PAGE 1 "StateofRorida DepartmentofEnvironmental Protection DavidB.Struhs,Secretary Division ofAdministrative and Technical Services Rorida Geological SurveyWalter Schmidt,State Geologist and ChiefPublished fortheRoridaGeological SurveyTaUahassee, Rorida1999 PAGE 3 LETTEROF TRANSMITTAL Florida Geological Survey Tallahassee Governor Jeb Bush Florida Department of Environmental Protection Tallahassee, Florida 32304 Dear Governor Bush: The Florida Geological Survey, Division of Administrative and Technical Services, Department of Environmental Protection is publishing two papers: "Seasonal variationinsandy beach shoreline position and beach width" and "Open-ocean water level datum planes: Use and misuseincoastal applications". The first paper identifies a methodology for predicting seasonal shifts in Florida's shorelines. A number of practical uses emerge from the research, two of which are the analytical assessment of long-term shoreline erosion data, and determination of the seaward boundary of public versus private ownership. The second paperisa companion paper to "Open-ocean water datum planes for monumented coasts of Florida" published by the Florida Geological Survey as a separate work. It identifies erroneous applications made when considering mean sea level (MSL), mean high water (MHW), mean low water (MLW), etc., tidal datum planes, illustrating why they are erroneous using practical examples, and details how proper applications shouldbedetermined. Walter Schmidt, Ph.D., P.G. State Geologist and Chief Florida Geological Surveyiii PAGE 5 CONTENTSPageSEASONAL VARIATIONINSANDY BEACH SHORELIN E POSITION AND BEACHWIDTH ABSTRACT 1 INTRODUCTION .......................................................1SEASONAL VARIABILITY 2 DATA AND RESULTS 3 Data 3 Results ........................................................7 DISCUSSION 9 The Single Extreme Event and the Combined Storm Season 9 Beach Sediments11Astronomicalndes..............................................14APPLICATIONOFRESULTS15General Knowledge16Seaward BoundaryofPublicversusPrivate Ownership ..................,6 Long-Term Shoreline Changes ...................................17 Project Design and Performance Assessment 19 CONCLUDING REMARKS...........................................20ACKNOWLEDGEMENTS20REFERENCES.....................................................20LISTOFFIGURESFigure 1. Relationship between seasonal shoreline variability, V$'and mean rangeoftide, hINt. .4Figure2.Monthly time seriesforTorrey Pines Beach, California,forshoreline variability, V; breaker height, HIl, and wave period, T. 5 Figure 3. Monthly time seriesforStinson Beach, California, for shoreline variability, V; breaker height, HIl, and wave period, T 5 Figure4.Monthly time seriesforJupiter Beach, Rorida,forshoreline variability,V;breaker height, HIl, and wave period, T. 6 Figure 5. Monthly time seriesforGleneden Beach, Oregon, for shoreline variability, V; breaker height, HIl, and wave period, T. 6 Figure 6. Illustrationofmathematicalfitforequation (1). 9 Figure7.Illustrationofmathematicalfitforequation (2). 9 Figure 8. Exampleofthe quick response and recoveryofthe beachtostormwaveactivity, Pensacola Beach, Rorida, December1974..'0Figure 9. Monthly average occurrencesofextreme event wave eventsforthe Outer BanksofNorth Carolina. ........................................,1v PAGE 6 Figure10.Typical examplesoftimeseries relationofmonthlydataforbreaker height,waveperiod, and foreshore slope grain sizeforCalifornia andnorthwesternFlorida panhandle. .'3Figure11.Monthlyvariation in sea levelforthecontiguous United States. .16Figure12.Exampleoflong-term shoreline change rate temporal analysis using seasonal shorelineshiftdata. .'8LISTOFTABLES Table 1. Force, response, and property elementsforseasonal shorelineshiftanalysis...4 Table2.Assessmentofthewavesteepness ratiofora selectionofexpressions relatedtoVS.8 Table3.Mean annual beach grain size (foreshore slope samples)frommonthlydata, and range in size. 12 Table4.Twocasesofsedimentologic responseofmomentmeasurestowaveenergy levels. 12 Table5.Seasonal range inmonthlyaveragewaterlevels15APPENDIX APPENDIX: PROPAGATION OFERRORSIN COMPUTING28OPEN-OCEAN WATER LEVELDATUMPLANES:USEAND MISUSE IN COASTAL APPLICATIONSABSTRACT29INTRODUCTION29INLETS/OUTLETSANDTHE ASTRONOMICAL TIDE 33WATER LEVELDATUMPLANES33SYNERGISTICTIDALDATUMPLANE APPLICATIONS36EXTREME EVENT IMPACT36LONGER-TERM BEACH RESPONSES37Seasonal Beach Changes41Long-Term Beach Changes42THE SURF BASE43SEA LEVELRISE47MONERGISTICTIDALDATUMPLANE APPLICATIONS48DESIGN SOFFIT ELEVATION CALCULATIONS48EROSION DEPTH/SCOUR CALCULATIONS49SEASONAL HIGH WATER CALCULATIONS49BEACHCOAST NICKPOINT ELEVATION50BOUNDARY OF PUBLIC VERSUS PRIVATE PROPERTY OWNERSHIP50INLETSANDASSOCIATED ASTRONOMICAL TIDES52CONCLUSIONS54ACKNOWLEDGEMENTS54REFERENCES54vi PAGE 7 LISTOFFIGURESFigure1.Relationship between open coast tidal datumsandNational Geodetic Vertical Datum for the Florida EastCoast.............................31Figure2.Relationship between open coast tidal datumsandNational Geodetic Vertical Datum for the Florida Lower GulfCoast........................32Figure3.Relationship between open coast tidal datumsandNational Geodetic Vertical Datum for the Northwest Panhandle Gulf Coast ofFlorida..........32Figure4.Erosion volumes,Qe'aboveMHWfor identical profiles impacted by identical storm events, but with different localMHWplanes...............37Figure5.Beach profile-related terms. .....................................39Figure6.Seasonal horizontal shorelineshiftanalysis41Figure7.Longterm shoreline shift analysis43Figure8.Semidiurnal tide curves for 6 tidal days46Figure9.Actual damage to the Flagler Beach Pier from the Thanksgiving Holiday Storm of 1984 (Balsillie, 1985c) usedtotest the MUltiple ShoreBreakingWaveTransformation Computer Model for predicting wave behavior, longshore bar formation, and beach/coast erosion ......................49Figure10.Beach/Coast nickpoint elevations for Florida .......................50Figure11.Comparison of Seasonal High Water(SHW)andMedian Beach/Coast Nickpoint Elevation(NJfor the Florida East Coast51Figure12.Comparison of Seasonal High Water(SHW)andMedian Beach/Coast Nickpoint Elevation(Ne ) for the Florida Lower Gulf Coast51Figure13.Comparison of Seasonal High Water(SHW)andMedian Beach/Coast Nickpoint Elevation(Ne>for the Florida Panhandle GulfCoast.............51Figure14.Departure of Florida inlet tide data and open coast tidedata...........53Figure15.Open oceanandinside astronomical tides forFt.Pierce and St. Lucie Inlets54LISTOFTABLES Table1.Tidal DatumsandRanges for Open Coast Gauges of Coastal Florida. .....30Table2.Selected North American Datums and Ranges ReferencedtoMSL ........38Table3.Florida Foreshore Slope StatisticsbyCountyandSurvey40Table4.Moment Wave Height Statistical Relationships45vii PAGE 8 SPECIAL PUBLICAliONNO.43SEASONAL VARIATION INSANDYBEACH SHORELINE POSITION AND BEACH WIDTHbyJames H. Balsillie,P.G.No.167ABSTRACTAnnual cyclic fluctuationsinbeach width due to seasonal variability of forcing elements(e.g.,wave energy) havebeena subjectofconcerted interest for decades.Seasonalvariabilitycanbeused to1)identifyandevaluate the accuracyofhistorical, long-term shoreline data interpretations,2)aidinthe identificationofthe boundaryofsovereignversusprivate land ownership,and3) predict expected seasonal behaviorofbeachnourishment projects, which shouldbea stated up-front design anticipation.Inthis paper, data representing monthly averagesareusedtocomparewinterandsummer wave heightandwave steepnessasthey relate to seasonal shoreline shifts. Coupled with astronomical tide conditionsandbeach sediment size,twoquantifying relationshipsareproposed for predicting seasonal shiftofshoreline position(i.e.,beach width). INTRODucnON Theconfigurationofthebeach in profileviewis primarily duetotidalfluctuationswhichcause periodic changes in sea level,andshore-breakingwaveactivity.Anychangeinwavecharacteristicsanddirectionofapproachwill,depending ontidalstage,resultina change inthesandybeachconfiguration.Systematicbeach changesthrougha singleastronomicaltidalcyclearewellnoted(Strahler,1964;Otvos,1965;Sonu and Russell,1966;Schwartz,1967).Cycliccutandfillassociatedwithspring and neaptides(ShepardandLaFond,1940;Inmanand Filloux,1960),andtheeffectofsuchphenomena as sea breeze (Inman and Filloux,1960;Pritchett,1976),cancontributeadditionalmodifyinginfluences. Beach changes are notedtooccurattimeintervalslongerthana tidalcycle(e.g.,Dolan andothers,1974),Smaller beach cusps.forexample,mayrangefrom10to50metersapart,whilesinuousformsmay1spandistancesoffrom450to700meters,andsuchfeaturesoftenmigrate alongshoreattimescales ontheorderofdaysorweeks(Morisawaand King,1974).Asthebaybetweencusphorns passes a profile line,thebeach becomesnarrower,and as a horn passes,thebeachwidens.Apredictionmodelfordailyshoreline change has been suggestedbyKatoh and Yanagishima(1988).Ofthepossiblecyclicchanges, perhapsthemostpronounced isthatoccurring ontheseasonal scale. Duringthewinter"season,whenincidentstormwaveactivityismostactive,high,steepwavesresult in shoreline recession. Generally,theberm is heightenedwitha gentleforeshoreslope, although erosion scarpsmayform.Sand removedfromthe beachisdepositedoffshorein oneormoresubmergedlongshore bars. During thesummer"seasonlowerwaveswithsmallerwavesteepness valuestransportsandstoredoffshorebackonshore, resulting in awiderbeach.Itshould be notedthatalongsomecoasts such astheapproximatelyeast-west PAGE 9 FLORIDA GEOLOGICAL SURVEYtrending coastlineofLong Island, New York (Bokuniewicz,1981;Zimmerman and Bokuniewicz,1987;Bokuniewicz and Schubel,1987),no seasonal variability canbedetected(H.J. Bokuniewicz,J.R.Allen, personal communications). Such lackofseasonal variabilitymaybe symptomaticofsub-seasonalstormwavegroups combinedwithanalmost imperceptible climatic change (J.R.Allen, personal communications), possibly exacerbated by changes in oceanicstormfrontazimuths relative to shoreline azimuths (Dolan and others,1988).Similarly, theeastwesttrending shorelineofthe northwestern panhandle coastofFlorida, while having annual net longshore transporttothewest,appearstobe characterized by dailytoweeklyrather than seasonal reversals in longshore current direction (Balsillie,1975).Itappears, therefore,thateast-westtrendingshorelinespose considerations deservingfurtherattention. However,formuchofthe Earth's open, ocean-fronting shoreline seasonal changes are clear,whichconstitutes the subjectofthis paper.SEASONALVARIABIUTYClassically, seasonal variability is associatedwithCalifornia beaches wheretheirgeometric character changes noticeablyfrom"summerto"winter"(e.g.,Shepard and LaFond,1940;Shepard,1950;Bascom,1951,1980;Trask,1956,1959;Trask and Johnson,1955;Trask and Snow,1961;Johnson,1971;Nordstrom and Inman,1975;Aubrey,1979;O'Brien,1982;Thompson,1987;Patterson,1988;Collins and McGrath,1989).A considerable numberofsuch studies have also been conducted along the U.S.east coast(e.g.,Darling,1964;Dolan,1965;Urban and Galvin,1969;DeWall and Richter,1977;DeWall,1977;Everts and others,1980;Bokuniewicz,1981;Miller,1983;Zimmerman and Bokuniewicz, 1987). Geometric characteristicsofseasonal2change have been described in terms of sand volume changes (Ziegler and Tuttle,1961;Dolan1965;Eliot and Clarke,1982;Aubrey and others,1976;Davis,1976;DeWall and Richter,1977;DeWall1977;Thorn and Bowman,1980;Everts and others,1980;Bokuniewicz,1981;Miller,1983;Zimmerman andBokuniewicz,1987;Samsuddin and Suchindan, 1987), bycontour elevlltionchanges (Shepard and LaFond,1940;Ziegler and Tuttle,1961;Gorsline,1966;Urban and Galvin,1969;Nordstrom and Inman,1975;Aubrey,1979;Felder and Fisher,1980;Clarke and Eliot,1983;Berrigan,1985;Brampton and Beven,1989),and in termsof botizontalshoTelineshilts or beach width changes (Darling,1964;Johnson,1971;DeWall and Richter,1977;DeWall,1977;Aguilar-Tunan and Komar,1978;Everts and others,1980;Clarke and Eliot,1983;Miller,1983;Garrow,1984;Berrigan and Johnson,1985;Patterson,1988;Kadib and Ryan,1989).Potential legal ramificationsofseasonal shoreline changes astheyrelatetothe jurisdictional shoreline boundary position have been addressedbyJohnson (1971), Hull (1978), O'Brien (1982), and Collins and McGrath (1989). While there are other seasonal shoreline change applications (discussed in the section on ApplicationofResults), the motivationforthisworkcenters about derivationofa least equivocal methodologyforidentifying probable realshiftsin historical long-term shoreline change.Inaddition towaveheight andwavesteepness, wave direction and beach sediment characteristics can influence the degreeofseasonal beach change. Wave directionisparticularly influentialforpocket beaches found along the U.S.westcoast. Along some beaches(e.g.,Oceanside BeachjustnorthofCapeMeares, Oregon) a sandy "summer" beachisremoved during the"winter"season exposing a cobble beach.Insuch cases, "summer"to"winter"grain PAGE 10 SPECIAL PUBLICATION NO.43size differences are significant.Inthis study, however,weshall dealwithrelatively straight, ocean-fronting beaches composed entirelyof material.DATAANDRESULTSInaninvestigationofseasonal beach changesatTorrey Pines Beach, California, Aubrey and others (1976) state: NNo field studies to date have been able to adequatelyquantifythese wave-related sedimentredistributions.In approaching a quantitative solution(s)tothe problem,itbecomes prudenttoidentifythe force and response elements involved. Basic force elements are identifiedtobe:1)astro nomical tides, 2)waveheight, and 3)wavesteepness. Response elements are: 1) vol ume change, 2) change in beach elevation, or 3) horizontal shoreline shift. While the beach sediment mightbeviewedasa response element, given the paucityofinformation about temporal/spatial sediment variationasitimpacts this problem,itmaybeprudenttotreat sediment characteristics (within the sand-sized range)asa property element (see section on Beach Sedimentsforfurtherdiscussion). The response element used here is the horizontal shoreline shift. Fortunately,weare dealingwitha measurewhich,comparedtothe others, has the largest range in possible values. For example, vertical contour changes are less than1-1/2to2 meters, and volumetric changeswouldbe3to4 times less than horizontalshift(" rule-of-thumb" guidance suggestedbyU.S.Army(1984)and Everts and others (1980)). while horizontalshiftmay range uptotensofmeters. Data While the amountofdata availabletoquantifyseasonal variationinshoreline positionisnotlarge,14data setsforwhichsufficient information appears to exist were3located to searchfora solution (Table 1). First. it mightbereasonable toinspecttherelationshipbetweenastronomical tidal conditions and horizontal seasonal shoreline shift, V5'since the tidal condition essentially constitutes a signature characteristicforeach site(i.e.,itcan vary considerably depending on the coast under study). Horizontal seasonal shorelineshiftisdefinedasV5=V max -Vmin,where V max isthe largest measurement representing thewidestseasonal beach, and Vminis smallest measurement representing the narrowest beach (in this paper Visthe distancefroman arbitrary permanent coastal monument to the shorelineatanyonetime). The mean rangeoftide, hmn,(i.e.,the difference between meanlowwaterand mean high water), is plotted against Vs in Figure1.While thereisscatter in the plot, a general trend is apparent. In additiontoastronomical tide conditions,weknowthatwaveclimate mustbeconsidered andthatit, like tidal conditions, varieswidelyfromcoasttocoast. Selectionofvaluesforvariables given in Table 1 canbeillustrated using time series plotsofmonthly averagesforshoreline shift andwavedata.AnexampleforTorreyPinesBeach, California, is plotted in Figure 2, which representstwoyearsofconcurrently observed monthly averagesforshoreline position, wave height,waveperiod, and sediment data (Nordstrom and Inman,1975;Pawka and others,1976).Further, the data have been smoothed by a threepointmovingaveragingsequence.Comparisonofhorizontal shoreline shifts and wave heights suggeststhatforthe monthsfromabout December through April stormwaveactivity prevailed, resulting in a narrower beach,withlull conditionsfromaboutMaythrough October coincidingwithbeach widening. Hence. the average storm wave height, Hs ,isthatoccurringfromDecember through April, and the average lullwaveheight, HL ,isthatoccurringfromMay PAGE 11 FLORIDA GEOLOGICAL SURVEYTable 1. Force,response,and propertyelementsforseasonalshoreline shift analysis.Site VsHs Hl Ts TLhm..0 CO/COs (m) (m)(m)(5) (5)m(mm)Gleneden,OR46.9 1.14 0.729.28.1 1.910.350.815Stinson Beach, CA42.71.280.9916.1 12.1 1.210.301.370Atlantic City. NJ32.01.040.777.47.01.400.300.820Torrey Pines, CA29.01.340.9911.811.41.280.280.794Goleta Point.CA22.91.070.7312.514.01.280.210.547Duck.,NC(1982)18.61.100.758.88.11.000.400.808(1983)20.41.260.739.28.10.980.400.749(1984)17.41.150.708.78.40.960.400.654Surfside-Sunset,CA20.11.100.7310.213.21.070.260.398Huntington Beach,CA18.31.140.9911.610.41.150.211.078Holden Beach, NC15.20.70 0.506.57.01.300.300.614Jupiter Beach.FL10.71.000.635.45.50.920.420.614Boca Raton.FL2.40.640.514.94.50.840.900.933Hollywood,FL2.10.49 0.474.74.50.790.601.037Vs=Seasonal range in shoreline positionorbeachwidth;H s=Storm season averagewaveheight; HL=Lull season averagewaveheight; Ts=Storm season averagewaveperiod; Tl=Lull season average wave period; hmn=Mean rangeoftide; D=Swash zone mean grain size; ll =Lull seasonwavesteepness; Is =Storm seasonwavesteepness; CA=California.FL=Florida,NC=North Carolina. NJ=NewJersey,OR=Oregon. Sourcesofdataaregivenby beach in thetext.4shorelineinclusive) consistently result in the 43-meter seasonal shorelineshiftreported by Johnson (1971) and O'Brien(1982).Concurrently observed dataforfouryears at Jupiter Beach, Florida (DeWall,1977;DeWall and Richter,1977)are plotted in Figure 4. ItisapparentfromFigure 4thatlull wave heightsoccurfromaboutMaythrough September resulting in awiderbeach,withstorm waves occurringfromabout October through at least JanuaryVs=21.9+37.6limnr=0.1302 6O_,.....,,.............