entirely on the present pattern of drainage canals and without any factual data on the streamflow from the upper basins prior to the development of the area, it appears that the most significant change has been a decrease in the area drained by Little Creek and an increase in the area drained by the Withlacoochee River. Major canals near the Polk-Lake County line were dug about 1948 and 1949 and appear to have intercepted the greater part of the flow from an area of about 60 square miles that was formerly the headwaters of the Little Creek basin. This area is roughly 18 miles long and 3 to 4 miles wide. It extends from the present southern divide of the Little Creek basin southward almost to the town of Lake Alfred. The greater part of the water from this area now drains to the Withlacoochee River. However, as discussed in the description of the Palatlakaha Creek basin, some flow still enters the Little Creek basin from its former headwaters. The changes in the drainage system predate streamflow records in the headwater basins. Therefore, the change in proportion of drainage between the two basins and the increased effectiveness of the drainage system may be inferred only on the basis of long-term streamflow records at downstream gaging stations. The runoff under present conditions, as compared with the runoff that occurred during the earlier years, is discussed under the heading "Effects of Man-Made Changes" in the following section.

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58 FLORIDA GEOLOGICAL SURVEY A levee now fills a saddle in the drainage divide between Green Swamp Run and the Withlacoochee River in northeastern Polk County south of the Polk-Lake County line (fig. 5). Prior to the construction of the levee (about 1956 or 1957), drainage from Green Swamp Run divided into flow westward into the Little Creek basin (now the Withlacoochee River basin) and flow northward into Big Creek basin. Lake Lowery and swamps in the upper Withlacoochee River basin are connected by a natural saddle (C-l) in the confining ridge northwest of the lake. This saddle is 200 to 300 feet wide and is one point at which flow may be diverted between the Palatlakaha Creek and Withlacoochee River basins. At high stages the two basins are interconnected at this point. Apparently water may flow through this saddle in either direction, depending on the distribution of rainfall and the relative water levels in the basins. There are four interconnections (C-2) between Big and Little creeks. These openings, all in Lake County, are small and their net exchange of water is probably negligible in comparison with the total flow from the basin. Other places, shown on the map in figure 5, where basins are interconnected are: (C-4) between the Withlacoochee River headwaters and Peace River headwaters; (C-5, C-6, C-7) between Lake Mattie, Withlacoochee River, and Pony Creek; and (C-8) between the Withlacoochee River and Devils Creek. Many of these interconnections act as equalizing channels through which water may flow in either direction, depending on relative water levels in connected basins. EFFECTS OF MAN-MADE CHANGES Many of the physical changes that have been made on the land surface through man's efforts have already been described. The most extensive developments of the area have occurred in recent years, but the first changes in the hydrologic characteristics undoubtedly occurred several years ago when logging trails and tramroads were built and much of the native timber was cleared from the area. The early developments of the area cannot be evaluated as they predate the period of data collection, but they probably had only minor effects on the hydrology. Changes in the drainage characteristics of the Green Swamp area can be detected by comparing the hydrologic data for years before drainage developments with the data collected since major

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REPORT OF INVESTIGATIONS NO. 42 59 developments have been made. Long-term records of rainfall and streamflow in the upper Palatlakaha Creek (stations 11 and 12) and Withlacoochee River (station 42) have been used to detect changes or trends in the pattern of discharge from the upper Palatlakaha Creek basin since 1946. Double-mass curves of cumulative measured runoff and cumulative computed runoff have been plotted to provide a means of examining the records of streamflow from the area of investigation to detect changes that may have occurred (Searcy and Hardison, 1960). The variables used in preparing the curves shown in figure 19 are the values of cumulative computed runoff, taken from the precipitation-runoff relations in the figures on pages 97 and 99 and cumulative measured runoff at each of the two gaging stations. The rainfall pattern is not affected by the progressive changes in the drainage system in the Green Swamp area. The theoretical or computed runoff based on rainfall is taken from an average curve for several years of record. Any change in slope in the double-mass curves of figure 19 would reflect progressive man-made changes in runoff. Figure 19a is the double-mass curve for the Withlacoochee River basin above the Trilby gaging station. Straight lines are drawn to average several points that show definite trends. These lines change in slope between 1942 and 1943, between 1945 and 1946, and between 1953 and 1954. The two changes in slope in the 1940's indicate changes in the runoff pattern but the authors have no knowledge of the causes of such changes. Minor deviations of the plotted yearly values of runoff are probably caused by variations of rainfall distribution and intensity during the year and are not necessarily indications of changes in the long-term trends. Yearly values of runoff for 1954-61 define an average line with less slope than that for any previous period. This change in slope indicates that a higher rate of runoff from the basin occurred during 1954-61 than that indicated from the same rainfall pattern of previous years. Figure 19b is the double-mass curve for the upper Palatlakaha Creek basin. The figures of annual runoff were adjusted for changes in storage in lakes. For the period 1946-49, the curve takes the general direction .as shown by the straight line. However, after 1949 a definite break occurs in the slope of the average line indicating, less runoff from the area.

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60 FLORIDA GEOLOGICAL SURVEY Figure 19c has been plotted to show the cumulative runoff from the combined Withlacoochee River and Palatlakaha Creek basins. The average line defining this curve has the same slope for the entire period, 1946-61. This indicates that there has been no significant change in runoff from the combined basins. 35C 300 ----S1960 / 250*'1955 " Z0 0 ---------_ _---------______ S 1950 1501945\ (a) Withlacoochee River 100 1940\ __ at Trilby, 1931-61 1939 50----________ -1939 S 0 50 to00 150 200 250 300 350 400 450 E 200-200 , (b) Palatlakaha Creek above (C) Combined Withlacoochee River W Mascotte, 1946-61 and Palatlakaha Creek |150__________________ ,basins, 1946-61 o 150 Ole^ 4955 55 19 5 0 O 1946 S50 100 150 200 0 50 100 150 200 Cumulative measured runoff, in inches Figure 19. Double-mass curves of measured runoff versus computed runoff, Withlacoochee River and Palatlakaha Creek basins.

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REPORT OF INVESTIGATIONS No. 42 61 The explanation for the significant decrease in runoff from the Palatlakaha Creek basin is a decrease in the size of the drainage area. Such a change in the headwaters of Little Creek, a tributary to Palatlakaha Creek, occurred during the period 1948-49 and has been discussed earlier in this report. This change has resulted in the diversion of part of the flow from the Little Creek basin into the Withlacoochee River basin. The gain to the Withlacoochee River basin is not as obvious as the loss from the Palatlakaha Creek basin because of the difference in size of the drainage basins. GROUND-WATER ACCRETIONS TO STREAMFLOW IN HORSE AND PONY CREEK BASINS Stream flow consists of direct surface runoff and ground-water runoff or base flow. Surface runoff is rainfall that drains directly into the stream channel during and after a storm. Ground-water runoff is rainfall that infiltrates to the ground and then discharges into a stream channel. In well-drained basins surface runoff ceases a few days after the occurrence of rainfall, and streamflow is then derived entirely from ground-water runoff. Surface contributions to streamflow continue for longer periods in basins containing lakes, swamps, or other surface storage features. Daily streamflow records were collected for the period June 1960 to June 1962 for Horse Creek at Davenport (station 19) and Pony Creek near Polk City (station 38). The runoff of these two streams probably represents the maximum variation in runoff of streams in the Green Swamp area. Horse Creek and Pony Creek basins have generally similar characteristics of geology and rainfall, but the two basins are situated differently with respect to the piezometric high. The basin slope of Horse Creek is higher than that of Pony Creek. Pony Creek basin above gaging station 38 is entirely atop the piezometric high. Horse Creek above gaging station 19 lies adjacent to the southeastern boundary of the Green Swamp area (fig. 5) and downslope from the piezometric high (fig. 35) in an area of artesian flow as indicated by hydrographs in figure 23. Graphs of monthly rainfall and runoff in inches for the Horse and Pony creeks basins for July 1960 to June 1962 are shown in figures 20 and 21. Base flows, expressed in inches of runoff from the two basins, were estimated for the low runoff period from November 1960 to June 1962. Base-flow recession curves were developed and used as a partial basis for separation of the

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62 FLORIDA GEOLOGICAL SURVEY 14.6" 14.5" 10 9 Totals for 1961: 8 inches Rainfall 37.2 Runoff 6.41 7 --Base flow 4.90 4 , 1960 1961 1962 Figure 20. Graphs of monthly rainfall and runoff for July 1960 to June 196i and estimated base flows for November 1960 to June 1962, Horse Creek al Davenport.

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REPORT OF INVESTIGATIONS NO. 42 63 14.6" 142" 10 8B inches S2 ainfall 38.4 Runoff .79 7 B t --Base flow .39 -2_ JUA SfO ND J FMAMJ JASON D J FMAMJ S960 1961 1962 Figure 21. Graphs of monthly rainfall and runoff for July 1960 to June 1962 and estimated base flows for November 1960 to June 1962, Pony Creek near Polk City.

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64 FLORIDA GEOLOGICAL SURVEY streamflow into the two component, base flow and direct runoff. The methods of separating streamflow into its components of base flow and direct runoff are hypothetical and the results are generally subject to some limitations. During months of high runoff, July to October 1960, streamflow was mostly from direct runoff and base flows could not be estimated with any degree of reliability. Monthly values of rainfall and runoff for Horse Creek and Pony Creek are summarized in table 7. Direct runoff was computed as the difference between total runoff and base flow. For the months of July, August, and September 1960, the average rainfall on the Horse Creek basin was 38.8 inches and the runoff was 13.0 inches. For the same period, the rainfall on the Pony Creek basin was 32.1 inches and the runoff was 19.4 inches. The greater runoff from Pony Creek resulted from less rainfall than that which occurred in the Horse Creek basin. This was probably caused by high ground-water levels in the Pony Creek basin and lack of storage capacity in the nonartesian aquifer as indicated by comparison of the hydrographs of wells in the basins (see fig. 23, well 810-136-2; and fig. 27, well 813-149-2). Comparison of the data for the year 1961 for the two stations in table 7 shows that Horse Creek received 37.2 inches of rainfall and Pony Creek received 38.4 inches. However, the runoff from the Horse Creek basin was 6.41 inches as compared to 0.79 inch from Pony Creek. The base flow or ground-water runoff for Horse Creek was 4.90 inches which was 76 percent of the total runoff. The base flow of Pony Creek was 0.40 inch which was 51 percent of the total runoff. Most of the additional runoff for Horse Creek in 1961 was probably gained by ground-water inflow. Base flow of the stream was sustained even during prolonged periods of little rainfall. On the other hand, Pony Creek basin is on top of the piezometric high and the stream received no ground-water flow during prolonged periods of low rainfall in 1961 and 1962. Flow-duration curves based on the 2 years of record for Horse Creek and Pony Creek are shown in figure 22. A comparison of the runoff characteristics for the two basins may be made from these curves. The curves have not been adjusted to a long-term base period, and therefore should not be used to estimate future long-term patterns. AQUIFERS Aquifers are classified as either nonartesian or artesian. Nonartesian aquifers are unconfined, and their water surface (the

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TABLE 7. Monthly water budgets for Horse Creek and Pony Creek basins, 1960-62 Horse Creek at Davenport (Station 19) Pony Creek near Polk City (Station 38) Baseflow Base flow Month J o -.. S * I -Direct .I * Direct S E. Runoff runoff Runoff runoff S E (inches) (inches) (inches) 4 PE (inches) (inches) (inches) .1960 July 14.6 8.98 _ 14.2 5.71 -August 9.7 2.86 8.3 5.14 September 14.6 6.16 _ 14.6 8.52 October 3.1 2.64 1.6 1.26 -. November .0 1.01 .06 .95 94 .0 .24 .05 .19 79 December 1.1 .84 .10 .74 88 2.0 .11 .03 .08 78 1961 W January 1.9 1.01 .20 .81 80 1.7 .07 .01 .06 86 February 2.0 .91 .17 .74 81 2.4 .08 .02 .06 75 March 2.0 .55 .04 .51 93 2.9 .10 .05 .05 50 April .7 .88 .05 .88 87 1.0 .09 .05 .04 44 May 2.8 .30 .07 .23 77 8.4 .002 .00 .002 100 O June 5.6 .18 .05 .13 72 6.8 .13 .08 .05 38 July 6.0 .53 .11 .42 79 8.8 .01 .001 .009 90 r August 9.4 1.15 .67 .48 42 9.2 .20 .13 .07 85 September 1.7 .80 .11 .69 86 1.6 .11 .05 .06 54 October 1.7 .28 .02 .21 91 2.8 .00 .00 .00 November .9 .18 .01 .17 94 1.6 .00 .00 .00 December 2.5 .19 .01 .18 95 2.7 .00 .00 .00 .. Year 37.2 30.8 6.41 1.51 4.90 76 88.4 37.6 .79 .39 .40 51 1962 January 1.2 .32 .03 .29 91 1.6 .03 .01 .02 67 February .7 .18 .01 .17 94 .6 .01 .00 .01 100 March 8.3 .22 .03 .19 * 86 3.8 .04 .02 .02 60 April 1.5 .17 .02 .15 88 2.1 .02 .00 .02 100 May 1.3 .03 .00 .03 100 5.2 .01 .008 .002 20 June 6.9 .38 .14 .24 63 8.4 .37 .22 .15 41 0 __

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66 FLORIDA GEOLOGICAL SURVEY water table) is free to rise and fall. Artesian aquifers are saturated, confined or semi-confined, and their water surface is not free to rise and fall. The water in an artesian aquifer is under pressure (greater than atmospheric) which causes it to rise above the top of the aquifer. The level to which water will rise in tightly cased wells, penetrating an artesian aquifer, is called the piezometric surface. i \ I t S1\ Fiure 22 Flow-duration curves for Horse Creek at Dvenport and Pony Creek near Polk City1960-62. tl CL .I __ ___:____ to1 1 2r | \ or Horse Creek C lat Davenportn r Pony Crek nea r Polk C itit -19\en 06r ---------_ -^ --_ -_ --\ --I ---_T Figure 22. Flow-duration curves for Horse Creek at Davenport and Pony Creek near Polk City, 1960-62.

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REPORT OF INVESTIGATIONS NO. 42 67 The principal importance of an aquifer is its ability to transmit and store water. The coefficients of permeability (P) and transmissibility (T) are measures of the capacity of an aquifer to transmit water. Permeability is usually determined by laboratory measurements of a minute part of the aquifer, whereas transmissibility usually determined in the field by aquifer tests, represents the average permeability for a localized area of the aquifer. The coefficient of storage (S) is a measure of the capacity of an aquifer to store water. The coefficient of storage for artesian aquifers is usually determined by pumping tests and may range from about 0.00001 to 0.001. The coefficient of storage for nonartesian aquifers can be determined by pumping tests or laboratory methods and may range from about 0.05 to 0.30 and, for all practical purposes, equals the specific yield. Coefficients of permeability were determined by laboratory analysis for samples from the nonartesian and artesian (Floridan) aquifers in the Green Swamp area (see tables 8 and 9). Aquifer tests were made at selected sites and the data were analyzed to determine coefficients of transmissibility using (1) the type curve TABLE 8. Hydrologic analyses of disturbed sand samples from a test hole in Lake Parker near Lakeland (Analyses by U. S. Geological Survey Hydrologic Laboratory, Denver, Colorado.) Depth below Specific Coefficient Sample lake bottom Porosity yield of permeability number (feet) (percent) (percent) (gpd/ft2) 1 5-7 37.1 36.3 75 2 11-12 34.0 33.4 40 3 15-16 35.0 34.6 50 4 20-23 32.7 32.1 80 5 24-26 34.2 34.0 20 6 27-28 35.2 38.4 60 7 35-37 36.9 35.8 90 8 44-45 36.2 34.5 150 9 50 32.2 31.0 95 10 55-56 39.7 37.3 180 11 60 44.8 43.9 110 12 70 45.4 41.7 115 13 73-77 43.2 39.0 40

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TABLE 9, Hydrologic analyses of core sampleu from a well (805-154-8) near Lakuland (Analytie by U. S, Geological Survey Hydrologic Laboratory, Denver, Colorado,) Formation: AP, Avon Park Limestone; CR, Crystal River; I, Inglis; LC, Lake City Limestone; 0, Oldsmar Limestone; S, Suwannee Limestone; W, Williston, Specific yield: The pore space that drains by gravity, Coefficient of permeability: Gallons per day at 600 F through cross section of 1 square foot under unit hydrologic gradient. Coefficient of Depth below Specifi permeability (gpd/ftt Sample land surface (percent) yield number (feet) Formation Lithology Porosity (percent) Horizontal Vertical 1 71,8 to S Limestone, tan, fragmental, very 81.5 14.0 0.1 0.03 72.4 soft 4 209 to CR Limestone, cream, chalky, coquina, 43.8 15.5 1. .0 260.5 soft 5 282.2 to W Limestone, tan, granular, hard 26.8 3.0 .2 .2 282.5 7 317.5 to I Limestone, cream, granular, hard 44.1 23.2 4 2 817.9 9 447.5 to AP Limestone, tan-gray, very dolo18.3 10.8 .0006 .0001 447.9 mitic, very hard 11 519.5 to AP Limestone, brown, very dolomitlc, 80.3 10.0 11 12 510.8 very porous 14 1,001.9 to AP Limestone, white, very chalky, 41.3 12.2 121 .4 1,002.5 very soft 16 1,169.5 to LC Limestone, cream, chalky, soft 35.1 21.6 19 15 1,169.9 with gypsum inclusions 17 1,886.8 to LC Limestone, tan, very dolomitic, hard 19.6 8.8 .004 .0008 1,886.6 19 1,476.8 to O Limestone, gray-brown, very dolo15.4 .2 .02 .02 1,477.8 mitic, with gypsum and anhydrite inclusion 'Sample fractured at end of test. Permeability may be too high.

