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State of Florida
Department of Environmental Protection
David B. Struhs, Secretary
Division of Administrative and Technical Services
midt, ogist a
6e(' (\-4r
IVoime ach d Coa r on
tDuep Stetand Iurricane I actJ
by
Jmes H. Bahsillie
Rorida Geological Survey
Tallahassee, Florida 1999
ISSN 1058-1391




CONTENTS
Page
ABSTRACT.1 INTRODUCTION.1 EXTREME EVENT EROSION AND ITS RELATION TO THE TYPE OF PRE-IMPACT
COASTAL PHYSIOGRAPHY 2
DATA .3 ANALYTICAL RESULTS 4
The Event Longevity Parameter (ELP) 7
Average Erosion Quantity Above Mean Sea Level and Probability
Density Function (PDF) 7
Average Erosion Quantity Above the Peak Storm Tide Level and
Probability Density Function (PDF) .12
Design Erosion Quantities 13 The Offshore Sink Efficiency Parameter (OSEP) 14 Return Period Volumetric Erosion Events 18 Post-Storm Recovery .20 APPLICATIONS 21
Post-Storm Beach and Coast Physiography .22 Encounter Period and Probability 23 An Erosion Damage Potential Scale 24 CONCLUSIONS .25 ACKNOW LEDGEMENTS 27 REFERENCES.27 A PPENDIX 35
TABLES
Table 1. Characteristics of storms and hurricanes used in this study. 5 Table 2. TYPE I erosion volume above mean sea level. 9 Table 3. TYPE I erosion volume above the combined peak storm tide. 15 Table 4. Amended Saffir/Simpson Hurricane Damage Potential Scale 25
FIGURES
Figure 1. Idealized pre-storm (solid lines) and eroded (dashed lines) profile scenarios
for the three basic types of coastal physiography 2 Figure 2. Relationship between the measured TYPE I average erosion volume above mean
sea level and the event longevity parameter. 8 Figure 3. Example of water surface hydrograph through an idealized storm tide, and
definition of storm tide rise time measure (after Balsillie, 1986). 11 Figure 4. Relationship between the storm tide rise time and event forward speed,
where the relating coefficient, 0.00175 is in units of hours squared (after
Balsillie, 1986). 11
Figure 5. Typical examples of density distributions for determination of the slope 0
relating 0 and ell (event I. D.s refer to Table 2). 12
I




Figure 6. Relationship between the event longevity parameter and distribution
coefficients for TYPE I average volumetric erosion above MSL 13 Figure 7. Relationship between the measured TYPE I average net erosion quantity above
peak combined storm tide and the event longevity parameter. 3 Figure 8. Relationship between the event longevity parameter and distribution
coefficients for the TYPE I average erosion volume above the peak combined
storm tide. 14 Figure 9. Tesselated relationship relating nearshore bed slope to the ELP
coefficient, f. .1 6
Figure 10. Comparison between a typical Florida nearshore profile and typical Cancun,
Mexico nearshore profile.1 7 Figure 11. Relationship between the initial nearshore bed slope, tan a, and the
power curve fit shape coefficient, a,. 18 Figure 12. Relationship between exceedence probability, P, return period, T., and
average TYPE I erosion volume above MSL. 19 Figure 13. Example of application for determining two-dimensional post-storm
physiography using volumetric data, and design wave conditions. 23 Figure 14. Nomograph for relating event return period, encounter period, and
encounter probability. 24 Figure 15. Beach and coast erosion damage potential scale as a function of event
forward speed at landfall and peak storm tide elevation. Erosion volumes are based on peak storm tide elevation classes of Table 4; even so, results apply
to storm events as well as hurricanes. 26
1H




VOLUMETRIC BEACH AND COAST EROSION DUE
TO STORM AND HURRICANE IMPACT
by
James H. Balsillie, P. G. No. 167
ABSTRACT
Prior to the initial work of the author during the early 1980s, methods to predict nearshore,
beach, and coastal erosion due to storm and hurricane impact were based on theoretical applications and estimation. However, with the acquisition of actual field data quantifying storm and hurricane erosive impacts, it became clear that, in addition to the combined storm tide (commonly termed the storm surge), the length of time that an event has to erode the beach and coast is a highly significant factor that could be quantified (i.e., given two events each producing identical storm tide hydrographs, the slower moving event will result in greater beach and coast erosion). Hence, based on actual field data, the et Apriv*y paramw(P) was introduced (Balsillie, 1985c, 1986) which incorporates both the combined
storm tide and its rise time, the latter of which can be computed from the event forward speed.
Since the published work of the mid-1980s, additional field data (a three-fold increase) have
become available to further verify the ELP approach, and to introduce new developments. It has, for instance, become apparent that in addition to the design peak storm tide elevation, the design erosion event requires attention in many coastal engineering design applications if they are to be successful. In fact, aside from design soffit elevations which are determined from the peak combined storm tide elevation and superimposed storm waves propagating upon the storm tide surface, it is the design erosion event that quantifies the final expression of all other impacts. Hence, probability density functions are defined for both erosion above mean sea level and peak storm tide level. In addition, it has been found that the pre-impact offshore bed slope can be used to indicate the "efficiency" or "receptiveness" of the offshore sediment sink to accept sand eroded from the beach and/or coast (termed the offshoe a** efiney pametr (OSP. Incorporation of the new data, and quantification of the two additional developments and an amended Saffir/Simpson hurricane damage potential scale constitute the subject
matter of this paper.
INTRODUC7ON coastal engineering practice. In this paper,
short-term impacts define the subject of Although, in the seasonal and interest. long-term sense, beaches are constantly being remolded by waves, tides and winds, For many years, only the peak
the most dramatic changes occur as the combined storm tide (also commonly termed
result of extreme event (i.e., short-term the storm surge) was employed in
impacts from storms and hurricanes). The determining and assessing nearshore, beach,
consideration of short-term, seasonal, and and coastal engineering design solutions.
long-term impacts (i.e., force elements such Consideration of the storm tide alone, as astronomical tides, storm tides, waves, however, does not provide a realistic
etc.) and the resulting outcomes (i.e., measure of impact potential. For instance, response elements such as beach and coast given two extreme events with identical
erosion, longshore bar formation, and storm tides, the slower moving event will
structural damage) are matters of standard result in greater beach and coast erosion.
1




The peak storm tide elevation plus recession is important in determining siting of superimposed storm wave activity coastal development activities, It is, propagating upon the storm tide surface is however, the maximum vertical recession usef ul in determining deck, floor, etc. (termed produced during event impact (Balsillie, "soffit") elevations, provided that any shift or 1984c, in manuscript) which is needed to erosion of the bed is known, since increased assess structural design constraints (e.g., water depth results in higher waves. All piling tip penetration, "first floor" soffit other design solutions are more nearly related elevations, etc.) based on hydraulic forces to erosion responses, such as pile tip such as shore-breaking wave impact penetration, seawall and bulkhead panel pressures (Balsillie, 1985b). Vertical embedment elevations, etc. In addition, recession should include effects due to both since storms cause nearshore erosion and scour, and sediment liquefaction (Zeevaert, bed shifts in response to longshore bar 1983, 1984). formation accompanying beach and coast erosion, resulting increased water depths can It is also important to bear in mind the significantly affect both horizontal and differences between the nearshore, beach (or vertical wave impact potentials which require shore), and coastal subzones of the littoral consideration in design solutions and environment (Figure 1). Under normal assessments. hydraulic littoral conditions, processes are
clearly different within each subzone The need for methodology to predict (discussed in detail in later sections). beach and coast erosion due to the impact of Whether or not the storm rises above the storms and hurricanes has been an issue of beach, or if not, has the longevity to erode ongoing and increasing concern. Moreover, it is one which, for the majority of the history of the discipline of coastal science, has eluded satisfactory quantifying solutions. The lack of methodology is not surprising considering the complexities involved in quantifying littoral processes. Ultimately, however, only through the acquisition of field data will confident, successful solutions be Overwauh realized. This paper provides a significant update (in terms of the number of hurricane and storm events) to previous work by the author (Balsillie, 1985c, 1986).
EX7REME EVENT EROSION AND NO-FLOODED
rS RELA 7ION 70 THE TYPE OF c
PREIMPACT COASTAL
PHYSIOGRAPHY
In this paper erosion is considered to
be the overall term encompassing horizontal Figure 1. Idealized pre-storm (solid lines) and and vertical recession components of beach eroded (dashed lines) profile scenarios for the and coast response due to storm and/or three basic types of coastal physiography hurricane impact. Depending on the type of (STL = peak storm tide level, MSL = mean coastal physiography, these components can sea level). result in quite different outcomes. Horizontal
2




the beach and begin to erode the coast, and consequence for relatively low-lying barriers. post-storm beach recovery, are important It does, however, introduce the aspect of an issues which shall be addressed later. additional "sink" for eroded sand due to overwash processes (Leatherman, 1,976,
Considering initial coastal 1977, 1979, 1981; Leatherman and others, physiography and responses due to extreme 1977; Schwartz, 1975). Combination of the event impact, three general types of preceding two physiographic-hydrographic geomorphic scenarios are suggested: scenarios leads to the breached profile non-flooded, flooded, and breached profiles condition illustrated in inset B of Figure 1 in (Figure 1). In assessing these profile types, which the overwash sink again occurs. several assumptions are made: 1) the beach
and coast are composed of relatively It is also apparent from the literature
unconsolidated sand-sized sediment, 2) that the success of grain-by-grain onshore-offshore sediment transport onshore-offshore sediment transport processes prevail and alongshore processes mechanics under littoral wave activity as yet are assumed static, and 3) "shallow water" remains to reach the status of satisfactory hydraulic processes are approximately quantification (Balsillie, 1984c, 1986). That constant for a given water depth, noting that existing attempts at quantification maybe a change in wave conditions (principally fraught with insensitivities is further shore-breaking and broken waves) will cause exaggerated when dealing with a rising and a shift in bathymetry which, in turn, will falling storm tide and with storm-generated affect the waves. littoral wave activity. Hence, pursuit of
alternative approaches is desirable. One
Where the coast is higher than the such approach is investigation of field data peak storm tide and is wide enough not to be quantifying actual storm and hurricane breached (i.e., the non-flooded condition), impact upon our shores. only the offshore "sink' is available for
deposition of sand eroded from the beach DATA
and coast. A major contributing erosional
mechanism is gravitational mass wasting, This subject has received much
because only a relatively few waves are attention in previous work, dating back for required to cause an unstable, steep sand about 3 decades. Perhaps the most face to collapse. As the sediment compelling work is that of Caldwell (1959) escarpment increases in height, increasingly just preceding the infamous U. S. east coast more sediment is potentially available for Ash Wednesday storm of 1962 introduction to the prevailing littoral hydraulic (Bretschneider, 1964; Harrison and Wagner, environment for redistribution. 1964; and O'Brien and Johnson, 1963), with
a resurgence of interest occurring with the
The barrier islands of the lower Florida works of Edelman (1968, 1972). There Gulf Coast may in many places be inundated have, in addition, been many studies reported by 1 to 2 meters of water due to impact of a in the literature providing descriptive 100-year return period peak combined storm accounts of the erosive power of extreme tide event (see Table 1 for definition). This occurrences. However, until this work was does not include the added hydraulic originally published (Balsillie, 1985c, 1986), elevation due to shore-breaking wave activity there were insufficient types and quantities which propagates upon the storm tide of field data on which to quantify beach and surface. Therefore, the contribution of coast erosion due to storm and hurricane gravitational mass wasting, important to the impacts. This work has increased the size of non-flooded scenario, may not be of special the field data base by a factor of three.
3




Fourteen erosion events for 11 only where erosion has occurred. Hence, in hurricanes, and 22 erosion events for 20 this paper, TYPE I erosion volumes are used. storms (Table 1) provides the largest field Using the data from events H4, H5, S17, data compilation amassed to date for the S18, H7, and H8, Balsillie (1985e, p. 33-34) purpose of quantifying beach and coast found that, on the average, TYPE II erosion is erosion due to extreme event impact. Seven 73% of TYPE I erosion (n = 13, sampled for events (H4, S17, S18, H7,H8, H9 and H10) over 200 profile pairs, r = 0.9515). were assessed through field data collection
of the State of Florida, Department of Natural Where possible, profiles were selected Resources (DNR, now the Department of to represent known extreme event impact Environmental Protection, DEP), Division of magnitudes. For instance, only DNR (now Beaches and Shores (now the Bureau of DEP) ranges R-33 through R-125 in Walton Beaches and Coastal Systems); field data County, Florida were selected for Hurricane collection techniques have been discussed Eloise, since it was this area that coincided elsewhere (Sensabaugh and others, 1977; with the first quadrant of Eloise in terms of Balsillie, 1985a, 1985c, 1985e, 1986, the combined storm tide height (see Balsillie, 1988). Thirteen events (S2 through S1l, 1983a). In other cases, one could only S14, S15 and S16) are the direct results of consider what pre- and post-storm profile the efforts of the Coastal Engineering data were available; an example is the Ash Research Center (CERC); field data collection Wednesday storm of 1962. techniques are discussed by Birkemeier
(1979); Birkemeier and others (1988). A ANALYTCAL RESULTS
more recent event has been reported by Kana
and Jones (1988) and Jones and Kana Two reference water levels have
(1988). Hurricane Hugo (H 11) information is commonly been used, above which presented by Birkemeier and others (1991) volumetric erosion is determined: 1. the and Stauble and others (1991). A tropical peak storm tide still water level (STL), and 2. storm (S20) was reported by Beumel and mean sea level (MSL. Campbell (1990). Ferriero (1994) reported
erosion from a Portuguese storm event that The first water level (STL is occurred in 1989. Remaining events are considered here because it has been used in from independent studies (references are other work. It is particularly accurate for listed in Table 1) that were previously non-flooded profiles since erosion volumes analyzed by the author (Balsillie, 1985c, represent single process losses above the 1986). reference water level due to gravitational
mass wasting, and include none of the
Of the aspects concerning the data, it complexities occurring below the reference is important to note for management level due to interactive hydraulic and purposes that there are two types of erosion sediment transport processes. It should be (Balsillie, 1985a, 1985e). One is the clear, however, that this reference water measure which represents those sampled level has no applicability in determining profiles where erosion only occurred (TYPE I volumetric erosion for breached or flooded erosion measure). The other (TYPE II) is that profiles and, therefore, its use results in only which includes all profiles regardless of gain partial success in volumetric erosion or loss. TYPE II erosion is important in determination. assessing actual beach and coast economic
losses. For design applications, TYPE I The mean sea level reference will, on
erosion is the better measure, since for the other hand, provide for volumetric design work we are interested in locations erosion determination for all three
4




Table 1. Characteristics of storms and hurricanes used in this study.
Peak Event Storm
Storm Forward Tide
Event and Location Tide (m Speed Rise Information Sources
1. D. ~ m Sed Time
1. D. ()MSL) (km/hr) Ti
(hrs)
Hi Hurricane Audrey, June
H1_____ 1957, Louisiana Gulf Coast 3.66 19.0 11.7 Morgan and others, 1958
Hurricane Carla, Sep. .Reid and others, 977; Neumann H2 1961, Texas Gulf Coast 2.30 6.3 51.0' and others, 1981; Schwerdt and
others, 1979; U. S. Army, 1962
Ash Wednesday Storm, Bretschneider, 1964; Harrison and
Si Mar. 1972, U. S. East 3,05 --- 28.0* Wagner, 1964; O'Brien and
Coast Johnson, 1963
S2 Nov. 1962 Storm, U. S. 1.50 -- 7.5'
East Coast
6 Nov. 1973 Storm, U. S.
S3 oaSt 1.40 --- 18.6' Birkemeier and others, 1988
East Coast
S4 13 Jan. 1964 Storm, U. S. 1.50 --- 12.4*
East Coast
Hurricane Betsy, Sep. Wanstrath, 1978; Neumann and
H3 1965, Mississippi Gulf 2.26 16.0 18.0' others, 1981; Schwerdt and
Coast others, 1979; U. S. Army 1979
S5 16 Sep. 1967 Storm, U. S. 1.40 -- 12.4'
East Coast
S6 12 Mar. 1968 Storm, U. S. 1.20 --- 6.1*
East Coast
12 Nov. 1968 Storm, U. S 1.60 1.
East Coast
2 Feb. 1970 Storm, U. S. .
East Coast
S9 17 Dec. 1970 Storm, U. S. 1.60 --- 12.4' Birkemeier and others, 1988
East Coast
Slo 19 Feb. 1972 Storm, U. S.
East Coast
S10a New Jersey 1.80 --- 6.1'
SlOb New York 2.00 --- 6.1'
S11 17-22 Mar. 1973 Storm,
U. S. East Coast
Sila New York 1.40 --- 12.2'
S11b New Jersey 1.30 --- 12.2'
$12 Nov-Dec. 1973 Events, -' --- Erchinger, 1974
German North Sea Coast
S13 23 Sep. 1974 Storm, U. S. 1.45 --- 9.0 Kana, 1977
East Coast
Hurricane Eloise, Sep. Balsillie, 1983a; Burdin, 1977;
H4 1975, N.W. Florida Gulf 3.15 42.6 5.0' Bii, 19'; Uri, 1977
CoastChiu, 1977; U. S. Ay 1976
Coast