-.,........""'T"""T"""'T"'""T"""".,..-_,.....,,....,.......-.,.....,....,..""'1 (m) 20hmrt (m)Figure1.Relationshipbetweenseasonalvariability, Vs ,andmeanrange oftide,h mrt .through October. Note thatwaveperiod varieslittlethroughout the yearforthis site. The classic exampleofseasonalshorelineshift(Johnson,1971;O'Brien, 1982)forStinson Beach, California. represents a22-yearperiod(1948-1970),suggestinganaverage shorelineshiftofabout43meters annually. These data are plotted against six yearsofwavedataforthe period1968to1973(Schnieder and Weggel,1982)in Figure 3. Sediment data arefroma separate source (Szuwalski, 1970). Notethatunlike the data plotted in Figure 2,waveperiodshowsa concerted seasonal trend. The inferencemaybemade. therefore,thatspecial attention shouldbegiven to seasonalwavesteepness values. More recent shoreline surveys published by Collins and McGrath(1989)forthree years(1984-1986 PAGE 12 SPECIAL PUBLICATION NO.4311TI0 JFMAMJJASONOJ MOfttll Figure3.Monthly time seriesforStinson Beach, California,forshoreline variability, V; breaker height, H b ; andwaveperiod,T.waveheight and period are given by HL ,and TlI respectively; similarly,stormseason variables are givenbyHs ,and Ts .Wave heights and periodswereselected to represent conditionsforthelead flanksofseasonal accretion/recession trends, sinceitis under these force element conditionsthatresponses are produced. Similar analyseswereconductedforBoca Raton andHollywoodBeaches in Florida (DeWall,1977;DeWall and Richter,1977)forfour yearsofmonthlydataforV,waveheight and period,withmean grain sizesforswash zone sediment. Data publishedforHolden Beach, North Carolina (Miller,1983)wereplotted by the original author sothatseasonal changes5 IS90 10 85 V 10 ",.;........"'"75 ,. ', ,,.(m) V, 70 .\ .,' \ tiS -,,.,\. 60 ,,(m),.I,,55 ,. I50 "' \ /. - '\IH b.5 /' --- 0 .. 35 (m) I.. I.JH b1.2(m) 1.l 1.00.9 MJJASONOJFMAMtlcMllIIRgure 2.Monthly time series for Torrey Pines Beach, California,forshoreline variability, V; breaker height, Hb ,andwaveperiod, T.producing anarrowerbeach.Monthlyaveragesforwaveheights and periodswereconcurrently measured,witha reported representative grain size.TA single yearofmonthly wave datawerecollected (Aguilar-Tunan and Komar,1978)atGleneden Beach, Oregon,fromwhicha seasonal shorelineshiftofabout47meters is evident. Because wave data reported by the authors are probably inappropriate(i.e.,theystrongly appeartorepresent the initial offshore breakingwaveheight), the multi-year data reportedbythe U.S.Army(1984)are used. A singleswashzonesedimentsizewasreported by Aguilar Tunan and Komar(1978).Shorelineshiftand wave data are plotted in Figure 5. Thesefourexamples illustratehowwavedata valuesweredeterminedtorepresent each season, where the lull season PAGE 13 v (m) (m)T(I)withsimultaneously measured seasonalwavedata. Sediment data arefromtheU.S.Army(1984).Perhaps themostcomplete data sets areforDuck, North Carolina,atthe Coastal Engineering ResearchCenter'sField Research Facility. All information necessaryforthisstudywascollected simultaneouslytoresult in dataforthree years (Miller,1984;Miller and others,1986a,1986b,1986c).JF M A M JJ A SON0J IIoIItll Figure5.Monthlytimeseries for Gleneden Beach, Oregon, for shoreline variability,V;breaker height, Hb ;andwaveperiod, T.Where the specific studies discussed above did not provide the necessary astronomical tide information, these datawereobtainedfromother sources (Harris, For a4-1/2year period, Patterson(1988)reports aVsof20.1 metersforSurfside-Sunset Beach, Orange County, California, alongwithseasonalwaveinformation. Sediment grain size informationisfromSzuwalski(1970).6TResultsforGoleta and Huntington Beaches, California (Ingle,1966)includeapproximatelymonthlysurveysfora one year period, including beach profiles,wave,and sediment data. Unfortunately,waveinformationforthese sites representsonlythose conditionsforthe day profilesweresurveyed. While informationforthese sites generallywasconsistent,waveperiod datafromSchneider and Weggel(1982)wereusedforGoleta Beach duetounresolvable dispersion in thefewdaily data.(I) Month Figure4.Monthly time series forJupiterBeach, Florida, for shore variability,V;breaker height, Hb ;andwaveperiod, T.vcouldbedirectlyassessed by measuring peaksofchange. The data representfouryearsofapproximatelymonthlyprofilesfor16alongshore profiles,withconcurrently measuredwavedata. Sediment data arefromthe U. S.Army(1984).(m)(m)FLORIDA GEOLOGICAL SURVEYSeasonal shorelineshiftdataforAtlanticCity,NewJersey (Darling,1964)weremeasuredforatwo-yearperiod along PAGE 14 SPECIAL PUBLICAliONNO.431981;U. S.Departmentof Commerce,1987a,1987b).ItisworthwhiletonotethatBerrigan and Johnson(1985)comparedwavepowercomputationstoshoreline positionforseven yearsofdataatfourlocalities along Ocean Beach, San Francisco, California. Deepwaterwavedataweremeasuredatsites rangingfrom3.9to26.7kilometers offshore (Berrigan,1985).While some refractioneffectsmayhave occurred duetothe San Francisco entrance bar, there appearstobea correlationbetweenan increase inwavepowerand decrease in beachwidth.ResultsThere is,fromFigure 1,anindicationthatastronomical tides play a role in seasonal variability. The mean rangeoftide, h mrt and seasonalwaveheight difference, ,;" H s H L ,mightbeexpressedasa sum,i.e.,hmrt+ orasa product,i.e.,hmrt Sinceenergyaccordingtoclassicalwavetheoryis proportional.tothe height squared, theproduct,i.e.,hmrt mightbemore appropriate. On the other hand, the sum hasmeritbecause laboratory data,ifavailable, could be used (i.e., since tides are almost never modelled in laboratory studies, a productwouldbe meaningless because the resultwouldalwaysbezero). Ineitherevent,manycombinationsofparameterswereinvestigated (Balsillie,1987b;see also Table 2forsomeoftheequations), anditwasfoundthatthesumwasnot nearly as successfulastheproduct;eitherscatterwasexcessiveasindicatedbyalowcorrelationcoefficient,r,and/orthefittedregression line didnotpassthroughthe originofthe plot.Manyresearchers have emphasized the importanceofwavesteepness in influencing the shore-normal directionofsand transport(e.g.,Johnson,1949;Ippen and Eagleson,1955;Saville,1957;Dean,1973;Sunamura and Horikawa,1974;Hattori andKawamata,1980;Sawaragi and7Deguchi,1980;Watanabe and others,1980;Quick and Har,1985;Kinose and others,1988;Larson and Kraus,1988;and Seymour and Castel,1988).In this paper, the "summer" or lull seasonwavesteepness is expressedas >L = H/(g T L2),and the"winter"orstormseason steepnessas CPs = HJ(g Ts2),Itbecame apparentthatincorporationofthewavesteepness ratioinducednumericalconsistencyinquantitative prediction.Whetherthe ratioisevaluatedas >/>s or >JCPL becomes important. Theformofthe ratioforvarious arrangementsofrelating expressionsforassessment purposes is given in Table2.Hence,if (>/>s) <1.0thenwaveheight during thestormseasonmustbemore important;if (>/>s) >1.0thenwavesteepness plays astrongerrole. Infact,itwouldbeexpectedthat >L/>S results inbettercorrelation, since beaches are erodedbysteeperwaves,withlowersteepnesswavesresulting in accretion. Inaddition,beachsedimentcharacteristics have beentoutedtoplay a significant role. The generalviewisthat,holding force elementsconstant,a beach composedofcoarser sediment is more stable than a beach composedoffinermaterial(e.g.,Krumbein andJames,1965;James,1974,1975;Hobson,1977),i.e.,a beach comprisedofcoarser sediment should exhibit less seasonal variability than a beach composedoffiner sediment (notethatthis explanation isnotsostraightforward,andwillbeaddressed in greater detail in thefollowingsection). Since a numberofinvestigatorshave published general quantifying relationshipswhichin additiontowaveheight and steepness, incorporate sand size(e.g.,Dean,1973;Hattori and Kawamata,1980;Sawaragi and Deguchi,1980;Watanabe and others,1980),itwouldbeprudenttoconsider granulometry in this study. Again,itistobe notedthatmanyformsofpossible relating parameterswere PAGE 15 FLORIDA GEOLOGICAL SURVEY Expressions Using CPL/CPS r Expressions Using CPS/CPL r h"",+41 L {4I sl0.9339 hmrt + 4Is/4IJ 0.7445 [hmrt + (AH)14lL/4lS 0.8843 [hmrt + (AH)] 0.4071 h"",(AH)4l L f4l s0.9047 hmlf(AH) 0.5498 h"", + 4l L /4l s1 hIM + 4ls/4l,J D0.8567D0.3837 hIM(11H)4l L /4l S hIM(liH) D0.9672D0.5478r= Pearson product-moment correlation coefficient between each expression evaluated using measured force and property element dataofTable 1, and measured Vsresponse dataofTable 1.Table2.Assessmentofthewavesteepnessratio for a selection of expressions relatedtoVconsidered in an earlier study,butthatonlythemostsuccessful are presented here. Incorporating the preceding considerations,twoequations are presented, thefirstwhichincludesforceelements only,whichposits:(1)and isplottedin Figure 6. The cubic least squares regressioncoefficient(forced through the origin)of78.5isin unitsofmlwherethemean rangeoftide, hmn,and seasonalwaveheight difference, are in meters. The standard deviationofthe datafromtheequation (1) regression line in the vertical direction (Ricker,1973)is11.4m. The second equation includes the meanswashzone grain size,0,toyield:(2)plotted in Figure7,wherein all variables are expressed in consistent units. Intermsofdimensions, onewillnotethatwhenall dimensional cancellations are made in equations (1) and (2), length only remains. Thecoefficientof0.025wasdetermined using the samefittingprocedure asforequation (1).Itis apparentfromthe figuresthatequation (2) reduces someofthescatterofequation (1). The standard error (Ricker,1973)ofequation (2) in the vertical direction is6.8m.Itmayalsobeofinteresttonotethatthecoefficientofequation (1)whenexpressed relativetothecoefficientof8 PAGE 16 __._-_..9 TheSingle Extreme Eventand theCombinedStonnSeason become availabletofurthertestand/or enhance the prediction relationships. Nevertheless, the results presented here are statistically valid; one should notbetimid in applying resulting computational values pending future refinement in prediction methodology.Onepurposeofthis paper istoactasa pleaformore data. Following are discussionsofafewconcerns relatedtoseasonal shoreline variation predictions. The sandy littoral zone is comprised,fromoffshoreto-onshore,ofthe nearshore, the beach, and the coast. Eachofthese three subzones is created and maintained by setsofforce elements normallydifferentfromeach otherwithinthe long-term temporal framework. When astormor hurricane impacts the littoral zone, the following scenarios are possible: 1) the extreme event produces a combinedtotalstorm tidewhichrises above the beach-coast interface elevation toaffectall three subzones,2)the combined total storm tide does not rise above the beach-coast"mrl (6N)41L/4's Vs = 0.025 D r.s 0.'.72oo 0.20.3 0." 0.5 0.6 07"mrl (6H)41L/41s(m2)figure 6.Illustration of mathematical fit for equation (1).1000""'r.(AN) 41L/4ls (m )DFigure7.Illustration of mathematicalfitfor equation (2).DISCUSSIONA favorable result from manyofthe prediction equations tested during the courseofthis investigation isthatmostshowedVs a trend between Vs and the relating 'lit) parameters(e.g.,column 1ofTable 2). Ostensibly, suchconsistencyshouldnotbesurprising since the major factorsknowntocauseseasonal variabilitywereconsidered, and the remainderoftheworkinvolved rearranging the variablestoreduce scatter. Further, the goaltodelineate seasonalitywasa simplified approach (comparedtorelating the entiretimeseriesofmonthlyvalueswhichbecomes increasingly complex).SPECIAL PUBLICATION NO.43equation(2)resultsina mean 60r--..,.---r--,.----r--.---,.-__ grain sizeof0.318mm which. usin9theWentworth Vs'-O classification scheme.isa medium-sized sand (Wentworth, ("'I 20'922).Equations (1) and (2) engender some heterogeneitythatneeds discussion. Both and t/Jl/t/JS are seasonal parameters. Granulometryasitappears in equation (2) is a property element application, although a seasonal response element application is possible and is discussedina later section. The quantity, h mrt however,isnota seasonal measure.Itis, rather,anaverage approximate hourly measure where one tide (diurnal)ortwotides (semi-diurnal) occur in one tidal dayof245/6hours. Hence, h mrt is also a property elementthatis a signature valueforeach site, notingthatitcan vary significantly depending upon the locale. Seasonal mean sea level changeforwhichthere are no site-specific dataforTable 1 localities,isdiscussed in a following section. The resultsofthisworkmightbebest viewedasafirstappraisal until more data PAGE 17 FLORIDA GEOLOGICAL SURVEY16021986;Savage and Birkemeier,1987),forevents described by scenarios 1, 2 and 3 above. Beach recoveryfollowingtheeffectsofastormwaveevent(i.e.,scenario 4)wasrecorded by JamesP.Morganathis Pensacola Beach, Florida, home (Figure 8);withina day followingstormwaveabatement, the beach had recovered to its pre-stormwidth.123 56189101112Day Figure 8.Exampleofthequickresponse and recoveryofthebeachtostormwaveactivity,Pensacola Beach, Florida, December1974;thestorm peak occurred on December 7 (data courtesyofJamesP.Morgan, personal communications).