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REPORT OF INVESTIGATIONS NO. 42 69 of the nonequilibrium formula (Theis, 1935), (2) the family of leaky aquifer curves (Cooper, 1963), or (3) a modified nonequilibrium formula (Jacob, 1950). Semi-confining beds that impede the movement of ground water comprise what is commonly called an aquiclude. Ground water will move through an aquiclude under hydrostatic pressure. For instance, when the water table is higher than the piezometric surface of an artesian aquifer, the potential leakage is downward (recharge to the artesian aquifer) and vice versa. The rate at which ground water moves through the aquiclude depends on the vertical permeability and the hydraulic gradient across the aquiclude. The aquifers of the Green Swamp area are discussed in order of occurrence from land surface downward: (1) the nonartesian aquifer; (2) the secondary artesian aquifer; and (3) the Floridan aquifer. NONARTESIAN AQUIFER DESCRIPTION OF THE AQUIFER The nonartesian aquifer is composed of undifferentiated clastic deposits (table 4) which consist of fine-to-coarse-grained quartz sand with varying amounts of kaolinitic clay. On the eastern side of the Green Swamp area (see fig. 8, A-A'), the aquifer ranges from about 50 to more than 100 feet in thickness. The permeability and specific yield is higher in the vicinity of the ridges than in the central and western areas. A relatively thin aquiclude, consisting of clay, forms the base of the aquifer. On the western side of the Green Swamp area, the aquifer ranges in thickness from 0 to about 50 feet. An aquiclude consisting of sandy clay which thickens eastward and grades into the sand of the nonartesian aquifer forms the base. RECHARGE AND DISCHARGE Ground water in the nonartesian aquifer is recharged primarily by local rainfall. It is discharged by (1) evapotranspiration, (2) flow into streams and lakes, (3) downward leakage into the Floridan aquifer, and (4) outflow to areas of lower head outside of the Green Swamp area.

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70 FLORIDA GEOLOGICAL SURVEY Most of the nonartesian ground water in the Green Swamp area is discharged by evapotranspiration because the water table is relatively close to the surface and surface drainage is poor. Evapotranspiration losses are least in the sandy ridge areas that rim the Green Swamp because the water table is farther beneath the ground than in the interior. Ground water percolates downward from the nonartesian aquifer to recharge the underlying Floridan aquifer because the water table is usually at a higher elevation than the piezometric surface as shown by the hydrographs in figures 23-29 and the aquiclude (undifferentiated clay) between the aquifers is relatively thin (see fig. 8) and permeable. The coincidence of areas of high water table and of high piezometric head is evidence of leakage. The amount of ground water that percolates downward is equal to the net outflow of artesian water from the underlying Floridan aquifer. The quantity of ground water leaving the Polk piezometric high in the Green Swamp area, hence leakage from the nonartesian aquifer, is presented in the table on page 116. Nonartesian ground water moves laterally to contribute to the surface runoff from the area. The direction of movement is generally governed by the topography. Therefore, ground-water divides in the nonartesian aquifer closely coincide with surface drainage divides shown in figure 5 except along the eastern boundary of the area where some nonartesian ground water flows laterally beneath the Lake Wales Ridge eastward to the Kissimmee River basin. The quantity of nonartesian ground water leaving the Green Swamp area by lateral seepage beneath the ridge was estimated to be insignificant in the water-budget analysis. Fluctuations of the water table were recorded in several shallow wells and water-table lakes in and near the southern and eastern parts of the area, shown in figures 23-29. No data were obtained in the western part because the nonartesian aquifer is thin or absent. The hydrographs of wells in the nonartesian aquifer are presented with hydrographs of wells in the secondary artesian or Floridan aquifers to show the hydraulic relation between aquifers and the potential movement of water in a vertical direction. No long-term records of water-table fluctuations are available within the Green Swamp area. However, records of water levels in a well located southeast of the Green Swamp area (810-136-2) show that the highest and lowest water levels since 1948 occurred during the period of investigation.

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REPORT OF INVESTIGATIONS No. 42 71 E Floridon aquifer) f P 104 4 -832-154-2 1 100 3 105 3 -(Nonortesion aquifer) 99 > 3 miles south of Moscotte Ranfal oa well 832-84-1,2 0 132 1 i 130 813 149-2 (Nonresi quifer) 1 4 -813-149-1 128 (Floridon aquifer) 25 miles north of Polk City . 821-202-3 (Floridaon oquiferl in unconfined area) 9 rle eat of Dode Ct y Rainfohll at well 821-2014 2-3 --QFE MAR APR MAY JUNE JULY AUG SEPT OC NOV DEC 1959 Figure 24. Hydrographs of water levels and rainfall at wells in the Green Swamp area, 1959. Water levels in most wells in the Green Swamp area show rises in response to local daily rainfalls. Only wells 810-136-2 and 815-139-3, located in the sandy ridges east of the Green Swamp area, show no response to local daily rainfall. Apparently, this is due to the high retention of the thick section of sand through which the water must percolate to reach the water table. Hydrographs of water levels in wells located in the central part of the Green Swamp area (figs. 27 and 28; wells 813-149-2, 813-150-2, 814-143-2, 822-149-2, 832-154-2) show that the water table declined less than 5 feet from a wet to a dry period (1959-62). During the wet years of 1959 and 1960, the water table remained near the surface and the aquifer afforded little capacity to store

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Well 808455. SFloridan aoquifer; 8 L120 .114 ý.T ^ --^---: 120 ,j Well 815-I57-2 4 1955 1956 1957 958 9 1960 1961 1962 S iFigure 26. Hydrographs of water levels in Wells (808-155-1, 2) 4 miles north of Lakeland and in a well (815-157-2) 12 miles north of Lakeland. -11 Well815-157-2 4 J JF MnAMJJ AS8o Ng J'F 'M'J'J'A'S IJFMAMJJA'SO J AFM'J'A AMJJ ASON D J F M A MJ J A OND AION 1955 1956 157 19581959 160 1961 962Figure 26. Hydrographs of water levels in Wells (808-166-1, 2) 4 miles north of Lakeland and in a well (815-157-2) 12 miles north of Lakeland.

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REPORT OF INVESTIGATIONS NO. 42 73 136 Well 810-144-2 2 134 Nonortesion oquifer \ 1324 -_ 132 Well 810-144-1 -8 28 Floridan aquifer _ 126 -12 12, 1242 132 Well 813-149-2 0 NIaoresian oquifer _ 0 -.-6--%-/-2 12 / Well 813-149-1 1 Floridon aquifer S124 ________V -J 128 Well 813-150-2 o S126 Nonartesion acqufer -2 LU 126 -Ur N/ ^X ^ ./ -4 c W' 124 -4 L4J -6 122 1 > 132 Well 814-143-2 ? 130 Nonortesion oquifer Well 814-143-6 F12 Floridan oquifer -L6 126 10 z"1 124________ ________ ________ ______ S94 Well 815-134-2 \ _ S.92 Nonaroesion oquifer -____ -______ 12 b Well 815-134-1 .Floidon aquifer -' 14 S90 ----188 -_________________ ______e416 130 Well 815-139-3 -60 SNonorlesion oquifer 3 _______ __ Well 815-139-2 -62 126 Floridon oquifer 24 -64 122 -66 68 12o70 118 ________ ________ _____TO ______ 126 Well 815-149-3 124 Floridian aquifer_ V A 6 122 .....1 .. ......... 8 1959 ,960 1961 1962 Figure 273: Hydrographs of water levels in wells (810-144-1, 2; 813-149-1,-2; 813-150-2; 814-143-1, 2; 815-149-3)in. south-central Green Swamp and in wells (815-134-1; 2 j:815-139-2, 3) about 9 miles north of Haines City.

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74 FLORIDA GEOLOGICAL SURVEY 94 -4 92 A 821202-3 6 It6 We1 822-138-2 -2 , i j\..\ -88 ___ft ------__-Well 822-138-1 8 O _Floidmo qwfer -10 06 114 A Wel 822-149-2-0 112 ' Ncresn fer Well 822-149-1 -4 > ldn afer F__ Vd Well 826-211-1 24 S74 Rddm aquifer 6 = S' ---38 7. 646 4 78 2 Figure 28. Hydrographs of water levels in wells (821-202-3; 822-149-1, 2 ; 64and in a well (83-137-2) 7 miles east of Clermont. 62-18 8 We 332-64-1 7--0 3 Wel832-454-2 4 SNcrcrten aquifer 82 Wl 833-137-2 -3 86 Pcndcn aqfer\ 82 --------40---42 78 -42 76_ -44 59 B60 161 1962 Figure 28. Hydrographs of water -levels in wells (821-202-3; 822-149-1, 2; 832-154-1, 2) in north-central Green Swamp; in a well (826-211-1) 5 miles north of Dade City; in wells (822-138-1, 2) 17 miles north of Haines City; and in a well (833-137-2) 7 miles east of-Clermont.

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REPORT OF INVESTIGATIONS NO. 42 75 136 I I I I 1 I I Well 810-14A-2 . Nonortesion oquifer 134 I -6 132 -S Floridn aquifer -10 126 -12 r 124 S 136 Lake Mattie 134 132 Lake Lowery 130 128 a'' I I L J FMAMJJASONDJ FMAMJ JASONDJFMAMJJASOND 1960 1961 1962 Figure 29. Hydrographs of water levels in wells 810-144-1, 2 and of Lake Lowery and Lake Mattie. additional rainfall. Therefore, the runoff was high. Although the hydraulic gradient between the water table and the piezometric surface indicated that water moved downward most of the time, a reversal in direction was noted for dry periods. Hydrographs of water levels in wells in the southwestern part of the Green Swamp area (fig. 25, well 805-155-1 and fig, 26, well 808-155-2) show that the water table fluctuated between 5 and 10 feet during the period 1959-62. The water table remained near the surface during the wet years of 1959 and 1960, and the aquifer afforded little capacity for storing rainfall. During the dry years of 1961 and 1962, the water table was progressively lowered by pumping from the Floridan aquifer south of the Green Swamp.

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76 FLORIDA GEOLOGICAL SURVEY The area of greatest decline was in the vicinity of well 808-155-2 where the secondary artesian aquifer is absent. Large fluctuationF of the water table in this area indicate good recharge to the Floridan aquifer and good hydraulic connection between the aquifers. Hydrographs of water levels in wells east of the Green Swamp area (figs. 23, 27, and 28, wells 810-136-2, 815-134-2, 815-139-3, and 822-138-2) show that the water table fluctuated between 5 and 10 feet during the period 1959-62. The water table occurs at depths ranging from about 2 feet to more than 70 feet below land surface. The area has a potentially large capacity to store rainfall. Water moves downward from the nonartesian aquifer to the Floridan aquifer in the Lake Wales Ridge and moves upward in the valleys of Davenport and Reedy creeks. The best hydraulic connection between aquifers in the eastern part of the Green Swamp area probably occurs beneath the Lake Wales Ridge. This is indicated by almost identical fluctuations of water levels in wells 815-139-2, -3 (fig. 27). Water levels in wells and sinkhole lakes, located in the southeastern part of the Green Swamp area, fluctuated about 5 feet (fig. 29). During wet periods, the water level is near or above land surface and water is stored in lakes and swamps. During dry periods, water levels decline due to lack of recharge and to pumping. Water levels in the nonartesian aquifer are generally higher than the piezometric surface indicating recharge to the Floridan aquifer. HYDRAULICS OF THE NONARTESIAN AQUIFER Permeability of a 3-foot section of the nonartesian aquifer was determined in a well (810-144-2) in southeastern Green Swamp and in a well (815-134-2) 5 miles east of Green Swamp by using the slug test method (Ferris, 1962). The field coefficients of permeability for the wells were determined to be about 50 gallons per day per square foot (gpd/ft2) and about 40 gpd/ft2, respectively. The results of laboratory tests of disturbed sand samples collected from a test hole in the bottom of Lake Parker near Lakeland (Stewart, 1959) ranged from 20 to 180 gpd/ft2 (table 8). The permeability of the aquifer is probably lower in the interior of the Green Swamp area than in the surrounding ridges because of greater clay content. The specific yield of the nonartesian aquifer was determined using a graphical analysis of rainfall and water-table fluctuations

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REPORT OF INVESTIGATIONS No. 42 77 ,n wells located generally along the eastern and southern boundaries and in the interior. Continuous records of water-level fluctuations and rainfall were collected at each well site. The data were analyzed to select short periods during which all of the rainfall was assumed to reach the water table. One or two-day periods were selected when (1) antecedent conditions compensated for moisture requirements of the unsaturated material above the water table; (2) the water table was far enough below the ground to store all the rainfall and none left as runoff; and (3) the rainfall was of short duration, high intensity, and widespread. The rise in the water table is directly proportional to the depth of rainfall. The specific yield of the aquifer therefore is inversely proportional to the ratio of rise in the water table in inches to the depth of rainfall in inches. EASTERN-SOUTHERN RIDGE AREA Well 810-144-2 (Nonortesian aquifer) Well 822-138-2(Nonorlesion aquifer)
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78 FLORIDA GEOLOGICAL SURVEY The specific yield of the sand comprising the nonartesian aquifer ranged from 31.0 to 43.9 percent by laboratory analysis (table 8) and from 12.5 to 47 percent by analysis of water-level fluctuations caused by local rainfall, shown in figure 30. The highest values (22.2 and 47 percent) are considered to be representative of the aquifer in the sandy ridges that surround the eastern and southern part of the Green Swamp area. The lower values (12.5 and 18 percent) are considered to be representative for the clayey sands in the central portion of the area. CHEMICAL CHARACTERISTICS OF NONARTESIAN GROUND WATER Water in the nonartesian aquifer in the eastern part of the Green Swamp area is less mineralized than that in the Floridan aquifer. The mineral content of water from the shallow wells in this area, ranging from 30 to 50 ppm, is due to the low solubility of the sand and clay which comprise the aquifer. The principal dissolved mineral constituents are sodium and chloride. The iron content ranged from 0.19 to 4.0 ppm. The 4.0 ppm in water from well 808-139-1 was the highest found in the Green Swamp area. The color of water from wells in the area was less than 15 units which is lower than that of surface water. In the western part of the area, the nonartesian aquifer is almost nonexistent. The chemical characteristics of water in most shallow wells and in the Floridan aquifer are similar. SECONDARY ARTESIAN AQUIFER RELATION TO GREEN SWAMP AREA The secondary artesian aquifer is composed of interbedded limestone in the undifferentiated clay (table 4). About 36 feet of the aquifer is present in well 810-144-1 in the southern part of the Green Swamp area. The aquifer thickens southward from the southern boundary of the area and is an important source of artesian water in southern Polk County. The aquifer pinches out northward and is absent in most of the Green Swamp area. The aquifer is recharged by downward percolation of water from the overlying nonartesian aquifer and discharges principally by. downward leakage to the Floridan aquifer. Fluctuations of the piezometric surface of the secondary artesian aquifer were recorded in well 805-155-3 (fig. 25) and the

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REPORT OF INVESTIGATIONS No. 42 79 surface is between the water.table of the nonartesian aquifer and the piezometric surface of the Floridan aquifer. The clay beds separating the aquifers are leaky as indicated by the conformance of the fluctuations of the piezometric surfaces. FLORIDAN AQUIFER DESCRIPTION OF THE AQUIFER The Floridan aquifer is the principal source of artesian ground water in Florida. In the Green Swamp area, the aquifer is exposed at the surface in the western and northwestern parts and occurs at depths ranging from 50 to more than 200 feet below land surface in the eastern part, shown in figure 31. The Floridan aquifer is composed of marine limestones that have been exposed to erosion and solution weathering. The formations that comprise the aquifer in the Green Swamp area range in age from middle Eocene to Oligocene (table 4). The Geologic cross sections (fig. 8) show the limestone aquifer and the position of the overlying clastic material. The top of the aquifer is highest (90 to 100 feet above msl) in the west-central part of the area as shown in figure 32. The base of the aquifer was determined by the first major occurrence of gypsum. Apparently, the gypsum fills the pores in the lower part of the Avon Park Limestone. The existing data indicate that the aquifer is about 1,000 feet thick in the central part of the area. The transmissibility of the Floridan aquifer will vary depending primarily on the occurrence of solution features such as caverns, cavities, and pipes. The presence of dolomite in the limestone is an indication of solution activity. Dolomite zones and cavities generally occur in the Inglis Formation and the Avon Park Limestone which are highly permeable. Logs of numerous wells in the Green Swamp area indicate that a large percentage of the cavities in the aquifer contain sand which reduces the transmissibility. The low yields of some wells in the Lake Wales Ridge area are attributed to sand-filled and clay-filled caverns. RECHARGE AND DISCHARGE The Floridan aquifer in the Green Swamp area is recharged by rainfall that percolates downward from the surface of the ground either through the nonartesian aquifer and aquiclude or directly