Table 1. Characteristics of storms and hurricanes used in this study (cont.).
Peak Event Storm
.Storm Forward Td
Event and Location Tide (m Speed Rise Information Sources
I. D. jTd(mjSed Time
1,__ D, _ _MSL) (km/hr ) is)
, (hrs)
S14 14 Oct. 1977 Storm, U. S. 1.80 --- 17.0
East Coast
S15 19 Dec. 1977 Storm, U. S. 1.40 --- 35.0 Birkemeier and others, 1988
East Coast
S16 6 Feb. 1978 Storm, U. S. 1.70 -. 19.9
East Coast
Balsillie and Clark, 1979; Parker
-1 Hurricane Frederic, Sep. 3.66 24.1 11.0. and others, 1981; Penland and
1979 Alabama Gulf Coast others, 1980; Schramm and
others, 1980
H6 Hurricane Allen, Aug. 2.74 32.2 6.0. DahI and others, 1983; U. S.
1980, Texas Gulf Coast Army, 1980
No Name Storm, 17-18
S17 June 1982, Lower Florida 1.68 40.2 8.0' Galvin, 1983; Trescott, 1983
Gulf Coast
H7 Hurricane Alicia, Aug. 3.86 12.0 18.0. Dupre, 1985; Garcia and Flor,
1983, Texas Gulf Coast 1984
Thanksgiving Holiday
S18 Storm, 21-24 Nov. 1984, 1.83 --- 21.0' Balsillie, 1985a
Florida East Coast
H8 Hurricane Elena, Sep.
1985, Florida Gulf Coast
H8a Pinellas County 1.37 14,5 20.0' Balsillie, 1985e
H8b Franklin County 2.32 16.1 13.4
H8c Gulf County 2.10 16.1 13.4
H8d Escambia County 2.29 25.7 8.0,
H9 Hurricane Kate, Nov. 1985' 2.60 --- 9.2 Balsillie, 1986
N. W. Florida Gulf Coast
S19 1 Jan. 1987 Storm, U. S. 1.50 -.- 12.0 Kana and Jones, 1988; Jones and
East Coast Kana, 1988
Hurricane Gilbert, Sep, Unpublished Florida Department of
1988, Cancun, Mexico Natural Resources data.
S20 Feb. 1989 Storm, 3.53 45.0 Ferreira, 1994
Portuguese Atlantic Coast
Birkemeier and others, 1991;
H11 1989 U. S. East Coast 3.80 32.2 5.0 Nelson, 1991; Stauble and others,
1991
Tropical Storm Marco, Oct
S21 10-11, 1990, Lower 1.13 16.1 9.0 Beumel and Campbell, 1990
Florida Gulf Coast I I I I
Notes: Peak storm tide is the combined peak storm tide level above NGVD including the astronomical tide and dynamic wave setup; Peak storm tide for event S12 was measured from the local datum; indicates the measure storm tide rise time, all other are predicted using equation (2).
6




physiographic scenarios of Figure 1 (except, There have been a number of extreme perhaps, for extreme cases such as inlet event erosion studies in which volumetric formation where erosion occurs below MSL). erosion calculations are based on single For breached or flooded profiles, overwash is averaged or composite pre-storm and eliminated from erosion volumes, so that post-storm profiles, even though multiple volumetric erosion for non-flooded profiles profiles were measured. In this study, (where only the seaward sink is available for however, pre- and post-storm profiles are deposition) and for flooded and breached surveyed from precisely located coastal (where the seaward and upland sinks are monuments, along azimuths established for available, but eliminated) profiles are each monument. Hence, volumetric changes comparable. Elimination of upland and have been calculated for each profile pair, and seaward sinks is desirable since, on the resulting data have been then statistically average, the sum should be equivalent to the treated to obtain point estimators and amount eroded. While at the seaward probability density functions (PDFs). extremity of the post-storm profile, some
material of the seaward sink (also including The Event Longeviy
some degree of post-storm beach recovery) Patametr (EL
may reside above MSL (determined to be about
6% of the seaward sink volume from 245 Average Erosion GuanftyAbove Mean Sea analyzed profile pairs from Balsillie, 1985c), Level and ProhabmW Densi Function the analytical method is fairly unbiased since
it is applied equally to all profiles investigated.
For erosion volume determinations handset of field data
Forlrosion voldaume etermiains andV amassed to date is now available to quantify applications, any datum other than MSL (i.e., becancosrspsedetexem
mean lower low water (MLLW), mean low becancosrspsedetexem water (MLW), mean high water (MHW), and event impact. However, such data have little wae Wmean hge high water (MH W) ando t b value if there does not exist a methodology for mean higher high water (MHHL)) is not to be predicting future occurrences of erosion. In employed. Their departure from MSL is not fatunirenlythehsben o
constant from locality to locality (Balsillie and cnsolae etly b h tre aize others, 1998). Hence, volumes will not be s ognstiction Rognin th e
comparable. sc rgotcto.Rcgiigta h
compaable.amount of erosion is significantly dependent
It should be noted that volumetric upon the length of time that an extreme event changes were investigated which included aes and boothroyd 1969) He autho offshore profile data. The results, however, (ays 18c 1986) deelpe the et introduced significant scatter. It is to be
understood that offshore profiling requires longevity parameter (ELP). In terms of the considerable time and resources (Sensabaugh 0v he region isagie b and others, 1977; Balsillie, 1985a, 1985e). e avgt Post-storm field measurements are most useful = 1622- 'S2)415 when the response time is swift, since any
delay increases the possibility of post-storm where g is the acceleration of gravity, S is the beach recovery which can be faster than combined peak storm tide elevation (see note previously thought. Based on the preliminary of Table 1 for definition), and tr is the storm analysis alluded to above, the inclusion of tide rise time. The relationship and data on offshore profile bathymetry does not yet which equation (1) is based are plotted in appear to be justifiable. Figure 2 and listed in Table 2. The data
7




ISOt
180
160 n r
140 m Hurricanes 14 0.9867 e Storms 22 0.9833
120 Total 36 0.9857
e avg 100 (m3/m) 80
60 4/5
40 Q avg 1 622-1 G1/2 t r S2)
20 0
0 50000 100000 150000 200000 250000 300000
(91/2 t. S2) 415 (m3Im)
Figure 2. Relationship between the measured TYPE I average erosion volume above mean sea level and the event longevity parameter (n = number of events; r = Pearson
product-moment correlation coefficient).
sample on which equation (1) is founded is introduced, when trying to interpret when the three times larger than that available to storm tide ends. The total value of tr for a Balsillie (1985c, 1986) in the original storm produced tide, maintained over development of the relationship, which multiple astronomical tides, is determined by allowed for refinement of the dimensionless adding the rise time components of each constant. The coefficient of equation (1) is, additional cycle. however, but 2.5% smaller than that reported in the earlier work. For analytical purposes, tr is an
excellent quantitative measure of event The storm tide rise time, tr, is the final longevity. However, for applied predictive continuous surge of the storm tide purposes, for an approaching event, the representing impact of the event at landfall. measure is not useful because it is available In some cases, pre-storm setdown (e.g., only after event impact. However, it was particularly for alongshore hurricanes not found (Balsillie, 1985c) that the storm tide considered here) and pre-storm setup can rise time and event forward speed, vf occur. These should be eliminated in (measured at the point when the radius of determining the value of tr, whose graphical maximum winds, or a facsimile thereof for determination is illustrated in Figure 3. extratropical storms, makes landfall), are related (Figure 4) according to:
Values of the storm tide rise time are
from measured storm tide hydrographs t = 0.00175 9 (2)
(references are given in Table 1). Such r records are not always simple to interpret, depending on gauge siting, distance of where 9 is in units of km/hr2 (je., g = 9.8 gauges from event landfall, and relationship mis2 = 127008 km/hr), vf is in units of of the storm generated tide and the km/hr, and the coefficient 0.00175 is in units astronomical tidal cycle. Consideration of the of hr. combined storm tide rise time rather than the total tide history does, however, The role of pre-storm setup as an
eliminate uncertainty, which may be
8




Table 2. TYPE I erosion volume above mean sea level.
Average Maximum Event
Erosion Erosion Longevity Elapsed Profile
LD. Event and Location Volume Volume n Parameter r, Time Type
(m2/m) (m3/m) (m/m) (months)
Hurricane Audrey,
Hi Jun. 1957, Louisiana 51.7 89.0 6 99,461 5.55 0.8449 29-48 F
Gulf Coast
Hurricane Carla, Sep.
H2 1961, Texas Gulf 89.8 --- 8 153,710 --- 5.3 NF,F
Coast
Ash Wednesday
S1 Storm, Mr. 1962, U. 93.0 --- 5 149,327 --- --- 60-96 NF
S. East Coast I
S2 Nov. 1962 Storm, U. 12.9 28.9 31 16,724 1.80 0.9721 0.36 NF
S. East Coast
S3 6 Nov. 1963 Storm, 20.5 47.3 28 30,970 2.95 0.9634 0.60 NF
U. S. East Coast
S4 12 Jan. 1964 Storm, 25.0 56.9 21 25,037 3.55 0.9703 0.50 NF,
U. S. East Coast IMS
Hurricane Betsy, Sep.
H3 1965, Mississippi Gulf 46.5 99.0 9 64,912 6.17 0.9939 4 F,B
Coast I
S5 16 Sep. 1967 Storm, 16.6 43.6 18 22,420 2.72 0.9637 0.16 NF
U. S. East Coast
S6 12 Mar. 1968 Storm, 9.7 24.9 18 9,919 1.55 0.9787 0.16 NF
U. S. East Coast
S7 12 Nov. 1968 Storm, 26.2 55.8 41 32,285 3.48 0.9610 0.72 NF,
U. S. East Coast MS
S8 2 Feb. 1970 Storm, U. 11.1 19.1 29 8,630 1.19 0.9404 0.52 NF
S. East Coast
S9 17 Dec. 1970 Storm, 17.7 43.5 37 27,724 2.71 0.9906 0.41 NF
U. S. East Coast
S10 19 Feb. 1972 Storm,
U. S. East Coast
SlOa New Jersey 9.5 18.8 34 18,977 1.17 0.9572 0.76 NF
SlOb New York 20.2 41.7 23 22,462 2.60 0.9630 0.82 NF
S11 17-22 Mar. 1973
Storm, U. S. East
Coast
S11a New York 23.6 52.9 16 22,102 3.30 0.8923 0.69 NF,
MS
S11b New Jersey 10.3 25.3 17 19,630 1.58 0.9768 0.66 NF,
MS
Nov,-Dec. 1973 Event,
S12 German North Sea 200.0 --- --- --- -- --- --- NF
Coast
513 23 Sep. 1974 Storm, 12.0 10 18,328 .-. --- 0.07 NF
U. S. East Coast
Hurricane Eloise, Sep.
H4 1975, N.W. Florida 20.0 50.7 62 39,628 3.16 0.9735 24 NF
Gulf Coast
9




Table 2. TYPE I erosion volume above mean sea level (cont.).
Average Maximum Event -lpe
l.D. Event and Location Erosion Erosion Longevity Elapsed Profile
L Volume Volume Parameter Time Type
(m'/m) (m'/m) (m3/m) (months)
S14 14 Oct. 1977 Storm, 18.5 34.8 22 43,085 2.17 0.9710 0.23 NF
U. S. East Coast
S15 19 Dec. 1978 Storm, 11.6 37.9 17 42,979 2.36 0.9800 3.25 NF
U. S. East Coast
S16 6 Feb. 1978 Storm, U. 11.6 37.9 17 42,979 2.36 0.9800 3.25 NF
S. East Coast
Hurricane Frederic, Sep.
H5 1979, Alabama Gulf 52.0 121.1 32 94,671 7.55 0.9738 6 F,B
Coast
HS Hurricane Allen, Aug. 28.0 --- 3 36,682 --- --- 30 NF,B
1980, Texas Gulf Coast No Name Storm, 17-18
S17 Jun. 1982, Lower 14.0 25.8 24 21,111 1.61 0.9917 3 NF
Florida Gulf Coast
H7 Hurricane Alicia, Aug. 92.4 1 152,259 --- 36 NF
1983, Texas Gulf Coast
Thanksgiving Holiday
S18 Storm, 21-24 Nov. 27.0 70.0 127 52,388 4.30 0.9077 3-20 NF
1984, Florida East
Coast
H8 Hurricane Elena, Sep.
1985, Florida Gulf
Coast
H8a Pinellas County 21.0 48.3 44 31,704 3.01 0.9622 130 NF
H8b Franklin County 40.0 75.4 35 54,456 4.70 0.9585 49 NF
H8c Gulf County 24.0 44.1 54 45,579 2.75 0.9753 13-21 NF
H8d Escambia County 19.0 38.3 112 34,653 2.39 0.9875 10 NF
Hunicane Kate, Nov.
H9 1985, N. W. Florida 22.0 51.2 18 47,481 3.19 0.9617 2 F,NF
Gulf Coast
$19 1 Jan. 1987 Storm, U. 19.4 --- 4 25,669 -- --- 0.3 NF
S. East Coast
Feb. 1989 Storm,
$20 Portuguese Atlantic 164.0 341.0 4 276,390 --*
Coast
H10 Hurricane Gilbert, Sep 144.7 297.0 8 89'782 18.52 0.9842 60 NF
1986, Cancun, Mexico 231,482'
H11 Hurricane Hugo, Sep. 28.0 52.5 19 53,501 3.98 0.9691 4 NF
1989, U. S. East Coast Tropical Storm Marco,
S21 Oct. 10-11, 1990, 3.9 11.4 28 9,317 0.57 0.9755 1 NF
Lower Florida Gulf
Coast
Notes: Elapsed time is the time between pre- and post-storm surveys; Profile types are: F Flooded, B = Breached, NF = Non-flooded, MS = Multiple Storms; adjusted value to account for increased offshore sediment sink efficiency, see text for discussion; data sources are listed in Table 1.
10




erosive agent deserves 7
additional comment. If
the general onshore 6
physiographic scenario Storm Ti _can be described as a S
beach that is backed by 4a coast comprised of a Elevation dune or bluff (see Figure Abov MSL 3
1 for graphical m
f or r ph ic I2 Normal Pie-Storm
definition), then the Tidal Conditions
elevation relative to MSL
which identifies where
the coast begins (i.e., 0
t he beach-coast -.
inflection point, or T 20o0rs)
nickpoint), becomes an Tm hus
nikontbcoe nFligure 3. Example of water surface hydrograph through an important measure. idealized storm tide, and definition of storm tide rise time That is, if the storm tide measure (after Balsillie, 199$). is less than the
beach-coast nickpoint
elevation, then more
time will be required to n 17
erode the beach before r 0.9278
the coast is affected, tr. 60 relative to the case (hrs) 40 tr -00175 Vf
where the storm tide is
higher than the 20
beach-coast nickpoint 0 Celvtosota oh0 10 20 30 40 so 60
teeacnd oEat willo I (km/hr)
E ~ ~ ~ ~ bv MS p e- ce wt
be afectedwithitimeFigur 4. Ratsip*Stwentesormiers im n vn
identification of the
beach-coast intersection for Florida beaches that pre-storm setup is an anomalous feature, (Lae., those for beaches preceding events the above further substantiates that it should listed in Table 1), tells us that it is the latter be deleted from consideration in erosion scenario which usually defines the design prediction. erosion condition. Current examples of average nickpoint elevations are + 2.19 m It is to be noted that the ELP contains
MSL for Florida's upper East Coast (St. both the peak storm tide, S, and the storm Johns County), + 2.25 mn MSL for the lower tide rise tm, ti. It is the introduction of the Gulf Coast (Charlotte County), and + 2.1 m latter which prompted the name event MSL for the northwestern panhandle Gulf longevity parameter. Utilizing stepwise Coast (Walton County). It is significant that regression (Krumbein and Graybill, 1965; of the events of Table 1 and those Balsillie, in press; Balsillie and Tanner, in
graphically reported by Harris (1963), none press), it has been determined that $ results resulted in a pre-storm setup in excess of in a relative net contribution in predicting about +1.5 m MSL, well below the v of 76%, and tr provides a net relative
beach-coast nickpoint elevation for Florida. contdbution of 24%. Even so, both are Hence, in combination with the observation required in order to obtain the success of
bechcostinesetin orFordabechs tht restrmstu i a aoalusfetue




equation (1) evident in Figure 2.
P
There are 29 events that 150 0.1 0.5 0.7 0.8 0.9 0.95 0.99
provide information on which to investigate an erosional probability density function (PDF). From 6 to 100- Event I. D. 6.17
127 profiles represent each of the H3
events (Table 2), and result in the 50 following equation:
*33*
1 3,19 0, (e3") (g'12 S2)ds (3) 0 M8
in which Qe is the volumetric coastal erosion quantity occurring above mean sea level corresponding to the erosion Ci 0 probability, P, which is the probability of erosion less than or (m2.71 0 equal to that stated, and f is a relating coefficient. Values of 0 (examples are plotted in Figure 5, results and correlation coefficients are listed in Table 2) are plotted against the ELP in Figure 6, showing remarkable agreement. The relating 0
coefficient f becomes 12344-'.
Correlation coefficients associated with 0 are all significantly large. Note that if we were to consider, say, median and 15 20
larger erosion values in the PDFs (see Figure 5), rather than all Figure 5. Typical examples of density distributions for values available, correlation determination of the slope 0 relating Q and e" (event coefficients would be even larger. I.D.s refer to Table 2).
Average Erosion Guantity Above the Figure 7, surfaces:
Peak Storm rwde Level and Prohah~ty .,,=39~ (gl/2 45)/ 4
Density y Function (PDF)00#y 39- r'2)4/()
The preceding has dealt with where 0'e avg is the TYPE I average erosion volumetric erosion occurring above mean sea quantity occurring above the peak storm tide level. While it has been noted that level. consideration of erosion above the peakUsndaafo22ent(Tbe3a storm tide elevation has no applicability forUsndaafo22ent(Tbe3a flooded or breached profiles, such a PDF may be proposed according to: consideration does have validity for non-flooded profiles. Based on available a*' = &I (W P) (g112 t 241 5
data listed in Table 3, the following s / 5
relationship based on 24 events, illustrated in
12




25
20 n Hurricanes 11 0.9803
* Storms 1 0.5935
Total 29 0.9603
10 e = e3 P, where 10 e e/
5 4 = 1234"(g1/2 tr 5
0
0 50000 100000 160000 200000 260000
(91/2 tr S2 )45
Figure 6. Relationship between the event longevity parameter and distribution coeffcients for TYPE I average volumetric erosion above
MSL.
100
0o' = 31051 (g1/2 tr 2415
so avgv '
0e avg r = 0.8965
40 n = 24
20a Hurranes 20p *oaJ.P' Storm
0 50000 100000 150000
(gi2 tr S2 5
Figure 7. Relationship between the measured TYPE I average net erosion quantity above peak combined storm tide level and the event
longevity parameter.
where the relating coefficient from Figure relative to MSL and the peak storm tide is 23630'. elevations, we can broaden our quantitative
expectations. We know that for engineering It is evident from results presented in design purposes, using TYPE I erosion Figure 8, that the correlation between volumes, an average measure is not variables is significantly less than those responsible. For engineering design purposes statistical assessments for analyses it is always prudent to consider some upper presented in Figures 2, 6, and 7. Even so, measure of a destructive force, or response the probability that a random sample of this element. A highly useful measure from size could result in sample correlations so substitution of equations (1), (3), (4), and large, is very small. (5), where Po linearity prevails, is given by:
Desiign Erosion Quantites 01_ OR -.-4 3P 6
Now that we have established 17Av '/A
successful relationships that quantitatively predict average erosion volumes for events inwhich and Q' are erosion volumes for
13




10
a = *3 P, where a Hurricanes
1 /2 2)415 e Storms
6 # = 23630-1 l/2 t S2)
4 r= 0.5797
4
n = 22
2 ***
0
0 20000 40000 60000
(g1/2 tr 82 41S
Figure 8. Relationship between the event longevity parameter and distribution coefficients for the TYPE I average erosion volume above the
peak combined storm tide.
a specified exceedence probability P above twice (te., 2.1) the average erosion volume. MSL and peak storm tide, respectively. Hence, the TYPE I median erosion volume It is to be noted that coefficients of
(i.e., P = 0.5) is about 61% less than the equations (7) and (8) precisely agree with TYPE I average erosion volume (for the fitted coefficients describing the graphically average erosion volume P = 2/3), the third estimated maximum erosion quantities of quartile TYPE I erosion volume (i.e., P = Tables 2 and 3.
0.75) is 130% greater than the average TYPE I erosion volume, etc. The Offshor Sink Effiency
Paamter (OSE.P)
Noting that pre-storm profiles are
seldom measured just prior to storm or The form of the event longevity
hurricane impact, some physiographic parameter has invoked some controversy. deviation might be reasonable to levy on a While the combined peak storm tide height PDF in assessing a design maximum erosion and storm tide rise time components have volume. This and purely random, generally been well received, the appearance anomalously high erosion volumes suggest of the acceleration of gravity and the that, perhaps, a probability P of between 0.9 dimensionless proportionality constant have and 0.95 would not seem inordinate to not. apply. Using a value of 0.925 and coefficients from equations (1) and (4), the If one compares erosion quantities application of equation (6) yields the above the combined storm tide to those following design relationships: above mean sea level, it is apparent that
r24/5 about half the eroded sand volume originates
1 701 (g" t' ) 7 from above the peak storm tide level (50% if
one compares coefficients from equations (1) for the TYPE I erosion volume above eSL, and(4), and (3) and (5), and 55% from the and: data). This should not be surprising from a
1 24/5 (8 geomorphic viewpoint, considering that our
=' 1473 -1 (g11/ t., $2 ) beaches and coasts have certain constraining
dimensions physiographically. it is for the TYPE I erosion volume above the recognized that the efficiency of gravitational combined peak storm tide level. Both acceleration is not only greater for steeper equations result in erosion volumes close to slopes when dealing with sand transport, but
14