(m)50(m)0The magnitudeofseasonal shoreline change may varyfromyear-toyear, sinceforanysite some years may have more frequent and intense storm tide andwaveactivitythanotheryears. Horizontal shoreline shifts duetodirect storm and hurricane impacts arenowusually recorded. However,forstormsthatdo not directlyimpactthe shore(i.e.,arefaroutatsea,forexample TropicalStormJuan (Clark,1986)whichaffected Florida) but generate stormwavesthatdo interface elevationbutdoes persist long enoughforthe beachtobeeroded and thecoastis attacked bystormwaves, 3) the combined storm tide doesnotrise above the beach-coast interface elevation and is short enough in duration sothatonly the nearshore and beach are affected, and 4) the extreme event remainsoutatseasothatimpactis indirect(i.e.,a combined totalstormtide doesnotoronlyfractionally reaches the shore) and storm waves primarilyaffectthe nearshore and beach. The combined totalstormtide used hereisdefinedbyDean and others (1989) as thestormsurge duetoastronomical tide,windstress, barometric pressure, and breaker zone dynamic setup,whichdefines the active phenomenaforscenarios 1, 2, and 3(i.e.,the stonn tideevent).Scenario 4 includes only theeffectsofbreakingwaveactivity,including dynamicwavesetup, andistermed the stonnw.ve event.Scenarios 1 and 2 are thosewhich,depending onstormstrength, duration, continental slope, and approach angle, usually produce the design erosion event (Balsillie,1984,1985a,1985b,1986).Probabilistically, the frequencyofoccurrence increasesfromscenario 1to4. Under certain circumstancesofevent longevity, astronomical tides, and nearshore slopes, exceptions can occur. One such exception occurredwhenHurricane GilbertstruckCancun, Mexico in1988.Because there is essentially no continental shelf and nearshore slopes are steep, all eroded sandfromCancun's beacheswasremoved and natural beach recoverywasnot possible. Potentially, other exceptions can occurwhere,forinstance, submarine canyonsmightactasa sediment transport conduit and sand is irremeably lostfromthe littoralsystem.Formostshores, however, continental shelves arewideand nearshore slopes gentle enoughthatbeach recovery to pre-storm dimensionsfollowingsinglestormimpactoccurs in a periodofonetoseveral days (Birkemeier,1979;Bodge and Kriebel,10 PAGE 18 SPECIAL PUBLICATION NO.43cause shoreline erosion, such erosion is usually not measured.Month Figure 9.Monthly average occurrencesofextremeeventwaveeventsfortheOuter BanksofNorth Carolina. P IJI IJo,JJ/IJ a JJII IJ D \'\', Q Beach Sedimentsa EXTREME EVENT TYPE o Extretroplcel(Dolan. Llna,andHayden,1981) "42-1184 oTropica'I(Neumannetal. Hurricane 1981)1940-1980Beach sediments engender some interesting concerns.Howweconsidersedimentsdependsuponwhethergranulometry is appliedasa property elementora response element,whichin turn has aneffecton the dimensional configurationofa numerical representation. As an example, equation (1) requires an additional parameterwithunitsofL1forthe equationtobeunit consistent. Equation (2) was rendered unit consistent by dividingbya granulometric parameterwitha length dimension.Ifthisistobethe applied case,itisusefultonote that when sedimentologic grain size is specified inS.I.units, the mean grain size and standard deviationmomentmeasures have unitsofmm,while51 '5c: o 2 .. c: &io 3... E z & 2... .I Dolan and others (1988) conducted an extensive study onextratropicalstormactivity,assessed alsointermsofstormwavehours,for41yearsofdata(1942to1984)along the Outer BanksofNorth Carolina. These data (Figure 9)showa concerted seasonal trend. In addition, the author extracted from Neumann and others(1981)tropical storms and hurricanes whose tracks camewithinabout250milesofthe Outer Banksforthe period1940to1980.These latter data, also plotted in Figure 9, are addedtothe extratropical data (plottedasa bold, solid line). Hence, the totalstormrecord is nearly represented and, exceptforonly afewdirectimpacts, representstormwaveevents (i.e., scenario' 4 above). For the mid-Atlantic, about35storms occur per year on the average (about26winterevents and 9 summer events),93%ofwhichare extratropical events. In termsofstorm wave duration, Dolan and others (1988), determined using hindcast techniques that on the average,stormwavesoccurforabout 571 hours per year (i.e.,24days per year)forextratropical stormsoffofthe Outer Banks;winterstormwaves persistforan averageof433hours (i.e.,18days), and summer stormwavesabout156hours (i.e.,6.5days). These data strongly correlatewiththe expectationofwidermid-Atlantic east coastsummerbeaches and narrowerwinterbeaches, and illustrate the importantfactthat a largenumber...notafew... winterstonnevents aTe requiredto maintain a nanuwer winterbeachrelativeto a widersummerbeach.11 PAGE 19 FLORIDA GEOLOGICAL SURVEY Table3.Mean annual beach grain size (foreshore slope samples)frommonthlydata,and range in size.Annual Range SiteD(mm)ofD Source (mm) FLORIDAS1.AndrewsSt. Pk.0.290.04Balsillie,1975Grayton Beach0.370.13" "Crystal Beach0.370.15" "J.C. Beasley St.Pk.0.400.11.."Navarre Beach0.410.14.."Fort Pickens Beach0.43 0.27""NORTHCAROLINA Duck0.40 0.19Miller.1984CALIFORNIA Goleta Pt. Beach0.210.16Ingle,1966Trancas Beach0.220.18,"Santa Monica Beach0.260.29.."Huntington Beach0.210.14".LaJolla Beach0.170.04""skewnessandkurtosisaredimensionless. Otherwise, the granulometricmomentmeasures canbespecified all in dimensionless phi units. Beach sands characteristically have a range in sizefrom0.1 mmto1.0mm(U.S.Army,1984)whichoccupies about46%ofthe sand sized rangeofWentworth(1922;i.e.,0.0625to2.0mm). From Table 3,itis apparentthatthe range in mean grain sizes occurring overanannual period is less than1/3ofthe commonly found range in beach sand size(i.e.,0.9mm). Therefore, the typical annual mean grain size,0,forany beachmightbean appropriate measuretoconsiderasaproperty elementprovidedthatsufficient samples are available annuallytoobtain a reliable measure(e.g.,a suiteofmonthlysamples). This impliesthatthere needstobea real difference in mean grain sizesfromsite-to-siteforthe applicationtohave meaning. Even so, theuseofmean grain size alonewithoutconsiderationofstandard deviation, skewness and kurtosis remainssomewhatofa curiosity other than: 1. its use results in a goodfitforequation (2), 2.isproperly applied in equation (2)(i.e.,the largerthevalueofD,the smaller becomes Vs)'3. produces the proper unit dimensionsforthe equation, and 4. has been a considered variable in other research results.Itis generally the case (CASE 1ofTable 4)thatthe coarsest beach sandisfound in theswashzone, andwhichis the only type of sample considered here sinceitdirectly represents energy expendituresofthe littoral hydraulic environment. One might suspectthatswash samples are coarser during the storm than the lull season. However, the range in sediment sizewithinthe sand-sized rangeislimitedforany beachtothe coarsest available materialTable4.Twocasesofsedimentologic responseofmomentmeasurestowaveenergylevels.CASE'CASE 2 EnetgyUveIsAle EnetgylewisAle&.cessive 10 NatfJcc:essive 10Se __1dDkigicSe6nentulagicRespawlSeRespmi5e MEAN GRAIN SIZE Ds-DLIOs>DLSKEWNESS Sk S-SkLISks-"' ........__ '""-e_1 It.Z '.1 ..&.....I.""""J...J.."SO.DJF SO.D_Ill figure 10.Typical examplesoftime series relationofmonthly data for breaker height.waveperiod, and foreshore slope grain size for California (data from Ingle, 1966) and northwestern Rorida panhandle (data from Salsillie. 1975) sites.whichmayormaynotdifferfromthecharacteristicallyrounded. quartzose feldspathicU.S.beach sands consideredinthiswork.There also occursthecase (CASE 2, example 2) where a beach is comprisedofsediments exceeding the sand-sized range.Anexample is Oceanside Beach, Oregon, mentioned earlier, inwhichallthesand-sizedsummerbeach material is removedtoexpose awintercobble beach. Under such conditions, one wouldexpectthatsediment coarsening,asreflectedbythe mean grain size and skewness, would resultfromhigherwaveenergy levels becauseofthe excessive sizeofcoarser sediments. When singularly considered, the 1stmomentmeasure (mean grain size) tellsusnothing about the natureofthe distribution. PAGE 21 FLORIDA GEOLOGICAL SURVEYFromthepreceding discussion,itis apparentthattwogeneral cases canbeidentifiedwherewaveenergy levelseitherexceedstabilityconstraintsofthe coarsest fractionofthe sedimentologic distribution, ortheydo not. For three moment measures consideredtobest represent sedimentologic responsetothewaveenergy force element,stormand lull season responses are listed in Table 4. Forthetwocases (Table 4)onlythe kurtosis persists in providing a response, because the4thmoment measure isnotrenderedineffectivetoregister a changebyexcessivewaveenergy levels. Therefore, a parameterforconsiderationthatmore nearly quantifies sedimentologic responsemightbe given by: The2ndmomentmeasure (standard deviation) tells us about the dispersion about the 1stmomentmeasure, but leaves no insightastohowthe distribution departs either symmetrically or asymmetricalfromthe normalbell-shaped frequency curve (orfromthe straight lineforthe cumulative curve plotted on standard probablity paper). Such departure is a characteristicofthe tailsofthe distribution aboutwhichknowledge is progressively imparted tousby considering the 3rd moment measure (skewness),4thmoment measure, (kurtosis), and highermomentmeasures (Tanner, personal communication; Balsillie, 1995).Itis, infact,the tailsofthe distributionwhichcan provide a great dealofenvironmental information.Ithas been demonstrated,forinstance,thatthere is an inverse relationship between the kurtosis and the levelofsurfwaveenergy expenditure (Silberman,1979;Rizk,1985;Rizk and Demirpolat,1986;Tanner,1991,1992).Tanner(1992)has reported a correlation betweensealevel rise and kurtosis, because the rise component is attendedbyan increase in surf wave energy expenditure. e =(20+Sk)KD(3)14where the moment measures are defined in Table 4. The 3rd moment measure (skewness) of equation (3) has a valueof20added to itinordertoassurethatpositive values will result. The parameter()when evaluated usingS.I.units has unitsof V' (dimensionlessunitsresultwhengranulometric measures are evaluatedinphi units). By using seasonal valuesof 8, thatis, 8 s forthe storm season and 8L forthe lull season,itmaybepossibletocompile a sedimentologicresponse elementparameterthatcanbeincorporated into equation (1). The proper formofthe parameter, including equation (3), however, requires additional data, research, and testing. AstrDllomicalTitles Thatmeanastronomicaltideelevations exhibitcyclicseasonal variability has long been established (Marmer,1951;Swanson,1974;Harris,1981)and is includedintide predictions. TheU.S.DepartmentofCommerce(1987a,1987b)states, however,thatat....ocean stations the seasonal variation is usually less than half afoot.Marmer(1951)notesthatseasonal variation in termsofmonthly mean sea levelforthe U.S.canbeasmuchas0.305m(1foot; Table 5); some examplesfortheU.S.east, Gulf, andwestcoasts are illustrated in Figure11.Based on the many yearsofmonthly data, researchers (Marmer,1951;Harris,1981)note slight variations in the seasonal cyclefromyear-to-year, but also recognize the periodicity in peaks and troughs over the years. For muchofourcoast, lower mean sea levels occur during thewintermonths and higher mean sea levels during the fall. Harris (1981 ) inspected the recordtodetermineifstormand hurricane occurrencewasin anywayresponsibleforthe seasonal change,butfound....nosystematic variability. Galvin (1988) reportsthatseasonal mean sea level changes are not completely understood,butsuggests that there appearstobetwoprimary causesforlowerwintermean tide PAGE 22 SPECIAL PUBLICATION NO.43levelsfortheU.S.east coast:1.strongnorthwestwinterwindsblowthewaterawayfromshore, and 2.watercontractsasitcools.Henotesthatwindsare moreimportantin shallowwaterwhere tide gauges are located,butthatcontraction becomes important in deeper waters.Swanson(1974)also notes....seasonal changes resultingfromchanges in direct barometric pressure, steric levels, river discharge, andwindaffectthemonthlyvariability. Seasonal variation in tidesisusuallyattributedtotwoharmonicconstitutents:onewitha periodofoneyeartermed thesolarannual tidalconstituent,and theotherwitha periodofsixmonthstermed the solar semiannualconstituent(Cole,1997).Someconsiderthesetobemeteoroligical in nature,ratherthan astronomic.However,becausetherootcauseofcyclicseasonalweatheristhechanging declinationofthe sun,theyshould more nearly be astronomical in origin. Harmonic analysisofthe annual tidal recordcaneasily determine the amplitude and phaseofeachofthese constituents, thereby providing a mathematical definitionofthe seasonal variation. (George M. Cole, personal communications.) Comparing the closest appropriatecurvefromFigure 11toFigures 2 through 5, itis apparentthatthelowestseasonal standofmean sea level and, therefore, average astronomical tideeffectsoccurswhenthe beach is narrowestforStinson Beach andTorreyPines Beach, California, andJupiterBeach, Florida. For Gleneden Beach, Oregon,narrowbeachwidthsandmonthlyaverage tidal highs seemtobemore nearly in phase. Therefore,itisnotclearthatseasonal changes in astronomical tidessignificantlyaffectseasonal shoreline variability,atleastnotin termsofaveragemonthlymeasures. Quite clearly, however,suchdata needs tobeprocuredforeach sitetoconfirma correlationorlack thereof. Should the proper correlation consistentlyTable5. Seasonalrange inmonthly average waterlevels.I SiIe I v:" IhII-I(m) Law U. S. fastCoast New York. 190.177Feb SepAtlanticCity190.165Feb Sep Baltimore190.238Feb Sep Norfolk190.177Feb Sep Charleston190.253MarOctMayport190.314MarOct Miami Beach 17 0.259MarOctU.S. a.Coast KeyWest190.216MarOctCedar Key100.244Feb Sep Pensacola190.232Feb Sep Galveston190.247JanSep Port Isabel40.262FebOctU.S. WestCoast Seattle190.159AugDec Astoria190.219AugDec CresentCity140.180AprDec San Francisco190.104AprSep Los Angeles190.152AprSepLaJolla190.143AprSep San Diego190.152AprSep Notes:1.h=seasonal range based on averageofn yearsofmonthly means wheremonthlymeans are averageofhourly heights;2.San Diego gaugeislocated in San Diego Bay; 3. Astoria gauge is located15miles upstream from the mouthofthe Columbia River.occur(e.g.,lowmonthly average mean sea level -widerbeaches, and highmonthlyaverage meansealevel -narrowerbeaches) then a relating parameter needstobeincorporated in the quantifying predictive relationship(s).Itisofconsequencetonote,forthedataofTables 1 and 4,thatthe seasonal rangeofmonthly average mean sea level isfrom9 to33%ofthe mean rangeoftide(hmrt).APPUCAnONOFRESULTSWhile horizontal shorelineshift(or beachwidthchange) addressesonlyone15 PAGE 23 FLORIDAGEOLOGICALSURVEY III u. S. GULF coasTMONTH u. s. weST COAST ,M A M A 0 DRgure11.Monthlyvariation in sea levelforthecontiguous United States (after Manner,1951).dimensionofa measureofbeach change,itdoes servetostraightforwardly punctuate the natureofthe phenomenon. The mannerofapproaching quantificationofthe phenomenon here, allowsfora simply applied methodologythatisusefulforeducational,technical,and planning purposes.General KnowledgeSeasonal beach shifts arenotgenerallyknownby the layman. In Florida,with35,000newresidents arrivingmonthly(Shoemyen and others,1988),newcoastal property owners have been alarmedafterpurchasing ocean-fronting property during the "summer"whentheir beach iswide,tofindorreturntofind a narrowwinter"beach, believingthattheyhaveunwittinglypurchased eroding property. OstensiblY, this might result in an applicationfora permittoconstructa coastal hardening structure suchasa bulkhead or seawallwithoutinvestigating seasonal beachwidthvariation on the partofthe applicant, the applicant's design professional,orthe permitting16agency. The resultsofthis paper provide a quantitative basis uponwhichtoinform the public, and a method to assess a permit application. SeawanlllDundary of PublicversusPrivate OwnershipThe boundary between private (i.e., upland) and public (i.e., seaward) beach ownership is fixed by some commonly applied tidal datum. For mostoftheU.S.this is the planeofmean highwater(MHW) which, whenitintersects the beach or coast forms, the mean highwaterline. However,unlikeotherriparianownershipdeterminations (i.e., fluvial, lacustrine and estuarine), littoral properties must, in addition, contendwithsignificantwaveactivitythat seasonally varies. Hence,ocean-frontingbeachesall-too-oftenexperience cyclic seasonalwidthchangesofa magnitude long recognizedasproblematic in affixinganequitable boundary (Nunez,1966;Johnson,1971;Hull,1978;O'Brien, PAGE 24 SPECIAL PUBLICATION NO.431982;Graber and Thompson. 1985; Collins and McGrath. 19891. Many investigators have suggestedthatthe legal boundaryforoceanfronting beaches should notbecontinuously movingwiththe seasonal changes. but shouldbethe most landwardor"winter"lineofmean highwaterINunez.1966).Selectionofthe"winter"MHWlinewouldbethe most practical to locate andwouldbethe most protectiveofpublic interest by maintaining maximum public accesstothe shoreline (Collins and McGrath,1989).InFlorida, the ocean-fronting legal boundary seasonal fluctuation issuewasdeliberated upon in StateofFlorida, DepartmentofNatural ResourcesvsOcean Hotels, Inc. (StateofFlorida, 1974)asitrelatedtolocating theMHWline fromwhicha50-footsetbackwastobedetermined. Judge J.R.Knott, upon considerationofall the options. renderedthefollowing decision: ThiseDUltu,.,.fotweoncludesth the winter and most1MHIwan/ mean highw.r.r line mustbeselectedasthe boundary Iwtween the stat.and the upland owner.In so doingthe eourthashad to balaneethepublicpoDey favoring private littoral ownership against thepublie poOey of holdingthetideland in trust forthe people,whetwthepreseNation of a vital pubHerightisseeured withbutminimal .ffectupontheinte,.sts ofthe upland owner.A1966California CourtofAppeal decision rejected the applicationofa continuously moving boundaryinPeoplevsKent Estate (StateofCalifornia,1966).However. no decision has been renderedastowhatlinetouse (Collins and McGrath,1989).More recently, however. Collins and McGrath (1989) report:The AttomeyGeneral'sOffiee in Califomia luis offetwdits informal opinion thilt, if squarelyfaeed withthe issue, Califomia eourts would followthe twasoning intheRorida ease and adoptthe "winter andmost landward lineofmeanhigh tide" as the legal17 boundarybetweenpublie tidelands and private uplands ... (it shouldbe undemoodthat such aboundary, while relatively stable, wouldnotbe permanently fixedbutwouldb.ambulatorytotheextent th.reoccurs long term aecretion or erosion). Collins and McGrath also discuss special issues suchasshore and coastal hardening structures,artificiallyinduced accretionofsand.etc.,and theirworkis highly recommendedforfurtherreading. However, no formal legal adoptionofthelittoral MHW boundary has found nationwideacceptance. This is symptomaticofmankind's tendencytogive credencetocodesofanthropicconductthrough the t.ws.fMan (published in local codes, statestatutes,and federal regulations, etc.) buttoessentially ignore the environment andhowitworksthrough the LrNs .f NIItuIe (published in scientific papers and journals). Untilabalance is more nearly achieved,weshallcontinuetoexacerbatetheenvironmental crisisthathas befallenusall. The resultsofthis paper provideforone small aspectofthe behaviorofnatureanopportunitytoachieve a balance betweenthetwosetsoflaws.Long-Term Shoreline ChangesThe initial motivationtoinvestigate this subject was the developmentofa methodologytoanalyze and assess longtermshorelinechanges.Quantitative behavioroflongterm shoreline changetoassess coastal stability is best accomplished using actual historical surveys. In Florida,asmanysurveysaspossible are locatedforthe period from about1850topresent (aerial photographyisusedwherean historical hiatus occurs), usually resulting in from 8 to14points to represent the historical shoreline position (Balsillie.1985a,1985b;Balsillie and Moore. 