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80 FLORIDA GEOLOGICAL SURVEY into the Floridan aquifer in outcrop areas. Water is discharged from the aquifer by (1) outflow to areas of lower piezometric head, (2) seepage and spring flow into the streams, (3) upward leakage to the nonartesian aquifer in areas of artesian flow, (4) evapotranspiration, or (5) pumpage. Piezometric maps of the area were made from water-level measurements in about four hundred wells. These maps were analyzed to determine areas of recharge and discharge and the direction and rate of ground-water movement. The first piezometric map of peninsular Florida was prepared by Stringfield (1936) and the latest, figure 33, was prepared by Healy (1961). Ground water moves from high head to low head in a direction perpendicular to the contour lines. Piezometric mounds, referred to as "highs," usually indicate areas of recharge to the aquifer. Piezometric depressions or troughs, referred to as "lows," usually indicate areas of discharge from the aquifer. Recharge and discharge may take place anywhere from the high to the low where geologic and hydrologic conditions are favorable. Therefore, there is no one point of recharge nor one point of discharge. The difference in head between contour lines divided by the distance between them is the hydraulic gradient of the piezometric surface. The hydraulic gradient varies because of (1) unequal amounts of recharge or discharge, (2) differences in permeability within the aquifer, (3) differences in thickness of the aquifer, or (4) boundary conditions within the aquifer. Ground water in the central part of the Florida Peninsula moves outward in all directions from an elongated piezometric high that extends approximately from central Lake County to southern Highlands County, generally referred to as the "Polk high," and from a smaller piezometric high in Pasco County, commonly referred to as the "Pasco high." The Green Swamp area occupies a relatively small part of the Polk high. The top of the Polk high occurs within the southeastern part of the Green Swamp area. Ground-water drainage areas in the Floridan aquifer do not coincide with the surface-water drainage areas in the Green Swamp, shown in figure 34. The ground-water divides in the aquifer shift slightly in response to recharge and discharge. Therefore, the positions of the divides as shown in figure 34 were considered to be average for determining the size of the ground-water drainage areas that contribute outflow from the Green Swamp area toward the major surface drainage areas. Water in the Floridan aquifer

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REPORT OF INVESTIGATIONS NO. 42 81 moves generally from the southeastern part of the Green Swamp area eastward toward the Kissimmee River Basin; westward toward Lhe Hillsborough and Withlacoochee River basins; southward toward the Peace and Alafia River basins; and northward toward the St. Johns River basin. Figures 35 and 36 show the shape of the piezometric surface of the Floridan aquifer in the Green Swamp area and vicinity during a wet period (November 1959) and during a dry period (May 1962). Analysis of the maps shows the direction of movement of ground water did not change appreciably from wet to dry periods but the elevations of the piezometric surface declined. The decline was greatest along the southern and western borders and least in the interior of the Green Swamp area. Lows or troughs in the piezometric surface indicate that ground water discharges into Withlacoochee River through a spring at the mouth of Gator Creek and downstream from Dade City; into Hillsborough River at Crystal Springs; into Blackwater Creek; into Davenport and Reedy Creeks; and into Horse Creek. Closed depressions, such as those in the vicinity of Lakeland, indicate the effects of pumping. Natural hydraulic gradients, indicated by the spacing of the contour lines in figures 35 and 36, are steep toward the Hillsborough River on the western side of Green Swamp and toward Reedy, Davenport, and Horse Creeks on the eastern side. The base flow of Hillsborough River below Crystal Springs is sustained by more than 50 cfs of ground-water inflow from the Floridan aquifer. The base flows of streams on the eastern side of the area are sustained by relatively small amounts of ground-water inflow from the Floridan aquifer. Obviously then, the steep gradient toward the east is caused by some factor other than a high rate of ground-water discharge. The geology along the eastern side of the Green Swamp area (see fig. 8, A-A') suggests that the steep eastward gradient is due to a barrier, or constriction in the aquifer, that was formed by natural grouting (sink-hole collapse and cavity-fill) along the fractures and joints in the limestone. Thus, the barrier effect decreases the ground-water outflow and a piezometric high is formed along the eastern side. Figure 37 shows the decline in the piezometric surface from the wet period (1959-60) to the dry period (1962). Water levels declined least in the interior of the Green Swamp, in the Hillsborough River basin, and in the Kissimmee River basin (Davenport, Horse, and Reedy-creeks). Water levels declined most along the southern (near Lakeland), western (near Dade City),

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82 FLORIDA GEOLOGICAL SURVEY and northeastern boundaries. Water levels declined about 5 feet in discharge areas (Hillsborough and Kissimmee River basins) because the ground-water discharge is relatively uniform regardless of seasonal variations in rainfall. Water levels declined less than 5 feet in the interior of the Green Swamp because there was little local pumpage and the rainfall during the dry period was about enough to balance the outflow; therefore, the aquifer remained relatively full. The area surrounding the Green Swamp is more populated and developed and increased pumping during the dry period (1962) caused a greater decline in piezometric levels than would have occurred under natural conditions. If there had been no appreciable increase in pumping, the map could be used to detect areal changes in the hydraulic characteristics of the aquifer, particularly changes in permeability. The northernmost extent of an area of heavy pumping for mining, industrial, municipal, and irrigational supplies is in the vicinity of Lakeland where the water levels declined about 20 feet. The drawdown is confined to the southern boundary of Green Swamp, suggesting that the area of the sinkhole-riddled ridges around southern Green Swamp is a recharge area. Water levels declined between 10 and 20 feet on the western side of Green Swamp in the vicinity of Dade City. This is considered to be an area of high permeability and good recharge. Water levels declined about 10 feet in the northeastern area which is also considered to be an area of high permeability and good recharge. The general conclusion is that increase in discharge (natural or pumping) does not appreciably increase the lateral movement of ground water from the interior of Green Swamp but does affect the border areas. HYDRAULICS OF THE FLORIDAN AQUIFER Coefficients of horizontal and vertical permeability were determined for selected core samples of the limestones that comprise the Floridan aquifer. The samples were obtained from well 805-154-8, located just north of Lake Parker. The laboratory determinations are presented in table 9. The permeability values ranged from 0.0001 to 19 gpd/ft2.The specific yields ranged from 0.2 to 23.2 percent. However, the specific yield determined in the laboratory represents that of the rock sample and not of the aquifer as confined.

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REPORT OF INVESTIGATIONS NO. 42 83 Pumping tests were conducted in Green Swamp area and vicinity to determine coefficients of transmissibility (T) and storage (S) for the Floridan aquifer. The results of the tests are presented in table 10. Values of T ranged from about 20,000 gpd/ft to about 700,000 gpd/ft. The storage coefficients ranged from 0.013 to 0.0018 which means that for 1 foot change in head of the piezometric TABLE 10. Pumping test data (Floridan aquifer) Aquifer Average field Coefficient Coefficient penetration coefficient of transmissibility Coefficient of leakage (nearest permeability Well number gpd/ft) of storage (gpd/ft2/ft) ten feet) (gpd/ft2) (a) Determined by one or more observation wells 807-154-4 "5r720,000 "0.0036 1,130 637 808-153-2 520.000 .0057 510 1,020 814-139-5 b'C680,000 .0018 .... 350 1,940 814-139-5 b'cl,150,000 .012 0.042 350 3,280 816-135-2 120,000 .011 ._360 333 821-202-1 c22,000 .003 .022 130 169 828-154-2 293,000 .013 .036 260 1,130 (b) Determined by observations in the pumped well 807-154-4 I*'1,150,000 1. .1,130 1,020 810-144-1 110,000 340 324 813-149-1 40,000 .. .. 140 286 813-201-1 62,000 ... .... 240 258 814-139-5 c120,000 ..350 340 814-143-1 77,000 -200 385 814-134-1 37,000 _160 231 815-149-3 29,000 .170 171 815-157-2 84,000 --. .130646 816-206-1 150,000 -.180 833 821-202-1 c22,000 _ _130 169 822-138-1 26,000 .230 113 822-149-1 .32.000 130 246 826-211-1 300.000 -190 -1,580 827-158-1 57,000 -160 356 832-154-1 28,000 -100 280 aAverage of two tests. bDetermined to be invalid. See pumping test analysis section. cAnalysed by Theis (1935) type curve and semilog method (Jacob, 1950).

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84 FLORIDA GEOLOGICAL SURVEY surface, the aquifer releases or takes into storage 0.013 to 0.0013 foot of water per square foot of surface area of the aquifer. A comparison of the results of laboratory tests with pumping tests indicate that the permeability of the Floridan aquifer is largely dependent upon the presence of solution holes (caverns, pipes, etc.) which, of course, are not represented in the small core samples. DavenportHorse Creek area -Eastern area ---*-*-Northwestern area -a-----Southwestern area ----x---x-Dode City area t---A // // i S/ / __ ! / / / 1 ' S/ / ./ / / SI I I 0,000 100,000 1,000,000 COEFFICIENT OF TRANSMISSIBILITY (gpd/ft) Figure 38. Graphs showing the relations between coefficient of transmissibility and depth of penetration in the Floridan aquifer. The values of T for the pumping tests in table 10 were plotted against depth of aquifer penetration, as shown in figure 38. The wide range in values of T are caused by unequal penetration and by areal and vertical variations in permeability. Areal analysis of the data indicate that generally the eastern side (DavenportHorse Creek area) of the Green Swamp area has a low value of T and the western side (Dade City) has a high value of T. Therefore. the test data were evaluated by location and depth of penetration.

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REPORT OF INVESTIGATIONS NO. 42 85 The average field coefficients of permeability (Pf) table 10) were averaged for each area and then multiplied by the approximate thickness of the aquifer (1,000 feet) to estimate the coefficient of transmissibility (Te) for each representative area. The data were analyzed for (1) the Davenport-Horse Creek area east of the Lake Wales Ridge; (2) the eastern area, which includes the general area between State Highway 33 and U.S. Highway 27; (3) the northwestern area, which includes the area west of State Highway 33 and north of the Withlacoochee River; (4) the southwestern area, which includes the area west of State Highway 33 and south of the Withlacoochee River; and (5) the Dade City area west of the Withlacoochee River. The results of the computations (expressed to the nearest hundred thousand gpd/ft) are presented in table 11. Computations of ground-water movement into or out of the area used in the water-budget analysis were based on the estimated coefficients of transmissibility shown in table 11. TABLE 11. Estimates of transmissibility T,, Area (gpd/ft) 1. Davenport-Horse Creek 200,000 2. Eastern 300,000 3. Northwestern 500,000 4. Southwestern 600,000 5. Dade City 1,200,000 Barrier boundaries caused variations in the values of T in the vicinity of the Lake Wales Ridge. Observation wells 815-139-2 and 815-140-1 were used to observe the effects of drawdown and recovery caused by pumping well 814-139-5. Water level measurements were also made in the pumped well. The data were analyzed by the Theis method (1935), the family of leaky aquifer curves by Cooper (1936), and the Jacob method (1950). The data defined three curves, figure 39, with T values of 680,000 gpd/ft and 1,150,000 gpd/ft, for the observation wells and 120,000 gpd/ft for the pumped well. The wide variation in T probably indicates that the basic assumptions prerequisite for the analysis of the data do not apply and is probably caused by heterogeneity of the aquifer and existence of a barrier boundary. The test site is in a faulted area (see fig. 8, C-C'). Figure 40 shows the location of the wells with respect to sand-filled fractures in the underlying limestone along the Lake Wales Ridge. The variation in T values is probably caused by sand-filled fractures which act as barriers

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86 FLORIDA GEOLOGICAL SURVEY I I I 11111 I I I I 1111 1 Observation well 815-'40-1 1.0 3750 feet from pumped well T= 680,000 gpd/ft. -S = 0.0018 LL -0= 1,600 gprm. LL. oo > .,to L.·* U-SObservotion well 815-139-2 2100 feet from pumped well T=l, 150,000 gpd/ft S= 0.012 O , I I I i II l I 1 1 10-6 10-5 10-4 Time(minutes) / Distance (feet) a Using Theis method (1935) and Cooper method (1963) 2289 -29I * 0 S T= 120,000 gpd/ft S30Q= 1,600 gp.m. 3 10 100 2C TIME, IN MINUTES b. Using Jacob method (1950) and pumped well. Figure 39. Graphs of pumping test at a well (814-139-5) about 9 miles norti of Haines City.

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REPORT OF INVESTIGATIONS No. 42 87 81040' 8139 20016e 17 Z O EXPLANATION Pumpf% well * Observation well Well TO 1, Upper number is well number S5 Lower number is the elevation of the zn top of the Florldon aquifer, in feet, o referred to mean sea level. M 52 -/00-SR 54 Contour represents the approximate o elevation of the top of the Floridon _ Waquifer, in feet, referred to mean -7 * 419 (sea level. Contour interval 100 feet Land surface contour, In feet, above meon sea level. Contour interval 25 foee 28015' 2 Sand filled fractures 3) Note: structure not shown lo0 39 I mile Figure 40. Map showing environment affecting pumping test at a well (814-139-5) about 9 miles north of Haines City. between the pumped well and the two observation wells. The barriers decrease the drawdown in the observation wells giving erroneously high values of T. Probably the best value of T was obtained from data from the pumped well which is comparable to the results of a nearby test (see table 10, well 816-135-2). CHEMICAL QUALITY OF WATER IN THE FLORIDAN AQUIFER The quality of water in the Green Swamp area is good. The total mineral content is generally less than 350 ppm. Water containing a mineral content of less than 500 ppm is usable for most purposes. The water of the Floridan aquifer is more mineralized (100-400 ppm) than surface water or water from the nonartesian aquifer (20-50 ppm). The higher mineral content is caused by contact of water with materials that are more soluble. About 75 percent (by weight) of the mineral constituents dissolved in water of the Floridan aquifer are calcium and bicarbonate that cause the water to be hard and alkaline. Hardness, illustrated in figure 41, is one of the more undesirable characteristics. The water ranges from moderately hard in the eastern part of Green Swamp to very hard in the western part. Figure 42 shows the iron content of water in the Floridan aquifer in the Green Swamp area. The highest concentrations of

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88 FLORIDA GEOLOGICAL SURVEY iron are found in the west-central part of the area. Iron greater than 0.20 ppm generally should be removed for most uses. Other dissolved mineral constituents, including silica, potassium, sulfate, and chloride, occur in concentrations generally less thain 10 ppm. Fluoride and nitrate are usually present in concentrations less than 1.0 ppm. The water is clear (color less than 5 units), the temperature ranges from 74 to 780F., and the pH ranges from 6.8 to 8.6 units. Water from a well (830-210-2) near the northwestern boundary had a sulfate concentration of 101 ppm. The high sulfate concentration is due to contact of water with gypsum. Samples of -0'o ° "O 55" 5o6 45 40' 35' a v .."I I I I I I I I ... .I HAEDNESS RANGE (PPM) GirKear than 10 Ver80 Hard P O area. :CIT area.

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REPORT OF INVESTIGATIONS NO. 42 89 2 i0 a a0 62 55 0 L 4 th M. 3 Figure 42. Iron content of water in the Floridan aquifer in Green Swamp area. a well (810-144-1) located on the piezometric high were analyzed for trace elements, none of which were present in a concentration that would impair the usability for most purposes. HYDROCHEMISTRY OF THE FLORIDAN AQUIFER IN CENTRAL FLORIDA a2*"' 05' BrW 55' 507 45" 46 3,' 3r Figure chem. Iron contentstry of water in the Floridan aquifer cn be used toSwamp area. gain a better understanding of the piehydrology of the Gh wereen Swamnalyed area and the relements, none of which were reen Swin a concentration othe r est of the central Florida area. The chemistry of the water HYDROCHEMISTRY OF THE FLORIDAN AQUIFER IN CENTRAL FLORIDA The chemistry of water in the Floridan aquifer can be used to gain a better understanding of the hydrology of the -Green Swamp area and the recharge potential of the Green Swamp as -Compared to the rest of the central Florida area. The chemistry of the wafter

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90 FLORIDA GEOLOGICAL SURVEY in an aquifer depends on the chemical character of the water entering the aquifer, the chemical character of the rocks and water in the aquifer, and the time the water entering the aquifer is in contact with these rocks and water. Water entering the aquifer in the Green Swamp area and in central Florida in general, is less mineralized than water already in the aquifer. Water is low in mineral content because the overlying sands and clays generally are less soluble than the limestone of the Floridan aquifer. Therefore, in recharge areas the mineral content should be lowest, other factors being equal. The mineral content of the water should increase as the water moves through the aquifer until it becomes saturated with calcium and bicarbonate. Using only the mineral content to indicate areas of recharge could be misleading because water entering the aquifer in some areas could be more highly charged with carbon dioxide than in other areas. High amounts of carbon dioxide in water dissolves more limestone than small amounts. In some coastal areas, the water in the aquifer already contains high concentrations of salt. The percentage of limestone that was dissolved by the water in the aquifer in central Florida was calculated from measurements of alkalinity, pH, temperature, and mineral content (Back, 1963) and is shown in figure 43. Saturation values less than 100 percent indicate that the water could dissolve more limestone. Values of more than 100 percent indicate that the water is oversaturated and would therefore tend to precipitate limestone. Figure 43 shows undersaturated water occurs in the aquifer along the eastern and western boundaries of the Green Swamp and to the north. Water in recharge areas should be undersaturated and the percent of saturation should increase as the water moves away from the recharge area (Hem, 1961, p. C-15). If the recharge occurs only in the Green Swamp area, then the saturation values should be lowest in this area and should increase in all directions from the area. Figure 43 shows that the area of undersaturation includes much of central Florida and thus implies that recharge occurs over much of this area. In the areas of undersaturation, caverns or fissures can be enlarged by limestone solution several hundred feet below the water table (Back, 1963). High rates of water movement through these caverns and fissures could account for the occurrence of undersaturated water at these depths. The time and area of contact of water with the limestone in these openings would be minimized.

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OCAIA DAYTONA BEACH 5r' -Lines of iquol percentage of solurallon 100 ol ICANAVERALO Figure 43. Mqap of central Florida showing the percentage of calcium carbonate saturation of water in the Floridan aquifer. Nots: Samples from wells of unequal depthe Figure 48. Map of central Florida showing the percentage of calcium carbonate saturation of water in the Floridan aquifer.