Table 3. TYPE I erosion volume above combined peak storm tide.
Average Maximum Event
1. D. Event and Location Erosion Erosion n Longevity
Volume Volume Parameter q r.
(m3Im) (m3/m) (m/m)
Si Ash Wednesday Storm, Mar. 1962, 53.0 --- 4 149,327
U. S. East Coast
S2 Nov. 1962 Storm, U. S. East Coast 6.3 18.6 32 16,724 1.16 0.9953
S3 6 Nov. 1963 Storm, U. S. East Coast 6.9 24.2 26 30,970 1.51 0.9552
S4 13 Jan. 1964 Storm, U. S. East Coast 11.7 26.1 37 25,037 1.63 0.9841
SS 16 Sep. 1967 Storm, U. S. East Coast 3.9 7.1 19 22,420 0.44 0.8918
56 12 Mar. 1968 Storm, U. S. East 58 18.6 37 9,919 1.16 0,9590
Coast
12 Nov. 1968 Storm, U. S. East 14.8 28.7 4 32,285 1.79 0.9879
Coast 1
S8 2 Feb. 1970 Storm, U. S. East Coast 6.9 15.6 31 8,630 0.97 0.9559
89 17 Dec. 1970 Storm, U. S. East 5.8 15.1 42 27,724 0.94 0.9316
Coast
S10 19 Feb. 1972 Storm, U. S. East Coast SlOa New Jersey 12.0 22.8 23 18,977 1.42 0.9815
S10b New York 7.6 15.7 38 22,462 0.98 0.9831
S11 17-22 Mar. 1973 Storm, U. S. East
Coast
S1la New York 7.5 16.4 17 22,102 1.02 0.9758
S1lb New Jersey 5.3 12.5 16 19,630 0.78 0.9909
S12 Nov,-Dec. 1973 Events, German 31.0 --- --- 92,944
North Sea Coast I
H4 Hurricane Eloise, Sep. 1975, N. W. 16.0 29.8 72 39,628 1.86 0.9557
Florida Gulf Coast
S14 14 Oct. 1977 Storm, U. S. East Coast 15.5 31.6 22 43,085 1.97 0.9890
S15 19Dec. 1977 Storm, U.S. East 11.8 23.4 20 51,356 1.46 0.9890
CoastI
S16 6 Feb. 1978 Storm, U. S. East Coast 12.3 30.5 17 42,979 1.90 0.9940
S17 No Name Storm, 17-18 Jun. 1982, 14.0 25.8 24 21,111 1.61 0.9917
Lower Florida Gulf Coast
S18 Thanksgiving Holiday Storm, 21-24 14.6 32.4 128 52,388 2.02 0.9807
Nov. 1984, Florida East Coast
H8 Hurricane Elena, Sep. 1985, Florida
Gulf Coast
H8b Franklin County 10.3 31.6 34 54,456 1.97 0.9661
H8c Gulf County 7.1 18.9 30 45,579 1.18 0.9958
H8d Escambia County 4.2 11.4 58 34,653 0.71 0.9459
H9 Hurricane Kate, Nov. 1985, N. W. 8.7 22.0 13 47,481 1.37 0.9247
Florida Gulf Coast
Note: The time between pre-storm and post-storm surveys, and comments are given in Table 2; data sources are Ilsted in Table 1.
15




due to inertial effects is less according to: response oriented under lower slope subaqueous than steeper slope subaerial littoral conditions. The result is a partitioning T (ta a,) (9)
of sediment transport between kinetic energy (i.e., by virtue of low-slope, near horizontal where tan is the initial or pre-impact motion due to shore-normal subaqueous nearshore bed slope, and: sediment transport mechanics) and potential energy (i.e., by virtue of subaerial elevation of dunes and bluffs and potential gravitational mass wasting due to wave Data and fitted relationship leading to impacts propagating upon an elevated water equations (9) and (19) are plotted in Figure 9. level). Based upon this logic, it would appear Results from equation (9) apply only where that the diminished effect of the acceleration the initial or pre-impact nearshore bed slope of gravity is not unwarranted, because it is greater than 0.01638; where the initial bed probably relates more to spreading rates slope is less than 0.01638 the value of Y is across the nearshore than to dune or bluff unity (i., 1.0). The final form of equation mass wasting. The latter is essentially (3) now becomes: instantaneous, while the former is timeconsuming. In fact, the prototype wave tank 0. 0 1
results of Dette and Uliczka (1987) appear to provide some elucidating information. First, The validity of Y can be tested using their results show that the pre-impact data obtained from Hurricane Gilbert which nearshore bed slope correlates with the struck Cancun, Mexico in September, 1986. magnitude of beach and coast erosion While the accuracy of data for Hurricane volumes and the rate of erosion. Gilbert is not touted to be of the standard for Specifically, the steeper the pre-storm the remainder of the data base presented nearshore bed slope, both the greater the here (and in particular for the Florida data), erosion volume above SWL, and the faster the magnitude of the event was so the removal rate. Second, regular and overwhelming that it cannot be neglected; irregular waves appear to erode the beach best known data are listed in Tables 1 and 2. and coast at different rates. A significantly important factor associated
with the Gilbert data are the very steep Dette and Uliczka (1(987)
report prototype results for initial
nearshore bed slopes of 0.25 and:
0.05, and Saville (1957) for a (10
slope of 0.0667. U. S. East and a Dftmnd Ulicz(te r i p
Gulf Coast natural nearshore Pnasont studybe
slopes (i.e., 300 to 800 m $3whr
offshore) are, however, 0.01638;= where
characteristically less than 0.02, 2 th2.07+13.2tana 16 tanal> 0.o16
averaging about 0.016 for 1 =12t1 for tanaT 0.016
Florida. Application of these data t i
relative to o the PDF coefficient fr oUm Hra Gew
of equation (3), yields a tan 18
dimensionless proportionality Figure 9. Tessellated relationship relating nearshore bed constant YG termed the offshore slope (tanr which occurs from 300 to 800 m offshore of sinkefficiencyparameter(OSEP), the MSL shoreline) to the ELf coefficiented
16




nearshore slopes off of Cancun as illustrated steeper nearshore and increased value of the in Figure 10. In fact, the nearshore slope is offshore sink efficiency parameter is the over twice Vie., 222%) as steep as slopes product of the ELP and OSEP, resulting in a commonly found off U. S. East and Gulf value of 231,462 m3Im. The goodness of fit Coast nearshores. Such a slope is steep of this result is illustrated in Figure 2.
enough that sand is not able to be Moreover, equation (11) results in an average
transported back onshore during post-storm erosion volume (ie., P = 2/3) of 144.5 m3/m conditions. Hence, the steep offshore slope which is very close to the measured amount becomes, for all practical purposes, a of 144.7 m/m, and a maximum erosion sediment sink. Given the following data for volume (e., P = 0.925) of 313.6 m3Im Hurricane Gilbert: which is within 5.6% of the measured value
of 297 m3/m.
tan a = 0.0363,
The final form of equation (5) for tr = 9.5 hours, volumetric erosion above the peak storm tide
S =3.8 1 m, level becomes:
stepe nerhr and inrese valu of/ the$2
Pfso0.68 (average erosion volume), (12)
P 0.92 5 (maximum erosion volume),
then: ELP = 89,782 mo/m, where by similitude, it is assumed that the
OSEP = 2.578, OSEP applies straightforwardly as in equation
(11) (field data are needed, however, for and: ee3r = v (ie, = 7.389 1, confirmation).
and, Nearshore geometry is now commonly
quantified by a power curve (Dean, 1977; e3P = e30.926v o 16.0386. Hughes, 1978; Balsillie, 1982a, 1987) given
by:
The adjusted ELY due to the effect of the d a, A43 (13)
in which d is the water depth, and f x is the distance offshore. Using
the data of Saville (1957), Dette S = 3.8 1 leePecms
i CsnS 0PO 8C(eueProfl and (liczka (1987), and average OSE = Vs 2.578,s OSEP applie staihfowadyfsineqato
(11 (data for Florida, tan a may be
approximately related to the shape qua e y acoeff icient (Dean, 1977), a5
- --- -.- -.- -.according to:
tana,=O.5a,' (14)
illustrated in Figure 11 (a5t in a2 200 4W0 60 low equations (11) and (12) has units
of i"3; if a is in units of ft" Figure 10. Comparison between a typical Florida multiply the value by 0.673 to nearshore profile and a typical Cancun, Mexico nearshore obtain consistent S. units). profile.
17




116 C.,
Returm Period Volunmaric 03 A
Erosion Events
The incidence of extreme phenomena may require site-specific treatment. Such is the case with the determination of the return period storm tide which is dependent not 0A /
only on historical storm/hurricane characteristics and water levels, but also, importantly, on local conditions such as 312
offshore and nearshore bathymetries. A t 0 W 0 os as
major problem in following such an approach for erosion responses is that site-specific quantitative erosion data are historically deficient. However, since uncertainties about erosion make simplified considerations Saville (1951)
a Dette and Uliczka (1997)
the most appropriate (Hallermeier and P Present Study
Rhodes, 1986), and because of the apparent success of foregoing quantitative results, it is assumed that physiographic responses to 0 01 0.2 0 OA 0.5 Oh 0.7 0,
storm attack need not be held to a site-specific treatment.
Figure 11. Relationship between the initial Further, it has been a major tenet of nearshore bed slope (tan @j occurring 300 to this and other works (Balsillie, 1985c, 1986) 800 m offshore of the MSL shoreline) and that the storm tide return period event and the power curve fit shape coefficient, a. the storm erosion return period event are seldom coincident. Until now there has been plot of Figure 12 is constructed using data insufficient information on which to specify from Table 2. Only Atlantic Ocean events the probabilistic erosion event. are considered in this analysis. There are 35
events listed in Table 2 which apply. These The frequency Pe used in plotting the events occupy a 34-year period from 1957 distribution is found (Gumbel, 1954) by through 1990. During this period some 324 ranking the erosion volumes from smallest to tropical storms and hurricanes formed in the largest and then dividing the rank of each of Atlantic. Of these, about 104 (or 32% of the the sample size plus one, i.e.: total) landfalling or exiting events affected
the Americas along the U. S. East Coast, and P, = m 1 (15) Gulf of Mexico coasts of the U. S. and
n + 1 Mexico. It is assumed that the applicable 35
events of Table 2 represent a random sample where m is the ranked value. If the theory of erosion conditions. The 35 events, does hold, the points should plot as a however, represent only one-third of the straight line on probability paper. The return actual number of events that affected period T, is then given by: coastal reaches. Therefore, for analytical
purposes, the 35-event sample is
- (16) 'triplicated" to yield 105 events (i.e., tripled
i P, in size to more nearly represent the 104
events that actually occurred); only the midUsing equations (15) and (16), the point of each 'triplicate" is plotted to
18




Segment A: Segment C:
1000- 1.25 -g 6.55 0.999'
500 1 + 0.006 0 ev 6.5 x 10 0e avg 0.998
200- T, (r 0.9629) To O. (r 0.9905)- 0.995
100 Segment 3: 0.99
0.00033 2.49 0.98
20 T, *s(r 0.788) *0 ag 0.95
To 10- A 0.9
s The peak stm tide rose above the beafltIcamt nickpoint 0.8
elevation and the reillie was rather nonofteeded or p ( breached, resulting hi both beach and coast erosion. 0.7
_ 0.6
2 -The peak terr did not rise abewe the beach/comet nickpIlat 0.5
elevatioa, but perslsted to result in both beach 4ed seest erslen or the prerite waoond CCIC 0.4
- 0.3
1.2S 0.2
c The Me*k stum tHis id not rise above the beacheoeest uicpoit 0.1 elevation an dd eat perest, resUng 1n beach eason only. 0.05 II I I II I I I I I II 0.02
0 50 100 10
0 avg (rn/rn)
Figure 12. Relationship between exceedence probability P, return period T, and average TYPE I erosion volume above MSL.
represent the associated probability and return period. It is noted that three O.r.7=60 [(In 7)-l]' (19)
straight-line segments are apparent for which possible explanations have been suggested By incorporating results from equation (6), (see Figure 12). Equations of immediate the design maximum erosion volume (i.e., for interest for coastal construction design P 0.925) results in a factor of 2.1 and: purposes are:
11.25
1 + 0.006 0a. (17) For segment B of Figure 12, which
describes events between about 1.25- and 4for segment A which describes extreme year return occurrences, the return period is
events with a frequency less than about a 4- given by: year return period, where Qe avg is specified 2.0
in cubic meters per alongshore meter of 0033
beach or coast (note: m'/m = 2.508 (ydl/ft)). Utilizing, by substitution, equation for which equations corresponding to (18),
(6) the corresponding probability of equation (19), and (20), become:
(17) is given by:
P, (18)
Further, by rearranging equation (17), the icran25 [(in T f (23)
return period erosion quantity in m(/m may be determined according to: and:
19




0. 5.5 (Inr 0A16 24)It is, however, notable that Figures 11
= 53.5 (In ) 1o (24) and 12 support the significance of
physiographic zonation between the beach
Following this methodology, similar and coast. equations may be developed for segment C
that represent events occurring more often Post-Storm Recovery than the 1 .25-year return period (see Figure
12). There seems to be considerable
interest among coastal scientists and
There is simply not yet sufficient field engineers in post-storm littoral recovery, data to reliably determine return period even though we are just now quantifying volumetric erosion events for erosion above details about magnitudes of physiographic the peak combined storm tide level (in responses during the "height" of extreme particular for that portion corresponding to event impact. While there exists some segment A of Figure 12). However, quantifiable representation of such recovery statistics indicate that erosion volumes above (Balsillie, 1985d, in manuscript), additional the peak storm tide level, on the average are work remains. Generally, based on what is about one-half those above MSL. Hence, in known about littoral processes, we can the interim, a reasonable estimation may be endeavor to find discernible and logical determined by doubling the value of conclusions about such recovery. Again, it O'e ave and using equations (17) through becomes of importance to delineate littoral
(24). subrones (see Figure 1), namely, 1. the
nearshore, 2. the beach, and 3. the coast. it
The quantifying equations developed is these three subzones which interactively in this section are of special consequence. define the extent of both extreme event Past return period damage elements have impacts and what are discernible "normal" or been assessed in terms of forces, specifically 'day-to-day littoral processes. the combined storm tide elevation and wave
heights. Now, for the first time, a return The nearshore, which is always period response element in terms of erosion subject to the effects of astronomical tides is provided which accounts for all the force and waves, is expanded when a rising storm elements, including longevity of the event. It tide encompasses the beach, and, under is envisioned that these equations will be design conditions, the coast. That longahore highly valuable in design and coastal bars are formed during extreme event impact management activities. has been a controversial issue. The problem
is, of course, that nearshore subaqueous
One might be inclined to believe that behavior has not been adequately monitored the developed approach is based upon broad to yield confident quantification during assumptions (e.g., global continuity in littoral extreme event impact. However, based on physiography) and a limited sample size. additional considerations and tested data Recognize, however, that errors creep into (Balsillie, 1984c, 1985d), and field design computations due to assumptions observations (Dette, 1980; Birkemeier, 1984; about convoluted littoral processes. At Sallengerand others, 1985) the formation of present, and at a minimum, equations (17) longshore bars during extreme event impact through (24) would seem to provide seems more nearly to be the case. information as a valuable check for the more Ramifications of the concept are not only involved design computations (methodology essential towards a new understanding of for application of volumetric erosion volumes coastal engineering design constraints that is discussed in the conclusions), might be required, but of interactive littoral
20




forces and responses that could occur during because it is detrimentally affected only extreme event impact (bearing in mind that during extreme event impact (or man's extreme prospects are probabilistic). activity). Where high sandy dunes or bluffs exist, the coast affords substantive
Further, longshore bars are nature's protection to the upland. It is nature's own protective device. During storm action physiographic reserve of particulate mass, they not only are formed but move offshore drawn upon to replenish the more active (Short, 1979; Birkemeier, 1984; Mason and beach subzone, when beach subzone others, 1984, Sallenger and others, 1985), dimensions are diminished. causing storm waves to break further
offshore than would normally occur. By Of the three sub-zones, the coast in
inducing breaking they cause the greatest its natural state can be expected to amount of energy dissipation that water experience no immediate recovery. An waves can experience and, should wave example is Dauphin Island, Alabama struck reformation occur, significantly reduce the by Hurricane Frederic in 1979, destroying elevation of destructive wave energy (.e., dunes which attained heights of up to +10 reformed wave heights are attenuated; Carter m MSL. Average volumetric dune losses and Balsillie, 1983; Balsillie 1984b, 1985b). were about 50 M3/M. Assuming the sand supply is available and that vegetation is
During storm impact, the width of the instrumental in natural dune reconstruction, surf zone dramatically increases. When, then based on the data of the U. S. Army following impact, surf width again attains (1984) and Dahl and others (1975), natural 'normal' width the bar(s) within the dune reconstruction would require 70 to 75 "normal" surf zone move onshore in a few years for American Beach Grass and Sea days. Outer bars either remain as relict Oats, respectively, and 180 years for features or disappear, although the latter Panicum (Balsillie, 1979a). requires months to occur (Birkemeier, 1984;
Mason and others, 1984; Sallenger and APPLICA77ONS
others, 1985).
The results of this work deal with
Beach (or shore) recovery appears to volumetric erosion of the beach and coast be considerably more rapid than has been due to extreme event impact. This presupposed by many coastal engineers. comprises, however, but one aspect of Although complexities occur (e.g., longshore interrelated natural processes in terms of transport) which can produce a large range in force and response elements that occur values, it is now quite clear that beach 'within nearshore, beach, and coast recovery often occurs within days. subenvironments of the littoral zone. Other Birkemeier (1979) found for the 19 December aspects include storm wave activity which is 1977 U. S. east coast storm (event S15) that instrumental in causing the erosion, from 38% to 100% beach recovery occurred producing dynamic and impact loads on within one or two days following event exposed structural members, and forming impact. Bodge and Kriebel (1985) also report longshore bars that house sand eroded from rapid recovery for beaches following impact the beach and coast. These various aspects of Hurricane Elena in Pinellas County, Florida are quantified and discussed in a series of (event H7a). Such rapid beach recovery papers, the sum total of which actually agrees with response time scales of describe the entire Multiple Shore-Breaking post-storm nearshore profile changes. Wave Transformation Erosion computer model (Balsillie, 1984c, 1985d). This
The coast is of special interest approach allows one to more succinctly
21




manage research by dealing with discrete or AB lying above the nickpoint of Figure 13) sets of discrete natural process units, and has a 1 on 1 slope. The segment BC is a also facilitates updating of each manageable slightly curved line smoothly continuing the unit as new developments are made. Even bar trough envelope to the nickpoint (where so, it is recognized that some guidance the coast is flooded only segment BC would be helpful to describe how the applies). Starting at the pre-impact shoreline, predicted volumetric erosion can be segment ABC (or segment BC where the practically applied. coast is flooded) is iteratively moved
landward until the erosion volume is attained
Post-Storm Beach and Coast (shaded area of Figure 13).
Physics graphy
PhysioraphyNearshore wave heights are
The problem in applying volumetric determined using the bar crest envelope to erosion quantities, is the determination of the represent the water depth at breaking, db resulting physiography of the profile. For the (Balsillie, 1983b, 1984b, in press). The two-dimensional case, the following amount of the breaking wave height lying simplified methodology is suggested as above the peak storm tide still water level, illustrated in Figure 13 (discussed by Balsillie Hb', has been determined from field data 1984c, 1985d). Following determination of (Balsillie, 1983d, 1985b, in press) to be the design erosion volume, plot the pre- given by: impact coast, beach, and nearshore profile.
The nearshore profile shape in Florida can be
determined using the power curve form
according to Balsillie (1982a, 1982b, 1987). in which HbX is the average height of the Plot the bar crest envelope, db (i.e., the line desired moment measure. The breaker connecting the crests of longshore bars height envelope illustrated in Figure 13, formed during the event) and the represents the significant height. Relating corresponding bar trough envelope, dbt (Le., equations developed by Balsillie and Carter, the line connecting the bar troughs, 1984a, 1984b) for other moment measures according to: commonly used in design work are:
dk = (S + a. xf) (25) H, 1.02 Hb (28)
where Hb rm is root-mean-square breaker
where S is the peak combined storm tide, a. height, and Hb is the average breaker height; is the shape coefficient given by Balsillie
(1982b) for Florida, and Xbc is the distance H offshore measured from the pre-storm MSL
shoreline, and:
in which Hb is the significant breaker height
4t = S + a,(x,, + 7 S)2r)(26) (ihe., average of the highest two-thirds of the
5 height record);
where Xbt is the distance offshore measured Ho = 1.37 H,, (30)
from the pre-storm MpcSL shoreline.
Inspection of post-storm profiles where Hblo is the average of the highest indicates that the portion of the eroded 10% of the wave record; and: profile above the peak storm tide (segment
22