1985; Balsillie and others,1986).These data are assessed alongshoreata spacing of approximately300m. Hence. historical change rate analysis PAGE 25 FLORIDAGEOLOGICAL SURVEYVF Rgure 12.Example of long-term shorelinechangerate (solid lines) temporal analysis using seasonal shoreline shift data(dashed lines);seetextfor explanation.Ofthe numerical methods availabletoanalyze such data, many can actually magnify the uncertainty and/or error associatedwiththe final resultsofaninvolved computational approach. Cautionwithrespecttothis aspectofanalysis cannotbeover emphasized. Infact,the topic is so importantthata seriesofstandard equationsforassessing the propagationoferror in computing have been provided in the Appendix.20001950a:-6.25m/YF c:-0.45m/YFb:+110m/YFd:+1.64m/yrmagnitudethatwemust keep the numberofcomputational stepstoa minimum in ordertominimize the propagationoferrorincomputing (bearinmind thatinadditiontothe tempol'lll analytical component a spatial component remains,whichfurther increases analytical computation). The bottomline"isthatweneedtousethemostappropriateandcomputationallysimpleanalyticalmethodologyavailable. Themostappropriate statistical analytical tool is undoubtedly tIendanalysis whichalready includes measuresofdetermining the associatederrororvariability.Inaddition,whatwemight learn andquantifyabout nature'sownsystematic variability canbeusedtoour advantage both in termsofassessing the acceptabilityofdata, and asananalytical tool. Such is the usefulnessofhorizontal seasonal shoreline change. An exampleoftemporal analysis is illustrated in Figure 12fora locality about2.7kilometers southofa major inlet on the east coastofFlorida. Equation (1)wasevaluated using the appropriate wave dataof1900Art""lalNou.Is_80".1JettyConstructionaeg_n ,"... I ... InletArtlflcl_lIyCut1I ....," a.b' ... .,... ..---_-.I,... ..,"C......'..._-'!. I --...... d. .. -,--'----,# 200100400300v(m)analyticalanalytical tempol'lll aspatialrequires both acomponentand component. The natureofhistorical shoreline location data is suchthatthere is associated error and variability. Surveying error includes inherent closure errors, error duetoolder technologies, and non-adjustment errorformore recent vertical and horizontal epoch readjustments. Survey nets establishedforcountysurveys may not precisely relatetoadjacentcountynetsastheywouldin a state-wide net. Long-term sea level changes, though slight,affectlong-term shoreline changes. These sourcesoferrormaybecalled map-source errorsafterDemirpolat and others(1989),forwhicha magnitudeof9to15mmaybeappropriate (Demirpolat and others, 1989). Interpretive plottingoferrorsofshoreline location (depending on data concentration) on original survey mapsmustbeassumed,especiallyforolder maps. Present digitizing technology results in an errorof3to4m (Demirpolat and others,1989).Exceptforrecenttechnologies,magnitudesoferrorsforexamples suggested above arenotknownwithcertaintyin the majorityofcases. Even so,itcanbeenvisioned thattheyareofsufficiently large 18 PAGE 26 ---SPECIAL PUBLICATION NO.43Thompson('977)and tidal data from Balsillie('987a). To the result.onestandard deviation was added to yield a predicted seasonal variability measure of50.5m.Startingwiththe most recent data and moving back in time, regression techniques are usedtodetermine a trend line (solid lineinFigure 12) aboutwhichplus and minus one-half the seasonal variability measureisaffixedinthe vertical direction (dashed lines in Figure 12). The slopeofthe trend lineofthe time seriesisthe rate of erosionoraccretion(azero slopeorhorizontal line represents stability).Nowthe seasonal variability measure becomes a valuable asset towards identifying spurious data or long term change segments in shoreline behavior. For instance,ifa point lies outsidetheseasonal variability envelop in the middleofsegment d, onewouldconclude that either seasonal variabilitywasextremeforthatyear (forwhichthere are undoubtedly no records)orthe survey was made immediately following extreme event impact (either storm tideorwaveeventforwhichthere are probably no records).Ineither case,wehave reasontonot include the data pointinour analysis, since there are sufficient data pointsforthe segmenttosuggest a strong trend. Interactively, trends in segment datlocalities upanddowncoast canbeusedtoverifysuch a trend in the spatial componentofthe change rate analysis. We also can use historical information about the areatoassist in analysis. For instance,weknowthatthe inletwasartificially constructed in1951,andjettyconstruction began in1953.Furthermore, artificial nourishment southofthe inlet began in1974.Eachofthese eventsiscoincidentwitha new episode in shoreline behavior, and maybeverifiedwithsimilar analysesatnearby upand down-coast sites. Notethatthere are toofewdata points to quantify the shoreline change trendforsegment c; either additional data points are required or verification/readjustmentfromanalysesat19nearby adjacent sites are required to assure quantificationofrepresentative shoreline change. Project Design and Pedonnance Assessment Both Iong-tenn changes and eJtt1'eme event impacts have long been considered in assessing coastal development design. activities (until recently the formerhasby and-largebeenqualitative).Inproper order,long-termchangesshouldfirstbe determined, followedbythe design extreme event impact. Thefirstdetermination allowsforprudent sitingofthe developmentactivity,and the secondforresponsible structural design solutionstowithstandstormtide, wave, and erosion event impacts. However,withoutknowledgeof BellSOIIII1shoteIineshifts fora particular locality, uncertainty willbeintroduced into suchassessment.Followinglong-termdeterminationofwherethe shorewillbe(e.g.,say, a standard 30-year mortgage period)itwould,forinstance,beprudenttoadjust the beachwidthofa given topographic surveytoits narrowest expected seasonal dimension, thentoapply extreme event analyses. Considering the significant outlayofresourcesforbeach nourishment projects,itwould seem appropriate to consider seasonal shoreline variability both in project design and in assessing performance. The controversial issueofwhether coastal hardening structures(e.g.,seawalls, bulkheads, revetments) promote the erosionofbeaches fronting them,isone of complex proportions. Without being long-winded, the issue might finallyberesolvedbyinspecting long-term shoreline location data. Again, however, seasonal shoreline shifts would require quantification and applicationinthe analysis.Atthe very least, methodology developed here would allow one to determineifseasonal shoreline change wasofsignificant proportions thatitshouldbeconsidered in design applications. Using PAGE 27 FLORIDAGEOLOGICALSURVEYknownwave. tidal. and sedimentological dataitwouldbea straightforward task to compile such results. particularlyinFlorida where the coasthasbeen monumented.CONCLUDINGREMARKSFor muchofour shoreline, seasonalshiftsin shoreline position occur. While the phenomenonhasbeen the subjectofconsiderableconcern,nospecificquantification has. untilnow,surfaced.Ithas been noted earlier that some shorelines(e.g.,east-west trending shores) apparently donotexhibit seasonal shifts. This maybeduetostormwaveimpacts occurring in groupsforperiodsofless thanmonthlyand/or duetoclimatic changeaffectingstormfrontazimuths relativetoshoreline azimuths. Correlation mightbeattainedbyselectingmostand least activemonthlyaverages, orbyapplying moment statistics.AnhistoricalstudyofGulfofMexicostormwaveand direct coastal impacts,asDolan and others(1988)conductedfortheAtlanticOceanoffNorth Carolina, is needed. Resultsofsuch astudywouldshed light on the regional behaviorofeast-west trending shoresofthe central Gulf, and would alsobeapplicabletothe more nearly north-south trending shoresofthelowerGulf coastsofFlorida and Texas. While the methodologyforassessing average seasonal shoreline and beachwidthvariability canbeusedfora varietyofimportantapplications, the developments presented here are afirstappraisal. Theintentofthisworkis to invoke interest in the subject andtoactasa pleaforadditional data onwhichtotestexisting predictive methodology and/or develop more exacting technology. For instance, while thisworktreats straight ocean-:fronting beaches composedofsand, seasonal changesofpocketbeaches mightbetreated by20including seasonal wave approach angle changes, and data for beaches composedofsand and pebbles (i.e.a very large standard deviation) would help in understanding the roleofthe sedimentologic property element. ACKNOWI.DGEMENTS Reviewofanearlier manuscript leadingtothis paper provided significant guidance, and those comments and suggestions fromPaulT. O'Hargan, Joe W. Johnson, George M. Cole, Alan W. Niedoroda, and Gerald M. Ward are gratefully acknowledged. JamesR.Allen and RalphR.Clark, and WilliamF.Tanner reviewed the presentformofthepaper and made several valuable suggestions. Special thanks are also extended to Kenneth Campbell,EdLane,Jacqueline M. Lloyd, Frank Rupert, and ThomasM.Scottofthe Florida Geological Surveyforthe many useful editorial comments.REFERENCESAguilar-Tunan,N.A.,and Komar,P.D.,1978,The annual cycleofprofile changesoftwoOregon beaches: TheOreBin, v. 40,p.25-39.Aubrey,D.G., 1979, Seasonal patternsofonshore-offshoresedimentmovement: JournalofGeophysical Research, v. 84,p.6347-6354.__ Inman,D.L., and Nordstrom,C.E.,1976, Beach profilesatTorrey Pines, California:inProceedings,15thInternationalCoastalEngineering Conference, v. 2,p.1297-1311. 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Eliot,I.G.,and Clarke,D.J.,1982,Seasonal andbiennialfluctuation in subaerial beach sediment volume on Warilla Beach, New South Wales: Marine Geology, v. 48,p.93-103.Everts,C.H.,DeWall,A.E.,and Czerniak, M. T.,1980,Beach and inlet changes at Ludlam Beach,NewJersey: Coastal Engineering ResearchCenterMiscellaneousPaper No. 80, 146p. Felder,W.N., and Fisher, J. S.,'980,Simulation model analysisofseasonal beach cycles: Coastal Engineering, v. 3,p.269-282.Galvin,C.J.,Jr.,1988,The annual tide in Chesapeake Bay: Coastal Engineer Notes,p.3-4. Garrow,H.C.,1984,Quantificationofshoreline rhythmicity:inProceed ings,17thInternational Coastal Engineering Conference, v. 2,p.2165-2180.Gorsline,D.S.,1966,DynamiccharacteristicsofwestFloridagulfcoast beaches: Marine Geology, v. 4, p.187-206.Graber,P.H.F.,and Thompson, W. 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PAGE 35 FLORIDAGEOLOGICALSURVEYWentworth,C.K.,1922,A scaleofgrade and class termsforclasticsediments: Journal of Geology,v.30,p.377-392.Ziegler.J.M., andTuttle,S.D..1961.Beach changes basedondaily measurementsoffourCapeCodbeaches: JournalofGeology, v.69,p.583-599.Zimmerman, M. S., and Bokuniewicz,H.J.,1987,Multi-year beach response along the south shoreofLong Island,NewYork: Shore and Beach, v. 55,p.3-8.APPENDIX: PROPAGA710NOFERRORSINCOMPunNG(compiled from formulations in Barry, 1978) Where R is the resultofsome numerical operation(e.g.,addition, subtraction, multiplication, division,powerfunction, average, etc.)formeasured quantities N N2 ,N3 ,...,Nn ,eachwithassociated measurement errors E1 ,E2 ,E3 ,..,En,respectively, then the total error Erorisapplied as: where Etorisdetermined according to:ADDITIONORSUBTRACTION EIr1I=0Je: + E; + + ...+ E; PRODUCTORQUOTIENTE ..=R ..... (;.) 28AVERAGE + + E; + ... + E; E ItJt -...!...-..:...-..---=:......---=..--_:,:,-,nCONSTANTERRORwhere E=E ,=E2=E3=...=En EIrJI'" E {n POWERwhere(R+E,}m=(N1+E1)m EhJI'"E.,11,""" ROOTwhere(R+E,}'/m=(N,+E,)1/mE -1 EItJt m1 N; PAGE 36 SPECIAL PUBLICATION NO.43OPEN-OCEAN WATER LEVEL DATUM PLANES: USE AND MISUSE IN COASTAL APPLICATIONSbyJamesH"Balsillie,P.G.No.167 ABSTRACT Swanson(1974)notes that tidal datum planes".., are planes of reference derived from the rise and fall oftheoceanic tide", There are numerous tidal datum planes. Commonty used datums in the United States include the planes of meanhigh., high w.", (MHHW), mean high WMer(MHW),"""tide__(MTl),""""1wrJI(MSl).,.."low... (MlW), and",."/owei'lowWI (MllW).Eachdatumisdefined for a specific purpose or to help describe some tidal phenomenon.Forinstance, MHW high water datums havebeenspecified by cartographersinsome states(e.g.,Florida)asa boundaryofproperty ownership.lowwater datum planes havebeenusedasa chart datum becauseitisa conservative measureofwater depth and, hence, provides a factorofsafetyinnavigation. High water tidal stages have historicallybeenofimportance because they identified when sailors should report for duty when "flood tide" conditions were favorableforocean-going crafttoleave port, safely navigate treacherousebbtidal shoals,andputtosea.Not only do tidal datum specifications vary geographically based on localtoregional conditions for purposesofboundary delineation, cartographic planes, designofcoastal structures, and landusedesignations, etc.,butthey have changed historicallyaswell. Moreover, given ongoing technological advancements(e.g.,computer-related capabilities including the adventofthe personal computer),howweapproach these data numericallyishighly importan't from a data management viewpoint.INTRODUC710NTide gauges are usually locatedinwater bodies connectedtothe oceans, suchasestuaries and rivers, and may evenbeusedtorecord seichessuchasthose occurring in the Great Lakes. Here, however, the concern iswithopen oceantides. Openoceantidegaugesaredefined" ... asthosegaugessiteddirectlyupontheopenoceannearshorewatersand SUbjecttotheinfluenceofoceanprocesses,excludingthoseundertheinfluenceofinlethydrodynamics....