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92 FLORIDA GEOLOGICAL SURVEY The presence of highly mineralized water in the Floridan aquifer may also be used to indicate the direction of movement of water. Assuming that at some time much of the aquifer of central Florida contained salt water, then the area in which the water now contains little or no salt (chloride), would be better flushed with fresh water than areas containing high amounts. The chloride content is generally higher at shallow depths near the coast than in the interior, shown in figure 44. However, water of low chloride content is present several hundred feet deep in local areas near the coast. Data from a few scattered deep wells indicate that fresh water extends to about 1,500 feet below sea level in much of the interior of central Florida from Marion County to Highlands County. Figure 44 and other data from the deep wells indicate that salt water has been flushed from the aquifer in much of the interior. Therefore, the total mineral content of the water in the Floridan aquifer in the interior of Florida is due to solution of limestone and not due to mixing with salt water. If recharge occurred only in the Green Swamp area, then the concentration gradient should increase in all directions from that area. Figure 45 shows that the concentration gradients do not increase immediately away from the Green Swamp but instead show a decrease over much of central Florida. The areas of low mineral content and areas of undersaturation generally coincide (figs. 43 and 45). This supports the implication that recharge is not confined to the Green Swamp area. ANALYSIS OF THE HYDROLOGIC SYSTEM The Green Swamp area is considered to be a self-sustaining hydrologic unit because most of its water supply is derived from rain that falls directly on the area. Water is imported from outside the area only in the vicinity of Dade City (see figs. 5, 11, 35, 36). Inflows in the vicinity of Dade City affect only the lower reaches of the Withlacoochee River. The amounts of water in the various parts of the hydrologic system and losses of water as the result of natural processes, are evaluated for the Green Swamp area. RAINFALL, RUNOFF, AND WATER LOSS Runoff is the residual of precipitation after all the demands of nature have been met. These demands taken collectively are called water loss. A simple definition for water loss is: Water loss equals precipitation minus runoff adjusted for change in storage and for

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(Cietowmlria Suraoe UI3) (12a1O ) ( (4) _ (a () 200i'S ' SI / "1 / I 400 0 I: 600 .1 . \ SAMPUNG LOCATION 8(I) DATONA BEACH (9500-5) \ / (2 DfYTONA BEACH 009064) 1000 _ 480 \ 13 ) DWTUNA BEACH 900117-2) 7 (4Q GENEVA 1200(5) SANFORD S/(9 FOREST CITY (0 140020 APOPKA S" / 0 HAINES CITY B 1600 ----GRDoVELAND 00 ZEPHYRfILLS S1800Gr swonp 0 (10 PLANT CITY (803-204-1) , \ / .Ae 4 02) PLANTCITY(801-207-0 S2000 -/ 03) TAMPA /-Li e ep nne remenng qppromna 9200p -T-el --IpOO ppm chlride Xo *-9 CSO 1* 6 50* I ji120 values indicate chlorde in ppm 3000 -W 32003400 5o , 3600 -lo600 3800Figure 44. Vertical distribution of chloride content of water in wells across central Florida.

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94 FLORIDA GEOLOGICAL SURVEY |------------------------r .al l d p t a o \is\ c i SIII l e l epo' I sidan; that is, water that returns to the atmosphere and thus is no longer available for use. As used in this report, water loss is not adjusted for seepage into or out of the bain. Thu, the equation for water loss is: L=P \--R-^S where, L is water lossl P. is effective precipitation R is streamflow .S is change in storage both surface and underground Use of an effective precipitation (Searcy and Hardison, 1960) is one .way of making allowance for the variable amouontent of water in the Floridan aquifer. seepage into and out of the basin. The basic concept is that water loss carried over from year to year as ground water storage in the basin.t returns to the atmosphere and thus is no longer available for use. As used in this report, water loss is not adjusted for seepage into or out of the basin. Thus, the equation for water loss is: L = P, -R ±t AS where, L is water loss Effective precipitation (P, s effcmmonly used, is that part of theation reiitation (P for the current year and the art of the AS is change in storage both surface and underground Use of an effective precipitation (Searcy and Hardison, 1960) is one way of making allowance for the variable amount of water carried over from year to year as ground water storage in the basin. Effective precipitation (P.), as commonly used, is that part of the precipitation (Po) for the current year and the part of the

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REPORT OF INVESTIGATIONS No. 42 95 precipitation (P,) for the preceding year that furnished the runoff for the current year, or Po = aPo + bP, The coefficients a and b are determined by statistical correlation. Long-term annual records of rainfall and runoff for the Withlacoochee River and Palatlakaha Creek basins have been used to determine the variations in water loss in the Green Swamp area. Areal variations in water loss are caused by: (1) climatic factors, the most important of which are rainfall, temperature, humidity, and wind; (2) drainage basin characteristics, which include size, shape, surface slope, the amount of water area, seepage as related to the surface and sub-surface geology, and the condition and type of vegetative cover; and (3) storage underground and in natural lakes, ponds, swamps, and artificial reservoirs. The effective annual precipitation determined for the Withlacoochee River basin above Trilby and for the Palatlakaha Creek basin above Mascotte is P, = 0.8P,, -0.2P, The annual water-loss curve for Withlacoochee River at Trilby is shown infigure 46. The Po = L line (dashed line) in figure 46 represents the theoretical limit of water loss which would occur if the loss equaled the precipitation and none ran off as streamflow. The average water-loss curve is shown by the solid line which was drawn to average the annual figures of effective precipitation and loss (P, -R) for the basin. The departures of the yearly data from the average curve may be caused in part by changes in storage and seepage and in part by differences in the distribution of precipitation within the year. No adjustment is made for these factors in the water-loss equation for Withlacoochee River at Trilby and they thus affect the apparent evapotranspiration. An effective annual precipitation of about 32 inches, indicated by the point where the downward extension of the curve coincides with the Po = L relation, is the most probable yearly amount below which little significant runoff would occur. Under some conditions of intensity and distribution of precipitation, there could be runoff with less than 32 inches of precipitation. As shown by the curve in figure 46, the average water loss increases with the precipitation until it becomes nearly a constant for higher values of precipitation. This is about the maximum loss that would occur regardless of the amount of precipitation and is called the potential natural water loss for the basin. The potential

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96 FLORIDA GEOLOGICAL SURVEY 80 --------------------_-----_---Potential notural waof loss L Water losss 10 -* / * / / */.* / S* * / 0 10 20 30 40 50 60 70 --0 S/ L Water loss L-R, in Fiure Relation of effective annual rainfall Runoff adjusted to include it20 divrsions aRibove station Sinto Hillsborough River. / / / / 0 10 20 30 40 50 60 70 Water loss, L t P -R, in inches Figure 46. Relation of effective annual rainfall and annual water loss, Withlacoochee River at Trilby, 1931-61. natural water loss for the Withlacoochee River at Trilby is shown to be 45 inches. This figure compares favorably with the 48 inches of average water loss shown for 72°F., the mean annual temperature for the area, in figure 7. Figure 47 shows the plotted yearly figures of rainfall and runoff for the Trilby station and an average curve. The average curve was determined by using the curve in figure 46 and plotting the departures of the potential water-loss curve from the limiting curve(P. = L).

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REPORT OF INVESTIGATIONS No. 42 97 80 70 ---------------------------____-----3-----7O 60 _ to include diversions Sabove station into Hillsborough River 30 20 I 40-/ ~-------------------0 Note -Total runoff adjusted to include diversions above station into Hillsborough River W 30 -----------------------0 5 10 15 20 25 30 35 Annual runoff, in inches Figure 47. Relation of effective annual rainfall and annual runoff, Withlacoochee River at Trilby, 1931-61. The runoff from the upper Palatakaha Creek basin has been measured since 1945 (stations 11 and 12 in table 1). The water-loss curve for the upper Palatlakaha Creek basin is shown in figure 48. Runoff was adjusted for annual changes in storage in the many lakes and swamps in the basin. No allowance was made for change in underground storage or for seepage into or out of the basin. The water-loss curves shown in figures 46 and 48 indicate that, for a year in which rainfall was 32 inches or less, the natural losses would nearly equal the rainfall and little or no runoff would occur from either the Withlacoochee River or the Palatlakaha Creek basins in the Green Swamp area. As shown in figure 48, the potential natural water loss for the upper Palatlakaha Creek basin is 48 inches which is the same as the annual water loss shown for 72°F. in figure 7. Figure 49 shows the • ,

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98 FLORIDA GEOLOGICAL SURVEY relation of the effective annual rainfall and runoff for the upper Palatlakaha Creek basin. The potential natural water loss, indicated by this analysis for each basin, includes both evapotranspiration and ground-water outflow. Further analyses show that about 2 inches more ground 80 Potential natural water loss * / 000 *// S// L = Water loss / Pe = Effective precipitation §o / S20 / R = Runoff / AS = Change in surface 2 / storage t / / 0 10 20 30 40 50 60 Water loss, L = P-R* AS, in inches Figure 48. Relation of effective annual rainfall and annual water loss, Palatlakaha Creek above Mascotte, 1946-61.

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REPORT OF INVESTIGATIONS NO. 42 99 70 c o 50 -60 -------•----------4Q S/ NoteTotal runoff adjusted S/ for change in storage in lakes and swamps above 30_ gaging station. a) 20 0 5 10 15 20 25 30 Annual runoff, in inches Figure 49. Relation of effective annual rainfall and annual runoff, Palatlakaha Creek above Mascotte, 1946-61. water flows from eastern basins than from western basins (table 14). The gain in streamflow by ground-water pumpage at Dade City reduces the apparent water loss in the Withlacoochee River basin above Trilby. The many large lakes and swamps in the upper Palatlakaha Creek basin afford the opportunity for high evapotranspiration losses. The differences in ground-water inflows and outflows in the Palatlakaha Creek and Withlacoochee River basins and the increased evapotranspiration losses from the large lakes and swamps could easily account for the 3 inches more potential natural loss from the Palatlakaha Creek basin. WATER-BUDGET STUDIES A water budget is a quantitive statement of the balance between the total water gains and losses of a basin or area for a period of time. The budget considers all waters, surface and subsurface, entering and leaving or stored within a basin. Water entering a

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100 FLORIDA GEOLOGICAL SURVEY basin is equated to that leaving the basin, plus or minus changes in basin storage. The budget equation was the basis of the expression for determining the water-loss equation in the foregoing discussion of rainfall, runoff, and water loss. The water-budget equation may be expressed in greater detail as P = R + ET + U+ AS, + ASg where: P is precipitation R is streamflow ET is evapotranspiration U is ground-water outflow AS, is change in surface-water storage (for net gain; -for net loss) ASg is change in ground-water storage (+ for net gain; -for net loss) Precipitation (P) and streamflow (R) are factors of the budget equation that can be measured directly. The other factors are not measured directly but are derived from observed or deduced data. Ground-water outflow (U) in the Green Swamp area is the net amount of water that moves out of the basin by subsurface flow through both the nonartesian and Floridan aquifers. The amount of water leaving the nonartesian aquifer by horizontal underflow is an insignificant factor in the budget where the water-table divides coincide with the surface-water divides. In the Green Swamp area, the divides on the eastern boundary do not coincide and a small quantity of water leaves the area via the nonartesian aquifer. The amount of water leaving the area via the Floridan aquifer was estimated by using the hydraulic coefficients of the aquifer and piezometric maps. The gain or loss of water by storage changes (AS, and AS,) in an area such as the Green Swamp may be a significant quantity for short periods. However, by using selected long-term periods, the effects of storage changes are minimized. The change in surfacewater storage (AS,) is indicated by change in stage of lakes, stream channels, and swamps in a basin. In this analysis, the open water surfaces were considered to be a small percentage of the total drainage area, and estimates for storage changes in the nonartesian aquifer were used for an overall storage change including AS,. The change in ground-water storage (AS,) is the net change in ground-water stage multiplied by the specific yield for (or storage

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REPORT OF INVESTIGATIONS NO. 42 101 coefficient) of the aquifer for a given period of time. .Separate analyses were made for both the nonartesian and the Floridan aquifers. Evapotranspiration (ET) cannot be measured directly for large areas such as the Green Swamp, but may be approximated by balancing the water-budget equation and determining the residual quantity. The other quantities of water loss are small in proportion to the quantity lost by evapotranspiration. Therefore, the residual quantity in the equation reasonably represents the evapotranspiration loss. EVAPORATION AND WATER BUDGET OF LAKE HELENE Most of the precipitation that falls on an area is dissipated through the natural processes of evaporation and transpiration. Because evaporation plays such an important role in the hydrologic cycle, much effort was expended to measure it directly at Lake Helene instead of calculating it as a residual in the storage equation. Harbeck (1962) describes a practical method for measuring the evaporation from an open-water surface utilizing the mass-transfer theory. A report by the U. S. Geological Survey (1954), and one by Harbeck and others (1958), may be consulted for additional information on the method. The mass-transfer method provides a technique for measuring the evaporation and for determining the seepage from a lake, two factors of the water budget that are generally determined indirectly or estimated. The change in volume resulting from evaporation on the water surface of a lake is computed by use of an empirical equation based on measurements of the evaporative capacity of the air. The water-budget equation is then balanced to account for volume changes from rainfall, surface inflow and outflow, evaporation, seepage, and other consumptive losses. Evaporation computed by applying a coefficient to measured evaporation from a pan may be subject to considerable error, particularly for periods of less than a year. The annual average Class-A pan coefficient for central Florida has been estimated by Kohler and others (1959, pl. 3) to be about 77 percent. The monthly evaporation-pan coefficients vary more widely and with a greater range of probable error than the annual coefficients. There is, therefore, the need to supplement pan records with direct measurements of evaporation. Evaporation from Lake Helene was measured in 1962 by use of the mass-transfer method. Lake Helene is located about 1 mile

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102 FLORIDA GEOLOGICAL SURVEY southeast of Polk City on top of the piezometric high (see figs. 5 and 35). The lake has no surface inlet and no surface outlet except at extremely high stages, and in 1962 its surface area ranged from 56.6 to 51.2 acres. It is nearly devoid of vegetative growth; consequently, transpiration losses are negligible. A map of Lake Helene showing depth contours is given in figure 50. The depthcontour map for Lake Helene is taken from a report by Kenner (1964): This map shows the locations of the water-stage and rainfall recorder and the raft in mid-lake supporting an anemometer and a water-surface temperature recorder. Figure 51 is the hydrograph of the daily stage of Lake Helene from March 31, 1961, to December 31, 1962. The evaporation station was established December 13, 1961. Computations of the evaporation data for the 1962 calendar year have been summarized and used to help define the annual water budget. Pumpage of water from Lake Helene to irrigate the surrounding citrus groves contributes to water loss from the lake. A pumping station capable of pumping 1,800 gallons per minute was installed in 1962 and operated intermittently during the year. The volume changes due to pumpage from the lake were computed from the recorded changes in stage and stage-volume relations. These computations were verified by records of the approximate periods of pumpage and the rated capacity of the pump. Nearly all the gains of water in the lake were derived from rain that fell directly on the water surface. The lake stage increased approximately the same amount as the recorded depths of rainfall during light to moderate rain storms. However, during a few heavy rain storms the lake stage increased slightly more than the depth of rain, indicating runoff from land. The increase in lake stage during these periods is equivalent to the total gain for rain falling directly on the lake and from runoff. Net seepage to or from the lake caused a gain in volume at times and a loss at other times. The water-budget equation for Lake Helene may be expressed as follows: AV= P + R + SeE-Pu where: AV is change in lake volume (+ for increase; -for decrease) P is precipitation on lake R is runoff from land Se is seepage (+ for net gain; -for net loss)

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REPORT OF INVESTIGATIONS NO. 42 103 R. 25 E. 34 Elevation: 140.6 feet above mean sea level .\ 33 I 23 // \ 15/ 20I 0 Raft supporting nernometler SI7 and woter -surface temperature . (D 1 recorder. Waoter -stoge and \ c rnrolltol recorder 4 .. / 3 N> LAKE HELENE (Polk County ) 200 0 200 400 690 e8o feet t 1 , , 1 I I " .I Date of survey: March 28, 1962 Contour Interval: 5 feet (After Kenner, 1964) R. 25 E. Figure 50. Map of Lake Helene showing depth contours and locations of data-collection equipment. 4 .

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146 145 -145 -------...----------------S 144 143 o142 o 1961 142 ,o 141 2 ge Jan Feb March April May June July Aug -Sept Oct Nov Dec 1962 Figure 51. Hydrograph of daily stage for Lake Helene, 1961-62.