[ -I _T I I
Measured Data
Pre-Storm Profile
10 Post-Storm
MSL = Mean Sea Level
PST SWL Peak Storm Tide Still Water Level Al Eroded Volume above MSL
**i
eiST SWL
Predicted Data
- ---Post-Storm Eroaton Proftile
----- Bar Tr-ough Profile ---- -Bar Crest Profile
.- --o -- Significant Breaker Height Envelop
-60 -so -40 .30 -20 -10 0 5 to 15 20 25
Distance from Pre-Storm Shoreline (m) Figure 13. Example of application for determining two-dimensional post-storm physiography using volumetric data, and design wave conditions.
H. (31) statistics to the design life of a project.
H. He =1.57 Ht,31 What we really wish to do is transform the
return period statistic to one of encounter in which Hb1 is the average of the highest probability, based upon a specified encounter
1 % waves of record. period.
Encounter Period and Proh~RyThsouinsteueofFgr14
A return period statistic is one neitreowhcishepidofim providing a measure of the probability of frwihapoeti ols ieisdsg annual occurrence. For instance, an event lf) ntecs fsnl-aiydeln
with a 1 00-year return period has a dsgteecutrpro ih e5
probability of 0.01 or a chance of 1% yasrpeetn ercainpro o
occurrence in any given year, an event with txproeec h riaeo iue1
a 5-year return period has a probability of gvsteEmme rhbt hc
0.20 or a 20% chance of occurrence in any rersnsteaigdrtunpioeqld given year, etc. Even if the return period orecddduigtesltd o& r
occurrence occurs during an annual period, rk.Cveinraltthgapaefo its probability of recurrence remains the same vrosRfnPrd soitdwt h
withinTh sohtio isren theua useewrk ofig Figuen14
The ~ ~ ~ ~ ~ ~ ~ h absfenlast cnuin Flogiss of Figure 14 give th ue
particularly ~ ~ ~ ~ fo whnoetist eaesc hichre apoeti toat (ie. wolis deig
.23
designgnthecmncouneererereightigntebop5
DitnefonPtaxo Spurpoele Th( rdnteonFgre1 Figue 1. Eamp, o aplictio fo deermninetw-dientesin pot-torm phyioeqaped
using volumetricddatanandtdesignewave conditions
staisd.iCurenra to the deingrefa p roefor
vrtun Reperiodisti tosocied ft ecuther inihichtHelcisrent anuleraeo k thdeses roinlvtbsduo. pcfe none
1 he waves o ftenrd ledstcnfson iollwnsaneapeofhwt.s
parthcuarly0-yea eun prertod hea asuch n the encounter period might bie 50
prbailt o 00 o acane f1 yas epeenin dprcatonprid3o




-Return Period-10
> .e
a
0
W- 0.6200
50 100 500 1000
Encounter Period (Years)
Figure 14. Nomograph for relating event return period, encounter period, and
encounter probability.
build your single-family beach-fronting can also be used for any other measure (e.g., dwelling so that it is relatively safe from the peak combined storm tide, wave event, 100-year return period erosion event. The event forward speed, etc.) provided that probability of a 100-year return period return period statistics are quantified. occurrence being equaled or exceeded during
the above assigned 50-year period (i.e., An Erosion Damae Potent Scab Encounter Period) is 0.4, as illustrated in
Figure 14. Hence, there is a 40% chance A beach/coast erosion damage scale
that the 100-year return period erosion event for extreme events has not, here-to-fore, will occur in the planned life time of the been proposed. Perhaps the best way in home. Had the dwelling been designed for which to assess an erosion damage potential a 500-year return period erosion event, the scale is to build upon the existing structure would have a much better chance Saffir/Simpson hurricane damage potential of surviving the critical event then only a scale (Table 4). Volumetric erosion is 10% chance of occurrence during its planned assessed using equation (1) for average life. erosion quantities and equation (7) for
maximum erosion quantities. The
Using the figure in another manner, if assessment of Table 4 is, therefore, a homeowner or prospective home owner is applicable to the U. S. Atlantic East Coast willing to take a 20% chance that the design and the U. S. Gulf of Mexico Coast which erosion event will occur during the 50-year have relatively low nearshore slopes (ie., design life of the structure, then the RtWr where tan a is characteristically less than Pedod of the erosion event that should be 0.02). Equations (1) and (7) were evaluated designed for is 250 years. using the Saffir/Simpson peak storm tide
(commonly termed the "storm surge")
The above example uses the return classes of values. Event forward speed period erosion event. However, Figure 14 classes were determined using the historical
24




Table 4. Amended Saffir/Simpson Hurricane Damage Potential Scale
Peak Eet Storm Avrg Maiu
Central Wind Storm Tide Forward Tide Erosion Erosion Damage
Category Pressure Speed Elevation FSpeed Rise Volume Volume Potential
(mb) (km/hr) above Th.e 13 3Pt t
MSL (m) (hr)
1 > 980 46-59 1.22-1.68 50-90 2.5-4.5 3-8 6.5-17 Minimal
2 965-979 60-68 1.68-2.60 30-50 4.5-7.5 8-25 17-53 Moderate
3 945-964 69-81 2.60-3.81 20-30 7.5-11 25-63 53-132 Extensive
4 920-944 82-96 3.81-5.49 10-20 11-22 63-188 132-395 Extreme
5 <920 >96 > 5.49 <10 >22 >188 > 395 Catastrophic
data of Schwerdt and others (1979). Storm category and damage potential scale to tide rise time was then determined using provide a pragmatically useful addition to the equation (2). scale.
The Saffir/Simpsonscale assessed the The other issue centers about the fact
damage potential in terms of the wind speed that extreme events with much lower and peak storm tide. There is, in fact, sound intensities than hurricanes (e.g., tropical reasoning for doing so, since both are largely storms, which are here identified under the dependent on event central pressure. collective term 'storms") can potentially
result in as much or more erosion than many
The same is not true of the event hurricanes (see Table 2). An example is a forward speed because the three-dimensional storm which essentially stalls just offshore geometry of surrounding weather systems for days. Hence, Figure 15 has been and conditions affect steering currents. compiled which, based on event forward Hence, factors other than central pressure speed and peak storm tide elevation, can be have significant effect on the propagation of used to assess erosion damage potential a hurricane, whether the event is a hurricane or a storm
There are two additional issues to be Table 4 and Figure 15 are transformed considered. to British Imperial Units and given in the
Appendix.
One is that it may be difficult to
envision just what a volumetric erosion value CONCLUSIONS
means in terms of erosion damage for a
specific coastal locality, unless cross- Analyzed information for storms (e.g.,
sections representing pre-storm and post- Birkemeier and others, 1988; Kana and storm profiles are assembled. A horizontal Jones, 1988; Jones and Kana, 1988; Beumel recession value rather than a volumetric and Campbell, 1990; Ferriero, 1994) and erosion value is an alternative, but this was more recent hurricanes (e.g. Birkemeier and found to result in many more problematic others, 1991; Stauble and others, 1991; complexities than the volumetric approach Nelson, 1991) has increased the existing (Balsillie, 1985c, 1986). Hence, while sample size of Balsillie (1985c, 1986) for volumetric erosion values may not obviously field data quantifying beach and coast identify the damage potential, they can be erosion due to extreme event impact. This correlated to the Saffir/Simpson hurricane addition data allows for testing of a
25




Peak Storm Tide Elevation (m MSL) S 1.0i 1.5 2,0 2.6 3.0 3.5 4.0 4.5 6.0 5.5 90
50
. . . .I. . . -----70
60
so MINIMAL
46 . . . .
V~40
E a MODERATE
20. . .
30
4)
ie EXTENSIVE
.~ .
LU 10 (
15
a EXTREME
. . .I.
4 CATASTROPHIC
2
Rgure 15. Beach and coast erosion damage potential scale as a function of event forward speed at landaU and peak storm tide elevation. Erosion volumes are based on peak storm tide elevation classes of Table 4; even so, results apply to storm
events as wed as hurricanes.
refinement of quantifying relationships. lagtime behind a change in wave characteristics. Because of the bathymetric A most important aspect of being able lag-time, bathymetry can in turn impose to predict beach and coast erosion due to significant influential effects on the character storm and hurricane impact is the capability of littoral wave activity. Hence, in addition to assess profile geometry during and as a to erosive outcomes, it is the destructive result of impact. By so doing, coexisting potential of storm-generated wave impacts storm-generated wave activity propagating that also must be considered if a successful upon the storm tide surface can be assessed assessment methodology is to exist. for management and design purposes. The Determination of profile geometry is then a fact remains, regarding waves and their matter of modeling interactive littoral modifying influence on a mobile bathymetry, processes, that is, both force (e.g., water that any change in wave characteristics level rise and waves) and response (e.g., induces an alteration in bathymetry but at a profile modification) elements. A computer
26




model exists (Balsillie, 1984c, 1985c, REFERENCES
1 985d, 1986) in which a bulk onshore-offshore sediment transport Balsillie, J. H., 1979a, Appraisal of beach mechanism, in terms of bedform movement stability and construction setback:
has been developed (Balsillie, 1982a, 1982b, Florida Department of Natural 1984b, 1984c), which is dependent on Resources, draft report, 7 p.
littoral wave activity (Balsillie, 1983a, 1983b, 1983c, 1983d, 1984a, 1984b, 1979b, Multiple shore-breaking
1984c,1985b; Balsillie and Carter, 1984a, wave transformation program for a 1984b). It is the volumetric erosion calculator (MSBWTM-OFSONS-3):
methodology contained herein which allows Florida Department of Natural for the real-time calibration of the combined Resources, Division of Beaches and assessment of combined storm tide, storm Shores. wave impact, horizontal and vertical physiographic recession force and response 1982a, Offshore profile descripelements due to extreme event impact. In tion using the power curve fit, part 1: addition, there now appears to be enough explanation and a discussion: Florida information to make a statement about the Department of Natural Resources, return period erosion event. Least equivocal Beaches and Shores Technical and results given by equations (17) through (24) Design Memorandum No. 82-1-1, 23 will, hopefully, be refined by future work. In p. the meantime, however, they are valuable as a check in design applications. 1982b, Offshore profile descriptio n usi ng the powe r c urve, f it, pa rt 11:
In addition, applications of the standard Florida offshore profile
volumetric erosion methodology have been tables: Florida Department of Natural discussed, including the determination of Resources, Beaches and Shores post-storm beach and coast physiography, Technical and Design Memorandum encounter period and probability, and an No. 81-1-11, 70 p. erosion damage potential scale.
_______, 1 983a, Horizontal recession of
ACKNOWLEDGEMENTS the coast: the Walton-Sensabaugh
method for Hurricane Eloise of
Robert J. Hallermeier with Dewberry September 1975: Florida Department and Davis, Inc., Washington, D. C., identified of Natural Resources, Beaches and several storm erosion events not included in Shores Technical and Design earlier versions of this work, and reviewed Memorandum No. 83.1, 63 p. the manuscript. The review and comments of William A. Birkemeier, CERC, are gratefully 1983b, On the determination of
acknowledged. when waves break in shallow water:
Florida Department of Natural
An extensive and valuable review of Resources, Beaches and Shores the manuscript was conducted by the staff Technical and Design Memorandum of the Florida Geological Survey. The No. 83-3, 25 p.
contributions of Jon Arthur, Paulette Bond, Ken Campbell, Ed Lane, Jacqueline M. Lloyd, Deborah Mekeel, Frank Rupert, Thomas M. Scott, and Walter Schmidt are gratefully acknowledged.
27




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Sons, p. 145-168. Hugo on the South Carolina coast:
Journal of Coastal Research, Special
Issue No. 8, p. 129-1 62.
32




Trescott, D., 1983, No-Name Storm, June
17-18, 1982, post-disaster hazard mitigation plan, FEMA-664-DR-FL: Florida Department of Community
Affairs, 102 p.
U. S. Army, 1962, Hurricane Carla,
September 9-12, 1961: U. S. Army, Corps of Engineers, Galveston
District, Galveston, TX.
, 1976, Post disaster report:
Hurricane Eloise, 16-23 September, 1975: U. S. Army, Corps of Engineers, Mobile District, Mobile, AL,
89 p.
-_ 1979, Grande Isle and vicinity,
Louisiana, Phase 1: general design memorandum, beach erosion and hurricane protection: U. S. Army, Corps of Engineers, New Orleans
District.
, 1980, Hurricane Allen, 3-10
August, 1980: U. S. Army, Corps of Engineers, Galveston District,
Galveston, TX, 62 p.
, 1984, Shore Protection Manual,
Coastal Engineering Research Center,
Vicksburg, MI, 2 vols, 1272 p.
Wanstrath, J. J., 1978, An open-coast
mathematical storm surge model with coastal flooding for Louisiana: U. S.
Army EngineerWaterways Experiment Station, Miscellaneous Paper H-78-5,
132 p.
Zeevaert, L., 1983, Liquefaction of fine sand
due to wave action: Shore and
Beach, v. 51, no. 2, p. 32-36.
-_ 1984, Errata: liquefaction of
fine sand due to wave action: Shore
and Beach, v. 52, no. 1, p. 38.
33




APPENDED
Table 4 and Figure 15 of main text transformed to British Imperial Units of Measure
35




Amended Saffir/Simpson Hurricane Damage Potential Scale Peak
Central Wi storm Event Average Mainum
Cate- Tide Forward I Erosion Erosion Damage
gory (nhes) (mph) E i S d Time Volume Volume Potential
above (mph) (hr) (yds"M) (yd3/f)
MSL (ft) I I
> 28.94
1 74-95 4-5.5 31-55 2.5-4.5 1.2-3.3 2.5-7 Minimal
(>980)
2 28.50-28.91 96-110 5.5-8.5 18-31 4.5-7.5 3.3-10 7-21 Moderate
(965-979)
3 27.91-28.47 111-130 8.5-12.5 12-18 7.5-11 10-25 21-53 Extensive
(945-964)
4 27.17-28.88 131-155 12.5-18 6.5-12 11-21 25-75 53-158 Extreme
(920-944)
5 <27.17 >155 > 18 <6.5 > 21 > 75 > 158 Catastrophic
920)1111
4 Central pressure in parentheses are in millibars.
Beach and coast erosion damage potential scale as a function of event forward speed and peak storm tide elevation, both at landfall. Erosion volumes are based on peak storm tide elevation clams of above table; results, however, apply to storm events as
weE as hurricanes.
Peak Storm Tide Elevation (ft MSL)
2 4 6 8 10 12 14 16 I18 20
50
4s MINIMAL /
. .-.- ----. -.-.
40
. 35
E 3o MODERATE
*. . .
& 20
15 .
12 EXTENSIVE
u. 10
. . . .
W 6 EXTREME
4
3
2 CATASTROPHIC
37

PAGE 1

lIfo. -StateofRoridaDepartmentofEnvironmental Protection DavidB.Struhs,SecretaryDivisionofAdministrative and Technical ServicesRorida Geological Survey Tallahassee, Rorida1999ISSN1058..1391

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--..-CONTENTSPageABSTRACT 1 INTRODUCTION 1EXTREMEEVENTEROSION AND ITS RELATION TO THETYPEOFPRE-IMPACT COASTAL PHYSIOGRAPHY 2 DATA 3 ANALYTICAL RESULTS 4 The Event Longevity Parameter(ELP)........ 7 Average Erosion Quantity Above MeanSeaLevel and Probability Density Function(PDF)........................... 7 Average Erosion Quantity AbovethePeak Storm Tide Level and Probability Density Function(PDF)............................12 Design Erosion Quantities .......................................13 The Offshore Sink Efficiency Parameter(OSEP)........................14Return Period Volumetric Erosion Events 18 Post-Storm Recovery.........................................20APPLICATIONS..................................................21Post-5torm Beach and Coast Physiography ........................... 22 Encounter Period and Probability.................................23AnErosion Damage Potential Scale24CONCLUSIONS25ACKNOWLEDGEMENTS 27REFERENCES27APPENDIX 35 TABLES Table 1. Characteristicsofstorms and hurricanes used in this study. 5 Table 2.TYPEI erosion volume above mean sea level. 9 Table 3.TYPEI erosion volume above the combined peak stonn tide 15 Table4.Amended Saffir/Simpson Hurricane Damage Potential Scale25FIGURESFigure 1. Idealized pre-storm (solid lines) and eroded (dashed lines) profile scenariosforthethree basic typesofcoastal physiography 2 Figure 2. Relationship between the measuredTYPEI average erosion volume above meansealevel andtheevent longevity parameter 8 Figure 3. Exampleofwatersurfacehydrograph throughanidealized storm tide, and definitionofstorm tide rise time measure (after Balsillie,1986)11Figure4.Relationship between the storm tide rise time and event forward speed, where the relating coefficient,0.00175is in unitsofhours squared (after Balsillie,1986)11Figure 5. Typical examplesofdensity distributionsfordeterminationofthe slope q: relatingQeand e3P(eventI.D.s refertoTable 2). 12

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Figure6.Relationshipbetweentheeventlongevity parameter and distribution coefficients forTYPEI average volumetric erosion aboveMSL..............13 Figure7.RelationshipbetweenthemeasuredTYPEI average net erosion quantity above peak combined storm tide andtheeventlongevity parameter. .13Figure8.Relationshipbetweentheeventlongevity parameter and distribution coefficients fortheTYPEI average erosion volume abovethepeak combined storm tide. .14Figure 9. Tesselated relationship relating nearshore bed slopetotheELPcoefficient,f.16 Figure10.Comparisonbetween a typical Florida nearshore profile and typical Cancun, Mexico nearshore profile. 17 Figure11.Relationshipbetweentheinitial nearshore bed slope,tanai'andthepower curve fitshapecoefficient,as................................18 Figure12.Relationshipbetweenexceedenceprobability, P, return period, Te ,and averageTYPEI erosion volume aboveMSL.19 Figure13.Example of application for determining two-dimensional post-stonn physiography using volumetricdata,and designwaveconditions23Figure14.Nomograph for relatingeventreturn period,encounterperiod, and encounter probability24Figure15.Beach andcoasterosion damage potential scaleasa function ofeventforwardspeedatlandfallandpeakstonntide elevation. Erosion volumes arebasedon peak storm tide elevationclassesof Table4;evenso,results applytostormeventsaswellashurricanes.. .26ii