(Balsillieandothers,1987a,1987b,1987c).Thelatterconstraintinthedefinitionisincludedeventhoughitisdifficulttodeterminetheextentofinfluencefrominlettoinlet. Open ocean tidaldatumapplicationsin29Florida are problematic becausethereare alimitednumberofgaugingstationstorepresentastronomicaltidalphenomena.Whileithas beenstandardpracticetolinearlyinterpolateopen oceantidaldatumsbetweengauges, such anapproachisnotrecommendedshouldthegauges bespacedfurtherapartthanabout6.2miles (Balsillie andothers,1987a).Ofthe33currentlyavailable open ocean gauges in Florida (Table 1),onlythree pairsofstationsmeetthisconstraint.Infact,theaveragedistancebetweenFlorida open oceantidegauges is27.4miles. Ostensibly,the6.2-mileconstraintisrecommendedsinceconcurrentlysimilar tidalstagedatumelevationscanvarysignificantlyoversegmentsofthecoastlinewhenthisdistance PAGE 37 FLORIDAGEOLOGICALSURVEYTable.1. Tidal Datums and RangesforOpenCoastGaugesofCoastal Rorida(Updatedin1992after Balsilie. Carlen and Watters.1987a,1987b,1987c). OpenPlane MHHWMHW M1l. MLW MLLW Coordinates station Name CoastMTR XGauge Easting Northing (Feet) (Miles)I.D. (Feet) (F..t) (Ft.NOVO)FLORIDA EAST COAST Femanclina Beach 0061 362649.81 2287406.62 3.52 3.11 0.25 -2.61--5]2 5.831little Tabot Island 0194372355.76 2216450.20 3.60 3.30 0.55 -2.19 -2.35 5.49 19.753 JacksonviUe Beach 0291 377952.02 2163090.54 3.25 2.94 0.39 -2.17-2.33 5.11 30.150St. Augustine Beach 0587 417053.67 2008422.56 2.73 2.48 0.15 -2.17 -2.33 4.62 60.491Daytona Beach 1020498405.18 1779242.33 2.52 2.27 0.19 -1.88 -2.06 4.15 106.820Daytona Beach Shores1120511704.59 1749549.40 2.44 2.06 0.07 -1.89 -2.06 3.98 112.990 Patrick Air Force Base1727628785.91 1421930.52 2.272.09 0.32 -1.45 -1.61 3.54 185.030Eau Gallie Beach 1804619782.34 1383121.82 2.25 2.07 0.33 -1.33 -1.49 3.40 191.810Vera Beach 2105707153.65 1213218.30 2.01 1.89 0.19 -1.51 -1.67 3.40 227.560Lake Worth Pier2670 815854.41 829171.49 1.93 1.87 0.47 .0.93 -1.10 2.80 304.910 HUlsbo roInlet2862800981.65 700015.89 1.79 1.73 0.43 .0.87 -1.03 2.60 329.700 Lauderdale-by-the-Sea 2899797331.41 675151.18 1.99 1.93 0.63 .0.67 .0.83 2.60 334.580North Miami Beach 3050 789219.52 581194.67 1.77 1.71 0.46 .0.79 .0.96 2.50 352.520 MiamiBeach(City Pier)3170785173.29 522409.95 1.76 1.67 0.42 .0.84 -1.00 2.51 363.780NoTE;Xisthe shoreMnedistance in miles south ot the centertine ofSt. MillY's Entrance Channel (origin: northing=2317969.50 teel: easting =366516.31teet). FLORIDA LOWER GULF COAST Bay Port7151 291286.83 1527111.33 2.31 1.88 0]0.0.48 -0.97 2.36 4.472Howard Pm 6904241667.70 1389244.60 1.87 1.50 0.43 .0.64 -1.19 2.14 33.555 Clearwater6724231561.35 1325079.09 1.62 1.29 0.33 .0.64 -1.17 1.88 46.634 Indian Rocks Beach Pier6623224898.87 1295432.55 1.50 1.13 0.25 .0.63 -1.15 1.76 52.650St. Petersburg Beach6430261046.14 1218243.36 1.52 1.16 0.42 .0.32 -0.83 1.48 69.560Anna Maria 6243268746.05 1150335.15 1.52 1.20 0.45 .0.29 -0.76 1.49 83.284 Venice Airport 5858 352475.83 995445.81 1.35 1.07 0.36 .0.35 -0.84 1.42 117.918Captiva Island. South5383 351707.10179m.OO1.52 1.27 0.42 .0.42 .0.94 1.69 163.464Naples5110 563431.54 652958.84 1.81 1.55 0.50 .0.54 -1.172.09205.226Marco Island 4967589299.92 572441.43 1.96 1.71 0.56 -0.59-1.20 2.30 222.015NoTES:1.XisIhe shoretine distance in miles south of an arbitrarylocation inHernando County, FL. (origin: northing=1551271.53leet; easting=287952.53leet).2.State Plane Coordinates and distances arebased onZone3 lranstonnalionsWherenecessalY. flORIDANORTHWEST PANHANDLE COAST Dauphin Island 5180472269.39 871380.81 0.87 0.82 0.26 .0.29 -0.34 1.11 -33.347Gulf Shores1269467866.88 999712.52 1.20 1.13 0.50 {l.12 -0.18 1.25 -9.228 NaVlllTe Beach9678 508373.97 1254261.65 1.20 1.13 0.50 -0.14 .0.21 1.27 39.737Panama CityBeach 9189434604.55 1579274.67 1.25 1.18 0.54 -0.09 {l.14 1.27 104.489st.Andrews Park 9141 414248.96 1610651.22 1.16 1.06 0.47 .0.12{l.231.18 "1.489Mexico Beach8995 346061.53 1706517.15 1.06 1.00 0.41 .0.17{l.22 1.17 134.479 Cape San Bias8942 244076.07 1726862.581.010.99 0.30 -0.38 -0.38 1.37 162.615 Alligato r Point8261 325491.24 2035385.12 1.73 1.49 0.53 -0.44 -1.02 1.93 232.302Bald Point8237 344903.70 2050145.99 2.09 1.76 0.62 .0.52 {l.98 2.28 238.633NOTE: Xisthe shoreline distance in miles east01the AJabamalFlorida border (oligin: northing", 478050.00feet; easting .. 1047360.00feet). QENERAL NOTES:1. Tidal datums are referenoed to NGVD of1929. 2.Source of inlormation Bureau01 Survey and Mapping. Division01State Lands, Florida Department01EnVironmental Protection.lorthe National Tidal Dalum Epoch 01 1960-1978. 3.MLLW=mean lower low water. MLW =mean low water. MTL .. mean tide level, Which along the open coast = MSl = mean sea level: MHW =mean high water: MHHW= mean higher high water: MTR = mean rangeoftide Ve ..MTR= MHW MLW).30 PAGE 38 SPECIAL PUBLICATION NO.43isexceeded.Inaddition, it was found that linear interpolation led to results that simply do not reflect the natural behavior of coastal processes. Hence. in1987,a non-linear nth order polynomial numerical methodologywasintroduced and utilized to determine quantitatively open ocean tidal datumsfora significant portionofFlorida's ocean-fronting coasts (Balsillie and others, 1987a, 1987b,1987c).Updated results (Balsillie and others, 1998)areplotted in Figures1,2, and3.Thisworkisa companion papertotidal datums listingsforFlorida originally published by Balsillie and others (1987a,1987b,and 1987c) and updatedbyBalsillie and others (1998).Itwasdetermined necessarytoundertake the present compilation because of an increasing numberofmisapplicationsoftidal datums appearing in the coastal engineering literature. For example, Foster(1989,1991),Foster and Savage (1989a,1989bl,and Schmidt and others (19931 consistently usedMHWastheirvertical referencefromwhichvolumetric beach changes were measured. Komar (1998) usedNGVD(itisassumed that thisisNGVDof 1929, although suchisnot stated) but stated thatforhis siteNGVD....isapproximately equal to mean sea level'".Lee and others (1998) usedNGVDataNorth Carolina coastal location;theydid not state, however, howNGVDdeparts from MSLattheir site. These exemplify instances in which tidal datums referencing can introduce significantly compounded error. One illustrates other cases wherenoexplanation detailinghowtidal datums are appliedisgiven, and one cannot be sureifheorshe can have confidence in final results.Toone extent or another, misapplicationoftidal datums maybedueto8lackofunderstandingasto howtheyhave beenNorth South40050100150200250300350Alongshore Distance (statute miles) /..... IiIiI "Ii I,i i1 ..j i ,,,. "'"I)iIIi : i.--.;; !IiiI i I,IIi---'M:::iL : IIiIIT iI III L.VVI i II I MILW I! : i rI I : II II i! i i,II II c o 0.5>0 com-0.5 E-1 .3 -1.5 etlCl -2-2.5 -3 o4_ 3.5 o 3> c.!) 2.5Z2 S 1.5Figure 1. Relationshipbetweenopencoastdial datums and National Geodetic Vertical Datum of1929fortheFlorida East Coast. Alongshore distance is measured fromthecenterline ofSt.Mary's Entrance Channel proceeding southtoCape Rorida. (Updatedin1992after Balsillie and others,1987a).31 PAGE 39 FLORIDAGEOLOGICALSURVEYNorthSouth200o50100 150Alongshore Distance (statute miles) --,I!I !... IMLVV' 1 I ,I ...... ilAI -._-,,,-!I!II!IIo-1-1.5-2-2.5-3 -50 4 -,-,-------,-------------3.5+-i ,0-3 +1 >2.5 -.-1-----., __ ----'"""---_!':1.==C I g 0.51 ,MSlias >Q)W-0.5E .....aso Figure2.Relationshipbetweenopencoasttidaldatumsand National Geodetic Vertical Datum of1929fortheFlorida Lower Gulf Coast. Alongshore distance ismeasuredfrom northtosouthwiththeorigin locatedatthenorthendofPinellas County (i.e., north endofHoneymoon Island) and terminatingtothesouthatCaxambasPass. (Updatedin1992afterBalsillie and others,1987b).West East250o50100150200Alongshore Distance (statute miles)iIIIII i h W' ,.. i I I\fHVV I,. ...... ......",.,.MdN -IIPtA IIW! ..............."""'-i I;II,-0.5-1-1.5-2-2.5 -3 -503.5Cl 3> c.!J 2.5Z2 E.. 1.514 c o 0.5>0Q)wE ..... coCl Figure3.Relationshipbetweenopencoasttidaldatumsand National Geodetic Vertical Datum of1929fortheNorthwestPanhandle GulfCoastof Florida. Alongshore distance is measured fromtheFlorida-Alabama bordereasttoOchlockonee River Entrance. (Updated after Balsillie and others,1987c).32 PAGE 40 SPECIAL PUBLICATION NO.43established, andwhattheyrepresent. Thefirstpart of this work, therefore, discusses the history of tidal datums determination and definitioninU.S.coastal waters. Guidance illustrating proper tidal datums applicationsforcoastal scientists and engineersisavailableforimportant basic tidal datums applications (e.g., Cole,1983,1991,1997;Pugh,1987;Lylesandothers,1988;Brown and others,1995;Gorman and others,1998;Stumpfand Haines,1998).For other specific casesitisabsent. Verbal communicationsbyafewprofessionals reach only a small audience.Eventhen, thelatteroften results in a blank stare, leavingtheinstructorwiththe message that the explanation wasnotcomprehended by the informant,thatheorshe has predeterminedthatitisnot important,orthatthe informant has already predeterminedjustwhatis proper. The author has, therefore, in thelatterportionofthisworkpresented a seriesofselected examples and discussion about tidal datums applications.Atthe outset, one needstounderstandthatthe surveying profession,inlarge part,isconcernedwiththemanagementoferror and variability associatedwithhorizontal and vertical control. Itisoften the case that oneisnot convinced by simple directive that thereisa proper methodology, so evidenced by recent improper usesofdatumapplications in coastal engineeringworkscited above. This occurs because there isnothing to convince one that the methodology is better or bestatreducing error or variability. Therefore, the authorhasoptedtopresent a seriesofcommon improper tidal datums applications andtodemonstrate, relativetothe proper application,justwhy,numerically, they are inappropriate. INlETS/OUTlETS AND THE ASTRONOMICALTIDEThe preceding definitionofopen ocean tides excludes the influence of inlets (perhaps more appropriately termed outlets after Carter,331988.p.470). Hence, exclusionofinlets mightbeanoversight, particularlyinview of the current inlet management effort undertakenbytheState. At a most basic level, the classificationofinletsiswellknowndepending upon theeffectof astronomical tides relativetovolumeoffluvial discharge (e.g., van de Kreeke,1992).Infact,for many inlets, selectionofthe proper datum plane assists in providing a least equivocal representative designwaterreference level. Hence, a sectiononinlets astheyrelate to astronomical tides in Florida is herein developed.WATERLEVELDATUM PLANESInendeavors concerning hydraulic phenomena with a free fluid surface, many practitioners have lost perspectiveinselection of the reference fluid plane across which force elements propagate,inboththe prototypical setting andthenatural environment. Given this assertion, pemaps itwould be appropriate to review the basics of historical development of tidal datum plane quantification that has withstood the practicable tests of time. The first recorded effort of geodetic leveling in the United States beganin 1856p 57. During ensuing years surveying control become better. As chronicled by Schomaker(1981),by the first quarter of this century:Aherthepreviousperiodof com".rative/y short intetVlI1s between adjustments, 17 yeanelapsed beforethenetwork was adjusted IIgain. In the meantime,ithad become more extensive and complex, andincludedmany more SeHevei connections.TheGenerslAdjustmentof1929incorporllted75,159/emofleveling in the United Stlltes end,forthe first time,31,565km of leveling in Canadll. TheU.S.snd Canadian networkswere connectedby24tiesbetween Calais, Me./Brunswick,NewBrunswick;lindBlaine Wash.! Colebrook, British Columbill. A fixed elevationofzero PAGE 41 FLORIDA GEOLOGICAL SURVEY WIIS IIssignedtothepointson mellnsell leveldetermined lit thefollowing26tide stlltions.Father Point, Ouebec St. Augustine, Ra. Halifax, Nova Scotia Cedar Keys, Ra. Yarmouth, Nova Scotia Ptlns8cola,Ra. Portland, Me. Biloxi, Miss. Boston, Mass. Galveston, Tex.Perth Amboy,N.J.'SanDiego, Calif. Atlantic City, N.J. San Pedro,Calif. Baltimore, Md. San Francisco, Calif. Annapolis, Md. Fort Stevens, Drs. Old Point Comfort, Va.Seattle,Wash. Norfolk,Va. Anacortes,Wash. Brunswick, Ga. Vancouver, British Columbia Fernandina,Ra.Prince Rupert, British Columbia 'Thers was no tide stationatPerth Amboy,butthe elevation of a benchmarieatPelth Amboy was establishedbylevelingfTomthe tide stationatSandy Hook. The 7929 adjustment provided the basis forthe definitionof elevations throughout the national ntItWork.. it existed in7929, and the resulting datumisstillused today.The elevation adjustment of 1929 was referred toasthe "Sea Level Datum of 1929", although it commonly became known as the "Mean Sea Level".Incoastal work, however, there are two standard Design Water Levels (OWls) that are applied. These and their definitions (GalVin, 1969) are: Mean Water Level (MWL) the time-averaged water levelinthe presence of waves, and Still Water Level (SWL) the time-averaged water level that would exist if the waves are stopped but the astronomical tide and storm surge are maintained. These water levels(i.e.,MWL and SWL) applyforany lengthoftime overwhicha field study or experimentisconducted, while MeanSeaLevel and other tidal datums are determinedasanaverageofmeasurements made over the 19-year National Tidal Datum34Epoch(i.e..the Metonic cycle; shorter seriesareappropriately named, e.g., Monthly MeanSeaLevel, etc.).Itwas not until1973thatthe confusion over theSeaLevel Datum or "MeanSeaLevel"asitpopularly cametobeknown and Mean Water Level was resolved by assigning the more appropriate nameof National Geodetic Vertical Datumof1929(NGVD) to replace Sea Level Datumof1929. NGVDof1929isadditionally defined (Harris, 1981)asa fixed reference adoptedasa standard geodetic datumforelevations determined by leveling.Itdoes not take into account the changing standsofsealevel. Because therearemany variables affectingsealevel, and because the geodetic datum represents a bestfitover a broad area, the relationship between the geodetic datum and local meansealevelisnot consistent from one locationtoanother in either time or space. For this reason NGVD should notbeconfusedwithmeansealevel, even thoughithas always been defined by a meansealevel (Schomaker, 1981). The various North American tidal datum planesaredefined(e.g.,Marmer,1951;Swanson,1974;U.S.DepartmentofCommerce,1976;Anonymous,1978;Harris,1981;Hicks, 1984)asfollows: National Tidal Datum Epoch the specific 19 year period adoptedbythe National Ocean Serviceasthe official time segment over which tide observations are taken and reducedtoobtain mean values for tidal datums. It is necessary for standardization because of periodicandapparent secular trendsinsea level. Itisreviewed annually for possible revision and mustbeactively considered for revision every25years. Mean Higher High Water (MHHW) the average of the higher high water heights of each tidal day observed over the National Tidal Datum Epoch. Mean High Water (MHW) the average ofallthe high water heights observed over the PAGE 42 SPECIAL PUBLICATION NO.43National Tidal Datum Epoch. Mean Sea Level (MSL) the arithmetic mean of hourly heights observed over the National Tidal Datum Epoch. Shorter series are specifiedinthe name:e.g.,monthly meansealevel and yearly meansealevel. Mean Tide Level (MTL) 4 a planemidwaybetween Mean HighWaterand MeanLowWaterthatmayalsobecalculated as the arithmetic meanofMean HighWaterand MeanLowWater. MTL and MSL planes approximate eachotheralong the opencoast(Swanson,1974,p. 4). MeanLowWater(MWL) the averageofall thelowwaterheights observedoverthe National TidalDatumEpoch. MeanLowerLowWater(MLLW) -theaverageofthelowerlowwaterheightsofeach tidaldayobserved over the National Tidal Datum Epoch. Mean astronomical tide elevationsexhibitcyclic seasonal variability (Marmer,1951;Swanson,1974;Harris, 1981) and are included in tide predictions. Marmer(1951)notesthatseasonal variationintermsofmonthly mean sea levelfortheU.S.canbeasmuch as onefoot.Basedonthemanyyearsofmonthlydata, researchers (Marmer,1951;Harris,1981)note slight variations in the seasonal cyclefromyea r4to-yea r,butalso recognize the periodicityinpeaks and troughsovertheyears. For muchofourcoast,lowermean sea levels occur during the wintermonthsand higher mean sea levels during the fall. Harris (1981 ) inspected the recordtodetermineifstormand hurricane occurrence wasinanywayresponsibleforthe seasonal change, but found ... nosystematicvariability. Galvin (1988) reportsthatseasonal mean sea level changes arenotcompletely understood,butsuggeststhatthere appears tobetwoprimary causesforlowerwinter mean tide levelsfortheU.S.east coast:1)strong35northwestwinterwinds blow thewaterawayfrom shore, and 2)watercontractsasitcools.Henotesthatwindsaremore importantinshallowwaterwhere tide gauges are located, butthatcontraction becomes important in deeper waters. Swanson (1974) also notes ... seasonal changes resultingfromchangesindirect barometric pressure, steric levels, river discharge, andwindaffectthe monthly variability. Cole(1997)notes that seasonal variationintides is usually attributedtotwoharmonic constitutents: onewitha periodofone year termed the solar annual tidal constituent, and theotherwitha periodofsix months termed the solar semiannual constituent. Some consider thesetobemeteoroligical in nature, rather than astronomic. However, because the root causeofcyclic seasonal weather is the changing declinationofthe sun,theyshould more nearlybeastronomical in origin. Harmonic analysisofthe annual tidal record can easily determine the amplitude and phaseofeachofthese constituents, thereby providing a mathematical definitionofthe seasonal variation. (George M. Cole, personal communications.) Shorter-term changesoccurbi-weekly and monthly; longer-term changes occur in the relative levelsofland andseathat areofeustatic or isostatic origins(e.g.,Embleton,1982).Itis apparent, therefore,thatthere is natural variability associatedwithany average representationoftidal datums. Given these natural insensitivities associatedwithaverages,itis importantthatwedonotexacerbatethemthroughimpropermanifestationsofourownmakingwhenapplying tidal datumsasreferences.Atthis pointitis necessarytodefine certain terms. If one is interested in merely referencing a vertical distancewithouta requirementofspatial comparability, the result is termed a monergistiespp/icBtion. That is, the resultofthe application is good onlyforthat particular location. If, however, in addition to a vertical datum, one has a PAGE 43 FLORIDA GEOLOGICAL SURVEYneed that the. resulting application will have spatial comparability(i.e.,it canbecompared to the same application at any other site), the resultisa synetgistic app/iclltion. Weshall discuss this latter class of application first.SYNERGISTICTIDALDAroMPlANEAPPUCA TlONSIthasbeenwidely recognized,asdemonstratedinthe introductiontothis paper, that selectionofthe proper tidal datum depends upon the purposetowhich itistobeapplied. The main purpose of this worK istodetennine the proper tidal datum for useincoastal science and engineering for referencing littoral forceandresponse elements.Forceelementsinclude astronomical tides, storm tides, nearshore currents, waves, etc. Responseelements include extreme event beachandcoast erosion, foreshore slope changes, long-term shoreline changes, seasonal shoreline changes, etc.Itbecame apparent during the courseofpreparation of this paper that determination of the proper datum planeisprobably best accomplished by discussing application/use examples.EXTREMEEVENTIMPACTFrom the preceding descriptionoftidal datu m planeswemust, from the scientific perspective,bequite carefulinselecting a reference water level from whichwedefine such response elementsasbeachandcoast erosion duetoextreme event impact,andsuch force elementsasthe peak combined stonn tide accompanying extreme events that,inpart, induces such erosion. As noted previously, water level datumplanes include certain insensitivities regardless of the rigorous natureofstatistical methods applied. It is necessary thatwedonot further exacerbate these insensitivities, creating additional variability and error through selectionofimproper reference datums. 