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REPORT OF INVESTIGATIONS No. 42 105 E is evaporation from lake Pu is pumpage from lake The monthly water budget for Lake Helene for 1962 is shown in table 12. The total loss from evaporation was 53.10 inches as shown in column 12. Seepage to or from the lake was variable as shown by the monthly amounts in columns 10 and 11. Net seepage for the year was 6.64 inches from the lake. The items of inflow and of outflow for Lake Helene were determined independently. Computed values of change in volume (column 16) are the algebraic sums of the items of inflow and items of outflow for each month. These values compare closely with the observed values of change in storage shown in column 17. Average annual lake evaporation in this part of central Florida for a 10-year period (1946-55) has been estimated to be about 49 inches (Kohler and others, 1959, pl. 2). Evaporation losses from Lake Helene for 1962 exceeded Kohler's estimate, based on a 10-year average, by about 4 inches. Records from several evaporation pan stations show that evaporation amounts are generally higher during dry years. Thus, the measured evaporation from Lake Helene during 1962, a dry year, may be higher than for an average year. COMPARISON OF EASTERN AND WESTERN BASINS Geology and topography, the two predominant factors affecting the water budget of the Green Swamp area, are somewhat different in the eastern and in the western parts of the area. The effects of these factors on the components of the water budgets have been determined by the selection of representative basins in each part for defining the budget equation. The drainage basins east of State Highway 33 are interconnected by swamp channels (see fig. 5) and flood runoff from each basin may not be representative of that originating within the basin. However, the sum of the discharges measured at Big Creek at station 3, Little Creek at station 5, and Withlacoochee River at station 36 represents approximately the natural streamflow from the combined drainage basin of 208 square miles. Small amounts of water may be exchanged with other basins at interconnecting points designated as C-4, C-5, C-6, and C-7 in figure 5. The amount and duration of flow through these openings are considered to be insignificant in comparison with the total amounts measured at the three gaging stations. In the following analysis of the water

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TABLE 12. Monthly water budget for Lake Helene near Polk City, 1902 Itenm of inflow Items of outflow Change in volume Change In Runoff (\V) Average stage Precipitation from land Seepage Evaporation Pumpage Lake stage surface during month (P) (R) (Be) (E) (Pu) Month at beginning area --omputed Observed 1962 of month (acres) (ft) in) (In) (ac-ft) (in) (ac-ft) (in) (ac-ft) (In) (ac-ft) (In) (ac-ft) (ac-ft) (ac-ft) (1) (2) (8) (4) (5) (6) (7) (80)(9) (10) (11) (12) (18) (14) (15) (16) (17) Jan. 141.464 56.2 -0.182 -2.18 1.28 5.99 0.11 0.52 -0.98 -4.30 2.88 18.25 -11.1 -10.2 Feb. 141.282 55.6 -.878 -4,54 .84 1.58 -1.08 -7.78 2.08 18.81 -20.0 -21.0 Mar. 140.904 54.7 -.859 -4.81 8.48 15.86 -2.17 -9.89 5.61 26.57 0.22 1.00 -20.6 -19.6 Apr. 140.545 58.8 -.485 5.22 1.69 7.58 -.00 -4.04 5.46 24.48 -20.9 -28.4 May 140.110 58.8 + .070 + .84 7.29 82.88 1.38 6.18 -2.17 -9.64 5,59 24.83 + 4.0 + 8.7 'une 140.180 53.6 + .160 +1.92 6.67 20,79 .44 1.97 -.80 -1.84 4.48 20.01 .50 2.23 + 8.2 + 8.6 July 140.840 68.7 -.088 -1.06 6.76 25.73 .36 1.01 -.81 -1.39 5.69 25.46 1.84 6.00 -5.5 -4.7 .140.22 68.9 + .808 +8.70 6.52 20,20 .O8 4.40 + .62 +2.78 4.44 10.94 +16.5 +16.6 Sept. 140.560 54.2 -.062 -.74 2.99 18.50 .06 .27 + .90 +4.06 4.97 22.45 -4.6 -8.4 Oct. 140.498 58.8 -.8832 -8.98 1.98 8.88 .27 1.21 -.81 -1.39 4.06 22.24 1.01 4.53 -18.1 -17.9 Nov. 140.166 58.0 -,286 -3.43 1.40 6.18 .19 .84 + .80 +1.32 3.62 15.99 1.65 7.29 -14.9 -15.2 )ec. 189.880 52.2 -.648 -7.78 .24 1.04 + .81 +1.35 2.47 10.74 5.76 25.06 -88.4 -88.8 Jan. 189.282 3a 89.63 177.80 3.79 16.95 -6.64 '-0.82 58.10 288.82 10.48 46.11 -120.4 -120.8 Computed change in volume -Precipitation + runoff + seepage -evaporation -pumpage. Observed change in volume change in stage during month X average surface area.

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REPORT OF INVESTIGATIONS No. 42 107 budget the combined basins east of State Highway 33 are referred to as eastern basins. Runoff of the Little Withlacoochee River at Rerdell (station 43) is representative of the natural drainage in the western part of the Green Swamp area. Streamflow at the gaging station is derived from rainfall on the Little Withlacoochee River basin. The drainage area at station 43 is 160 square miles. Water budget analyses were made for the eastern and western basins. Figure 52 shows the daily streamflow from these basins for the calendar years 1959-61. Streamflows, ground-water levels, and lake levels were nearly the same at the beginning and end of the year both in 1959 and 1960. Although these were the 2 wettest years of at least 60 years of record in central Florida, the indicated year-end storage changes were small and insignificant. The year 1961 was one of the driest of record, and the annual runoff was low. Stream discharges were less and water levels, as indicated at representative ground-water observation wells and lake gages, were generally 1 to 3 feet lower at the end of 1961 than at the beginning. The surface runoff from the eastern basins in 1961 was 1.7 inches and that from the Little Withlacoochee River basin was 0.8 inch. Ground-water outflow from the Floridan aquifer in the eastern and western basins was computed using the piezometric maps (figs. 35 and 36). The piezometric surfaces shown by the map for November 1959 (fig. 35) and the map for May 1962 (fig. 36) represent the flow conditions and the probable range in the rates of ground-water movement during wet and dry periods, respectively. The piezometric surface representing flow conditions for the year 1961 was assumed to be the average between that shown by maps for November 1959 and May 1962. The western part of the Green Swamp area, as represented by the Little Withlacoochee River Basin received more rainfall each of the 3 years than did the eastern part of the area. Runoff from the eastern basins was almost as much as that from the Little Withlacoochee River basin in 1959 and 1960 even though the rainfall was 3.4 inches less in 1959 and 5.6 inches less in 1960. In 1961, a dry year, 0.9 inch more runoff occurred from the eastern basins than that from the Little Withlacoochee River basin although the yearly rainfall was 0.9 inch less. Where and when the ground-water and surface-water divides coincide, some ground water from the nonartesian aquifer discharges from a basin as the base flow of the stream draining

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108 FLORIDA GEOLOGICAL SURVEY the basin. The divides do not coincide along the eastern boundary of the Green Swamp area because little or no water reaches the water table beneath the ridge. During dry periods, the water-table divide is located about 3 miles west of U. S. Highway 27, and nonartesian ground water moves laterally beneath the Lake Wales Ridge from the St. Johns River basin to the Kissimmee River basin. During seasonally wet periods, however, there is sufficient downward seepage through the ridge sediments to build up a temporary ground-water divide beneath the Lake Wales Ridge. This low wet-season divide recedes rapidly and the hydraulic gradient is resumed from the Green Swamp eastward to the chain of lakes, swamps, and streams which lie at the base of the eastern side of the Lake Wales Ridge. Ground water moves eastward in the nonartesian aquifer beneath the ridge along a 25-mile stretch from Haines City almost to Clermont. Data from wells drilled on each side of the ridge indicate that the nonartesian aquifer is about 100 feet thick. Hydraulic gradients to the east in the nonartesian aquifer, measured across the ridge at 10 locations, averaged 6.6 feet per mile. The coefficient of permeability of the nonartesian aquifer beneath the ridge probably ranges from 20 to 180 gpd/ft' on the basis of data shown in table 8. Using an assumed coefficient of 200 gpd ft.-, the computed ground-water discharge from the nonartesian aquifer in the eastern area was about 5 cfs in 1961. This discharge from the 208 square-mile area is equivalent to 0.3 inch, an insignificant budget factor. The ground-water outflow from the basins through the Floridan aquifer was computed as follows: (1) the drainage basin map (fig. 5) was overlain by the piezometric maps and streamlines were drawn to intersect and subdivide the boundary of each selected basin into numerous flow sections, shown in figure 53; (2) the hydraulic gradient (I), computed from the map, was multiplied by the length of the flow section, also scaled from the map, to obtain a flow factor for each flow section; (3) the discharge through each section was computed by multiplying the flow factor by the coefficient of transmissibility; (4) the sum of discharges through all flow sections around the boundary represents the net groundwater discharge from the basin. The total discharge was computed in units of million gallons per day (mgd) and converted to cubic feet per second (cfs); (5) ground-water discharge from a drainage basin was expressed in terms of outflow in inches for the basin so that it could be compared readily with rainfall and surface runoff.

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REPORT OF INVESTIGATIONS NO. 42 109 The net ground-water outflow (U) thus computed from the Floridan aquifer for the .eastern and western basins for November 1959 and May 1962 are presented in table 13. About 80 percent of the outflow from the western area originated from rainfall within the basin; the remaining 20 percent was inflow from the eastern basin. All outflow from the eastern area originated from rainfall within the basin. More than half of the total amount of ground water leaving the eastern basin flows to the Kissimmee River basin. The mean annual ground-water outflows from the eastern and western basins for the years 1959 and 1960 are assumed to be the same as those shown in table 13 for November 1959. The mean annual values for 1961 are assumed to be averages between the values for the two periods in table 13. Mean annual ground-water outflows thus computed for the 3 years are summarized in table 14. Annual changes in the amount of ground water in storage in the nonartesian aquifer were determined for the period 1959-61. The net change in storage for the years 1959 and 1960 is negligible. However, the net loss in water from storage during 1961 amounted to about 7.4 inches in the eastern basin and about 2 inches in the western basin. These storage losses add to precipitation as a source of supply in the water-budget equation. Coefficients of storage of the artesian Floridan aquifer are small (table 10). Therefore, changes in ground-water storage during the period 1959-60 were insignificant quantities. During 1961, the net decrease of the piezometric surface was about 2 feet, which is equivalent to a loss of about 0.2 inch of water from the basins. This is an insignificant budget factor. Thus, change in storage shown in table 14 was computed for only the nonartesian aquifer. Comparative results of the annual water-budget for the eastern and western basins are summarized in table 14. OUTFLOW FROM GREEN SWAMP AREA The total surface runoff from 818 square miles, which includes most (94 percent) of the Green Swamp area, was measured at each of the five major outlets. Listed in table 15 are the mean monthly discharges determined at each of these outlets from the beginning of the investigation in July 1958 to June 1962. Table 15 shows the distribution of total discharge from month to month as well as that from the individual streams draining from the area. The effects of wet and dry years on the amount and

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Ir" 0 TABLE 18. Ground-water outflow from the Floridan aquifer for eastern and western basins Ground-water outflow, bGround-water outflow, November 1959 May 1962 Basin Coefficient of Area transmissibility IInches Anches Basin (Sq mi) (gpd/ft) (mgd) (cfa) per year (mgd) (cts) per year Eastern 208 800,000 49.9 77.2 5.0 61.1 79.1 5.2 Western 160 500,000 21.2 82.8 2.8 25.8 89,9 8.4 *Assuming computed outflow is mean annual discharge. blncreased outflow during dry period due to Increased pumping near the boundaries. '.

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TABLE 14. Comparison of budget factors for eastern and western basins. Eastern Basins (Big Creek, Little Creek Western Basin (Little Withlacoochee River, .and Upper Withlachoochee River, 208 sq. mi.) 160 sq. mi.) Items of supply Items of disposal Items of supply Items of disposal (inches) (inches) (inches) (inches) PrelpiChange in Runoff by aGroundEvapotransPrecipiChange in Runoff by 'GroundEvapotransYear tation storage streamflow water outflow piration tation storage streamflow water outflow piration (P) (AS) (R) (U) (ET) (P) (AS) (R) (U) (ET) ' 1959 71.8 * 27.8 5.0 89.5 75.2 * 29.0 2.8 48.4 1960 69.4 * 27.0 5.0 86.6 7.0 * 27.5 2.8 44.7 1961 88.2 -7.4 1.7 5.1 88.8 89.1 -2.0 .8 8.1 87.2 * -----------------------------T-1-1 8-year 59.8 -2.5 19.0 5.0 88.8 63.1 -.7 19.1 2.9 41.8 average Note.-ET = P -AS -R -U *Negligible aGround-water outflow for 1950 and 1960 assumed to be same as that for November 1959 and that for 1961 assumed to be the average for the two periods (table 18). I-A

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TABLE 15, Surface-water outflow from Green Swamp area, July 1058 to June 1012 Mean ldicharge in cubic feet per second Sta. No. 48 Sta. No. 8 Sta. No. 5, Sta. No. 42 Little WithUig Creek 6, Little Sta. No. 80 Withlacoochee lacoochee Cfe Moth near Creek near WithlacoocheeRiver at River at Total of per Runoff Month Clermont Clermont Hillaborough Trilby Rerdell all outlets sq. In overflow near mile Inches (Drainage (Drainage Richland Drainage (Drainage (Drainage area, 68 area, 10 area, 580 area, 160 area, 818 sq. ml. sq. ml. sq. ml, sq. mi.) so. mi.) 1958 July .... .... 17 . August 4.1 .. 0 227 114 .. September 6.9 -. 0 76.5 28.9 .... October 20.7 .... 0 55.1 12.5 -November 88.2 .... 0 98.9 85.4 ..December 11.8 .._ *10 75.8 21.1 -'1959 January 62.9 *50 *00 600 182 984.9 1.20 1.88 February 81.6 '15 *4 884 99.9 " 584.5 .658 .68 March 128 *115 *850 1,457 760 2,810 8.44 8.97 April 168 *105 *250 1,742 459 2,724 8.88 8.72 May 72.2 *40 *80 790 122 1,054.2 1.29 .1.49 June 68.8 *65 *220 915 178 1,441.8 1.76 1.96 July 205 *90 *270 1,921 488 2,974 8.64 4.20 August 152 *75 *160 1,461 622 2,470 3.01 8.47 September 188 *60 *210 1,942 701 8,046 8.72 4.15 October 152 *45 *100 1,409 808 2,014 2.46 2.84 November 112 *25 *20 890 117 1,164 1.42 1.58 December 58.6 *5 0 822 41.8 426.9 .522 .60 Year 112 *58 *144 1,157 842 1,804 2.21 80.04 Percent of total 6.2 8.2 7.9 68.8 18.9 100

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1960 January 48.5 *8 0 258 28.6 888 .407 .47 February 58.7 *10 *5 882 00.8 800.5 .612 .66 March 268 *210 *490 8,049 1,045 5,062 6.19 7.14 April 200 *75 *70 1,785 408 2,688 3.10 8.46 May 62.8 *7 .1 408 61.2 628.6 .640 .74 June 87.8 6.5 0 212 89.6 295.4 .861 .40 July 54.5 82.2 104 : 724 ,186 1,100.7 1,85 1.56 August .190 58.6 872 .2,777 695 4,087.6 5.00 6.76 September 418 141 521 2,822 707 4,104 5.02 6.60 October 288 566.4 177 1,941 488 2,900.4 8.66 4.09 November 97.8 12.4 1.8 488 81.5 681.0 .771 .86. December 44.4 2.9 0 206 29.1 281.4 .844 .40 Year 142 51 146 1,209 824 1,868 2.28 31.14 Percent of total 7.6 2.7 7.8 64.6 17.8 100 1961 January 85.6 2.9 0 199 27.5 264.9 .824 .87 February 47.1 9.6 .5 245 60.6 862.8 .444 .46 March 28.6 2.7 0 158 15.0 204.8 .250 .29 April 7.6 .8 0 128 1.8 188.1 .168 .18 May .4 0 0 88.7 .4 84.5 .108 .12 June .1.7 0 0 68.8 .1 65.6 .080 .09 July 2.5 0 0 71.5 .6 74.6 .091 .10 August 6.8 0 1.8 106 1.8 116.4 .142 .16 September 10.1 0 1.5 217 4.5 288.1 .285 .82 October 2.4 0 0 42.9 .2 45.5 .056 .06 November 3.2 0 0 84.5 .5 88.2 .047 .05 December 2.8 0 0 41.8 .6 45.1 .055 .06 Year 12.2 1.8 .3 115 9.1 139 .170 2.26 Percent of total 8,9 .9 .2 88.4 6.6 100 1962 January 4.1 0 0 88.2 1.6 88.9 .109 .18 February ,. 2.1 0 0 70.9 2.0 75.0 .092 .10 March 8.6 .1 0 58.0 .9 57.6 .070 .08 April 1.2 0 0 42.8 .4 48.9 .054 .06 May ' ' .1 0 .0 * .665.6 0 55.6 .068 .08 June .2 0 8.4 185 .4 144.0 .176 .20 *Estimated on basis of discharge measurements at monthly intervals and records for other stations. *Estimated on basis of discharge meoauremnents at monthly intervals and records for other stations.