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VOLUMETRIC BEACHANDCOAST EROSION DUETOSTORMANDHURRICANE IMPACTbyJames H. Balsillie,P.G.No.167ABSTRACTPriortotheinitial work oftheauthor duringtheearly1980s,methodstopredict nearshore, beach, andcoastalerosion duetostorm and hurricane impactwerebasedon theoretical applicationsandestimation. However, with the acquisition of actual fielddataquantifying storm and hurricane erosiveimpacts,itbecameclearthat,inadditiontothecombined storm tide (commonly termedthestorm surge),thelength of timethataneventhastoerodethebeach andcoastis a highly significant factorthatcould be quantified (i.e., giventwoeventseachproducing identical storm tide hydrographs,theslower movingeventwill resultingreater beachandcoasterosion). Hence,basedon actual field data,the .".",IDntIevitr"...".,..(B.P} wasintroduced (Balsil\ie.1985c.1986)which incorporates both the combined storm tide and its rise time,thelatter of which canbecomputed fromtheeventforward speed. Sincethepublished work ofthemids,additional fielddata(a three-fold increase) havebecomeavailabletofurther verifytheElPapproach, andtointroducenewdevelopments.Ithas, forinstance,becomeapparentthatinadditiontothedesign peak storm tide elevation,thedesign erosioneventrequires attentioninmanycoastalengineering design applicationsiftheyaretobesuccessful.Infact,aside from design soffit elevations which are determined fromthepeak combined storm tide elevationandsuperimposed storm waves propagating uponthestorm tidesurface,itisthedesign erosioneventthatquantifiesthefinal expression ofallother impacts. Hence, probability density functions are defined for both erosion above meansealevel and peak storm tide level.Inaddition,ithas been foundthatthepre-impact offshore bed slopecanbe usedtoindicate the "efficiency or "receptiveness" oftheoffshoresedimentsinktoacceptsanderoded fromthebeach and/orcoast(termedthe off6hote.mkefIicieney"..".,.,{OSEP}. Incorporation ofthenewdata,and quantification ofthetwoadditional developments and an amended Saffk/Simpson hurricane damage potentialscaleconstitutethesubjectmatterof this paper.INTRODucnONAlthough,intheseasonal and long-term sense, beaches areconstantlybeing remoldedbywaVes, tides andwinds,themostdramaticchangesoccuras the resultofextremeevent(i.e.,short-termimpactsfromstormsand hurricanes). The considerationofshort-term, seasonal, and long-termimpacts(i.e.,force elements such asastronomicaltides,stormtides,waves,etc.)andtheresulting outcomes(i.e.,response elements such as beach andcoasterosion, longshore bar formation, andstructuraldamage) are mattersofstandard1coastal engineering practice. In this paper, short-termimpactsdefine the subjectofinterest. Formanyyears,onlythe peak combinedstormtide (alsocommonlytermedthestormsurge)wasemployed in determining and assessing nearshore, beach, and coastal engineering design solutions. Considerationofthestormtide alone, however, doesnotprovide a realistic measureofimpactpotential. For instance, giventwoextremeeventswithidenticalstormtides, theslowermovingeventwillresult in greater beach and coast erosion.

PAGE 5

-----------....----_ A.. -....--.....::::.:::::=.=:.:: recession isimportantin determining sitingofcoastal developmentactivities.Itis,however,the maximumverticalrecession produced during eventimpact(Balsillie,1984c,in manuscriptlwhichis neededtoassess structural design constraints(e.g.,pilingtippenetration,"firstfloor"soffitelevations,etc.)based on hydraulicforces suchasshore.breakingwaveimpactpressures (Balsillie,1985b).Vertical recession should includeeffectsduetoboth scour, and sediment liquefaction (Zeevaert,1983,1984).Itisalsoimportanttobear in mindthedifferencesbetweenthe nearshore, beach (or shore), and coastal subzonesofthelittoralenvironment(Figure 1). Under normal hydraulic littoral conditions, processes are clearlydifferentwithineach subzone (discussed in detail inlatersections).Whetherornotthestormrises abovethebeach,orif not, has thelongevitytoerode-------------"..-FLOODED ..--The peakstormtide elevation plussuperimposedstormwaveactivitypropagating upon thestormtide surfaceisuseful in determining deck, floor,etc.(termed II soffit")elevations, providedthatanyshiftorerosionofthe bedisknown,since increasedwaterdepth results in higherwaves.Allotherdesign solutions are more nearly relatedtoerosion responses, such as piletippenetration, seawall and bulkhead panelembedmentelevations,etc.In addition, since storms cause nearshore erosion and bedshiftsin responsetolongshore barformationaccompanying beach andcoasterosion, resulting increasedwaterdepths cansignificantlyaffectbothhorizontal andverticalwaveimpactpotentialswhichrequire consideration in design solutions and assessments. The needformethodologytopredict beach andcoasterosion duetotheimpactofstormsand hurricanes has been an issueofongoing and increasing concern. Moreover,itis onewhich,forthemajorityofthehistoryofthedisciplineofcoastal science, has eludedsatisfactoryquantifyingsolutions. Thelackofmethodologyisnotsurprising consideringthecomplexities involved inquantifyinglittoral processes. Ultimately,however,onlythroughtheacquisitionoffield datawillconfidentsuccessful solutions be realized. This paper provides a significant update (in termsofthenumberofhurricane andstormevents)topreviousworkbytheauthor(Balsillie,1985c,1986).Figure 1. Idealized pre-storm (solid lines) and eroded (dashed lines) profile scenariosforthethreebasictypesofcoastal physiography (STL=peak stormtide level, MSL=mean sea level).NON-FLOODED\C \,":'".. ....... .........._-.....----------...EXTREMEEVENTEROSIONAND ns RELAnONTOTHE TYPE OFPRE-IMPACT COASTALPHYSIOGRAPHYIn this paper erosionisconsideredtobetheoveralltermencompassing horizontal and vertical recession componentsofbeach andcoastresponse duetostormand/or hurricane impact. Depending on thetypeofcoastal physiography, these components can result in quitedifferentoutcomes. Horizontal2

PAGE 6

_. .... the beach and begintoerode the coast, and post-storm beach recovery, are important issueswhichshallbeaddressed later.Consideringinitialcoastalphysiography and responses duetoextreme event impact, three general types of geomorphic scenariosaresuggested: non-flooded, flooded, and breached profiles (Figure 1). In assessing these profile types, several assumptions are made: 1) the beach and coast are composedofrelatively unconsolidated sand-sized sediment, 2)onshore-offshoresedimenttransportprocesses prevail and alongshore processes are assumed static, and 3)shallowwater"hydraulic processes are approximately constantfora givenwaterdepth, noting that a change inwaveconditions (principally shore-breaking and broken waves)willcause ashiftin bathymetry which, in turn,willaffectthe waves. Where the coast is higher than the peak storm tide and iswideenoughnottobebreached(i.e.,the non-flooded' condition), only the offshore sink" is availablefordepositionofsand erodedfromthe beach and coast. A major contributing erosional mechanism is gravitational mass wasting, because only a relativelyfewwaves are requiredtocauseanunstable, steep sand facetocollapse. As the sediment escarpment increases in height, increasingly more sediment is potentially availableforintroductiontothe prevailing littoral hydraulic environmentforredistribution. The barrier islandsofthe lower Florida Gulf Coast may in many placesbeinundatedby1to2 metersofwaterduetoimpactofa 1 OO-year return period peak combined storm tide event (see Table 1fordefinition). This doesnotinclude the added hydraulic elevation duetoshore-breaking waveactivitywhichpropagates upon the storm tide surface. Therefore, the contributionofgravitational mass wasting, importanttothe non-flooded scenario, may notbeofspecial 3 consequenceforrelatively low-lying barriers.Itdoes, however, introduce the aspectofanadditional "sink"foreroded sand duetooverwash processes (Leatherman,1976, 1977,1979,1981;Leatherman and others,1977;Schwartz, 1975). Combination of the precedingtwophysiographic-hydrographic scenarios leadstothe breached profile condition illustrated in inset B of Figure 1 in which the overwash sink again occurs.Itis also apparent from the literaturethatthesuccessofgrain-by-grainonshore-offshoresedimenttransportmechanics under littoral waveactivityasyetremainstoreach the statusofsatisfactory quantification (Balsillie,1984c,1986).That existing attemptsatquantification maybefraughtwithinsensitivities isfurtherexaggeratedwhendealingwitha rising and falling storm tide andwithstorm-generated littoralwaveactivity. Hence, pursuitofalternative approaches is desirable. One such approach is investigationoffield data quantifying actual storm and hurricane impact upon our shores.DATAThis subject has received much attention in previouswork,dating backforabout 3 decades. Perhaps the most compellingworkisthatof Caldwell(1959)justpreceding the infamousU.S.east coastAshWednesdaystormof1962(Bretschneider,1964;Harrison and Wagner,1964;and O'Brien and Johnson,1963),witha resurgenceofinterest occurringwiththe worksofEdelman (1968,1972).There have, in addition, been many studies reported in the literature providing descriptive accountsofthe erosive powerofextreme occurrences. However, until thisworkwasoriginally published (Balsillie,1985c,1986),there were insufficient types and quantitiesoffield data on whichtoquantify beach and coast erosion duetostorm and hurricane impacts. Thisworkhas increased the sizeofthe field data base by afactorofthree.

PAGE 7

Fourteen erosion eventsfor11hurricanes, and22erosion eventsfor20storms (Table 1) provides the largest field data compilation amassedtodateforthe purposeofquantifyingbeach andcoasterosion duetoextreme event impact.5evenevents (H4,517,518,H7,H8, H9 andH10)wereassessed through field data collectionofthe5tateofFlorida, DepartmentofNatural Resources (DNR,nowthe DepartmentofEnvironmental Protection,DEP),DivisionofBeaches and Shores(nowthe BureauofBeaches and Coastal Systems); field data collection techniques have been discussed elsewhere (Sensabaugh and others,1977;Balsillie,1985a,1985c,1985e,1986,1988).Thirteen events (S2 throughS11,514,515andS16)are the direct resultsoftheeffortsoftheCoastal Engineering Research Center (CERC); field data collection techniques are discussed by Birkemeier(1979);Birkemeier and others(1988).A more recenteventhas been reportedbyKana and Jones(1988)and Jones and Kana(1988).Hurricane Hugo (H11) information is presentedbyBirkemeier and others(1991)and 5tauble and others (1991). A tropicalstorm(520)wasreported by Beumel and Campbell(1990).Ferriero(1994)reported erosionfroma Portuguesestormeventthatoccurred in1989.Remaining events arefromindependent studies (references are listed in Table 1)thatwerepreviously analyzedbytheauthor(Balsillie,1985c,1986).Ofthe aspects concerning the data,itisimportanttonoteformanagement purposesthatthere aretwotypesoferosion (Balsillie,1985a,1985e).One is the measurewhichrepresents those sampled profileswhereerosiononlyoccurred (TYPE I erosionmeasure). Theother(TYPEII)isthatwhichincludes all profiles regardlessofgainorloss. TYPEIIerosion is important in assessing actual beach and coast economic losses. For design applications, TYPE I erosion is thebettermeasure, sincefordesignworkweare interested in locations4only where erosion has occurred. Hence, in this paper, TYPE I erosion volumes are used. Using the datafromevents H4, H5,517,518,H7, and H8, Balsillie(1985e,p.33-34)foundthat, on the average, TYPEIIerosion is73%ofTYPE I erosion(n=13,sampledforover200profile pairs, r=0.9515),Where possible, profiles were selectedtorepresentknownextreme eventimpactmagnitudes. For instance,onlyDNR(nowDEP)ranges R-33 through R-125 in Walton County, FloridawereselectedforHurricane Eloise, sinceitwasthis areathatcoincidedwiththefirstquadrantofEloise in termsofthe combinedstormtide height (see Balsillie,1983a).In other cases, one could only considerwhatpreand post-storm profile data were available; an example is the Ash Wednesdaystormof1962.ANAL YTleALRESUL7STworeferencewaterlevels havecommonlybeen used, abovewhichvolumetric erosion is determined: 1. the peakstormtide stillwaterlevel (5TL), and 2. mean sea level (MSL). Thefirstwaterlevel (STL)isconsidered here becauseithas been used in otherwork.Itisparticularly accuratefornon-flooded profiles since erosion volumes represent single process losses above the referencewaterlevel duetogravitational mass wasting, and include noneofthe complexities occurringbelowthe reference level duetointeractivehydraulic and sediment transport processes.Itshouldbeclear, however,thatthis referencewaterlevel has no applicability in determining volumetric erosionforbreachedorflooded profiles and, therefore,itsuse results in only partial success in volumetric erosion determination. The mean sea level referencewill,on the other hand, provideforvolumetric erosion determinationforall three

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Table 1. Characteristics ofstormsandhurricanes usedinthis study.PeakEvent Stonn Stonn Forward Tide Event and Location Tide1mSpeedRiseInfonnation Sources I.D.MSL) (krnlhr) Time lhr$) HlHurricane AUdrey, June3.6619.011.7Morganandothers, 19581957,Louisiana Gulf Coast Hurricane Carla, Sep.Reidand others.977;Neumann H22.306.3S1.0andothers, 1981; Schwerdtand1961, Texas Gulf Coast others. 1979;U.S.Army.1962Ash Wednesday Storm, Bretschneider,1964; Harrison andS1Mar. 1972,U.S.East 3.0S---28.0'Wagner, 1964; O'Brien and Coast Johnson,1963S2 Nov.1962Storm, U.S.1.50---7.S'East Coast S3 6 Nov.1973Storm,U.S.1.40---18.S Birt.emeier and others,1988East CoastS413Jan.1964Storm, U.S.1.S0---12.4'East Coast Hurricane Betsy, Sep. Wanstrath, 1978; Neumann and H31965,Mississippi Gulf2.2616.018.0'others, 1981; Schwerdt and Coast others, 1979;U.S.Army1979SS16Sep.1967Storm,U.S.1.40".12.4'East Coast S612Mar.1968Storm,U.S .. 1.20--6'" East Coast S7 12 Nov.1968Storm,U.S.1.60---15.0'East Coast582 Feb.1970Storm,U.S.1.10--6'" East Coast5917 Dec.1970Storm,U.S.1.6012.4' Birkemeier and others, 1988._-East Coast S10 19 Feb.1972Storm,U.S.East Coast S10a New Jersey1.80---6.1'SlObNew York 2.00---6.,.511 17-22 Mar.1973Storm. U.S.East CoastS11a New Yort. 1.40...12.2'S11b New Jersey1.30---12.2'S12 NovDec.1973Events, 3.S7------Erchinger,1974German North Sea Coast51323 Sep.1974Storm,U.S.1.45---9.0Kana,1977East Coast Hurricane Eloise, Sep.BalsilJie.1983a; Burdin, 1977; H4 1975, N.W. Florida Gulf3.1542.65.0'Chiu, 1977;U.S. Army, 1976Coast5

PAGE 9

Table 1. Characteristicsofstormsand hurricanes used inthisstudy(cont),, Peak Event Storm Storm Forward Tide Event and Loc:ation Tide(mSpeedRiseInfonnation SourcesI.D.MSLI(kmlhr)Time(hrs)51414Oct.1977Storm,U.S.1.80 17.0 East Coast---51519 Dec.1977Storm,U.S.1.4035.0 Birkemeier and others, 1988 East Coast---5166 Feb. 1978 Storm,U.S.1.70_..19.9'East Coast Balsillie and Clark, 1979; Parker H5 Hurricane Frederic, Sep.3.6624.111.0'and others, 1981; Penland and1979Alabama Gulf Coast others,1980;Schramm and others,1980H6 Hurricane Allen, Aug.2.7432.26.0'Dahl and others,1983;U.S.1980,Texas Gulf CoastArmy,1980No Name Storm, 17517June1982,LowerFlorida1.6840.28.0'Galvin, 1983; Trescott,1983Gulf Coast H7 Hurricane Alicia, Aug.3.8612.018.0'Dupre, 1985; Garcia and Flor,1983,Texas Gulf Coast1984Thanksgiving Holiday518Storm,21-24Nov. 1984,1.83...21.0'Balsillie, 1985a Florida East Coast H8 Hurricane Elena,Sep.1985,Florida Gulf Coast H8a Pinellas County1.37 14.520.0'Balsillie, 1985e H8b Franklin County2.3216.113.4H8c Gulf County2.1016.113.4Had Escambia County2.2925.78.0'H9 Hurricane Kate, Nov. 1985,2.609.2Balsillie,1986N. W. Florida Gulf Coast...S19 1 Jan.1987Storm, U.S.1.50...12.0 Kana and Jones, 1988; Jones and East Coast Kana,1988H10 Hurricane Gilbert, Sep. 3.81.--9.5Unpublished Florida Departmentof1988,Cancun, Mexico Natural Resources data. S20 Feb.1989Storm,3.5345.0Ferreira,1994Portuguese Atlantic Coast..-Hurricane Hugo, Sep. Birkemeier and others, 1991;Hll3.8032.25.0Nelson, 1991; Stauble and others,1989.U.S.East Coast 1991 Tropical Storm Marco. Oct 52110-11,1990.Lower1.1316.19.0Beumel and Campbell,1990Florida Gulf Coast Notes: Peak storm tide is the combined peak storm tide level above NGVD including the astronomical tide and dynamicwavesetup;Peakstorm tideforevent S 12 was measured from the local datum; indicates the measure storm tide rise time, all otherarepredicted using equation(21.6

PAGE 10

physiographic scenariosofFigure 1 (except, perhaps,forextremecases suchasinletformationwhereerosion occurs below MSL). For breachedorflooded profiles, overwash is eliminatedfromerosion volumes, sothatvolumetric erosionfornon-flooded profiles (where only theseawardsinkisavailablefordeposition) andforflooded and breached (where the seaward and upland sinks are available, but eliminated) profiles are comparable. Eliminationofupland and seaward sinks is desirable since, on the average, the sum shouldbeequivalenttotheamounteroded. Whileatthe seawardextremityofthepost-stormprofile, some materialoftheseawardsink (also including some degreeofpost-stormbeach recovery)mayreside aboveMSL(determinedtobeabout6%oftheseawardsinkvolumefrom245analyzed profile pairsfromBalsillie,1985c),the analyticalmethodisfairlyunbiased sinceitis applied equallytoall profiles investigated. For erosionvolumedeterminations and applications,anydatumotherthan MSL(i.e.,meanlowerlowwater(MLLW), meanlowwater(MLW), mean highwater(MHW), and mean higher highwater(MHHL)) isnottobeemployed.TheirdeparturefromMSL isnotconstantfromlocalitytolocality (Balsillie and others,1998).Hence, volumeswillnotbecomparable.Itshouldbenotedthatvolumetric changeswereinvestigatedwhichincluded offshore profile data. The results,however,introducedsignificantscatter.Itistobeunderstoodthatoffshoreprofiling requires considerable time and resources (Sensabaugh and others,1977;Balsillie,1985a,1985e).Post-storm field measurements aremostusefulwhenthe responsetimeisswift,sinceanydelay increases the possibilityofpost-storm beach recoverywhichcanbefaster than previously thought. Based on the preliminary analysis alludedtoabove, the inclusionofoffshore profilebathymetrydoesnotyetappeartobejustifiable.7There have been a numberofextremeeventerosion studies inwhichvolumetric erosion calculations are based on single averagedorcomposite pre-storm and post-storm profiles, even though multiple profiles were measured. In this study,however,preand post-storm profiles are surveyedfromprecisely located coastal monuments, along azimuths establishedforeach monument. Hence, volumetric changes have been calculatedforeach profile pair, and resulting data have been then statisticallytreatedtoobtainpointestimators and probability densityfunctions(PDFs). The Event Longevity Parameter(EU')AverageErosionQuantity Above MeanSeaLeveland Probablity DensityFunt:lion (PDF)The most completesetoffield data amassedtodate isnowavailabletoquantifybeach and coast response duetoextremeeventimpact. However, such data have little valueifthere doesnotexista methodologyforpredicting future occurrencesoferosion. Infact,until recently, there has been no consolidated methodologybywhichtorealize such prognostication. Recognizingthattheamountoferosion issignificantlydependent upon the lengthoftimethatan extreme eventaffectsthe beach andcoast(Hayes,1967;Hayes and Boothroyd,1969),theauthor(Balsillie,1985c,1986)developed the eventlongevityparameter (ELP). In termsofthe average TYPE I erosionquantityabove MSL,Qe avg' the relationship is given by: Q.IIIf!1 =1622-1(g 1/2 I, S2t/5 (1)wheregisthe accelerationofgravity, Sisthe combined peakstormtide elevation (see noteofTable 1fordefinition), and t r is thestormtide rise time. The relationship and data onwhichequation (1) is based are plotted in Figure 2 and listed in Table2.The data