36Asanexample, suppose thatweareanalyzingandinterpreting profile datatodetermine volumetric erosionofsandy beachesandcoastsduetoextreme event impact. Further, letusselectasour reference water level datumMeanHighWater,MHW.Thatis,weshall assess erosion volumes above MHW toanupland point that mustbecarefully deliberated depending upon whether the coastwasnon-flooded (interpretations are normally straightforward) or flooded and/or breached (interpretationscanbeproblematic)asdiscussedbyBalsillie (1985b, 1986).Itmustberecognized that MHWcanbeassigned the statusofa signature value for a particular locality, representing its National Tidal Datum Epoch. This assessmentcanbelevied becauseMHWcanchange significantly from locality-to-Iocality. For instance,inFlorida MHW variesfrom+3.12 feet MSL (or +3.36 feet NGVD; Balsillieandothers, 1987a) along thenorthemportionofNassau Countyonthe Atlantic east coast,to+0.66 feet MSL (or +0.90 feetNGVD;Balsillie and others, 1987c) along the westem portion?of Franklin Countyonthe northwestem panhandle GulfofMexico coastofFlorida. This embodies a potential maximum difference of almost 2.5 feetinMHW elevation about the StateofFlorida. Suppose that for the above two areas, profile conditions are comparable. Furthermore, suppose that extreme events embodying precisely the same magnitudesandcharacteristics producing identical force elements impacted the two areas, resultinginidentical response elements, thatis,the same erosion volumes(i.e.,theareaabove the dashed linesandbelow the solid linesofFigure4).If, however,wereference the erosion volumes to MHW (shaded areas)asillustratedinFigure4,8.12cubic yards of sand per footareeroded above MHW along the northern portion of Amelia Island,33per cent less than the 12.05cubic yardsofsand perfooteroded above MHW along western St. George Island. It becomes quite clear, therefore, that erosion volumes around the state cannotbecompared using MHW, since the MHWbaseelevationisnot only PAGE 44 SPECIAL PUBLICATION NO.43LONGER-TERMBEACHRESPONSESMHWisnot the proper referencewaterlevel datumtoapply for erosion volumes.Italso becomes apparent thatitisnot proper tousethe datumforreferenceforsuch a force elementasthe peak combined storm tide. Similar logic results in the conclusion that useofthe MHHW, MLWiand MLLW datum planes would alsobeimproper.Itshould,infact.beclearthatMSL (or MTL) is the only tidal datumthatistobeusedforreference.-eas.IeNot1MmAIMIIeI.-rd,......,County,lIIiW'" +3.12 rtMSL Q. '"yct3/M ,.I I .... 6 .. 12 :; 2 o2 0 IISl .-:.. 10 ....j \;:/:.!............_eo*-............DimnCetram1MIISlInten:ePt("'1)Agare 4. &osion volumes. 0..above MHWfor identicalproIIesimpacted by identical stormevents.butwith clfferent Ioc* MHWplaDes.geographically variable, but significantly so. Onewillnotefurtherthat,forother North AmericanMHWdatums(seeTable 2), theproblemcanbecomeevenfurtherexaggerated. Infact.ithasbeen demonstratedthatMSListhe best datumfromwhichtoreference erosion volumes; ...atthe seaward extremityofthe poststormprofile, some materialofthe seaward sink (also including some degreeofpost storm beach recovery) may reside above MSL (determinedtobeabout6%ofthe seaward sink volumefrom245analyzed profile pairs), the analytical methodisfairly unbiased sinceitis applied equallytoall profiles investigated" (Balsillie,1986).Seaward datumsordepthofprofile closure are not suitable references,ifonly because survey responseisslowcomparedtothe responseofsubaqueoussandsizedsediments in the energetic force element surf environment(e.g.,Pugh,1987;Lyles and others,1988).It becomes apparent, therefore,thatIt is clear why the MSL datumisthe desired convention to apply for extreme event impacts to which force and response elements are tobereferenced. MSL datum should alsobeapplied to longertermforceandbeach responses. Notwithstanding the need for a standardized convention already required for extreme event impact, thereissound reasoning that it applies to longerterm scenarios, although, such application is more subtle than for the extreme event impact case. The preceding extreme event impact scenario has dealt with physical beach and coast conditions of a sort which transcend certain physiographic limitations. That is, the energetics associated with storms andhurricanesso exceed physical stability constraints that individual gradients comprising the beach and coast(e.g.,shoreface, foreshore slope, berm(s), duneorbluff stoss slope; see Figure5)do not, in themselves, impose limiting conditions. Under normallittoralforceconditions,however,physiographic slope characteristics become more nearly a limiting condition. Perhaps the most importantofthese gradientsisthe foreshore slope, a subjectthatneeds some discussion prior to addressingtwoadditionalsynergisticapplication/useexamples,namely, seasonal beach changes and long 37 PAGE 45 FLORIDA GEOLOGICAL SURVEY Table2.Selected North American Datums and Ranges ReferencedtoMSL (after Harris,1981).ISt.tionIMHHWIMHWINGVDIMTLIMLWIMLLWIMTRIEastport,ME9.328.88-0.20-0.10.01 -9.4118.20Portland,ME4.87 4.45-0.220.00-4.46-4.808.91Boston, MA5.164.72-0.31-0.15-4.86-5.199.58Newport,AI2.181.93-0.23+0.15-1.69-1.753.62New London,CN1.48 1.22-0.43-0.10-1.34-1.452.60Bridgeport,CN3.61 3.31-0.54-0.05.36-3.526.70Willets Point,NY3.853.59-0.58-0.05.58-3.787.10New York,NY2.512.19-0.49+0.05-2.29-2.424.50 Sandy Hook,NJ2.66 2.33-0.510.00-2.34 -2.474.60Breakwater Harbor,DE2.462.04-0.41-0.05.08-2.154.10Reedy Point,DE3.072.73-0.35-0.10-2.77-2.855.51Baltimore, MD0.740.51 -0.43 -0.03-0.52-0.641.03Washington,DC1.541.39 -0.54 0.00-1.37-1.422.76Hampton Aoads,VA1.411.22 -0.02 +0.03-1.22-1.262.44Wilmington,NC2.26 2.02 -0.38 +0.02-2.24-2.334.26Charleston,SC1.882.87 -0.05 +0.21-2.67-2.815.17Savannah Aiver Entr.3.773.38 -0.28 -0.15-3.56-3.706.94FLORIDA Listed it T.bIe1.Mobile, AL0.730.65 -0.05 -0.05-0.62-0.701.27Galveston,TX0.570.47 -0.10 -0.05 -0.44 -0.850.91San Diego, CA2.902.11 -0.21-0.05 -2.09-3.06 4.'-0 Los Angeles, CA2.631.91-0.080.00-1.87-2.823.80 San Francisco, CA2.592.04+0.06+0.30-1.93-3.144.00Cresent City, CA3.222.56-0.120.00-2.49-3.755.10South Beach,OA3.222.56 -0.49 +0.02-3.09-4.486.30Seatle,WA4.833.94-0.350.00-3.75-6.487.60NOTES:MfA= Mean rangeoftide; averege valueofMfLis-0.01feet MSL; average valueofNGVD(1929)is-0.29feet MSL; these stations do not necessarily represent open coast gauging sites.termbeach changes. The foreshore slopeorbeach face slope (Figure 5) is definedbythe ShoteProtectionManual (U.S.Army,1984)as" ...thatpartofthe shore lyingbetweenthe crestoftheseawardberm (or upperlimitofwavewashathigh tide) and ordinarylowwatermark,thatis ordinarily traversedbythe uprush andbackwashofwavesas tides rise and fall. Komar(1976)elaboratesfurther, statingthatthe foreshore slope"...isoftennearly38synonymouswithbeachfacebutiscommonlymore inclusive, containing also someofthe beach profilebelowthe bermwhichis normally exposedtothe actionofthewaveswash.The bermorbeach berm is the ... nearly horizontalpartofthe beachorbackshore formedbythedepositofmaterial by wave action ... some beaches have no berms, others have oneorsevera'" (U.S.Army,1984).The berm and foreshore (or beach face) are separatedatthe berm crest or berm edge. PAGE 46 CHUoloreBotro'" Neon'If,.e Inshore or Shore foeeThe slopeofthe foreshore tendstoincrease withanincreaseinthe grain size of the sediment (U.S.Army,1933;Bascom,1951;King,1972).Dubois(1972)foundaninverse relationship betweengrainsizeandforeshore slope where the foreshore sediments contain appreciable quantitiesofheavy minerals. Sediment porosityandpermeability effectsonthe foreshore are discussedbySavage(1958).GeneraJly,foreshore slope increaseswithanincreaseinnearshore wave energy(allother factorsheldconstant),andaninverse relationshipisfoundwhenwave steepness is applied(e.g.,Bascom, 1951; Rector, 1954; King, 1972).Forinstance, steeper eroding waves suchaswinter waves will resultinflatter foreshore slopes, while longer (less steep) accretionaIY waves suchaspost storm or summer waves produce steeper slopes. Average foreshore slope statistics for FloridaarelistedinTable 3. While this treatmentofforeshore slopesisgeneral,it39 Figure 5. BeachplCllfiIerelatedterms (fromU.S.Amy,1984). "wffor ... th6tportion ofthe beach or coastthllt is, on a daily basis, subject tothe combined influenceofhighlindlowtides,lind Wave activityincluding waveupl1JshOfbackwash. For purposesofthis Chllpter,itincludes thlltpatt ofthe beach between mean higher high wsfer (MHHW) and meanlowerlow wllter (MUW). SPECIAL PUBLICATION NO.43In Florida, the foreshore slopeisdefined (Chapter 168-33, Florida Administrative Code, StateofFlorida)as:The slopeofthe foreshore, the steepest portion of the beach profile, is a useful design parameter since along with thebermelevation it determines beach width(U.S.Army,1984,p.4-86).Asa response, element the foreshoreisa function of force elements suchasastronomical tides, waves, currents, and property elements suchasgrain size. sedimentporosity,andsediment mass density. PAGE 47 FLORIDA GEOLOGICAL SURVEYTable3_ Aorida Foreshore Slope Statistics byCountyandSurvey.County Survey Type Survey Date n Average Standard Slope Deviation FLORIDA EAST COAST Nassau Control LineFeb1974810.03590.0235Nassau Control Line Sep-Oct 1 981850.04740.0344Duval Control Line Mar1974680.01990.0178St. Johns Control Line Aug-Sep19722030.05230.0322St. Johns Control Line Feb-May19842100.03390.0384Flagler Control Line Jul-Aug1972990.10770.0273Volusia Control Line Apr-Jun19722270.03480.0306Brevard Control Line Sap-Nov19722170.07980.0413Brevard Control LineAug1985-Mar19862190.07190.0347Indian River Control Line Nov 19721160.11630.0335Indian River Control Line1986 119 0.12010.0793St. Lucie Control Line Jun19721150.10120.0358St. Lucie Condition Jan-Feb1983360.09190.0248Martin Control Line Oct-Nov 19711150.09390.0378Martin Control Line Jan-Feb1976960.08670.0287Martin Control Line Feb-Apr19821040.08450.0301 Palm Beach Control Line Nov 1974-Jan19752260.10110.0347Palm Beach ConditionAug1978240.1113 0.0334Broward Control Line1976-19761270.10990.0423Dade Condition Nov 1985-Feb1986280.12430.0328Total nand Weighted Averages2,5150.07600.0359FLORIDA LOWER GULF COAST Pinellas Control Line Sep-Oct 19741850.07470.0447Manatee Control LineAug1974670.10090.0419Manatee Control LineAug1986670.09420.0377Sarasota Control Line Jun-Aug19741810.09830.0375Sarasota ConditionApr1985620.10510.0469Charlotte Control LineMay1974670.07570.0343Charlotte Control Line Dec1982680.11270.0363LeeControl LineFeb19742380.08430.0415LeeControl Line May-Sep19822360.09800.0419Collier Control Line Mar-Apr19731440.07960.0265Collier Condition Sep1984400.09270.0277Total n and Weighted Averages1,3550.09030.0389FLORIDA NORTHWEST PANHANDLE COAST Franklin Control Line May-Jul19731470.09330.0349Franklin Control Line Jun-Sep 1 9812440.11550.0472Franklin Condition Oct1982310.07690.0322Gulf Control Line Jul-Sep1973 610.10320.0540Gulf Condition Jan1983450.07850.0327Bay Control LineFeb1971-Feb19731410.0707 0.0255Walton Control Line Oct19731300.09910.0699Walton Control Line May 19811300.10600.0578Okaloosa Control Line Nov-Dec1973490.06500.0406Escambia Control Line Jan-Feb19742130.09880.0429Total n and Weighted Averages1,2190.09700.0458Grand Total nand Weighted Average5,0890.08480.0391INOTE:n =0 numberofprofiles per survey.,40 PAGE 48 -_.:. SPECIAL PUBLICATION NO.43 -10-40 -20 "'10:----MSL51.'tt. Like Figure 4, Figure 6 is a simplification,IIII III --...."""""""-----...'.!.'-------3 --,.0::;:----.;-'MSL.-------.l ,, 40tt. -IBalsillie,1998).Here,however,beachwidthis used since, comparedtothe others,itoffersthe largest range in magnitudes.Letusinvestigate such seasonal changesfortwolocalitieswithidentical profileconditionsand average seasonal MSL shoreline variations,butdifferentMHWdatums.First, however,weneed some representative foreshore slope data. From Table3,letusselect the average foreshore slopeoftanafs=0.085torepresent awinterforeshore slope and amaximumoftanafs=0.2(i.e.,0.085+3 standard deviations)torepresent asummerforeshore slope. Thetwocases, eachwitha summerandwinterprofile are illustrated in Figure6. ....... --17.1fL --""1 100 1010 WINTER -.nil" = 0.085 CASEIIMHW=+4.0fl.MSLWINTER a.II..'"0.085 CASEIMHW=+2.5ft.MSL12041o-2 ...-I +2 +I +2 '"'Il:""'""---MHW---l"""--MIL g+I...... = +4 : +2 iii 0 .....,,-+4 +2_0 """ en::E... i of -40 200Distance (feet)Figure6. Seasonal horizontalshorelneshiftanalysis.will suffice for the following use/application examples. Seasonal BeachChangesBeach changes due to extreme impacts from storms and hurricanes are considered to more nearly represent isolated events. There are, however, beach changes that are more nearly episodic or cyclic. For instance, systematic beach changes through an astronomical tidal cycle(e.g.,Strahler,1964;Sonu and Russell,1966;Schwartz,1967),cutand fill associatedwithspring and neap tides(e.g.,ShepardandLaFond,1940;Inman and Fil/oux,1960),andeffectsofsea breeze(e.g.,InmanandFilloux,1960;Pritchett,1976),arewellknown.Ofthe possible cyclic occurrences, however, perhaps themostpronounced isthatoccurring on the seasonal scale. Using the above prescribedrules,thefollowingscenarioscanbesuggested. During thewinterseason,whenincidentstormwaveactivityismostactive,high, steepwavesresult in shoreline recession. Normally,theberm is erodedandagentleforeshore slope is produced. Sandremovedfromthe beach isstoredoffshorein oneormore longshore bars. Duringthesummerseason smallerwaveswithsmallerwavesteepness values transport the sandstoredin longshore barsbackonshore, resulting in awiderbeach berm andsteeperforeshore. Seasonal beach changes have been described intermsofsand volume changes,contourelevation changes,andhorizontal shorelineshiftorbeachwidthchanges (see PAGE 49 FLORIDAGEOLOGICALSURVEYalbeit representative since the slopes and distances presentedareprecise. First, letusfocus our attentionontheCASEI locality whereMHW=+2.5feet MSL. Onewillsee thatifweutilizeMSlasthe reference datum, the seasonal variability in beachwidthshiftsby40feet. If, however, one usesMHWasthe reference datum, theshiftis56.9feet. Thetwovalues departfrom.each otherby30per cent. If,onone hand, the CASEIlocality weretobesingularly assessed using the MHW reference plane shoreline, consistent results would emerge. If,ontheotherhand, one wouldwishtorelate force elements (e.g., wave and tide characteristics)tothe shoreline response, theuseofMHWwould pose problems (more about this later). Similar assessmentforthe CASE/Ilocality(MHW=+4.0feetMSl)results in a departureofthe MHW -MSlshoreline changeof40per cent. AsforCASEI,application results similarly apply.Nowletus compare the resultsofshorelineshiftatthetwolocalities.MSlshorelineshiftswould remain comparable from localetolocale, since they directly represent both the tide base and surf base.MHWshoreline shifts, however, departfromeach otherby15 per cent. Again,aswithextreme event impact, MHW shoreline shifts can notbecompared from localitytolocality (the samewouldhold trueforother datums suchasMHHW,MlW,MllW,etc.). Infact,ifweevaluated seasonal beach changes volumetrically,MHWoranyofthe other site specific variable datums would result in precisely the same non-comparability problemsoftheextreme event example previously given.Long-TennBeach Changeslong-term beach changes pose some highly important concerns. Profile type surveys provide a source of detailed coast. beach, and nearshore conditions. Such data 42 offertheopportunity for calculationofvolumetric changes which, if sufficient alongshore profiles are surveyed, allows for sediment budget detenninations. Profile surveying for temporal beach changes, however, requires a monument system maintained over many years. For instance, Florida's coastal monument system has beeninplace for some26years. Other such efforts occurona site-specific basis. For most of our coasts thereisinsufficient monumentation,orithas notbeeninplace for enough time to assure long-term records. Even the26years fortheFlorida program is not lengthy. Moreover, early surveys measured shoreline positions.Inorder to obtain volumetrics from shoreline position data, horizontal shoreline change (.boX) and volumetric change (.bo V)have been related in the ShIItePtrIteetionMaIlUlll (U.S.Army, 1984) according to: where cisa relating coefficient.Ifnotverycarefully applied, suchanapproach can produce highly misleading results (Balsillie, 1993a).long-termshoreline change rate dataforFlorida (Balsillie and Moore, 1985; Balsillie,1985f,1985g; Balsillie, and others,1986)are determinedfromshoreline position dataforthe periodfromabout1850to present. Commonly uptoabout a dozen data points are available fromwhichto conduct temporal analyses. Bywayof example, letusinspect the applicationofMHWasthe reference datum planefordeterminationofhorizontal shoreline change.letusselectanaverage MHW valueof+1.7 feetMSlandamaximum valueforMHWof+3.0feetMSl,bothofwhich are representative of Florida conditions (from Table 1). Using these data, three casesofcombinations of MHW and foreshore slope values are illustrated in PAGE 50 --....