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114 FLORIDA GEOLOGICAL SURVEY Stream line ( indicates direction of flow) , ^FLOW SECTION No. I 7 I. Flow factor = IXL ft. Where I is the hydraulic gradient (-~' 100-90 foot contours d (miles) and L is the length of the section in miles 2. Flow section Discharge (gpd)= Flow factor x Coefficient of transmissibility Figure 53. Sketch showing analysis of a flow section. distribution of runoff from the area. are shown in this table. The years 1959 and 1960 were the wettest of record and 1961 and 1962 were the driest. The discharges given in table 15 indicate that Little Creek and Withlacoochee-Hillsborough overflow carry significant amounts of water from the area only in wet years. During 1961, Little Creek carried only 0.9 percent and the Withlacoochee-Hillsborough overflow carried only 0.2 percent of the total surface outflow from the area. Both channels were dry during most months in 1961 and 1962. Ground-water outflow (U) from the Polk high was also computed using the flow net method of analysis of the piezometric

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REPORT OF INVESTIGATIONS NO. 42 115 surfaces of November 1959 (fig. 35) and May 1962 (fig. 36). These computations exclude the ground-water inflow from the Pasco high to the Green Swamp area in the vicinity of Dade City. Outflows from each major basin were computed using groundwater areas enclosed by the divides as shown in figure 34. The distribution of the outflows from the Polk high to the major drainage basins is shown in table 16. Most of the natural outflow is contributed to the Kissimmee and Withlacoochee River basins. Increased pumping for mining, irrigation, and municipal supplies in the southern part of the area (from Lakeland to Haines City) during the dry period caused about 50 percent increase in outflow to the Peace and Alafia River basins. Significant changes in outflow in the dry period also were experienced in the Withlacoochee and St. Johns River basins. The decrease in outflow to the Kissimmee River basin and the corresponding increase to the Peace River Basin were caused by slight shifting of the ground-water divides. The ground-water outflow in 1959 is considered to be more representative of natural outflow. Net ground-water outflow (U) from the Green Swamp area was computed using the same method as used for the eastern and western areas. The total outflow via the nonartesian aquifer was determined to be an insignificant quantity (0.08 inch per year). The total outflow via the Floridan aquifer was computed along the boundary of the 870 square-mile area. The net ground-water outflow from the Floridan aquifer during November 1959 and May 1962, adjusted to equivalent amounts of runoff in inches per year, are presented in table 17. The estimated mean annual ground-water outflows interpolated for 1959, 1960, and 1961, on the basis of yearly totals in table 17, are presented in table 18. The net change in ground-water storage in both the nonartesian and Floridan aquifers for 1959 and 1960 are considered to be negligible. However, water levels in both aquifers declined significantly in 1961. The average net decline of water levels in the nonartesian aquifer in 1961 was equivalent to about 4.3 inches of water over the Green Swamp area. The average net decline of the piezometric surface of the Floridan aquifer in 1961 was equivalent to an insignificant change in storage (0.2 to 0.3 inch) because of artesian storage coefficients. Rainfall, surface-water outflow (table 15), ground-water outflow (table 17), and changes in ground-water storage are combined in

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TABLE 16, Ground-water outflow from the Polk plezometric high in Green Swamp area Outflow from aOutflow from the Floridan aquifer the Floridan aquifer, November 1959, May 1062, Basin receiving Ground-water a period of high water levels a period of low water levels ground-water contributing Coefficient of drainage from area transmissibility Percent Percent Green Swamp area (sq. mi,) (gpd/ft) (mgd) (cfa) of total (mgd) (eta) of total St. Johns River (Palatlakaha Creek) 100 800,000 18.5 20.0 12 24.7 38.2 15 Kissimmee River 75 800,000 31.6 48.9 27 25.7 89.7 15 Peace River 60 600,000 18.1 28.0 15 89.1 60.5 28 Alai'a River ,5 600,000 3.0 4.6 3 15.1 23.8 9 Hillsborough River 280 I 600,000 12.7 19.6 11 9.8 15.2 6 Withlacoochee River 855 500,000 38.0 58.8 32 52.6 81.4 82 (excluding 45 sq. mi. area in vicinity of Dade City) Total 825 116.9 180.8 100 167.0 258.8 100 Assuming that the computed outflow is the mean annual discharge: Ground-water for a wet year would be 8.0 inches. Ground-water outflow for a dry year would be 4.2 inches. aIncreased outflow during dry period due to increased pumping near the boundaries.

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TABLE 17. Ground-water Qutflow from Green Swamp area Outflow from bOutflow from the Floridan aquifer, the Floridan aquifer, November 1959, May 1962 Basin receiving Ground-water a period of high water levels a period of low water levels ground-water contributing Coefficent of a pi g drainage from area transmissibility Inches Inches . Green Swamp area (sq mi) (gpd/ft) (mgd) (cfs) per year (mgd) (cfs) per year St. Johns River 100 300,000 18.5 20.9 2.8 24.7 38.2 5.2 (Palatlakaha Creek) Kissimmee River 75 800,000 81.6 48.9 8.8 25.7 89.8 7.2 Peace River 60 600,000 18.1 28.0 6.3 '9.1 60.5 13.7 Alafia River 5 600,000 8.0 4.6 12.5 15.1 23.8 62.2 Hillsborough River 280 600,000 12.7 19.6 1.2 9.8 15.2 .9 0 Withlacoochee River 400 ( 500,000 d-6.2 d-9.6 d..3 d-.1 d_7.9 gd.8. S_(1,200,000 _ Total 870 72.7 112.4 1.8 109.3 169.1 2.6 0 *Assuming computed outflow is mean annual discharge. tO bIncreased outflow during dry period due to increased pumping near the boundaries. CTransmissibility of 500,000 gpd/ft used east of Withlacoochee River and 1,200,000 used west. dNet minus outflow is result of greater inflow from Pasco high. I-A

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118 FLORIDA GEOLOGICAL SURVEY the water-budget analysis of the Green Swamp area for the period 1959-61. Yearly summaries of the budget factors are presented in table 18. Surface runoff is directly dependent on rainfall and varies through a wide range as shown by comparison of the wet years of 1959 and 1960 with the dry year of 1961. On the other hand, the ground-water outflow from the area varied little from the wet to dry years. Though the difference is small, the ground-water outflow was more during the dry year than during either wet year. The increase in ground-water outflow during 1961 was caused primarily by increased pumpage from the Floridan aquifer in the area along the southern and western boundaries of the Green Swamp area. The net loss in ground-water storage during 1961 also was greatest along the boundaries reflecting the drawdown effects caused by the pumpage. The 3-year average evapotranspiration loss was 36.8 inches from the Green Swamp area as shown in table 18. Evaporation from Lake Helene in 1962 amounted to 53.1 inches (table 12). Comparison of these values indicates that exposure of the water surface by impoundment in reservoirs would increase the evaporation loss by about 16 inches per year per unit area in the Green Swamp. Other studies indicate that the increased evaporation loss would be less than 16 inches. Estimates by Kohler and others (1959) indicate that the average annual lake evaporation in central Florida is 49 inches. From table 14 the evapotranspiration loss for two representative basins averaged about 40 inches for the 3-year period. Based TABLE 18. Summary of water-budget factors in Green Swamp area, 1959-61 Items of supply Items of disposal (inches) (inches) Change Runoff "Ground-water EvapoPrecipitation in storage by Streamflow outflow transpiration Year (P) (AS) (R) (U) (ET)) 1959 70.9 * 30.0 1.8 39.1 1960 69.5 * H1.1 1.8 36.6 1961 34.7 -4.3 2.3 2.2 34.5 3-year average 58.4 -1.4 21.1 1.9 36.8 Note. ET = P -S -R-U *Negligible *Ground-water outflow for 1959 and 1960 assumed to be same as for November 1959 and that for 1961 assumed to be the averaze for twb periods (table 17).

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REPORT OF INVESTIGATIONS NO. 42 119 on these values the increased evaporation loss would be about 9 inches. EVALUATION OF PROPOSED PLAN OF WATER CONTROL A comprehensive plan of improvements proposed by the U. S. Corps of Engineers (1961) provides for diversion canals and flood-control conservation reservoirs in the Green Swamp area, and in the upper Oklawaha, Peace, Hillsborough, and Withlacoochee River basins, shown in figure 54. Green Swamp Reservoir, largest of those included in the plan of improvement, would be located in the Withlocoochee River basin near the center of Green Swamp. The proposed Green Swamp Reservoir would provide for a total of 460,000 acre-feet of storage (134,000 acre-feet at conservation pool level of 100 feet above msl and 326,000 acre-feet above the conservation pool for flood control at level of 107 feet above msl). The surface area of the flood-control pool would be about 61,000 acres. The Southeastern Conservation Area (Johnson, 1961), also designated the Lowery-Mattie Conservation Area (Corps of Engineers, 1961), would be located in the southeast corner of the Green Swamp area. This proposed water-conservation area would cover about 46 square miles in three pools and provide for maximum storage of about 72,000 acre-feet at pool levels ranging from 133.0 to 134.5 feet above msl. Also within the Green Swamp area and included in the comprehensive plan of improvement are the Little Withlacoochee Reservoir, the Upper Hillsborough Reservoir, Big Creek upper and lower diversion canals, and Lowery Canal. REDUCTION OF FLOOD PEAKS IN THE HILLSBOROUGH RIVER The annual runoff to the Hillsborough River basin through the Withlacoochee-Hillsborough overflow was 104,000 acre-feet for 1959 and 106,000 acre-feet in 1960. The flood-control pool of the proposed Green Swamp Reservoir is capable of impounding the total annual runoff contributed by the Green Swamp to the Hillsborough River basin. For the purpose of computing the effectiveness of the proposed Green Swamp Reservoir in reducing flood peaks of the Hillsborough River at Tampa, the flood of March 1960 has been taken as a typical case. The maximum extent that

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120 FLORIDA GEOLOGICAL SURVEY the total Green Swamp area could reduce floods in the Hillsborough River would be by the impoundment of all the discharge that drains through the Withlacoochee-Hillsborough overflow channel al station 39. Hydrographs of mean daily discharge for WithlacoocheeHillsborough overflow, Hillsborough River near Zephyrhills, and Hillsborough River near Tampa for the flood of March 1960 are shown in figure 55. The hydrographs were plotted using mean daily discharges at the gaging stations. The discharge at the Tampa station was slightly regulated by the waterworks dam but the effect is not apparent on the mean daily values of discharge. The peak discharge at the Zephyrhills station, which is 2 miles downstream from Blackwater Creek, occurred on March 18, the same day as the peak from Blackwater Creek. The peak discharge at Withlacoochee-Hillsborough overflow occurred on March 19 while 16.0 .0S1, 0 3 doays 12V00 --Hillsborough River I I\ near Tampa 2 days .600S * -Hillsborough River SI near Ztphyrhills Withiacoachee -Hillsborough -0 Overflow near Richland 1S 16 17 I8 19 20 21 22 23 24 25 26 27 28 29 30 31 March 1960 Figure 55. Hydrographs of mean daily discharge for three Hillsborough River gaging stations, flood of March 1960.

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REPORT OF INVESTIGATIONS NO. 42 121 the peak for Hillsborough. River near Tampa was on March 21. The flood peak at the Tampa station occurred about two days later than that at the Withlacoochee-Hillsborough overflow and about 3 days later than that at the Zephyrhills station. The gaging station near Tampa is in the upper pool at the waterworks dam. In March 1960, the stage of the upper pool was regulated between narrow limits by tainter gates and flashboards. A stage-discharge relation was defined at 22nd Street, 0.5 mile downstream from the dam, by measurements made during the floods of 1959 and 1960. Mean daily discharges for the gaging station at the dam were used with the stage-discharge relation to compute the stage hydrograph for 22nd Street as shown in figure 56. l8 16 14 E // o 12 -/ _y_-------_l l -0 109 EXPLANATION Mean daiolly stage at 22nd Street computed from mean daily discharge at gaging ° 6 station 0.5 mile upstream. Mean daily stage at 22nd Street inferred from discharges at gaging station adjusted for no flow at WithlacoocheeHillsborough overflow. 16 17 18 19 20 21 .22 23 24 '25 26 27 28 29 30 31 March 1960 Figure 56. Hydrographs of computed mean daily stage of Hillsborough River at 22nd Street,.Tampa, flood-of March 1960.

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122 FLORIDA GEOLOGICAL SURVEY Mean daily discharges for Withlacoochee-Hillsborough overflow were subtracted from the mean daily discharges for the Tampa station two days later to synthesize the effective discharge that would have occurred at the Tampa station if all the flow from Green Swamp to the Hillsborough River had been impounded. This adjusted discharge was used to compute the inferred stage hydrograph for 22nd Street shown by the broken line in figure 56. The difference between the two hydrographs on March 21 was 1.2 feet which indicates the maximum reduction in crest stage at 22nd Street that would have occurred if the total flow from Green Swamp to the Hillsborough River had been impounded. Similar computations of the theoretical flood reduction at 22nd Street by complete impoundment of the flow from Green Swamp were made for the September 1960 flood. This flood crest would have been reduced by about 1 foot, approximately the same as that of the March flood. Other reservoirs and channel changes proposed for the Hillsborough River basin (Corps of Engineers, 1961) would further reduce the flood peaks at Tampa. REDUCTION OF FLOOD PEAKS IN THE WITHLACOOCHEE RIVER The effect on the lower Withlacoochee River by storage of flood discharge in the proposed reservoirs in Green Swamp was also estimated on the basis of the March 1960 flood. Table A-1 of the Corps of Engineers Comprehensive Report (1961) shows that the total drainage area of the Withlacoochee River above Green Swamp Reservoir is 328 square miles, and that above the Upper Hillsborough Reservoir is 66 square miles or a total of 394 square miles above the Trilby gaging station. Figure 57 shows the relation between runoff in acre-feet and drainage area for the Withlacoochee River basin for the flood period March 16 to April 20, 1960. From this relation, the indicated flood runoff from a drainage area of 394 square miles was about 200,000 acre-feet during the March flood. The allocated flood storage capacity of Green Swamp Reservoir is 326,000 acre-feet. Assuming that the flood-control pool would be empty at the beginning of the flood period, the entire volume of runoff from the basin above the reservoir could be impounded for a flood greater than that of March 1960. This would be equivalent to reducing the effective drainage area for uncontrolled flood runoff above the Trilby gaging station to about 186 square miles (580

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REPORT OF INVESTIGATIONS No. 42 123 6000000 S600PO Holder 0 400,000 Croom Croom Trilby f toopoo --^ ---o , '200p00 S/ Note: C Runoff at Trilby, 'Croom, and Holder -100,000 adjusted to include ./ diversion from basin o -Rerdell through Withlacoocheea, Hillsborough overflow. 50,000 -EvaI I " I I I 100 200 500 1000 2000 Drainage area, in square miles Figure 57. Relation between basin runoff and drainage area for Withlacoochee River, March 16 to April 20, 1960. square miles at gaging station minus 394 square miles above the two reservoirs). Peak discharges for the flood of March 1960 have been plotted against drainage areas at gaging stations in the Withlacoochee River basin as shown in figure 58. The peak discharge at Withlacoochee-Hillsborough overflow was 1,880 cfs. From the relation in figure 58, the drainage area that would produce a peak discharge of 1,880 cfs for the March flood would be 100 square miles. Effective drainage areas for the gaging stations downstream from Withlacooche-Hillsborough overflow have been computed by subtracting 100 square miles from the measured drainage areas of each. The curve shown by the broken line in figure 58 represents the theoretical relation of drainage areas to flood peaks that would have prevailed if no flood discharge had been diverted from the basin.

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124 FLORIDA GEOLOGICAL SURVEY S o Croo S -Holder = -*Trilby Dade City .--SL 5pO00----r ------.5 0 EXPLANATION o Rerdell o Actual drainage area Sat gaging station. o / Effective (contributing) S2p00 Eva drainage area at gaging station. I00 i00 200 500 o000 2,000 Drainage area, in square miles Figure 58. Relation between peak discharge and drainage area for Withlacoochee River, flood of March 1960. From the curve represented by the broken line in figure 58, the peak discharge from a 186 square-mile drainage area would be 3,400 cfs. This discharge at the Trilby gaging station would occur at gage height 15.4 feet, which is 4.0 feet lower than the crest stage of March 1960. Flood stages at the Croom station would be further reduced by storage in Little Withlacoochee Reservoir (drainage area, 86 square miles). The total reduction in crest stage for a flood equivalent to that of March 1960 would be 1.7 feet at this station. The reduction in crest stage by flood storage in reservoirs proposed in Green Swamp would continue to decrease at points further downstream on the Withlacoochee River. At the crossing of State Highway 200 at the Holder station, reduction of crest stage by storage in Green Swamp would be small. However, the Jumper Creek Reservoir would provide additional storage for flood control in the lower Withlacoochee River basin.