PAGE 11

I/?b 300000 250000 (g 4/5Q = 16221 1/2t 52) e avg r0.9857r0.9867 0.9833n14223650000 Hurricanes StormsTotal180160140120100806040200 ....... ......-.........-.... ...... _--......... __ .....................-...................-----' oQeavg(m3/m)The roleofpre-stormsetupas an where gisin unitsof km/hrl (i.e.,g=9.8m/s2=127008 km/hrl), vfis in unitsofkrn/hr, and the coefficient0.00175isin unitsof hrl. introduced,whentryingtointerpretwhenthestormtide ends. Thetotalvalueoft rforastormproduced tide, maintained over multiple astronomical tides, is determinedbyadding the rise time componentsofeach additional cycle. For analytical purposes, t r is an excellent quantitative measureofevent longevity. However,forapplied predictive purposes,foran approaching event, the measure isnotuseful becauseitis available onlyafterevent impact. However,itwasfound (Balsillie,1985c)thatthestormtide risetimeand eventforwardspeed,vf(measuredatthe pointwhenthe radiusofmaximum winds, or a facsimilethereofforextratropical storms, makes landfall), are related (Figure 4) according to:(2)Ir=0.00175gv,Thestormtide rise time, t r is the finalcontinuoussurgeofthestormtide representingimpactofthe eventatlandfall. In some cases, pre-stormsetdown(e.g.,particularlyforalongshore hurricanesnotconsidered here) and pre-stormsetupcan occur. These shouldbeeliminated in determining the valueoft r ,whosegraphical determination is illustrated in Figure3.sample onwhichequation (1) is founded is threetimeslarger thanthatavailabletoBalsillie(1985c,1986)in the originaldevelopmentofthe relationship,whichallowedforrefinementofthe dimensionlessconstant.Thecoefficientofequation (1) is,however,but2.5%smallerthanthatreported in the earlierwork.Valuesofthestormtide rise time arefrommeasuredstormtide hydrographs (references are given in Table 1). Such records arenotalwayssimpletointerpret, depending on gauge siting, distanceofgaugesfromevent landfall, and relationshipofthestormgenerated tide and the astronomical tidal cycle. Considerationofthe combinedstormtide rise time rather than thetotaltide history does, however, eliminate uncertainty,whichmaybe8

PAGE 12

Table2.TYPEI erosion volume above meansealevelAv.... ge Maximum event erosion &oslonLongevity Elapsed ProfileJ.D.Event and Location Volume Volume Parameter cp Time n r. Type (m3/m) (m3/m) (m3/ml(months) Hunicane Audrey,H1Jun.1957,Louisiana 51.789.06 99,4615.550.844929-48 F Gulf Coast Hurricane Carla, Sep. H21961,Texas Gulf89.8---8153,710---...5.3 NF,F CoastAshWednesdayS1 Stonn, Mr.1962,U.93.0..-5149,327 .-..-60-96NFS. East Coast S2 Nov.1962Storm, U. 12.928.93116,7241.800.97210.36NFS. East Coast S3 6 Nov.1963Storm.20.547.32830,9702.950.96340.60NFU.S.East CoastS412Jan.1964Storm,25.056.92125.0373.550.97030.50NF,U. S. East Coast MS Hurricane Betsy, Sap. H31965,Mississippi Gulf46.599.0964,9126.170.99394 F,B Coast S5 16 Sap.1967Storm,16.643.61822.4202.720.96370.16NFU. S. East Coast S612Mar.1968Storm,9.724.9189,9191.550.97870.16NFU. S. East Coast S7 12 Nov.1968Storm,26.255.84132,2853.480.96100.72NF,U. S. East Coast MS S8 2 Feb.1970Storm, U. 1 1.1 19.1 298,6301.190.94040.52NFS.East Coast S9 17 Dec.1970Storm, 17.743.53727,7242.710.99060.41NFU. S. East Coast S10 19 Feb.1972Storm, U. S. East Coast S10aNewJersey9.518.83418,9771.170.95720.76NFSlObNewYork.20.241.72322,4622.600.96300.82NFS1117Mar.1973Storm, U.S.East Coast S11aNew York. 23.652.91622,1023.300.89230.69NF, MS S11bNewJersey 10.325.31719.6301.580.97680.66NF, MS Nov.Dec.1973Event, S12 German North Sea200.0... ...---_.. .. ---NFCoast S1323Sep.1974Storm, 12.0...1018,328... --0.07NFU. S. East Coast Hurricane Eloise, Sep.H41975,N.W. Florida20.050.76239,6283.160.973524NFGulf Coast9 .----_._.

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Table2.TYPEI erosion volume above meansealevel (cont ).. Ave,.ge Maximum Event1.0.Event and Location Erosion &O.ionLongevity Elapsed Profile n Time Volume Volume Parameter Q) r.Type(m3/m) (m3/m) (m3/m) (months)S1414Oct.1977Storm,18.534.82243,0852.170.9710U.S.East Coast0.23NFS1519 Dec.1978Storm,11.637.91742,9792.360.9800U.S.East Coast3.25NFS166 Feb.1978Storm, U.11.637.91742,9792.360.98003.25NFS.East Coast Hurricane Frederic, Sep. H51979,Alabama Gulf52.0121.13294,6717.550.97386 F,B Coast H6 Hurricane Allen, Aug.28.0...336,682---30NF,B1980,Texas Gulf Coast-..No Name Storm,17-18S17Jun.1982,Lower14.025.824 21.111 1.610.99173NFFlorida Gulf Coast H7 Hurricane Alicia, Aug.92.4...1152,25936NF1983,Texas Gulf Coast.,....Thanksgiving HolidayS18Storm,21Nov.27.070.012752,3884.300.90773-20NF1984,Florida East Coast H8 Hurricane Elena, Sep.1985,Florida Gulf Coast .H8aPinellas County21.048.344 31,704 3.010.9622130NFH8bFranklin County40.075.435 54,456 4.700.958549NFH8cGulf County24.044.15445,5792.750.975313-21NFH8dEscambia County19.038.311234,6532.390.987510NFHurricane Kate, Nov. H91985,N. W. Florida22.051.21847,4813.190.96172 F,NF Gulf CoastS191 Jan.1987Storm, U.19.4---425,669...0.3NFS.East Coast---Feb.1989Storm,S20Portuguese Atlantic164.0341.04276,390.,.----.-.,.CoastHl0Hurricane Gilbert, Sep.144.7297.0889,78218.520.984260NF1986,Cancun, Mexico231,462-Hll Hurricane Hugo, Sep.28.052.51953,5013.980.96914NF1989,U.S.East Coast Tropical Storm Marco, S21 Oct. 10-11, 1990,3.911.4289,3170.570.97551NFLowerFlorida Gulf Coast Notes: Elapsed timeisthe timebetweenpreand post-storm surveys; Profile types are: F :: Flooded, B :: Breached,NF :: Nonf1ooded, MS :: Multiple Storms; adjusted valuetoaccountforincreased offshore sediment sink efficiency, seetextfordiscussion; data sources are listed in Table 1.10

PAGE 14

60,.II I _1,-': I I____ ....J.... ...Setup., tr 0.00175 !f thatpre-storm setupisananomalous feature, the above further substantiatesthatitshouldbedeletedfromconsideration in erosion prediction.ItistobenotedthattheELPcontains both the peak storm tide,S,and thestormtide rise time, t r .Itis the introductionofthe latterwhichprompted the nameeventlongevity parsmeter. Utilizing stepwise regression (Krumbein and Graybill,1965;Balsillie, in press; Balsillie and Tanner, in press),ithas been determinedthat5 results in a relative net contributioninpredicting0e av.g of76%,and t r provides a net relative contributionof24%.Even so, both are required in ordertoobtain the successofn=17r=0.9278Normal P,Storm Tidal Conditions 7 JoB 2o2080100 ElellaUonAbow MSL 3(mJo o102030 040 50Vf(kmlhr)Figure4.Relationship betweenthestorm tide rise time and event forward speed, where the relating coefficient,0.00175isinunits of hours squared (after Balsillie, 1986).-1 ....... Time (houu) Aigure3.Example ofwatersurface hydrograph through an idealized storm tide, and definition of storm tide rise time measure (after Balsillie, 1986).erosive agent deserves additional comment.Ifthe general onshore physiographic scenario canbedescribedasa beachthatisbacked by a coast comprisedofa duneorbluff(see Figure 1forgraphicaldefinition), then the elevation relativetoMSLwhichidentifies where thecoastbegins(i.e.,thebeach-coastinflectionpoint,ornickpoint), becomes animportantmeasure.Thatis,ifthe storm tideislessthanthebeach-coast nickpoint elevation, then more timewillberequiredtoerode the beach before thecoastisaffected, relativetothe case(hrs) 40 where the storm tideishigherthanthebeach-coast nickpoint elevation, sothatboththebeach and coastwillbeaffectedwithintime constraintsofthe event.Experiencewithidentificationofthe beach-coast intersectionforFlorida beaches(i.e.,thoseforbeaches preceding events listed in Table 1), tellsusthatitisthelatterscenariowhichusually defines the design erosion condition. Current examplesofaverage nickpoint elevations are+2.19mMSLforFlorida's upper East Coast (St. Johns County),+2.25m MSLforthelowerGulf Coast (Charlotte County), and+2.1 m MSLforthe northwestern panhandle Gulf Coast (Walton County).Itissignificantthatofthe eventsofTable 1 and those graphically reported by Harris (1963), none resulted in a pre-storm setup in excessofabout+1.5m MSL, well below the beach-coast nickpoint elevationforFlorida. Hence, in combinationwiththe observation11

PAGE 15

equation (1) evident in Figure 2.0.50.7Event501500.1 JoB 100Qe (m,",) 592.71$12.3602.15$150S61.550SlOa1.17There are29events that provide information on which to investigateanerosional probability density function (PDF). From 6 to 127 profiles represent eachofthe events (Table 2), and result in the following equation: in which0eisthe volumetric coastal erosionquantityoccurringabovemeansealevelcorrespondingtothe erosion probability,P,whichis the probabilityoferosion less than or equaltothatstated, and f isa relating coefficient, Valuesof I (examples are plotted in Figure 5,resultsandcorrelationcoefficients are listed in Table 2)areplotted against theELPin Figure 6, showing remarkableagreement.Therelatingcoefficient f becomes 12344-1 ,Correlationcoefficientsassociatedwith I areall significantly large. Notethatifweweretoconsider, say, median and larger erosion values in thePDFs(see Figure 5), rather than all values available, correlation coefficients wouldbeeven larger.Average ErosionOuantityAbove theFigure 7, surfaces: PeakStormTideLevel and ProbabBityDensity Function (PDF) =3299-1(g1(2IT$2)4/5(4)The precedinghasdealtwithvolumetric erosion occurring above mean sea level. Whileithasbeennotedthatconsiderationoferosion above the peak storm tide elevation has no applicabilityforflooded or breached profiles, such a consideration does have validityfornon-flooded profiles.Basedonavailable data listed in Table 3, the following relationship based on24events,illustrated in whereA'eavgisthe TYPE I average erosion quantity occurring above the peak storm tide level. Using data from22events (Table 3) aPDFmaybeproposed according to:(5)12

PAGE 16

25r-----------------------,2015105 Hurricanes .Stonns Total110.9803 18 0.593529 0.9603..... ...... ......................_......I._...Io ..... __-...I o50000 100000150000 200000 250000 415 (g1/2tr52)Figure6. Relationship betweentheevent longevity,.rameter and distribution coefficients forTYPE I average volumetric erosion aboveMSL.150000 415 Q'=3105. 1(g1/2t52)__ eavgrr=0.8965n=24100,...-------------------...... 8060 Qeavg40 Hurricanes 2: ... o50000 100000 415 (g1/2tr52)Figure7. ReI8tionship between the measuNd TYPEI averageneterosionquantity above peak combined storm tidelevelandtheevent longevity parameter.wherethe relatingcoefficientffromFigure is23630".Itis evidentfromresults presented in Figure8,thatthe correlationbetweenvariables issignificantlyless than thosestatisticalassessmentsforanalyses presented in Figures2,6,and 7. Even so,theprobabilitythata random sampleofthis size could result in sample correlations so large, isverysmall. relativetoMSL and the peakstormtide elevations,wecan broadenourquantitativeexpectations.Weknowthatforengineering design purposes, using TYPE I erosion volumes, an average measure isnotresponsible. For engineering design purposesitisalwaysprudenttoconsider some upper measureofa destructive force,orresponse element. A highly useful measurefromsubstitutionofequations (1), (3),(4), and (5),wherePDFlinearity prevails, is given by: inwhich0eand0'e are erosion volumesfor Design Erosion Ouantities Nowthatwehave establishedsuccessfulrelationshipsthatquantitativelypredictaverage erosion volumesforevents0'= --'=0.1314e3 P,o (6)13

PAGE 17

forthe TYPE I erosion volume aboveMSL,and:forthe TYPE I erosion volume above the combined peak storm tide level. Both equations result in erosion volumes closetoa specified exceedence probability P above MSL and peak storm tide, respectively. Hence, the TYPE I median erosion volume(i.e.,P=0.5)isabout61%less than the TYPE I average erosion volume(forthe average erosion volume P=2/3),the third quartile TYPE I erosion volume(i.e.,P=0.75)is130%greater than the average TYPE I erosion volume,etc.Itistobenotedthatcoefficientsofequations (7) and (8) precisely agreewithfittedcoefficients describing the graphically estimated maximum erosion quantitiesofTables 2 and 3.The 0IIsh0Te Sink EfficiencyParameter (OSEP)Theformofthe event longevity parameter has invoked some controversy. While the combined peak storm tide height and storm tide rise time components have generally beenwellreceived, the appearanceofthe accelerationofgravity and the dimensionless proportionality constant have not.twice(i.e.,2.1)the average erosion volume.Ifone compares erosion quantities above the combined storm tidetothose above mean sea level,itisapparentthatabout half the eroded sand volume originatesfromabove the peak storm tide level(50%ifone compares coefficientsfromequations(1) and(4), and (3) and (5), and55%fromthe data). This should notbesurprisingfroma geomorphic viewpoint, consideringthatour beaches and coasts have certain constraining dimensions physiographically.Itis recognized that the efficiencyofgravitational accelerationisnot only greaterforsteeper slopes when dealingwithsand transport,but(7)(8)Notingthat pre4storm profiles are seldom measuredjustpriortostorm or hurricane impact, some physiographic deviationmightbereasonabletolevyon aPDFin assessing a design maximum erosion volume. This and purely random, anomalously high erosion volumes suggest that, perhaps, a probability Pofbetween0.9and0.95wouldnotseem inordinatetoapply. Using a valueof0.925and coefficientsfromequations (1) and (4), the applicationofequation (6) yields thefollowingdesign relationships:14

PAGE 18

Table3.TYPE I erosion volume above combined peak storm tideAverage Muimum EventI.D.Eventand Location&osion&osionLongevity nVolumeVolumeParameter >r.(m3/m) (m3/ml (m:l/mlSlAsh Wednesday Stonn, Mar. 1962,53.0---4 149,327U.S.East Coast..-._-S2 Nov. 1962 Stonn,U.S.East Coast6.318.63216,7241.160.9953S3 6 Nov. 1963 Stonn,U.S.East Coast 6.9 24.22630,9701.510.9552S413 Jan.1964Stonn,U.S.East Coast 11.7 26.1 3725,0371.63 0.9841S516 Sep. 1967 Stonn,U.S.East Coast3.97.1 1922,4200.440.89185612 Mar. 1968 Stonn,U.S.East 5.818.6379,9191.160.9590Coast5712Nov.1968Storm,U.S.East 14.8 28.74332,2851.790.9879Coast582 Feb.1970Stonn,U.S.EastCoast6.915.6318,6300.970.9559S9 17 Dec.1970Stonn,U.S.East5.815.14227,7240.940.9316Coast S10 19 Feb.1972Storm,U.S.East Coast S10a New Jersey12.022.8 23 18,9771.420.9815SlabNewYork7.615.7 3822,4620.980.9831S1117-22Mar.1973Storm,U.S.East Coast S11aNew Yo",7.516.41722,1021.020.9758Sl1bNewJersey5.312.5 1619,6300.780.9909S12 Nov.-Dec.1973Events, Gennan31.0._-._-92,944.,....NorthSeaCoastH4Hurricane Eloise, Sep. 1975,N.W.16.029.87239,6281.860.9557Florida Gulf Coast S1414Oct.1977Stonn,U.S.East Coast15.531.6 2243,0851.970.9890S15 19 Dec. 1977 Storm, U.S.East 11.823.42051,3561.460.9890Coast S16 6 Feb. 1978 Stonn,U.S.East Coast12.330.51742,9791.900.9940S17 No Name Stonn, 17-18 Jun. 1982,14.025.82421,111 1.610.9917Lower Florida Gulf Coast S18 Thanksgiving Holiday Storm,2114.632.412852,3882.020.9807Nov.1984,Florida East Coast H8 Hurricane Elena, Sep. 1985, Florida Gulf Coast H8b Franklin County 10.331.634 54,456 1.97 0.9661 Hac Gulf County 7.1 18.9 3045,5791.180.9958H8d Escambia County4.211.45834,6530.710.9459H9 Hurricane Kate, Nov. 1985,N.W.8.722.0 13 47,481 1.370.9247Florida Gulf Coast Note: The time between pre-stonnandpoststonn surveys,andcommentsaregiven in Table 2; data sourcesarelisted in Table1.15 __ .._._.._.._.