--SPECIAL PUBLICATION NO.435040302010o -.......::----MSl (SURF BASE)-----4 -10, ,II I I: ..10.2ft.: processes.THESURFBASEThe preceding application/use examples, while rigorously identifying inconsistencies resulting from the use of extreme datum planes for coastal science and engineering purposes, have not specifically addressed coastal processesinterms of the forces that cause beach responses.Inordertounderstand how the sillbase applies, one needs a basic understandingofhowwavestatistics are derived and applied.Ata givenwaterdepth a woretrain is a near-periodic setofwaveswitha characteristic average wave crest heightH,wavelength L. period T, and having aCASE3 ,-"alaso0.016 4r---------r-------------. 3o CASE 1 Berm'a"a,.'"0.085 2 WfW .. ---------1 2 ... I MHW =+1.1It -------.j I I CASE 2I :--''''ftlana,. =0.2; 0 (StR:BASE)----i I III I .........""+3.0 It _+o 2 31 ...HI Figure7. shorelne shift analysis. Figure 7. Additional data could have been selectedaswellasadditional combinations; however. the threeillustratedcaseswillmore than sufficeforour purposes. The profilesofthe three examples are plotted sothatthe MSL (Surf Base) intercepts define the originsofthe plotsthattheymaybecompared. Horizontal differencesofMHWintercept locations are identifiedbyvertical dashed lines. Deviations range from10.2to25.6feet, allofwhichare significant illustrating the inappropriate natureofusingMHWforsuch a purpose. Again, aswithextreme eventimpactand seasonal shoreline change,MHWshoreline shifts are not comparablefromlocalitytolocality (the same would hold trueforother datums suchasMHHW, MLW, MLLW, etc.).Infact,ifweevaluated long-term beach changes volumetrically,MHWoranyofthe other site specific extremal variable datums wouldresultinpreciselythesame non comparability problemsofthe extreme event and seasonal shorelineshiftexamples previously given. We can approach the subject from adifferentperspective.IfMSL is not used as a reference Surf Base plane, thenwhatshouldbeused?Ifone selectsanextreme tidal datum plane such as MHW, doesitrepresent a base towhichaktological force and response elements canbebased? Doesithave spatial continuity?Isitapplied in a conceptually correct sense? Allofthese questions needbedirected toward coastal43 PAGE 51 -_.. FLORIDA GEOLOGICAL SURVEYspecific directionofpropagation. Wherewaterdepthsaresuch that waves remain relatively stable, the wave record (suchasthat measured by a wave gauge) will represent all wave trains(i.e.,multiple trains) passing the gauge. Multiplewavetrain height and period measurements are termed the speetTalwavereconl or wave field. Shote-brea/dng waves, however, do notconformtospectral wave statistics. This occurs becauseinnearshore waters, waves are ultimately limited bywaterdepth accordingtodb=' ,.28 H b (McCowan,1894;Balsillie, 1983a; Balsillie,1999b;Balsillie and Tanner,1999)where H b is thewavecrest heightatshore-breaking anddbis thewaterdepth where thewavebreaks. Hence, shore-breaking waves engendermomentwavestatisticsfor singletrains since a wave trainwithlargerwaveswillbreakfurtheroffshore than onewithsmallerwaves.Itfollows,then,thatmomentwavestatisticsvarydepending uponwhethertheyrepresent the spectralwaverecord or single shore-breaking wave trains. Themostcommonlyapplied nearshorewaveheight statistics are the averagewaveheight H, root-mean-squarewaveheight Hrms' significantwaveheight H s (averageofthe highest30per cent wavesof record). H10(averageofthe highest10percentwavesofrecord) and H1(averageofthe highest 1 percentwaves). Eachofthese moment measures is applied in the designofcoastal engineering solutions by defined prescription. Relatingmomentmeasuresforspectral and shore-breaking wave cases are listed in Table 4toillustrate the variabilityofrelatingcoefficients. Letuslookatanexampleoftide conditionstowhichwemight superimpose certainwaveconditions. Figure8illustrates6daysofanastronomical tide record. Suppose one inspects the case whereMHWand H s are,forwhatever reason(s). selectedforuse. From the plots, each peakofthe44tide mightbeconsidered tobemaintained, say.for1/2to1 hour. Doubling this value, sincetwohighs occurineach tidaldayforthe semidurnal tide, then MHW is actually maintainedforabout 4 to 8 per centofthe time (e.g.,14and 28 days a year). Superimposed upon MHWisthe significant wave height which, by definition, neglects70percentofthe wave record (assuming that H s adequately includes any significant zerowaveenergy component; Balsillie, 993b). Clearly, suchanapplicationwouldbeinappropriateforone applying such force elementstoannual or long-term conditions. Unfortunately, however, such misapplica tions,ofwhichthis isjustone example, are commonplace.Onthe other hand, such an application might have more viable applicationifitincluded a storm surge(i.e.,peak combined storm tide minus the astronomical tide) to represent the peak combinedstormtide and attendantwaveactivitywhichoccurred coincidentwiththe peak astronomical tide. This latter case, however, has application onlytoidentifya conservative design elevationfora structure (e.g., perhaps a pier)whichis a monergistic tidal datums application, but certainlynottoprofile response which constitutes a synergistic application. Previously discussed use/application examples have already ledtothe eliminationofextreme datum planes (i.e., MHHW, MWH, MLW, MLLW)ashasthe preceding example, and MSL andNGVDremainforconsideration. TheNGVDreference is not,ofcourse, a tidal datum.Itis rather,forall practical purposes a geodeticdatumforcomputational reference,thatalthoughforopen-coast gaugeshasa departure generally less than0.5ofa foot from MSLforFlorida, the longterm primary departureofMSL andNGVDis subject to influencesofsea level rise or fall (shorteHerm natural deviations have been discussed above). Hence,itshouldnotbeutilizedasa datum, particularly where global data are involved(i.e.,where the non-tidal vertical reference PAGE 52 SPECIAL PUBLICATION NO.43Table4.MomentWave Height Statistical Relationships(afterBalsllie andCarter.19848.1984b).Portionof Wave Record Spectral Relationships Shore.Breaking Relationships Considered All Waves Average WaveAverage Breaker Height "H Height= It AllWavesH=0.885 HrmsIt =0.98 ftHighest30%H=O.625 It =O.813 Hbs Highest 10% H=-O.493 f(o =O.73 Highest 1 % H=-0.375 f( =O.637 ,"" Definitions: Average WaveRoot WaveN W'=significant Height =H= 1 Height =-Hrms wsve height N.N.,NOTE:Formulas applytoboth H and HH,o.and H,arecalculated using the formofthe equationasforthe average wave height.represents a conceptual planenotlocated and/ornotcalculated suchthatitisnotnecessarily comparabletoNGVD). The remaining tidaldatumis, then, MSL.Otherthanitsidentificationbyeliminationofotherdatums,thereare strong motivating reasonswhyMSLis the proper tidaldatumreferencetousewhendealingwithcoastal processes(i.e.,forceand response elements).Aswehave already learned, principalforceelements include astronomical tides,stormtides, andwaves.Astronomical tides are,bydefinition,already accountedforwhenusing MSL, andstormtides are extreme events thoughaccountedforas described in the preceding section. Waves.however,constitutean ubiquitous phenomenon nearconstantin nearshore coastalwaters(exceptforcoastswitha substantial zerowaveenergycomponent).45Therefore,bythe processofelimination MSL is defined as the sudbase (it is also the tide base,nottobeconfusedwiththeconceptofthe wavebase). Upon inspectionofFigures 1,2,and 3,itisreadily apparentthatMSL, like the other datums, has variability.Why,then,wouldweselectitas a conventionforreference?Waterlevels arenotglobally coincident in the vertical senseforvery real reasons. However, MSL is a measure representativeofthe entire distributionofthe metonic astronomical tide, and is the only oneofthe tidal datumsthathas statisticalcontinuityand comparabilityofresultsfromplacetoplace. Notingthatforopen coastalwatersMSL is equivalenttoMTL (Swanson,1974,p.4), then the MTL measure remainstorepresent the central tendencyofthe tide distribution since metonic measuresofhighs andlowsare used in its determination. The PAGE 53 FLORIDA GEOLOGICAL SURVEYoneshouldviewitinthe statistical sense whereweknow more about its central tendency thanwedo about the behavior of the lower foreshore (corres pondingtoMLW or MLLW) or higher foreshore (corresponding to MHW or MHHW). Whenweapproach the extremes of theslope,exceptionsduetophysiographic irregularities can occur. Hence, one needstoview the surf base foreshore slope intersectionasa focal point about which the foreshore rotates. In this context, the focal pointisdirectly relatedtoincoming force elements. Furthermore,itisconceptuallynotsubjecttovariationstowhichthe upper and lower partsofthe foreshorearesubject, sinceitis an origin both common and comparabletothe focal pointatother localities. From a slightly differentviewpoint,oneargumentFigure8. SelDiciumai tideCUlVesfor6 tidal_ys(froID proffered by a colleaguewhoManner,1951).took the "devit's advocate" position,isthatthe MHW intercept represents the most stable portionofthe foreshore slope. While this may appear appropriatetothe layman,fromthe geological perspectiveitis not.Itis, infact,the least stable in termsofrepresenting a normal slope. The most stable position of the foreshore is probablyatthe MSL intercept (Le., relativetoother submerged portionsofthe profile) sinceitisreflectiveofaverage, ongoing force elementstowhichitismodifiedasa response element. By comparison, the foreshore in the vicinity of the MHWorMHHW intercepts is affected only during high tide stages and canbereflectiveofextremal impacts(e.g.,storm wave events). Extreme impacts affecting the MHW foreshore are likelytoresult in relict featureswhichpersist until continual average force conditions finally issue becomes particularly poignant from inspectionofFigure1where the behavioroflowwaters(i.e.,MLWand MLLW) and high waters(i.e.,MHWand MHHW)areanythingbutsymmetrical intheirrelationshiptoMSL (or MTL), signifying a needforanaverage surf base measure. Statistically extreme average point measures providing numerical valuesofupper(i.e.,MHWand MHHW) andlower(i.e.,MLW and MLLW) tidal datums are robustly founded. Corresponding extremesofsuch physiographic featuresasthe foreshoremaynotbeso robustlyfounded,sinceitsformationandmaintenance has not been rigorously defined in termsofforces and responses(e.g.,Kraus and others,1991,p. 3). Given the manner inwhichwecurrently define the foreshore,46 PAGE 54 SPECIAL PUBLICATION NO.43return the upper portionsofthe slope to normal slope status.Whatpoint estimatorofwave parameters, representing the appropriate force element, does one subscribeforanextremeaveragemeasureoftheastronomical tide, sayforMHW?Onedoesnotapply such point estimatorsforwave transformation synergistic applications, because none wouldbeappropriate. Hence, unless an averagesealevel(MSlor MTL)iscombinedwithanaverage wave height, one is mixing apples and oranges.Itisimperative when undertaking such a task,werender the tasktosimplest terms. For instance, when transforming wavestothe pointofshore-breaking, including anywavereformation and rebreaking, the waves shouldbeexpressedasan averagewaveheight or, perhaps, root-mean-squarewaveheight since these measures include allwavesofrecord.Donotuse the significantwaveheight, averageofthe highest10percentofheights, averageofthe highest 1 percentofwaveheights, etc. Whetherornota significant zero wave energy component is included dependsonthe purposeofthework(Balsillie, 1993b).Anyconversionofthe averagewaveheighttoextreme wave height measuresofTable4,sayfordesign purposes,isaccomplishedbyconverting the average measure, butonlyafterwavetransformationasanaverage height has occurred. Kraus and others (1991) note the importanceofthe averagewaveheight andtoutits usetobethe ... Rosettastoneforconversion...., no less important is the proper applicationofthesurfbase (MSL)whichbecomes the Rosetta Stoneforreferencing tide andwavephenomena.Anothergood reasonforusing averages throughout any numerical transformation processisbecause oneisoften unabletodeterminefrompublished resultsifthetransformationmethodologyistrulycommutative.MSL is, therefore, the only datum47planethatisrelevant to the surf base. For a relatively short experiment or field study,MWLorSWL references are suitable to represent the time frameofthe experiment or study. Such referenced results, however, maynotbecomparable to results referenced to MSLatother localities. For this reason, all applicable datums ... MSL,MWl,and SWL, where known ... collectively termed DesignWaterLevels (OWLs), shouldbeprovided in documentationofresults.SEALEVB.RISESofar,wehave butinpassing mentioned the effects of sea level rise, recalling that the primary difference between NGVD and MSL (or MTL) is sea level rise.Inanhistorical context, the effect of sea level riseonthe current metonic period has. thus far, been insignificant from a surveying perspective.Itsfuture effect. however. remains controversial(e.g.,Titus and Barth(1984)and Titus (1987) versus Michaels (1992),tomention butonlyseveral published works among avastnumber on the subject). Otherworkindicates detailsofsealevel reversals or pulses (Tanner,1992,1993),also characterizedascrescendos (Fairbridge, 1989). There are certain applications where temporal specificationsofsea level rise areofpotential consequence. Hence,froma data management and processing viewpoint,itbecomes in certain cases necessarytostartwithNGVD and calculate the relative date-certainsealevel rise component. The result,ofcourse, becomes the date-certainMSl(or MTL). For the1960National Tidal Datum Epoch, the following relationship assessed in British Imperial unitsisposited: MSLD NGVO+c(D 1969.5)where MSLoisthe date-certain valueforMSl(or MTL),C = 0.0060forFlorida's east Coast), c=0.0064forFlorida'sLowerGulf Coast, andc=0.0069forthe Florida PAGE 55 FLORIDA GEOLOGICAL SURVEYPanhandle Gulf Coast (Balsillie and others,1987a,1987b,and1987c,respectively), and 0isthe survey date. Please notethatthe valueofc changeswithtimeand location; thecurrentvalueofcfora particular coast is a representative regression value.MONERGISncTIDAL DA TUM PLANE APPUCAnONSThus far,theabove