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REPORT OF INVESTIGATIONS No. 42 125 EFFECTS OF WATER IMPOUNDMENT IN GREEN SWAMP RESERVOIR ON GROUND-WATER LEVELS Comparison of figures 31 and 54 show that the proposed Green Swamp Reservoir is underlain at shallow depth by the Floridan aquifer. A reconnaissance of the area indicated that limestone of the aquifer crops out for about 6 miles along the north-south portion of the proposed levee. The head created by the reservoir will cause additional amounts of water to move through the aquifer beneath the levee. The principal factors controlling the underseepage are the horizontal and vertical permeabilities of the materials beneath the reservoir and the percentage of the reservoir area immediately underlain by the Floridan aquifer. Aquifer tests in adjacent areas indicate that the coefficient of transmissibility varies considerably from point to point. The coefficient of transmissibility in the reservoir area is estimated to range from 125,000 gpd/ft to 500,000 gpd/ft. Significant amounts of underseepage will probably occur along about 14 miles of the north-south portion of the proposed levee because the predominant direction of water movement is from the east to the west. Underseepage will be greatest in the channel of the Withlacoochee River because the channel is well incised into the aquifer. The hydraulic gradients scaled from the piezometric maps (figs. 35 and 36) were used to compute the existing wet and dry period flow of ground water beneath the area of the proposed levee. During the wet period (1959), the average elevation of the piezometric surface beneath the 14-mile length of proposed levee was about 95 feet, the average hydraulic gradient across the proposed levee was about 2 feet per mile, and the estimated mean daily underflow ranged from about 5 to 20 cfs. During the dry period (1962), the average elevation of the piezometric surface beneath the 14-mile length of proposed levee was about 89 feet, the average hydraulic gradient across the proposed levee was about 2.6 feet per mile, and the estimated mean daily underflow ranged from about 10 to 30 cfs. In order to estimate future underflow it was assumed that the amount of water that seeps into the limestone will raise the piezometric surface to the same level as that of the conservation pool (100 ft). If the impoundment occurred during a wet period, then the piezometric surface would rise from 95 to 100 feet, the gradient would increase from 2 to 7 feet per mile, and the estimated

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126 FLORIDA GEOLOGICAL SURVEY mean daily underflow would range from about 20 to 80 cfs. If the impoundment occurred during a dry period, then the piezometric surface would rise from 89 to 100 feet, the gradient would increase from 2.6 to 13.6 feet per mile, and the estimated mean daily underflow would range from about 40 to 150 cfs. Seepage and evaporative losses from the shallow reservoir indicate that the amount of water that would be available for release during dry periods such as that in 1962 would probably be small. The position of the reservoir with respect to contributing recharge to the heavily pumped portions of the Floridan aquifer is poor. However, benefits derived from the reservoir would be increased base flow of the upper Withlacoochee and Hillsborough rivers and reduction of flood crests. EFFECTS OF WATER IMPOUNDMENT IN SOUTHEASTERN CONSERVATION AREA ON GROUND-WATER LEVELS The primary purpose of a plan for water impoundment in the Southeastern Conservation Area (Johnson, 1961), also designated the Lowery-Mattie Conservation Area (Corps of Engineers, 1961), is to maintain and to increase recharge to the Floridan aquifer. The three pools that would comprise the Southeastern Conservation Area proposed by Johnson would cover about 46 square miles, with pool levels ranging from 133 to 134.5 feet above msl. The pools would overlie an area of high piezometric levels in the Floridan aquifer. In this area, water normally seeps downward from the nonartesian aquifer through a bed of clay (aquiclude) into the underlying Floridan aquifer. Here, the water level in the nonartesian aquifer and in surface-water bodies are above the piezometric surface of the Floridan aquifer. The difference in levels is caused by relative differences in the permeabilities of the nonartesian aquifer, of the Floridan aquifer, and of the aquiclude. The rate of seepage through the aquiclude is directly proportional to the difference between the water levels; therefore, raising the water table or lowering the piezometric surface will increase the rate of seepage. In order to evaluate the importance of the three conservation pools, a comparison was made of seepage rates during wet and dry periods in the vicinity of Lake Lowery with seepage rates that would occur had the pools been at the proposed levels. The average vertical permeability of the aquiclude was estimated and used as the basis of computations of seepage rates for existing hydraulic

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REPORT OF INVESTIGATIONS NO. 42 127 ,radients and for future hydraulic gradients. The vertical permeability computed from the movement of 5 inches of water a year through the 15 feet of aquiclude with a head difference of 2 feet is about 0.003 gpd/ft2. During a wet period (November 1959), the average yearly seepage from the eastern part of the area was determined to be about 5 inches (table 14) when the level of Lake Lowery was about 134 feet and the piezometric surface was about 132 feet. During a dry period (May 1962), the indicated yearly seepage from Lake Lowery was about 21 inches when the level of Lake Lowery was about 128 feet and the piezometric surface was about 120 feet. If during May 1962 the water level in the Lowery pool had been maintained at about 133 feet, the resulting gradient (13 feet) would cause a yearly seepage rate of about 34 inches which is 60 percent greater than that computed for May 1962. The piezometric surface will decline progressively in response to increased pumping in the populated and industrialized areas south of Green Swamp (see fig. 37). Therefore, maintaining high water levels in the southeastern part of the Green Swamp area will make additional water available for future recharge. SIGNIFICANCE OF THE HYDROLOGY OF THE AREA The Green Swamp area is unique because it is a headwaters area for five major rivers and for part of the Floridan aquifer. The proximity of the headwaters of the streams and their interconnections by swamps at relatively high elevation suggest that the area can be used effectively for flood control and water conservation. Because of the high piezometric surface, Stringfield (1936) and others have inferred that high rates of recharge for the Floridan aquifer occur on the Polk high in the Green Swamp area and that ground water flows outward in all directions from the area. In order to meet the demands of present and future water-use and for flood prevention, a water-management plan was proposed to utilize the Green Swamp area for impoundment of flood waters and for increasing the amount of recharge to the Floridan aquifer. Thus, the significance of the hydrology of this area in relation to central Florida has been appraised on the basis of the findings of this investigation. In general, with other water-budget factors being equal, surface runoff would be low in areas where high rates of ground-water recharge occur. Therefore, comparison of streamflow from two

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128 FLORIDA GEOLOGICAL SURVEY areas, similar in other respects, would indicate the relative amount of water recharged to the aquifers. Table 7 shows that the total surface runoff during July, August, and September 1960 from Pony Creek, a basin located on the Polk piezometric high, was about 6 inches more than that from Horse Creek, a basin located downslope from the Polk high, although the rainfall on the Pony Creek basin was about 7 inches less. This indicates a smaller ground-water storage capacity in the Pony Creek basin than in the Horse Creek basin. Table 14 shows that during the years 1959-61 surface runoff from the eastern basins, which include the Polk high, was nearly the same as that from the western basin although the rainfall was less. The conclusion derived from comparing the data shown in Table 14 is that the rate of ground-water recharge on the Polk high is about the same as that in an area downslope from the Polk high. Ground-water outflow from the Green Swamp area is almost entirely via the Floridan aquifer. The net outflow over a significant period of time is approximately equivalent to the average amount of recharge to the aquifer during the period if there were no appreciable change in ground-water storage. Table 14 shows that the outflow is about 5 inches per year from the eastern part of the Green Swamp area and about 3 inches per year from the western part. Therefore, this infers that the eastern part contributes about 2 inches more recharge to the Floridan aquifer. The net groundwater outflow from the Polk piezometric high (table 16) was estimated to range from 181 to 258 cfs or about 3 to 4.2 inches per year. Part of the outflow discharges into streams and swamps in the western part of the Green Swamp area so that the net amount that leaves as ground-water outflow probably ranges from 112 to 169 cfs, or about 1.8 to 2.6 inches per year (table 17). Mineral content and calcium carbonate saturation with respect to calcite in water in the Floridan aquifer implies that recharge is about the same in the Green Swamp area as in other parts of central Florida. The presence of low mineral content in water in the interior of central Florida and high mineral content in water toward the coasts (figs. 44 and 45) suggests a general movement of water from the interior to the coasts. A comparison of the degree (percentage) of calcium carbonate saturation of water with respect to calcite in the Floridan aquifer throughout central Florida shows that under-saturation occurs throughout much of central Florida (fig. 43). Hem (1961, p. C-15) states that the degree of

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REPORT OF INVESTIGATIONS No. 42 129 saturation should be lowest in recharge areas, and should increase as water moves through the aquifer. It would appear then that factors other than high recharge rates contribute to the causes of the Polk high. It can be inferred from geologic and hydrologic data that a relation exists between the water movement and structural deformation in the Green Swamp area. This is indicated at the surface by the parallel linearity of ridges and surface drainage systems, and in the subsurface by the presence of an anticline and related faults. Also of importance is the relation between structural deformation and subsequent solutional deformation indicated by the parallel linearity of sinkhole lakes. High piezometric levels in the southeastern part of the Green Swamp area are believed to be the result of a relatively slow rate of ground-water outflow which is probably caused by sand-filled fractures, caverns, and sinkholes. These act as a natural grout which decreases the transmissibility of the aquifer. Although the coefficient of transmissibility of the Floridan aquifer is generally high, it is variable, ranging from about 200,000 to 1,200,000 gpd/ft (table 11). The lower value applies to the eastern part of the Green Swamp area where the piezometric high exists. Flood-control and conservation reservoirs proposed for the Green Swamp area would provide a partial solution to the flood problems in the lower Hillsborough River and lower Withlacoochee River basins. Total impoundment in the Green Swamp area of a flood equal to that of March 1960 would reduce the flood crest of the Hillsborough River at Tampa by about 1 foot. Impoundment of the March 1960 flood in reservoirs proposed for the Green Swamp area would have reduced the flood crest of the Withlacoochee River at the Trilby gaging station by about 4 feet and at the Croom gaging station by about 1.7 feet. Reservoirs in the Green Swamp area would be less effective in reducing flood stages further downstream on the Withlacoochee River. Impoundment of floodwaters. in the Green Swamp reservoirs would probably have little effect on net ground-water outflow from the Green Swamp area but would increase base flows downstream from the reservoirs. Impoundment of flood waters in the Southeastern Conservation Area would increase the rate of seepage to the Floridan aquifer. The rate of seepage would be more significant during dry periods when the piezometric surface is lowered by pumping in the developed areas south of the Green Swamp. Therefore, water

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130 FLORIDA GEOLOGICAL SURVEY storage in this area at the beginning of a dry period would become more important as the demand for water increases. Further drainage of the area could change the proportional amounts of water disposed of by the various routes. The time of concentration of water in stream channels would be decreased. More water would be moved from the areas as streamflow. Water would remain on the land surface for shorter periods and therefore evapotranspiration would be decreased. Certainly if the water-table in the whole area were lowered, this would effectively lower the piezometric surface and decrease ground-water outflow from the area. However, at present, the central and western parts of the area are downgradient from the piezometric high and generally are poorly drained both on the surface and subsurface. The area is generally wet and runoff is high after intense rainfall because the aquifers are always nearly full and the rate of ground-water movement from the area is slow. Although water management in the Green Swamp area would not be the sole solution to the water problems in central Florida, Green Swamp is hydrologically important and must be considered in any overall plan of water management.

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REPORT OF INVESTIGATIONS NO. 42 131 REFERENCES Alverson, D. C. (see Carr, W. J.) Applin, Esther R. (see Applin, Paul L.) Applin, Paul L. 1944 (and Applin, Esther R.) Regional subsurface stratigraphy and structure of Florida and southern Georgia: Am. Assoc. Petroleum Geologists Bull., v. 28, no. 12, p. 1673-1753. 1951 Preliminary report on buried pre-Mesozoic rocks in Florida and adjacent States: U. S. Geol. Survey Cir. 91. Back, William 1963 Calcium carbonate saturation of ground water in central Florida: Intern. Assoc. Scien. Hydrol., v. 8, no. 3, p. 43-51. Baker, D. R. (see Kohler, M.A.) Black, A. P. 1951 (and Brown, Eugene) Chemical character of Florida's waters 1951: Florida State Bd. of Cons., Water Survey and Research Paper 6. Brown, R. H. (see Ferris, J. G.) Brown, Eugene (see Black, A. P.) Carr, W. J. 1959 (and Alverson, D. C.) Stratigraphy of middle Tertiary rocks in part of west-central Florida: U. S. Geol. Survey Bull. 1092. Cherry, R. N. (see Pride, R. W.) Collins, W. D. 1928 (and Howard, C. S.) Chemical character of waters of Florida: U. S. Geol. Survey Water-Supply Paper 596-G. Cooke, C. W. 1945 Geology of Florida: Florida Geol. Survey Bull. (and Mansfield, 1936 W. C.) Suwannee limestone of Florida: (abstract) Geol. Soc. Am. Proc. for 1935, p. 71-72. Cooper, H. H., Jr. 1963 Type curves for nonsteady radial flow in an infinite leaky artesian aquifer: U. S. Geol. Survey Water-Supply Paper 1545-C. Corps of Engineers, U. S. Army 1961 Comprehensive report on Four River Basins, Florida: Jacksonville District Rept. of Recommendation. Espenshade, G. H. 1963 (and Spencer, C. W.) Geology of phosphate deposits of northern peninsular Florida: U. S. Geol. Survey Bull. 1118. Ferguson, G. E. (see Parker, G. G.) ** t *;

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132 FLORIDA GEOLOGICAL SURVEY Ferris, J. G. 1962 (and Knowles, D. B., Brown, R. H., and Stallman, R. W.) Theory of aquifer tests: U. S. Geol. Survey Water-Supply Paper 1536-E. Harbeck, G. E. 1962 A practical field technique for measuring reservoir evaporation utilizing mass-transfer theory: U. S. Geol, Survey Prof. Paper 272E. 1958 (and others) Water-loss investigations-Lake Mead studies: U. S. Geol. Survey Prof. Paper 298. Hardison, C. H. (see Searcy, J. K.) Healy, H. G. 1962 Piezometric surface and areas of artesian flow of the Floridan aquifer in Florida, July 6-17, 1961: Florida Geol. Survey Map Series No. 4. Hem, John D. 1959 Study and interpretation of the chemical characteristics of natural water: U. S. Geol. Survey Water-Supply Paper 1473. 1961 Calculation and use of ion activity: U. S. Geol. Survey WaterSupply Paper 1535-C. Howard, C. S. (see Collins, W. D.) Jacob, C. E. 1950 Flow of ground water, chap. 5 in Rouse, Engineering hydraulics: New York, John Wiley and Sons. Johnson, Lamar 1961 Preliminary investigation and report on proposed impoundment areas in Southeast Green Swamp: Report by consulting engr. Kenner, W. E. 1964 Maps showing depths of selected lakes in Florida: Florida Geol. Survey Inf. Circ. 40. Kohler, M. S. 1959 (and Nordenson, T. J., and Baker, D. R.) Evaporation maps for the United States: U. S. Weather Bureau Tech. Paper 37. Kohout, F. K. 1959 (and Meyer, F. W.) Hydrologic features of the Lake Istokpoga and Lake Placid areas, Highlands County, Florida: Florida Geol. Survey Rept. Inv. 19. Knowles, D. B. (see Ferris, J. G.) Langbein, W. B. 1949 (and others) Annual runoff in the United States: U. S. Geol. Survey Circ. 52. Love, S. K. (see Parker, G. G.) Mansfield, W. C. (see Cooke, C. W.)

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REPORT OF INVESTIGATIONS NO. 42 133 Menke, C. G. 1961 (and Meredith, E. W., and Wetterhall, W. C.) Water resources of Hillsborough County, Florida: Florida Geol. Survey Rept. Inv. 25. Meredith, E. W. (see Menke, C. G.) Meyer, F. W. (see Kohout, F. K. and Pride, R. W.) Nordenson, T. J. (see Kohler, M. A.) Parker, G. G. 1955 (and Ferguson, G. E., Love, S. K. and others) Water resources of southeastern Florida: U. S. Geol. Survey Water-Supply Paper 1255. Pride, R. W. 1958 Floods in Florida, magnitude and frequency: U. S. Geol. Survey open-file report. 1961 (and Meyer, F. W. and Cherry, R. N.) Interim report on the hydrologic features of the Green Swamp area in central Florida: Florida Geol. Survey Inf. Circ. 26. Puri, H. S. 1957 Stratigraphy and zonation of the Ocala Group: Florida Geol. Survey Bull. 38. 1964 (and Vernon, R. 0.) Summary of the geology of Florida and a guidebook to the classic exposures: Florida Geol. Survey Spec. Publication 5 (revised) Searcy. J. K. 1960 (and Hardison, C. H.) Double-mass curves: U. S. Geol. Survey Water-Supply Paper 1541-B. Spencer, C. W. (see Espenshade, G. H.) Stallman, R. W. (see Ferris, J. G.) Stewart, H. G. 1959 Interim report on the geology and ground-water resources of northwestern Polk County, Florida: Florida Geol. Survey Inf. Circ. 23. Stringfield, V. T. 1936 Artesian water in the Florida peninsula: U. S. Geol. Survey Water-Supply Paper 773-C. Theis, C. V. 1935 The relation between the lowering of the piezometric surface and the rate and duration of discharge of a well using groundwater storage: Am. Geophys. Union Trans., pt. 2, p. 519-524. Tolman, C. F. 1937 Ground-Water: New York, McGraw-Hill Book Co. U. S. Geological Survey, 1954, Water-loss investigations-Lake Hefner studies, technical report: U. S. Geol. Survey Prof. Paper 269. * 1

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134 FLORIDA GEOLOGICAL SURVEY Vernon, R. 0. 1951 (and Puri, H. S.) Geology of Citrus and Levy Counties, Florida: Florida Geol. Survey Bull. 33. Wetterhall, W. C. (see Menke, C. G.) White, W. A. 1958 Some geomorphic features of central peninsular Florida: Florida Geol. Survey Bull. 41. Williams, G. R. 1940 (and others) Natural water loss in selected drainage basins: U. S. Geol. Survey Water-Supply Paper 846. GLOSSARY Anticline. An upfold or arch of rock strata, dipping in opposite directions from an axis. Aquiclude. A formation which, although porous and capable of absorbing water slowly, will not transmit it fast enough to furnish an appreciable supply for a well or spring. Aquifer. A formation, group of formations, or part of a formation that will yield water in usable amounts. Artesian ground water. Water that is under pressure sufficient to cause it to rise above the top of the aquifer in which it occurs. Base flow. The discharge entering stream channels from ground water. Clastic. Pertaining to fragmental material derived from pre-existing rocks transported mechanically into its place of deposition, for example, sand and clay. Coefficient of permeability. The rate of flow of water, in gallons per day, through a cross-sectional area of 1 square foot under a unit hydraulic gradient at a temperature of 600 F. Coefficient of storage. The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in the component of head normal to that surface. In artesian aquifers it is related to the compressibility of the material comprising the aquifer and of the water. In non-artesian aquifers it is primarily related to gravity drainage and is approximately equal to specific yield. Coefficient of transmissibility. The rate of flow of water, in gallons per day, at the prevailing water temperature through each vertical strip of the aquifer 1 foot wide having a height equal to the thickness of the aquifer and under a unit hydraulic gradient. Color. The color of water is due only to materials in solution. Color is determined by comparison with standard colored disks that are calibrated in units according to the platinum-cobalt scale.