PAGE 19

0l-_-..I._--'---'-.................."'""""'"-li..L.__ 0.01 OJ 0.10.5tanaiFigure9.Tesselatedrelationship relating nearshore bed slope(tanaiwhich occurs from300to800m offshore oftheMSLshoreline)totheELPcoefficient f. according to:(9)(10) 4> =2.07+13.2tan"j The validityof 4J canbetested using data obtained from Hurricane GilbertwhichstruckCancun, Mexico in September,1986.While the accuracyofdataforHurricane Gilbert is not toutedtobeofthe standardforthe remainderofthe data base presented here (and in particularforthe Florida data), the magnitudeofthe event was so overwhelming thatitcannotbeneglected; best known dataarelisted in Tables 1 and 2. A significantly importantfactorassociatedwiththe Gilbert data are the very steep Data and fitted relationship leadingtoequations (9) and (19) are plotted in Figure 9. Results from equation (9) apply only where the initial or nearshore bed slope is greater than0.01638;where the initial bed slope is less than0.01638the valueof 4J isunity(i.e.,1.0). The finalformofequation (3)nowbecomes: where tanajisthe initialor nearshorebedslope, and: 6J8,0 5Saville (1957) ,,/ a De11e andUliczka (1987) /''.. Present study ",,'.p_-o-pt/',___-------'"'I' = (lanai) where 24 =2.07+13.2tanaifortanai>0.0161 '" = 12344""1 fortanaj>0.016duetoinertialeffectsislessresponse orientedunder lower slope subaqueous than steeper slope subaerial littoral conditions. The resultisa partitioningofsediment transport between kinetic energy(i.e.,by virtueoflow-slope, near horizontal motion duetoshore-normal subaqueous sediment transport mechanics)andpotential energy(i.e.,by virtueofsubaerial elevationofdunes and bluffs and potential gravitational mass wasting due to wave impacts propagating uponanelevatedwaterlevel). Based upon this logic,itwould appearthatthe diminishedeffectofthe accelerationofgravityisnot unwarranted, becauseitprobably relates moretospreading rates across the nearshore thantodune or bluff mass wasting. The latterisessentially instantaneous, while the formeristime consuming. Infact,the prototype wave tank resultsofDette and Uliczka (1987) appeartoprovide some elucidating information. First, their resultsshowthatthe pre-impact nearshore bed slope correlateswiththe magnitudeofbeach and c()ast erosion volumes and the rateoferosion. Specifically, the steeper the nearshore bed slope, both the greater the erosion volume above SWL, and the faster the removal rate. Second, regular and irregular waves appeartoerode the beach and coastatdifferent rates. Dette and Uliczka (1987) report prototype resultsforinitial nearshore bed slopesof0.25and0.05,and Saville(1957)fora slopeof0.0667.U.S.East and Gulf Coast natural nearshore slopes(i.e.,300to800moffshore)are,however,characteristically less than0.02,averaging about0.016forFlorida. Applicationofthese data relativeto f thePDFcoefficientofequation (3), yields a dimensionlessproportionalityconstant 4J termed the offshore sinkefficiencyparameter(OSEP),16

PAGE 20

nearshore slopesoffofCancunasillustrated in Figure 10. In fact, the nearshore slopeisovertwice(i.e.,222%)assteepasslopes commonly foundoffU.S.East and Gulf Coast nearshores. Such a slope;ssteep enoughthatsandisnot abletobetransported back onshore during post-storm conditions. Hence, the steep offshore slope becomes,forall practical purposes, a sediment sink. Given the following dataforHurricane Gilbert: tanUj=0.0363,t,=9.5hours,S=3.81m,P=0.68(average erosion volume), P=0.925(maximum erosion volume), steeper nearshore and increased valueoftheoffshoresinkefficiency pa/'Bmeter isthe productoftheELPandOSEP,resulting in a valueof231,462m 3 /m. The goodnessoffitofthis resultisillustrated in Figure 2. Moreover, equation(11) results in an average erosion volume(i.e.,P=213)of144.5m3/m whichisvery closetothe measured amountof144.7m 3 /m, and a maximum erosion volume (/:e., P=0.925)of313.6m3/m Whichiswithin5.6%ofthe measured valueof297m3/m. The finalformofequation (5)forvolumetric erosion above the peak storm tide level becomes: (12) then: and:ELP=89,782m3/m,OSEP=2.578,e3 P=e3 (2/3)=7.3891,and, e3P=e 3(0_925)=16.0386.where by similitude,itisassumedthattheOSEPapplies straightforwardlyasin equation ( 1 1) (field data are needed, however,forconfirmation) Nearshore geometry isnowcommonly quantified by apowercurve (Dean,1977;Hughes,1978;Balsillie, 1982a, 1987) given by: The adjustedELPduetotheeffectofthe(13)in which d is thewaterdepth, andxisthe distance offshore. Using the dataofSaville (1957), Dette and Uliczka (1987), and average dataforFlorida, tanUjmaybeapproximately relatedtothe shape coefficient (Dean, 1977),as'according to:,.,,1.,.1CMlCUlI'rolUe ----Fit .." c__._ c.ww. "0111.-_ . typic.' FI.... '.'-rCurw."0'10_._-----.._-------------. -._--------'--_.----tana, ::0 0.5 8.3(2 (14) _..i.--::lIOO=---L_-;;,ooo DI.,...c.(Ill'Figure10.Comparisonbetweena typical Rorida nearshore profileanda typical Cancun, Mexico nearshore profile. -17illustrated in Figure 11(asinequations(11)and (12)hasunitsOfm'/3.ifaisin unitsofftl /3 smultiply the value by0.673toobtain consistentS.I.units).

PAGE 21

II!?C!-, Using equations (15) and (16), the ReturnPedodVolumetric Erosion Eventswhere misthe ranked value.Ifthe theory does hold, the points should plotasa straight line on probability paper. The return period Teisthen given by: Saville(1957)oDetteandUliczka(1987)PresentStudy0.1 all/ / / // // / / I I "'" 3/2010tanaj 0.5asIIII/ //I I II0.01 o v tanajnosas cm'/3, Figure11.Relationshipbetweentheinitial nearshore bed slope (tanajoccurring300to800m offshore oftheMSLshoreline) andthepowerCUNefitshapecoefficient,as'plotofFigure 12isconstructed using datafromTable 2. OnlyAtlanticOcean events are considered in this analysis. There are35events listed in Table 2whichapply. These events occupy a 34year period from1957through 1990. During this period some324tropical storms and hurricanes formed in the Atlantic. Of these, about104(or32%ofthe total) landfalling or exiting events affected the Americas along theU.S.East Coast, and GulfofMexico coastsoftheU.S.and Mexico.Itisassumedthatthe applicable35eventsofTable 2 represent a random sampleoferosion conditions. The35events, however, represent only one-third of the actual numberofeventsthataffected coastal reaches. Therefore,foranalytical purposes, the 35event sample is "triplicated"toyield105events(i.e.,tripled in sizetomore nearly represent the104events that actually occurred); only the mid pointofeach "triplicate"isplottedto(15) ( 16) 1 -p. The frequency Peused in plotting the distributionisfound (Gumbel,1954)byranking the erosion volumes from smallesttolargest and then dividing the rankofeachofthe sample size plus one,i.e.:P=m1 n+1The incidenceofextreme phenomena may require site-specific treatment. Suchisthe casewiththe determinationofthe return period storm tidewhichisdependent notonlyonhistoricalstorm/hurricanecharacteristics andwaterlevels, but also, importantly, on local conditions suchasoffshore and nearshore bathymetries. A major problem in following suchanapproachforerosion responsesisthat site-specific quantitative erosion dataarehistorically deficient. However, since uncertainties about erosion make simplified considerations the most appropriate (Hallermeier and Rhodes,1986),and becauseofthe apparent successofforegoing quantitative results,itis assumedthatphysiographic responsestostormattackneed notbeheldtoa sitespecific treatment. Further,ithas been a major tenetofthis and otherworks(Balsillie,1985c,1986)thatthe storm tide return period event and the storm erosion return period event are seldom coincident. Untilnowthere has been insufficient information on whichtospecify the probabilistic erosionevent.18

PAGE 22

0.999 0.9980.9950.990.98 0.950.90.8P0.70.60.50.4 0.30.2S.gm.ntC: -g6.858.5x 10Q vg T. ,.. If 0.982') T,.. ...... M_Ud. ro.._._... .en,.,o nIc:.......... -----\ ".".'ID ..__ P.olll ,, __"'-d o. ......tIng .. =h _IITilIO.ID didlID 1.. __ II .,..'.,0 ' _p...... "bulp.......d '010 "oth"" "D 0Dr.,..p.o." ftoOll ... T.......... 'arm ....._ IIOt ,_ ........._,Goa.,_poIItt...... tloa and tlltIllO' p.,,,.,,'.-uncIIII.,....,onlY. --------------------------S .....nl A:1.251+0.006O. evg T ..... S.gm.ntB:2.490.00033O. avg T. ,.. 1000500200100SO20 Te 105(years)3 21.250.10.05 0.02o50100150Q eavg (m3/m)Figure12.Relationshipbetweenexceedence probability P, return periodT.,and average TYPE I erosion volume above MSL.Byincorporatingresultsfromequation(6),thedesignmaximumerosionvolume(i.e.,forP=0.925)results in afactorof2.1and:(21)(19)(20)Q. IIfIg =60((InT.) 1]0.8 Q._ =126 [(In T:) _1]For segment BofFigure12,whichdescribeseventsbetweenabout1.25-and yearreturnoccurrences,thereturn period is givenby:0.00033 T. =e forwhichequations correspondingto(18), (19), and(20),become: representtheassociatedprobabilityandreturnperiod.Itisnoted threestraight-linesegmentsareapparentforwhichpossible explanations have been suggested (see Figure12).Equationsofimmediateinterestforcoastalconstructiondesign purposes are:1+0.006Q 1.25"-tJ (17)T" =e forsegmentAwhichdescribesextremeeventswithafrequencylessthanabouta4yearreturn period,whereQe8Vgis specified incubicmetersperalongshoremeterofbeachorcoast(note: m3/m=2.508(yd3/ft)).Utilizing,bysubstitution,equation(6)thecorrespondingprobabilityofequation(17)is given by:( 1.25 )-1 Pili =1-e1+0.006 Q,.", (18)(22)Further,byrearrangingequation(17),thereturnperiod erosionquantityin mJ/mmaybedeterminedaccordingto:Q vg= 25((InT.)-1] 0.4016 and:(23)19

PAGE 23

06max =53.5[(In T6 ) -1]0.4016(24) Following this methodology, similar equationsmaybedevelopedforsegmentCthatrepresent events occurring moreoftenthan the1.25-yearreturn period (see Figure 12). There is simply notyetsufficientfield datatoreliably determine return period volumetric erosion eventsforerosion above the peak combined storm tide level (in particularforthatportion correspondingtosegment AofFigure 12). However, statistics indicatethaterosion volumes above the peakstormtide level, on the average are about one-half those above MSL. Hence, in the interim, a reasonable estimationmaybedeterminedbydoubling the valueofQ'e avgand using equations (17) through (24). The quantifying equations developed in this section areofspecial consequence. Past return period damage elements have been assessed in termsofforces, specifically the combinedstormtide elevation andwaveheights.Now,forthefirsttime, a return period response elementintermsoferosion is providedwhichaccountsforall theforceelements, inclUding longevityofthe event.Itis envisionedthatthese equationswillbe highly valuable in design and coastal management activities. Onemightbeinclined to believethatthe developed approach is based upon broad assumptions(e.g.,global continuity in littoral physiography) and a limited sample size. Recognize, however,thaterrors creep into design computations duetoassumptions about convoluted littoral processes.Atpresent, andata minimum, equations (17) through (24)wouldseem to provide information as a valuable checkforthe more involved design computations (methodologyforapplicationofvolumetric erosion volumesisdiscussed in the conclusions).20It is, however, notablethatFigures11and 12 support the significanceofphysiographic zonation between the beach and coast.Post-Storm RecoveryThere seemstobeconsiderable interest among coastal scientists and engineers in post-storm littoral recovery, even thoughwearejustnowquantifying details about magnitudesofphysiographic responses during the "height"ofextreme event impact. While there exists some quantifiable representationofsuch recovery (Balsillie,1985d,in manuscript), additionalworkremains. Generally, based onwhatisknownabout littoral processes,wecan endeavor to find discernible and logical conclusions about such recovery. Again,itbecomesofimportancetodelineate littoral subzones (see Figure 1), namely, ... 1. the nearshore, 2. the beach, and 3. the coast.Itis these three subzoneswhichinteractively define the extentofboth extreme event impacts andwhatare discernibly "norma'"or"day-to-day littoral processes. The nearshore,whichis always subject to theeffectsofastronomical tides and waves, is expandedwhena rising storm tide encompasses the beach, and, under design conditions, the coast. That longshore bars are formed during extreme event impact has been a controversial issue. The problem is,ofcourse,thatnearshore subaqueous behavior has not been adequately monitoredtoyield confident quantification during extremeevent impact. However, based on additional considerations and tested data (Balsillie,1984c,1985d),andfieldobservations (Dette,1980;Birkemeier,1984;Sallenger and others,1985),the formationoflongshore bars during extreme event impact seems more nearlytobethe case. Ramificationsofthe concept are not only essential towards anewunderstandingofcoastal engineering design constraintsthatmightberequired,butofinteractive littoral

PAGE 24

21forces and responsesthatcould occur during extreme eventimpact(bearinginmindthatextreme prospects are probabilistic). Further, longshore bars are nature'sownprotective device. During storm actiontheynot only are formed but move offshore (Short,1979;Birkemeier,1984;Mason and others,1984,Sallenger and others,1985),causing stormwavestobreakfurtheroffshore thanwouldnormally occur. By inducing breakingtheycause the greatest amountofenergy dissipationthatwaterwaves can experience and, shouldwavereformation occur, significantly reduce the elevationofdestructivewaveenergyV.e.,reformedwaveheights are attenuated; Carter and Balsillie,1983;Balsil/ie1984b,1985b}.Duringstormimpact, thewidthofthesurfzone dramatically increases. When,followingimpact,surfwidthagain attains "normal"widththe bar(s)withinthe normal" surf zone move onshore in afewdays. Outer bars either remain as relict features or disappear, although the latter requires monthstooccur(Birkemeier,1984;Mason and others, -1984;Sallenger and others,1985).Beach (or shore) recovery appears tobeconsiderably more rapid than has been presupposed bymanycoastal engineers. Although complexitiesoccur(e.g.,longshore transport)whichcan produce a large range in values,itisnowquite clearthatbeachrecoveryoftenoccurswithindays.Birkemeier(1979)foundforthe 19 December1977U.S.east coaststorm(event S 15)thatfrom38%to100%beach recovery occurredwithinone ortwodays following event impact. Bodge and Kriebel (1985) also report rapid recoveryforbeaches following impactofHurricaneElenain Pinellas County, Florida (event H7a). Such rapid beach recovery agreeswithresponse time scalesofpost-storm nearshore profile changes. The coastisofspecial interest becauseitisdetrimentally affected only during extreme eventimpact(or man's activity). Where high sandy dunes or bluffs exist, the coast affords substantive protectiontothe upland.Itisnature's physiographic reserveofparticulate mass,drawnupontoreplenish the more active beach subzone, when beach subzone dimensions are diminished. Of the three sub-zones, the coast in its natural state can be expectedtoexperience no immediate recovery. An exampleisDauphin Island, Alabama struckbyHurricane Frederic in1979,destroying duneswhichattained heightsofupto+10m MSL. Average volumetric dune losseswereabout50m3/m.Assuming the sand supplyisavailable andthatvegetationisinstrumental in natural dune reconstruction, then based on the dataoftheU.S.Army(1984)and Dahl and others(1975),natural dune reconstructionwouldrequire70to75yearsforAmerican Beach Grass andSeaOats, respectively, and180yearsforPanicum(Balsillie, 1979a).APPUCAnONSThe resultsofthisworkdealwithvolumetric erosionofthe beach and coast duetoextreme event impact. This comprises, however,butone aspectofinterrelated natural processes in termsofforce and response elementsthatoccur .withinnearshore, beach, and coast subenvironmentsofthe littoral zone. Other aspects include stormwaveactivitywhichisinstrumental in causing the erosion, producing dynamic andimpactloads on exposed structural members, and forming longshore bars that house sand erodedfromthe beach and coast. These various aspects are quantified and discussed in a seriesofpapers, the sum totalofwhichactually describe the entire Multiple Shore-Breaking Wave Transformation Erosion computer model (Balsillie,1984c.1985d).This approach allows onetomore succinctly

PAGE 25

manage research by dealingwithdiscrete or setsofdiscrete natural process units, and also facilitates updating of each manageable unitasnewdevelopmentsaremade. Even so,itisrecognized that some guidance wouldbehelpful to describehowthe predicted volumetric erosion canbepractically applied.Post-StormBeachandCoastPhysiographyTheproblem in applying volumetric erosion quantities,isthe determinationofthe resulting physiographyofthe profile. For the case, thefollowingsimplified methodology is suggestedasillustrated in Figure13(discussedbyBalsillie1984c,1985d).Following determinationofthe design erosion volume, plot the pre impact coast, beach, and nearshore profile. The nearshore profile shape in Florida canbedetermined using the power curveformaccordingtoBalsillie (1982a,1982b,1987).Plot the bar crest envelope, dbci'V.e., the line connecting the crests of longshore barsformedduring the event) and the corresponding bar trough envelope, dbtV.e.,the line connecting the bar troughs, according to: AB lying above the nickpoint of Figure 13) has a1on1 slope. The segmentBeisa slightly curved line smoothly continuing the bar trough envelope to the nickpoint (where the coastisflooded only segmentBCapplies). Startingatthe pre-impact shoreline, segment ABC (or segmentBCwhere the coastisflooded)isiteratively moved landward until the erosion volumeisattained (shaded areaofFigure 13).Nearshorewaveheightsaredetermined using the bar crest envelopetorepresent thewaterdepthatbreaking,db(Balsillie,1983b,1984b,in press). The amountofthe breaking wave height lying above the peak storm tide stillwaterlevel,Hb',has been determined from field data (Balsillie,1983d,1985b,in press)tobegiven by: (27) in whichHbxis the average heightofthe desired moment measure. The breaker height envelope illustrated in Figure13,represents the significant height. Relating equations developed by Balsillie and Carter, 1984a, 1984b)forother moment measures commonly used in designworkare: where S is the peak combined storm tide, as is the shape coefficient givenbyBalsillie (1982b)forFlorida, andXbcisthe distance offshore measuredfromthe pre-storm MSL shoreline, and: whereHbrmsisroot-mean-square breaker height, andHbisthe average breaker height; (28) (29) in which Hbsis the significant breaker height(i.e.,averageofthe highest two-thirdsofthe height record); (25)(26)whereXbtis the distance offshore measuredfromthe pre-storm MSL shoreline.(30)Inspectionofpost-storm profiles indicatesthatthe portion of the eroded profile above the peak storm tide (segment where Hb10isthe averageofthe highest10%of the wave record; and:22

PAGE 26

10MeuredDe.ePre-StormProfile----Post-Storm----PSTSWL -----t MSL=M_nSea Level PSTSWL =: PeakStorm Tide StillWate, Level[ITJ ErodedVolumeabove MSt. PredictedData-._._._ Post-Storm ErosionProfile----Ber lrough Profile_..__ --earCrtProfl'.......-..........SignificantBrker HeightEnvelope 5CI):..!.I:.2 >.!! 0w -60 -50202$DlatancefromPre-Stonn ShCM'eUne (m)Figure13.Exampleofapplication for determining two-dimensional post-storm physiography using volumetricdata,and designwaveconditions.(31) inwhichHb1is the averageofthe highest 1% wavesofrecord. statisticstothe design lifeofa project.Whatwereallywishtodoistransform the return period statistictooneofencounter probability, based upon a specified encounter period. EncounterPeriod and Probablity A return period statisticisone providing a measureofthe probabilityofannual occurrence. For instance, an eventwitha100-yearreturn period has a probabilityof0.01or a chanceof1%occurrence inanygiven year,aneventwitha 5-year return period has a probabilityof0.20or a20%chanceofoccurrence in any given year,etc.Evenifthe return period occurrence occurs duringanannual period, its probabilityofrecurrence remains the samewithinthe current annual framework. The solution is the useofFigure 14. The abscissaofFigure14gives the EncotmteTPeliod whichisthe periodoftimeforwhicha project istolast (i.e., its design life). In the caseofsingle-family dwelling design, the encounter period mightbe50years representing a depreciation periodfortaxpurposes,etc.The ordinateofFigure14gives the Ent:ountet'Probability which represents the assigned return period equaledorexceeded during the selected EncounterPBIitHI. Curves internaltothe graph areforvarious Retum Pe/iods associatedwiththe design event. The aboveoftenleads to confusion, particularlywhenone triestorelate such Followingisanexampleofhowto use the figure. Supposethatyou would liketo23