application/use examples have been describedassyner gistic.Thatis, horizontal shorelineshiftand volumetric change results are referencedtoa datum sothattheycanbecompared spatiallywithinaNorthAmerican or globalcontext.Thescientificneedtodo so has been robustlydemonstrated.Even more, considerable analyticalworkis requiredtodeterminesuch synergistic resultswhichcannotbesimplyrecalculatedtoanother datum. As described intheintroduction there are, however,otherquitedifferentconcep tual applicationsofastronomical tidaldatumplanes. Someofthese arenotnecessarily boundbytheneedfora spatial tidaldatumconvention. These are describedasmonergistic applications. The purpose, here, istodemonstrate several such examples.DESIGNSOFFITELEVATIONCALCULATIONS"Soffitelevation"is a generictermmeaning the elevationtotheundersideofthelowestsupportingstructuralmember exclud ing the pilingfoundation,say,fora pier or singleormuti-familydwelling. Such elevations are calculatedforextreme elevations associatedwiththeimpactofextreme events(i.e.,stormsand hurricanes). The goal istoraisethestructuretoan elevation sothatitis above thedestructivehydraulicforceelementswhichwillpassbelowthesoffitand through the piling foundation. For a pier,forinstance, a peak48combined storm tide (super-elevatedwaterlevel including contributionsofwindstress, barometric pressure decrease, dynamic wave setup and astronomical tides) correspondingtoa 50-year return period elevationisnormally usedfordesign calculations. Superimposed uponthestorm tide stillwaterlevel is a designwaveheight, normally a breakingwaveheight correspondingtoHb10orHb1.As previously noted, where awaveshore-breaksisdependent on thewaterdepthwhich, in turn, is dependent on patternsofsediment redistribution occurring during event impact. Sediment redistribution is largely afunctionofoffshore sedimenttransportand longshore bar formation (Balsillie,1982a,1982b,1983a,1983b,1983c,1984a,1984b,1984c,1985a,1985b,1985c,1985d,1985e,1986;Balsillie and Carter,1984a,1984b,etc.).Anexampleis illustrated in Figure 9. Such designworkcalculations are site-specific because resultswillbeinfluencedbythepre-impactsite-specific profile configuration. There is no intention, noratthistimea needtocompare such resultstoother localities. Should suchanapplication need arise(e.g.,a generalized modelingeffortor an accounting needtoassure consistency in design application(s)),thenthe reference base shouldbeMSL. However, suchtransformationstootherdatumscanbeeasily accomplished, comparedtomuchmore involved re calculationofsynergistic data (Le., volumes or horizontal distances).EROSION DEPTH/SCOUR CALCULATIONSSite-specific designworksuchasminimumpileembedmentrequiresknowledgeofthe design surface elevation. This elevation necessarily includes erosiondepth(e.g.,longshore bartroughelevation or beach erosion elevation), additional scour caused by the pile, and sediment liquefaction.Inessence these design elevation calculations are treated in the samemannerasdesignsoffitelevation PAGE 56 SPECIAL PUBLICATION NO.43 Damaged Section --t--Destroyed Section --o-i 40 .2 10 iiiiQ 30> 20 __ __ --.Lt _.-'-':::.::.:'" ._ ::-.:::::::::::::.::-.:'.::':.:-:.:.:::::.l1I:__ -...ST SWL,....---------...,,!r---::::'-''-'-'-.-.oPot Storm -=-;;.-r-:-::_-=. .....-_-. -"'''''.''=--. --.---.---.--.--.-_-.-_-.-_-._---s--'Prof".-._._.-._._-_.-._._.-'-'-'_.-'-'-'-'Pre-Storm Profle ._.-.--_. -".,7' _.-.._.Bar 'D'oughEnveIope---"'" -.-. ........ DistancefromNGVD Shotelne(feet) Agure9.ActualdamagetotheRagler Beach PierfromtheThanksgiving HolidayStormof1984 (Balsilf.e. 1985c)usedtotesttheMultiple Shore-Breaking Wave Transformation Computer Modelforpredictingwavebehavior. longshore bar formation. and beachlcoast erosion (after Balsillie.1985b).calculations.SEASONAL HIGHWATEACALCULAnONSIn addtiontoshort-term erosiveimpactsduetoextremeevents, our coasts aresubjecttolong-term changes. In1972,theStateofFloridaincorporatedconsiderationofstormlhurricaneerosion inaffixingthelocationofCoastalConstructionSetbackLines. In1978,itadopted a posture inwhichquantitativeextremeeventerosion becametheprimarymeansbywhichCoastalConstructionControl Lineswerelocated.Itwasnotuntil1984,however,thatlong-term erosionwasofficiallyrecognizedbytheStateofFlorida (Balsillie and Moore,1985;Balsillie,StateofFlorida (Balsillie and Moore,1985;Balsillie,1985f;1985g;Balsillie and others,1986;etc.,).In1985,theGrowthManagementAmendmentrequiredassessmentoferosionatany coastal siteforwhichapermitapplicationwastenderedtobe assessedfora30-yearperiod.Associatedwith30-yearlong-term erosion projections isthelocal Seasonal HighWater(SHW)defined as ...the line formedbythe intersectionofthe rising shoreandthe elevationof150percentofthelocalmean tidal range abovelocalmean highwater...(para.161.053(6)(a)1,F.S.).Thatis:SHW=(1.5MRT)+MHWinwhichMRT isthemean rangeoftide(commonlyreferredtoasthemeantiderange). Onemightassumethatthe30-yearerosion projection istobeassessedattheSHWelevation. This issimplynottrueand, infact,aswehave seen earlierwouldbe a misapplication leadingtospatialdiscontinuityintroducing computational error (Balsillie and Moore,1985).Rather,theerosion projection needstobe assessedatMSL. The, requiredmethodologyspecifiedbyrule (para.16B-33.024(3Hhl,F.A.C., republishedasStateofFlorida,1992,62B33.024(3)(h)1.,F.A.C.) specifies NGVDastheassessment elevation. The original rule,however,waswrittenbefore compilationofdatumelevations, foreshore slope, and sea level rise informationfortheState. SubsequentworkIBalsillie, Carlen, and49 PAGE 57 FLORIDA GEOLOGICAL SURVEYWatters. 1987a.1987b, 1987c)hasremedied the situation, and theruleneedstobereassessed. Followingisanalternative for consideration. from the figures that only the upper east coastissignificantly affected by the SHW, attesting to thelowimpact figure of Curtis and others (, 985).BEACH-COAST NICKPOINT aEVA nONBOUNDARYOFPUBUCVERSUS PRIVATEPROPERTYOWNERSHIP IISL----I-BNdI.....,..-+-1.. _-The boundary between private(i.e.,upland) and public(i.e.,seaward) beach ownershipisnormally fixed by some commonly applied tidal datum. For mostofthe U.S.this boundaryisdetermined by the planeofMHW whichwhenitintersects the beachorcOast forms the lineofmean highwater.However, unlike other riparian ownership determinations(i.e.,fluvial, lacustrine and estuarine), littoral properties must, in addition, contendwithsignificantwaveactivitythat seasonally varies. Hence, ocean-fronting beaches all too often experience cyclic seasonalwidthchangesofa magnitUde long recognized as problematic in affixinganequitable boundary (Nunez,1966;Johnson,1971;O'Brien,1982;Graber and Thompson,1985;Collins and McGrath, 1989). ---------JI:)"-" -_ .. ----DI.ne or IIIuff......---Coatzf 10EAST j ... i1: LOWERGULF COAST I 000.10.20.30.40.50.80.70.80.9 EJrc....1Ce PFigure10.Beach/coast niekpoint elevations for Aorida. Inreality, SeasonalHighWaterisa misnomer. First, the components necessary for computation are metonically derived(i.e.,1 9-year averages). Second, the results have notbeendemonstratedtorepresent seasonal variation in astronomical tide behavior. Third,ithasbeen demonstrated that upon application, only about13%to15%ofundeveloped beach property in Florida wouldbeaffected by the SHW application (Curtis and others,1985).An alternative considerationforsuchanapplication, and others,isthe beach/coast nickpoint elevation. The nickpoint represents the point where the beach intersects the coast, normally identifiedasthe baseofa dune or bluff. Generation and maintenanceofthe nickpointisprimarily a functionofdirect extreme event impact. These elevationsforFlorida areprobabilisticallyinvestigated; the results are plotted in Figure10.Median(i.e.,50thpercentile)nickpoint f elevations, Ne ,forFlorida areasfollows: 1) East :. Coast:+7.15feet NGVD (1929), 2) Lower Gulf Coast:+5.65feet NGVD (1929), and 3) Panhandle Gulf Coast:+6.45feetNGVD (1929). The relationshipbetweennickpointelevationsandSHWelevationsforFlorida is illustrated in Figures 1 1, 12. and 13.Itisapparent50 PAGE 58 SPECIAL PUBLICATION NO.43 PALMBEACH BREVARDSHW ---------------------MedlIn Ne ij 5 w -00100 200300 400...... )Figure11. eom,.risonofSeason ... High Wmer (SHW) and MecillnBeach/CoastNickpointBevatioa (NJfor theRoridII East eo.st.u. iI 0 IldE I, e.illrJI 5...,.,.-....... N. S"_ i 5---------------------------iiiSHWo ............L.J o100200 DIst8nce(min)Figure 12. eom,.risonofSeasoal High Wider (SHW) and MecIiInBeach/CoastNickpointBevnon (N.)forthe RoridIILower Gulf CoIIst. 51200o IoNIc c !2 I !ci BAY GU.FFRAtLJNC1;en III-L.... Ne-----------------------------_.._-------.--/--I.Io j 5 I 100 D6stIInce("...)Figure 13. eom,.risonof Seasonal High Water (SHW) and Mecian Beach/CoastNickpoint 8evation(Ne )forthe Aorida Panhancle Gulf COiIst. PAGE 59 FLORIDA GEOLOGICAL SURVEYMany investigatorshavesuggested that the legal boundary for ocean.fronting beaches should notbecontinuously movingwiththe seasonal changes, but shouldbethe most landward or "winter"lineof mean high water (Nunez. 1966). Selectionofthe "winter" MHW line wouldbethe most practical to locate and wouldbethemostprotectiveofpublic interest by maintaining maximum public access to theshore(Collins and McGrath. 1989),InFlorida, the ocean.fronting legal boundary seasonal fluctuation issue was deliberated uponinState of Florida, Department of Natural ResourcesvsOcean Hotel, Inc. (State of Florida,1974)asit relatedtolocating the MHW line fromwhicha 50-foot setbackwastoberequired. JudgeJ.R.Knott rendered the following decision:Thiscoufftherefore concludes thllt thewinterlind most IlIndwllrd mean high wllter linemustbe selectedliS theboundllry between the stlltelUJd theup/lind owner.In so doing thecouff hilS hlldto bMlInce thepublicpolicyfllvoring prlvllte littorlllownership IIgainst thepublicpolicyofholdingthetidelllnd intrustforthe people, wherethe preservation of II vital publicright issecured withbut minimMeffect uponthe interests oftheuplllndowner.A 1966 California Court of Appeals decision rejected the application at a continuously moving boundaryinPeoplevsKent Estate. However,nodecisionhasbeen renderedastowhat linetouse (Collins and McGrath, 1989). More recently, Collins and McGrath (1989) report:TheAttomey Generlll's Officein Clllifomill hilSoffereditsinformlll opinion thllt, ifsqullrely fllced withthe issue, ClIlifomill courtswouldfollowthe rellsoning in the52Floridll ClIse lind IIdopt the "winterlindmost Ilmdwllrd lineof melln hightide"liSthe leglll boundllry betweenpublictideJlInds lind privllteuplllnds ...(itshould be understoodthlltsuch1Iboundllry,whichreilltive/y stllble, would not be permllnently fixedbutwouldbe IImbullltory tothe extent there occurs long-term IIccretion orerosion).Theuseof the MHW datum plane for the determinationofa boundaryisstraightforwardly a monergistic application; one mustbecareful, however,tonote that determinationofthe seasonal shoreline shift (or beach width)isnot. This will require a synergistic application using MSL. Similarly, any periodic review and boundary relocation duetolong-term shoreline changes will require the synergistic approach.INLETSAND ASSOCIATEDASTRONOMICAL nOES It hasbeenspeCUlatedthat tidal inletscansignificantly affect the characterofopencoast tide behavior. Thereare,however, insufficient alongshore data crossing inlets, both upcoastanddowncoast, upon whichtoassesstheeffect of inlets (termedthe"shadow effeer). Inaddition, flow characteristics varyfrominlettoinlet and a multitude ofsuchinvestigations wouldbereqUiredtoinvestigate the alongshore influence of inlets. There are, however, some isolatedopencoasttidedata near inlets or within inlet throats closetotheshoreline. There aremoredatainteriortoinlets.Suchinformation for 24 Florida tidal inletsandpasses are plottedinFigure 14fromwhich some significant elucidating conclusions maybegleaned. ThedataofFigure14are displayedintenns ofthemeasuredinlet tide data minus theopencoasttidedataof Balsillie and others (1987a, 1987b,1987C).Inthiswaythe PAGE 60 SPECIAL PUBLICATION NO.43 53reference planefora synergistic application (e.g., storm impact, seasonal,orlong-term beach changes), the amountoferror introducedispotentially highly significant.Itwould,inaddition, occur over a quite short segmentofshoreline.ForMHW,39%ofthe data are acceptable (i.e., liewith :t 0.1ft.ofthe open coast data)with61%ofthe data being unacceptable. For MLW76%ofthe data are unacceptable. However,forMTL almost70%ofthe data are acceptable. Thisshiftin data acceptabilityforMTL is not aberrant. Rather,itistobea moderating expectation since MTL is the plane lyinghalfwaybetweenMHWand MLW and should, therefore much more closely approach open coast MTL values than anyofthe otherextremaltidaldatumplanes .Therefore,dependingontheapplication, the locally measured MSL (MTL)datumplaneorthe open coast MSL (MTL)datumplane shouldbeusedforsynergistic applications in the vicinityofinlets (whichisused shouldbeclearly specified). Hence, MTL (or the MSLsurfbase) is, once again, the proper datum planetouseforinlets.Infact,O'Brien (1931)intentionallyincludedinhisdefinitionsfortidal characteristics (e.g.,flowarea, tidal prism)thattheybereferenced specificallytoMSL. Ideally, the alongshore "shadoweffect"ofinlets on astronomical tides shouldbequantitatively assessed. Suchworkis, however, expensive and time consuming andisnot expectedtobeforthcoming any time soon.Itisalsoofsignificance to notethatCole(1997,p.38) has foundthatnth order polynomial equations precisely determine tidal datums within estuaries. The orderofthe bestfitpolynomialforanestuary was MHWI MLW f------------_--------------..0.2 .. .. -0.6 ........ ,__ -'__ --.I", __ --L1'L....-_..:.HI:.:.lI o0.5 1.0 1.5 2.0 2.5 ...fromSftoreIIne0.2fi------------------------o.' ... _1.1..._ ..... : -0.4i-0.8l. -0.1 ; .0 iif e.2 :IO.2f->, .Ii-,.... --------------------------O'i 0.4,.....---..L..---'---........--"'-----4 o U 0.2MTl c .M_-, -----.-r ----------Q, O.I. c. i! 0.1 t5 0.6" 0.4 Aggre 14. Oep8rtureofRoridaMt tide data andopen coast tide Uta (measured tidedata fromDNR, Bureau of Surveyand Mapping). See textfor clscussion. acceptability of the data within the dashed lines (i.e., plus and minus 0.1 ft.) canbeeasily assessed. DataforMHHW andMLLWplot similartoMHWand MLW datawithsomewhatgreater variability, and arenotshown. ThefirstconclusiontobedrawnfromFigure 14, isthatthe amplitudeofthe tide is attenuatedbythe inlet (i.e., MHW becomeslowerinelevation andMLWgains elevation); this is illustrated in a different mannerfortwoFlorida inlets in Figure 1S.Hence,ifone were(asbefore) to use MHWasthe PAGE 61 FLORIDA GEOLOGICAL SURVEY __ _ 2.00 I I I I I I : :: I I ,. I I 6" I 1,,.-.... 1.00 --!--,--.. i --r ---r : "'" I tl II '-"'t i' 'i I il I I J I 10 I g 0.00i '"_:_'_-\-aI I \\ > Q) ....,..1i1.".J .,'W\,' -I'to L _-1.00"\' --", -Io I I "D I t:I I I I I-200.,.1'. ".,1." ".11.""'",I"1""".,1",,,,"1"",,,,(.0.0010.0020.0030.0040.0050.0060.0070.00Time (Hours) Rgure 15.Open oceanandinside astronomical tidesfor Ft. PierceandSt.LucieInlets, Aorida (fromAnonymous,1992).foundtobepredictable based on the lengthofthe estuary and the travel speedofthe tidalwavewithinthe estuary.CONCLUSIONSA considerable amount of information, hopefully simplifiedasmuch as possible, has been presentedinthe above application/use examples. It would not serve further purpose to restate conclusions here that couldbemore succinctly touted, other than to state that MSL (or open-coast MTL) is the proper datumtoemploy for synergistic coastal engineering applications. It is hoped that this work has rendered it apparent that how we perceive and treat such subject matterina scientific context is sensitively critical. The considerations presented herein embody not just philosophy, but engender intellectual contemplation and deliberation necessary to arrive at a deductive, reasonable, and robustly correct convention for application.Inthis day and age, itisunfortunate that while we are finally realizing such enhanced data processing capabilities, we are fraught with misapplication that all-too often render good data to inaccurate results.ACKNOWLEDGEMENTSReviewofthisworkbyselectedstaffofthe Florida Geological Survey is gratefully acknowledged,inparticular those editorial contributionsofJacqueline M. Lloyd, Thomas M. Scott, Kenneth M. Campbell, JonArthurand Walter Schmidt. Review by the BureauofBeaches and Coastal Systemsisalso acknowledgedwithspecial thanks to RalphR.Clark and Thomas M. Wattersfortheir interestinthe subject and/or editorial comments. Special thanks are extendedtoGeorge M. 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