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REPORT OF INVESTIGATIONS No. 42 135 Confining bed. A bed which, because of its position and its impermeability or low permeability relative to that of the aquifer, gives the water in the aquifer either an artesian or subnormal head. Confluence. The meeting or junction of two or more streams. Diffuence. Flowing apart. A term used to describe a stream which branches in a downstream direction. Direct surface runoff. The runoff entering stream channels promptly after rainfall. Discharge. Flowing or issuing out. Also used to designate the volume of water flowing past a cross section of a stream in a unit of time. Double-mass curve. A plot of the cumulative values of one variable versus the cumulative values of another. Drainage area. The size of a drainage basin usually expressed in square miles. Drainage basin. An area enclosed by a topographic divide such that direct surface runoff from precipitation normally would drain by gravity into the river basin. Drainage divide. The boundary line, along a topographic ridge, separating two adjacent drainage basins. Drainage system. A surface stream or a body of impounded surface water, together with all surface streams and bodies of impounded surface water that are tributary to it. Effective precipitation. A weighted average of current and antecedent precipitation that is "effective" in correlating with runoff. Evaporation. The process by which water becomes vapor at a temperature below the boiling point, including vaporization from free water surfaces and from land surfaces. Evapotranspiration. Evaporation plus transpiration. Fault. A fracture or fracture zone along which there has been displacement of rock material on the two sides relative to one another parallel to the fracture. Ground water. That part of the subsurface water that is in the zone of saturation. Hydraulic conveyance. The water-carrying capacity of a stream channel. Hydraulic gradient. As applied to an aquifer, it is the rate of change of pressure head per unit of distance of flow at a given point and in a given direction. Hydrograph. A graph showing stage, flow, velocity, or other property of water with respect to time. Infiltration. See seepage.

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136 FLORIDA GEOLOGICAL SURVEY Instantaneous load. The quantity of dissolved material carried by a strearr at the point and time indicated. Marine. Of or belonging to or caused by the sea. Mineral content. A summation of the individual values, in parts per million. of the determined dissolved chemical constituent in the water. Nonartesian ground water. Water in an aquifer that is unconfined. Parts per million (ppm). A unit weight of a chemical constituent dissolved in a million unit weights of water. Percolation. The movement of water by gravity through the pores in a rock or soil, excluding the movement through large openings such as caverns. pH. An index of the acidity of water. A value of 7 is neutral. Values above 7 indicate alkalinity-values below 7, acidity . Piezometric surface. The level to which water will rise in tightly cased wells that penetrate a given aquifer. Potential natural water loss. The maximum water loss that could occur naturally in a basin with optimum or full moisture supply and native vegetation. Recharge (of ground water). Intake. The processes by which water is absorbed and is added to the zone of saturation. Also used to designate the quantity of water that is added to the zone of saturation. Retention. The part of storm rainfall which is intercepted, stored, or delayed, and thus fails to reach the concentration point by either surface or subsurface routes during the time period under consideration. Runoff. That part of the precipitation that appears in surface streams, having reached the stream channel by either surface or subsurface routes. Runof in inches. The depth to which an area would be covered if all the runoff from it in a given period were uniformly distributed on its surfaces. Seepage (infiltration). Percolation of water through the earth's crust, or through the walls of large openings in it, such as caves or artificial excavations. Specific conductance. Specific conductance is the measure of the capacity of water to conduct an electric current. It varies with the concentration and degree of ionization of the different constituents in solution. It may be used to estimate the mineral content but does not indicate the nature of, or the relative amounts of, the various mineral constituents. Specific yield. The ratio of the volume of water that will drain from the saturated material of the aquiferto the volume of the material, expressed in percent. Streamlow. The actual discharge of surface streams. It includes runoff modified by artificial causes. Surface water. Water that occurs above the surface of the ground.

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REPORT.OF INVESTIGATIONS NO. 42 137 Time of concentration. The time .required for the water to flow from the farthest point on the watershed to a gaging station or to another specified point. Transpiration. The process by which water vapor escapes from a living plant and enters'the atmosphere. Water loss. The difference between the average precipitation over a drainage basin and the runoff adjusted for changes in storage and for interbasin movement of ground water. The basic concept is that water loss is equal to evapotranspiration; that is, water that returns to the atmosphere and thus is no longer available for use in the area. However, as used in this report, the term applies to differences between measured inflow and outflow even where part of the difference may be seepage. Zone of saturation. The zone in which the permeable rocks are saturated with water under pressure equal to or greater than atmospheric.

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Report of Investigations No. 42 2°15' 10' 05" 82*00' 55' 50 45' 40' 35" 81°30 2* EXPLANATION -\ 1_r^ I 1 ' I Boundary of Green Swamp oreo V Rainfall station I I .1 .5 Well and well number @ Surface water data -_ _ collection point. ---• 4d -T40p 35' 35 i :GROVELAND CLERMONT-5" 0. WOSLEV O LOYOSCEOLA O 5 Y IL Ti ,' I I -o .,I T ^^^~7"i UJ i' ,z I 82 5 0 05' 800 55' 50' 45 40 35 .8 3025' Survey tspographic quadrangles Figure 2. Map showing data-collection points in Green Swamp area. 0 _T-__-_ LAKE -1 -COUNTY 17 -·· .'J _ _ _ _ I | _ _ _ _j POLK|^ " i \| _f !OUNTY \ __ f^TT OSCEOLA \COUNTY; M_ SI iEq, -.i I I ! i ~I' S Is l-I \ I I lo' tc5 .iur 2. MO Figure 2. Map showing data-collection points in Green Swamp area.

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Report of Investigations No. 42 82030' 15' 82000' 45' 30' 81025' 28"45 -III I I I I 28045' 0* e/0 " _ -i, I Clermont L Brooksville I ! S3' o0 o 3' 4, I . 0 I .. \ '" / j -5' City S W A at A iR E A .-. .-' .. ..,Cl / \( SWA -Lakeland Winter 2800'Plant Cty 2800' 45150 to 200Bt ow (ft above msl) 45' 150 to 200 45' /'Supplementary contour in Green Swamp area 27 4 5 0 5miles 2 ~ ~7*40' 82*30' 15' 8200' 45' 30' 81025' Base map and contours from U. S. Army Map Service maps Figure 4. Map showing topography of central Florida and its relation to Green Swamp area.

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Report of Investigations No. 42 8215' 10 05' 82*00' 55' 50' 45' 40' 35' 81*30' 28'45' 1 3830' I4'CeII I I I I 2 8 45 BUSHNELL CENTER --• \ -0' SHILL O 1Lake Lake SIT, Le -_ Apopo 35WEBSTER MASCOTTE L _, ,, Lake 35L SHROVELANOE 2 S\Minne-ho --..i , \ o I-P-.AC S"r O I az 30a HOEN N G ln C-CITYY 0 I ZU ' o a F:igure-5.Map si ua t iefea o ,--\ / /_\ 5 r-= I -2_5_ c --o\,Z O 2 -DAL D O' 05.1 55' 5 45' 4 35' 8, 0 CITY 0 r a: area.

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Report of Investigations No. 42 82°15' 10' 05' 82"00' 55' 50' 45' 40' 35' 81M30 2845' EXPLANATION 28 --50-Contour represents the elevation, in feet referred to mean ., seo level, of the top of the Avon Pork Limestone. ConWell and well number tour Intervol is 50 feet. Dashed where estimated D n Spring and spring identification number I U V 40' Fault,doshed where probable, D, downthrown side; U,upRdnfoll station thrown side. Queried where uncertain . -:. Stream gaging station BDudory of Green Swamp Areao Lke ~ r MASCOTT -V r 35' 35 R D U0 CE5SLE 2O5 '* 2S 85 0 05 8 5 50 45 40 3' 80' u0ey --pogr'al quadranglesy -= Pr2 1 25' *.2 . 2L*00S 28*oO, Survey topographic quadrangles

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Report of Investigations No. 42 81I 1 05s' 820 55 50' 81a45' I-1 |May 25 3 Discharge, 123 cts tP / Mineral ccntent, 176 ppm May 25 Sta44 Discharge, 0.10 cfs "CR // LMineral content, 224 ppm N 282 35' 8 35. CROOM a 35 Sta.43 L/// -RERDELL I May 25 , SDischarge. 84.0 cfs -30 3 Mineral content, 189 ppm s/ O Sta.42 " BAY LAKE TRILBY y ] LACOOCHEE No flow SSouh \5 May 23 30 Dica 25 7 c Discharge, 0.18 cfs 2 O Discharge, 71.8 cfs Mineral content, 47 PPM 25 Mineral content, 177 ppm SSt 36 c eODischarge, 74.8 cfsM a M i n Mineral content, 2174 ppm E May 24 -icareDischarge, 0.02 f cfsa /flow Mn\ Mineral ocontent, 52 PpV :m a 2o 0May 24 May 2J EV Ao o Discharge, OL53 cfs Ma 2\ SMineral content, 75 Ppm R 2 6 a y 24 SNo Iflow y 2 l. 0 I 2 3 4 5 6 7 8 9 0 miles Discharge, t.i2 cfn s02 r"I"^ / iure 1. Map showing results of low-flow investigation of Withlacoochee StRiver May 23-25, 1961. 24May 23 Sa.38 20 cf reDischarge, 0.01 cfss 26* 15' Mineral content, 130 ppm May 24 Minera content, 224 Ppm M 23 915' to' 05' 82 00' 55 5d845 0 1 2 3 4 5_6 7 8 9 10 miles Figure 11. Map showing' results of low-flow investigation of Withlacoochee River, May 23-25, 1961.

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Report of Investigations No. 42 114 112 L 110U Well 810-136-1 4 -108 -Floridon aquifer 4mi.north of Haines City cn 106 1 .116--I "' Well 810-136-2 Nonortesion aquifer "4mi. north of Hoines City 42 > 114 m,,, -44 u_ 112 _ _.---LII ,,, 46 > IIO 1 ---48 w V I r LLJ 82I 54\ Well 816-211-1 S80 -Floridon aquifer -5 "' 2mi. north of Zephyrhills 76 -58 | 62 ----------------_---__ ----62---U] 68 .-.-.. .---.. 7 -670 62 -74 0 0C 00 o> 7 ,ct m o o Figure 23. Hydrographs of long-term records of ground-water levels near the Green Swamp area. C) Ln O CD C ro L LOII I 1 6 M 12_ Gre wm ra

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Report of Investigations No. 42 Weil 805-155-1. 0 134 Nonartesian aqgifer A =2 133 132 v 131 ji 12 4 I I i i i i I i I 1 " I i i11 i t I 1 1 1 I l t il l l l l IN t t l l -[ ll l l 1 1l l II I It i l l ll l 2 1-1"11 1 1 122 13 £ 123 ________ ___A_________ ___________ __________ I X 1221 _________ ___ __\______-: S Well 805-155-2 < 121 Secondry artesian equifer /14 .120E /v I Al A -15 C Io0 120 /V J7 m -V < 119 16 " 118 A -17 113l \J------------------------------" ---\ / \i 22 LI_117 ' -18 116 -19 115 113 j 22 112 23 Well 805-155-3 1II Floridan aquifer 110 --, -25 -' .10 9 I li i l l 1 1 1 I I I IlllI I I 1 ! 4 1 I tll.i. .r li iL 1 1 1 1 1 1 1 1 1 1 1 1 1 I1 1 1 1 1 1 1956 1957 1958 1959 1960 1961 1962 Figure 25. Hydrographs of water levels in wells (805-155-1, 2, and 3) near Lakeland.

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Report of Investigations No. 42 82'15' 10 05' 82*00' 55 50' 45' 40' 35' 81i°0 EXPLANATION 285' Deptn to top of tie Floriden aquifer, in feet below land surface 0-10 E50-75 E] Greater than 200 S10-25 75-ICO Proposed ievee for Green Swomp -: ---.25-50 10 -230 and Little Wilhlocoochee reservoirs ' 025-50 Tjr --O 0* HUSHNELL' -""f "' 40 --0"-i 4 $I ISL : iT 505 3 255 Surey t raph, adranles Floidan aquife. :A WNTE Floridan aquifer. Floridan aquifer.

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Report of Investigations No. 42 82l5' 10' 05' 8200' 55' 50' 45 40' 35' 81'30 EXPLANATION Contour representsi-e -ele on -eet referred to mean EXP TION Ssea level, of the top of the Floridian aquifer. Contour Well and well number interval is 25 feet. Dashed where estimated Suwannee Limestone D III] Spring and spring identification number U I SFoult, dashed where probable, D, downthrown side; U, upOcalo Group Rainfall station thrown side. Queried where uncertain S0 Stream gaging station Boundary of Green Swamp Area Avon Pork Limestone SCO 02 2 igure 32. Map of Green Swamp area showing the limetone formations that se the top of the ordan aqufer and contours on ts upper surface. 25 -2S4 -0~ P1.T I '*I-LKF NPO .Y YIO UNTY Y/I i.,; | "^E^ I ISLEWO20 J, ..-24-l ? 9 L-2 -M11 LP ases ^ ^ ' " rnfUSoco Cs a o. l~.1 2 VAc o Jj W fl 05' d2 utonliprise the top of the Floridan aquifer and contours on its upper surface.

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Report of Investigations No. 42 87" 86" 85" 84' 83" 4 f V ' L ' -....72 o -^ , Io / 2 .-Z , . 128* EXPLANATION -i / I , Contour en the heig, in fee r e to ea level, to which water would have risen in tightly eased a pen ate the major water-bearing formai ns in the Floridan aquifer, July 6-17, 1961. Extent and distribution of flow areas vary with fluctuations 04L Ai .' -...nj_ .: '" .-f h pi. "a.-t.n o f , paoicud'. s in cons o '.a, pl iping. Relatvel smal aras f.ifl n otRID incuded immediately adjacent in and parlleling te* Sand any and pin-. ) -" .", 267 0 10203040 50mles 84' 83' 82.. 81' 80' " ,X "^.-.'.In Figure 33. Map of Florida showing contours on the pizo he height, feet referred ' etric surface of the in the Floridan aquifer 6-17. 1961. 1. ..'^ ,, 9S ^',, 0 10 20 30 40 50 miles / Figure 33. Map of Florida showing contours on the pizometric surface of the Floridan aquifer, 1961.

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Report of Investigations No. 42 15 C' 05' 82X00' 55' 50 45 4ý 35 BO30 EXPLANATION I Sain:ge divde for major stream basins roxrmcoe position of ground-water ooundory ' In the lorldcn aquifer . ^,_^j^--^^^S_'---__ :"^^^^^^^^ ^ RNIlouj_ rr L S -cs general direction of 40rou'd-wter movement. " .-. 40 /0 ' BUSHNELL' " 77 -_L _ -, x-!ii 0 .-RLL N-BO.ROUG COuNTY __„ _ ,, __ ..__T ' ' \ A, p 25 ' : 35;O 82*l5 10 05 82o00 55 50 45 35I Wr3 cse toen from US Geological o 2 3 4 5 6 7 m T__ -o Sr.ey -opographic quedrongles Figure 34. Map showing major surface drainage areas and their groundwater contributing areas in the Floridan aquife Lo ke ;_ r 0ý CIY SF-r-ey O h u n 7 2i a wae 0tbi areas ,n the od aquUNTi Y 2_L :5'~ ZErlYHILS -.-.--jl:2~ 4 2· water contributing areas in the Floridan aquifer.

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Report of Investigations No. 42 s48215' o1 05' 82'00 55' 50' 45' 40' 35' 830 E\PLANATION i I 2845 -50 --~ !Contour represents the elevation, in feet obde mean sea level, of the piezometric surface of the Florldan aquifer, -' November, 1959. Dashed where inferred. Contour interval 10 feet. -.-I j~ ' J BUSH lNE LL : GROVELAN( y NT i: I? k,9I IN i I * 'K LIN -At .72 e tpograph quadrngles 4 6 9 m isurface of the Floridan aquifer during a wet period, November 1959. Itt 25' 'o .11 '1 2, iiSe tken b,, 2U S l r,,2 t

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Report of Investigations No. 42 82*15' 10' 05' 82"00' 55' 50' 45' 4 35' 81°30 28"45' i --' '-'' ' -' -r -7 ' --~ --I I 1 28*45 EXPLNATION Contour represents the elevotion, in feet above mean sea level, of the piezometric surface of the Flondon aquifer May, 1962. Dashed where inferred. Contour interval 10 feet 0Z I i i ni k J 40' I N_--_ I4 a op *a PASCs ui = SO TTE -^t o35 L R EENR 1j 1 E»R4ANiDO cIDNTjj .. kT* .g .;ktj m^ jSC$OLIj i205' l0' Brod) !5 so10j ' 45' 40' 35' 8 o0' Base taken from US Geolo icot I 2 4 S" 6 ? POL 9 \I r ,, *'-'I Go LLJ ISL T I A ^ I \3lv e

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Report of Investigations No. 42 05' 82000. 55' 50' 45' 40' 35' 8130 EXPLANATION |I I ·I I28*45 S Decre in oDezometric levels (November 1959 to May 1962) .. .0-5 trel 10-20 feet S5-10 feet M More thon 20 feet 40 _ S BUSHNELL'+ O MASGROVCE E.D, 35' sr 75----l _ LgI OU NTICC U T0' S20 --LO-----C--CUNTY NES' C) Ir U25O 5005 5025 40 8°0 Survey topographic quadrangles 0 i 2 3 4 5 6 7 B 9 10 males Fig:ure 37. Map showing decline in piezometric surface of the Floridan aquifer, November 1959 to May 1962. C.aquifer, November 1959 to May 1962.

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Report of Investigations No. 42 January February March April May June July August September October November December r70 IOOO--\ V"--.." "7' t 5000 too ---I------------J--I ---------I -------I --------------1959 1, i ,n a. 2000-\ 0 __________,__ *'' -r 100 200 as Etr b _n _Su ofBto \------,,---------, 2 to oo evr__dl 1960 I g to . I' \ \ I" __ __Creek ner Clermt, ad i S Western basin (Little Withlo __ 1961 Ete Figure 52. Hydrographs-of streamflw from eastern and western basins in reek ner waClermnt Littlearea, 1959-61. Creek near COermont, and ____________ _ _____ 05 -Withlacoochee River near Eve) Western basin (Little WithinI I 2 coochee River at Rerdelt) L Jany February March A Jue t September October November December 1961 Figure 52. Hydrographs of streamflow from eastern and western basins in Green Swamp area, 1959-61.