PAGE 27

I1I 1/V/I""'"VI""'" _ReturnPeriod /"I.-'/ (Years) // II V / v )" / I'""1I/ / IIii' /I V IIl"'iI.1I1/'or7 V)1VVV ..." 1/ 1/;tr1/V // Vr-,,! j/ f7,,'V-II1/""J / ./ V V vll!/lJ' V L/L,.-/./v1,.;1'1,.01.0"..-/l...,...-'VL-L.-7-',,/I.---'I.-'"" .. L..ol,..oloo"1..---'1-"" ..... 1.0 >0.8= :aIID 0.60... a. ... I) -0.4 :I 0 U W0.2o1510501005001000Encounter Period (Years)Figure14.Nomographforrelatingeventreturn period,encounterperiod,andencounterprobability. buildyour dwellingsothatitis relatively safefromthe1 DO-year return perioderosion-event.Theprobabilityofa1 DO-year return periodoccurrencebeing equaledorexceeded duringtheabove assigned period (i.e.,EncounterPeriod) is0.4,as illustrated in Figure14.Hence, there is a40%chancethatthe1 OO-year return period erosioneventwilloccurintheplanned lifetimeofthehome. Hadthedwellingbeen designedfora SOO-year return period erosionevent,thestructurewouldhave amuchbetterchanceofsurvivingthe criticalevent...thenonlya10%chanceofoccurrence duringitsplanned life. Using thefigure inanothermanner,ifahomeownerorprospective homeowneriswillingtotake a20%chancethatthedesign erosioneventwilloccurduring the50-yeardesign lifeofthestructure,thentheRetum Petiod oftheerosioneventthatshould be designedforis250years.Theabove example usesthereturn period erosion event.However,Figure1424can alsobeusedforanyothermeasure (e.g., peak combinedstormtide,waveevent,eventforwardspeed,etc.)providedthatreturn periodstatisticsare quantified. AnErosion Damage PotentialScale A beach/coast erosion damage scaleforextremeevents has not, here-tofore, been proposed. Perhapsthebestwayinwhichtoassess an erosion damagepotentialscale istobuild upontheexistingSaffir/Simpson hurricane damagepotentialscale (Table4).Volumetricerosion is assessed using equation (1)foraverage erosion quantities and equation (7)formaximumerosion'quantities.TheassessmentofTable 4 is, therefore, applicabletotheU.S.AtlanticEast Coast and theU.S.GulfofMexicoCoastwhichhave relativelylownearshore slopes (i.e.,wheretanQjischaracteristically lessthan0.02).Equations (1) and (7)wereevaluated using the Saffir/Simpson peakstormtide(commonlytermedthestormsurge)classesofvalues. Eventforwardspeed classesweredetermined usingthehistorical

PAGE 28

Table4.Amended Saffir/Simpson Hurricane Damage Potential ScalePeak Event StormAvera"e Maximum Centrel Wmd Storm Tide Tide Category Pressure Speed Elevetion ForwardRiseErosion Erosion Damage Speed Volume Volume Potential (mb) (kmlhr) above (kmlhr)Time(m 3 /m) (m 3 /m)MSL(m)(hr)1>98046-591.22-1.68502.5-4.5 3-86.5Minimal2965-97960-681.68-2.60304.5-7.58-2517-53Moderate394569-812.60.81207.52553-132Extensive4920-94482-963.81.49101163-188132-395Extreme5<920>96>5.49<10>22>188>395CatastrophicdataofSchwerdtand others (1979). Storm tide rise time was then determined using equation (2). The Saffir/Simpsonscale assessed the damage potential in termsofthewindspeed andpeak.stormtide. There is, infact,sound reasoningfordoing so, since both are largely dependent on event central pressure. The sameisnot trueofthe event forward speed because the threedimensional geometryofsurrounding weather systems and conditionsaffectsteering currents. Hence, factors other than central pressure have significanteffecton the propagationofa hurricane. There aretwoadditional issuestobeconsidered. One isthatitmaybedifficulttoenvisionjustwhata volumetric erosion value means in termsoferosion damagefora specific coastal locality, unless cross sections representing pre-storm and post storm profiles are assembled. A horizontal recession value rather than a volumetric erosion valueisan alternative, but this was foundtoresult in many more problematic complexities than the volumetric approach (Balsillie,1985c,1986). Hence, while volumetric erosion values may not obviously identify the damage potential, they canbecorrelatedtothe SaffirlSimpson hurricane25category and damage potential scaletoprovide a pragmatically useful additiontothe scale. The other issue centers about thefactthatextreme eventswithmuchlowerintensities than hurricanes(e.g.,tropical storms, which are here identified under the collective termstorms")can potentially resultinasmuch or more erosion than many hurricanes (see Table 2). An exampleisa storm which essentially stallsjustoffshorefordays. Hence, Figure15hasbeen compiled which, based on event forward speed andpeak.storm tide elevation, canbeusedtoassess erosion damage potential whether the eventisa hurricane or a storm. Table 4 and Figure15are transformedtoBritish Imperial Units and given in the Appendix.CONCLUSIONSAnalyzed informationforstorms(e.g.,Birkemeier and others,1988;Kanaand Jones, 1988; Jones and Kana,1988;Beumel and Campbell,1990;Ferriera, 1994) and more recent hurricanes(e.g.,Birkemeier and others,1991;Stauble and others, 1991 ; Nelson, 1991) has increased the existing sample size of Balsillie (1985c, 1986)forfield data quantifying beach and coast erosion duetoextreme eventimpact. This additiona I data allowsfortestingofa

PAGE 29

PeakStormTideElevatlo.n(mMSL)0.5 1 1.0 j 1.5 2.0 j 2.6 3.0 i 3.5 1 4.0:4.5 ; 5.0 ; 5.5Figure1.5. Beachand COIIsterosion damage potentialscale as a functionof eventforward speed atlanclfaland peakstormtideelevation. &osion volumes are based on peakstormtide elevation classes of Table4;evenso,results applytostormevents asweias hunicanes. refinementofquantifyingrelationships. Amostimportantaspectofbeing abletopredict beach andcoasterosion duetostormand hurricaneimpactis the capabilitytoassess profilegeometryduring and as a resultofimpact.By so doing, coexisting storm-generatedwaveactivitypropagating upon thestormtide surface canbeassessedformanagement and design purposes. Thefactremains, regardingwavesandtheirmodifyinginfluence on a mobilebathymetry,thatanychange inwavecharacteristics induces an alteration inbathymetrybutata26lag-time behind a change inwavecharacteristics. Becauseofthebathymetriclag-time,bathymetrycan inturnimposesignificantinfluentialeffectsonthecharacteroflittoralwaveactivity.Hence, in additiontoerosive outcomes,itis thedestructivepotentialofstorm-generatedwaveimpactsthatalsomustbeconsideredifa successful assessment methodology istoexist. Determinationofprofilegeometryis then amatterofmodelinginteractivelittoral processes,thatis, bothforce(e.g.,waterlevel rise and waves) and response(e.g.,profile modification)elements. Acomputer

PAGE 30

model exists (Balsillie.1984c.1985c.1985d.1986)inwhichabulk sedimenttransportmechanism,intermsofbedform movement has been developed (Balsillie, 1982a,1982b,1984b,1984c),whichisdependent on littoral waveactivity(Balsillie, 1983a.1983b,1983c,1983d,19848, 1984b. 1984c,1985b;Balsillie and Carter, 1984a,1984b).Itis the volumetric erosion methodology contained herein which allowsforthe calibrationofthe combined assessment of combined storm tide, stormwaveimpact, horizontal and vertical physiographic recession force and response elements duetoextreme event impact. In addition, therenowappearstobeenough informationtomake a statement about the return period erosion event. Least equivocal results given by equations (17) through (24)will,hopefully,berefinedbyfuturework.In the meantime, however,theyare valuableasa check in design applications. In addition, applicationsofthe volumetric erosion methodology have been discussed, including the determinationofpost-storm beach and coast physiography, encounter period and probability, andanerosion damage potential scale. ACKNOWLEDGEMENTS RobertJ.HallermeierwithDewberry and Davis, Inc., Washington,D.C., identified several storm erosion eventsnotincluded in earlier versionsofthiswork,and reviewed the manuscript. The review and commentsofWilliam A. Birkemeier,CERC,are gratefully acknowledged. An extensive and valuable reviewofthe manuscript was conducted by thestaffofthe Florida Geological Survey. The contributionsofJon Arthur, Paulette Bond, Ken Campbell,EdLane, Jacqueline M.lloyd,Deborah Mekeel, Frank Rupert, Thomas M. Scott, and Walter Schmidt are gratefully acknowledged.REFERENCESBalsillie,J.H., 1979a, Appraisal of beach stability and construction setback: Florida DepartmentofNatural Resources, draft report, 7p.____ 1979b, Multiple shore-breaking wave transformation programforacalculator(MSBWTM-OFSONS-3): Florida DepartmentofNatural Resources, DivisionofBeaches and Shores.____ 1982a, Offshore profile descrip tion using the power curvefit,partI:explanation and a discussion: Florida DepartmentofNatural Resources, Beaches and Shores Technical and Design Memorandum No. 82-1-1,23p.____, 1982b, Offshore profile descrip tion using the power curve,fit,part II: standard Florida offshore profile tables: Florida DepartmentofNatural Resources, Beaches and Shores Technical and Design Memorandum No. 81-1-11,70p.____, 1983a, Horizontal recessionofthe coast: the Walton-Sensabaugh methodforHurricane EloiseofSeptember1975:Florida DepartmentofNatural Resources, Beaches and ShoresTechnicaland Design Memorandum No.83,63p.____,1983b,Onthe determinationofwhen waves break in shallow water: Florida DepartmentofNatural Resources, Beaches and Shores Technical and Design Memorandum No. 83-3,25p.27 L-----

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,1983c,The transformationof----thewaveheight duringshorebreaking: the alpha wave peaking process: Florida DepartmentofNatural Resources, Beaches and ShoresTechnicaland Design Memorandum No. 83-4,33p.,1983d,Wave crest elevation above the designwaterlevel during shore-breaking: Florida DepartmentofNatural Resources, Beaches and ShoresTechnicaland Design Memorandum No.83-5,41p.____,1984a,Wave length and wave celerity during shore-breaking: Florida DepartmentofNatural Resources, Beaches and Shores Technical and Design Memorandum No. 84-1,17p.____,1984b,Attenuationofwavecharacteristicsfollowingshore breaking on longshore sand bars: FloridaDepartmentofNatural Resources, Beaches and Shores Technical and Design Memorandum No. 84-4,81p.1984c,A multiple shorebreakingwavetransformationcomputer model: Florida DepartmentofNatural Resources, Beaches and ShoresTechnicaland Design Memorandum No. 84-4,81p. IJ'(J ____,'1985c,Calibration aspectsforbeach and coast erosion due to storm and hurricane impact incorporating event longevity: Florida DepartmentofNatural Resources, Beaches and ShoresTechnicaland Design Memorandum No.85-1,32p.1985d,Verificationofthe MSBWT numerical model: coastal erosionfromfourclimatological events and littoral wave activity from three stormdamaged piers: Florida DepartmentofNatural Resources, Beaches and Shores Technical and Design Memorandum No. 85-3,33p.1985e,Post-storm report: HurricaneElenaof29Augustto2 September1985:Florida DepartmentofNatural Resources, Beaches and Shores Post-Storm Report No. 85-2,66p.____,'1986,Beach and coast erosion duetoextreme event impact: Shore and Beach, v.54,no. 4,p.22-37.1987,Nearshore profiles: geometric prediction, spatial and temporal sampling adequacy: Florida DepartmentofNatural Resources, Beaches and Shores Technical and Design Memorandum No. 87-2,102p.__ 1985a,Post-storm report: the Florida east coast Thanksgiving holidaystormof21-24November1984:Florida DepartmentofNatural Resources, Beaches and Shores Post Storm Report No. 85-1,74p.____,1985b,Redefinitionofshore breaker classificationasa numerical continuum and a design shore breaker: JournalofCoastal Research, v. 1, no. 3,p.247-254.28____"1988,Florida's beach and coast preservation program: Florida DepartmentofNatural Resources, Beaches and Shores Special ReportNo.88-2,34p.____, in press,Onthe breakingofnearshore waves: Florida Geological Survey, Special Publication.

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Balsillie, J. H., and Carter,R.W. G., 1984a, Observed wave data: the shore breaker height: Florida DepartmentofNatural Resources, Beaches and ShoresTechnicaland Design Memorandum No. 84-2,70p.____, 1984b, The visual estimationofshore-breaking wave heights: Coastal Engineering, v. 8,p.367-385.Balsillie, J. H., and Clark,R.R.,1979,Preliminary report on coastal and shoreline damage resulting from impactofHurricane Frederic on the northwestern panhandleofFlorida, September12-13,1979:Florida DepartmentofNatural Resources, DivisionofBeaches and Shores,182p.Balsillie, J.H.,Carlen, J. G., and Watters, T. M.,1998,Open-oceanwaterlevel datum planesformonumented coastsofFlorida: Florida Geological Survey, Open File Report No.73,92p.Balsillie, J. H., and Tanner, W.F.,in press, Stepwise regression in the earth sciences: a coastal processes example: Environmental Geology. Baumel,N.H., and Campbell,T.J.,1990,Post-storm survey, Tropical Storm Marco, Captiva Island and northern Sanibel Island: Boca Raton,FL,Coastal Planning and Engineering, Inc.,11p.Birkemeier, W.A,1979,the effectsofthe 19 December1977coastal stormonbeaches in North Carolina and New Jersey: Shore and Beach, v. 47, no.1,p.7-15.29____" 1984, Time scalesofnearshore profile changes: Proceedingsofthe19thInternational Coastal Engineering Conference, chap.102,p.15071521.Birkemeier,W.A,Bichner,E.W.,Scarborough,B.L,McConathy, M.A,and Eiser,W.C.,1991,Nearshore profile response caused by Hurricane Hugo: JournalofCoastal Research, Special IssueNo.8,p.113-127.Birkemeier,W.A,Savage,R.J.,and Leffler, M. W.,1988,A collectionofstorm erosion field data:U.S.Army, Coastal Engineering Research Center Miscellaneous Paper CERC-88-9,187p.Bodge,K.R.,and Kriebel,D.L.,1985,Storm surge and wave damage along Florida's Gulf coastfromHurricane Elena: Gainesville,FI,UniversityofFlorida, DepartmentofCoastal and Oceanographic Engineering,22p.Bretschneider,C.L.,1964,The Ash Wednesday east coast storm, March 5-8,1962,a hindcastofevents, causes and effects: Proceedingsofthe9thInternational Conference on Coastal Engineering, chap.41,p.617-658.Burdin,W. W.,1977,Surge effects from Hurricane Eloise: Shore and Beach, v. 45, no.2,p.3-8. Caldwell, J. M.,1959,Shore erosion by storm waves:U.S.Army, Beach Erosion Board Miscellaneous PaperNo.1-59,17p.Carter,R.W. G., and Balsillie, J. H.,1983,A noteonthe amountofwave energy transmitted over nearshore sand bars: Earth Surface Processes and Landforms, v. 8, no. 3,p.213-222.

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....... ...-Chiu, T. Y.,1977,Beach and dune response to Hurricane Eloise of September1975:Coastal Sediments'77,p.116-134.Dahl,B.E.,Cotter,P.C., Wester,D.B.,and Drbal,D.D.,1983,Post hurricane surveyofexperimental dunes on Padre Island, Texas:U.S.Army, Coastal Engineering Research Center Miscellaneous ReportNo.83-8,70p.Dahl,B.E.,Fall,B.A., Lohse,A.,and Appan,S.G.,1975,Construction and stabilizationofcoastal foreduneswithvegetation: Padre Island, Texas:U.S.Army,CoastalEngineering Research Center Miscellaneous Paper 9-75,188p.Dean,R.G.,1977,Equilibrium beach profiles: U.S.Atlantic and GulfofMexico coasts: Ocean Engineering Report No.12,DepartmentofCivil Engineering, UniversityofDelaware,45p. Dette,H.H.,1980,Migration of longshore bars: Proceedingsofthe17thCoastal Engineering Conference,p.1476-1492.Dette,H.H., and Uliczka,K.,1987,Prototype investigation on time dependent dune recession and beach erosion: Coastal Sediments'87,American SocietyofCivil Engineers, v. 2,p.1430-1444.Dupre, W. R.,1985,Geologic effectsofHurricane Alicia (August 18,1983)on the upper Texas coast: Transactionsofthe Gulf Coast AssociationofGeological Societies,v.35,p.353359.30Edelman, T.,1968,Dune erosion during storm conditions: Proceedings of the11th International ConferenceonCoastal Engineering, chap. 36,p.719-722.____,1972,Dune erosion during storm conditions: Proceedings of the13thInternational Conference on Coastal Engineering, chap.170,p.13051311. Erchinger,H.F.,1974,Protectionofsandy coasts in dependenceofthe dune beach type: Proceedingsofthe14thInternational Coastal Engineering Conference, v.2,chap.68,p.11641176.Federal Emergency Management Agency,1987,Proposed rules: Federal Register, v.52,no.212,p.4211742119.Ferreira,C.,1994,Beach erosion inducedbystorms, a tentative previsionforthe northwest Portuguese coast: Gaia, v. 8,p. 157. Galvin,C.J.,Jr.,1983,Manatee Beach and Bradenton Beach groins damage assessment: Federal EmergencyManagementAgencycontractthrough Dewberry and Davis, Fairfax,VA,85p.Garcia,A.W., and Flor, T. H.,1984,Hurricane Alicia storm surge and wave data: Coastal Engineering Research Center Technical Report CERC-6. Gumbel,E.J.,1954,Statistical theoryofextreme values and some practical applications: Applied Mathematics Series 33, National BureauofStandards, Washington,D.C.,51p.

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APPENDIXTable 4 and Figure15ofmaintexttransformedtoBritish Imperial UnitsofMeasure35

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r Amended SaffirlSimpson Hurricane DamagePotential ScalePeak Storm Centr.l1WDI Storm EventrKieAverageMaximume.te-PressureSpeedrKieForwardliseErosionErosionDamagegory (Inches)(mph) BentionSpeedTme Volume Volume Potential.bove (mph)(yds31ft)(yds31ft)MSL(ft) (Iv) 1>28.9474-95 4-5.5 31-552.5-4.51.2.32.5-7Minimal (>980)" 228.50.9196-1105.5-8.518-314.5-7.53.3-107-21Moderate(965-979)327.91.47111-1308.5-12.512-187.5-111021-53Extensive(945-964)427.17-28.88131-15512.5-186.511-2125-7553Extreme(920-944)5<27.17>155>18<6.5>21>75>158Catastrophic(<920)-Centralpressure in parentheses are In millibars.Peak Storm Tide Elevation(ftMSL) : CATASTROPHIC .......'!+* **+ .. +5550 4S MINIMAL 40 353025201512102 !4j 6 8 j 10 12 14 18 18 j 20371 :2Q. E 'D11.ICbrIJ'EIII o LL l:Cb >W6Beach andcoast erosion damagepotential scale as afunctionof eventforwardspeedandpeakstormtideelevation,bothatlandfal. &osion volumes are based onpeakstormtideelevation classes of abovetable;results, however, applytostorm events asweIas hurricanes.