PRESIDENTGregory Woodell - LosAngeles,California

PAST PRESIDENTOrville T. Magoon - Middletown, California

VICE PRESIDENTSThomas J. Campbell - Boca Raton, FloridaMichael Chrzastowski, Ph.D. - Champaign, IllinoisGeorge W. Domurat - Pacifica, CaliforniaGerard Stoddard - Long Island, New York

SECRETARYRussell H. Boudreau - Long Beach, California

TREASURERThomas R. Kendall - Pacifica, California

DIRECTORSSteve Aceti -Encinitas, CaliforniaDavid R. Basco, Ph.D. - Norfolk, VirginiaLynn M. Bocamazo - New York, New YorkKevin Bodge, Ph.D. - Jacksonville, FloridaRobert G. Dean, Ph.D. - Gainesville, FloridaRichard Dornhelm - Walnut Creek, CaliforniaBilly L. Edge, Ph.D. - College Station, TexasKaryn Erickson - Gainesville, FloridaLesley Ewing - San Francisco, CaliforniaJohn S. Fisher, Ph.D. - Chocowinity, North CarolinaCharles H. Fletcher 1lI, Ph.D. - Honolulu, HawaiiDouglas Gaffney - Voorhees, New JerseyPeter H. F. Graber - Greenbrae, CaliforniaJohn G. Housley - Vienna, VirginiaJames R. Houston,Ph.D. - Vicksburg, MississippiNicholas C. Kraus, Ph.D. - Vicksburg, MississippiHonorable Ann J. Kulchin - Carlsbad, CaliforniaStephen P. Leatherman, Ph.D. - Miami, FloridaCraig B. Leidersdorf, Ph.D. - Chatsworth, CaliforniaSusan Lucas - Philadelphia, PennsylvaniaPatricia C. Newsom - Houston, TexasBernard 1. Moore - Toms River, New JerseyRon Noble - Tiburon, CaliforniaJoan Pope - Vicksburg, MississippiAnthony P. Pratt - Dover, DelawareCharles W. Shabica, Ph.D. - Chicago, IllinoisKenneth Smith - Manahawkin, New JerseyKim Sterrett - Sacramento, CaliforniaChris Webb - Long Beach, CaliforniaJ. Richard Weggel, Ph.D. - Philadelphia, Pennsylvania

DIRECTORS EMERITICharles L. Bretschneider, Joe W. JohnsonPaul Dennison, Thorndike Saville, Jr.Kenneth Thompson, George M. Watts,Henry M. von Oesen, Robert L. Wiegel

LEGISTRATIVE COORDINATORHoward Marlowe - Washington, D.C.

EDITORNicholas C. Kraus, Ph.D. - Vicksburg, Mississippi

EDITORIAL-ASSISTANTJ. Holley Messing - Vicksburg, MississippiSubmit electronic manuscripts to the email address:editorial. assistant@asbpa.org

NEWS AND POLICY EDITORPeter Ravella - pravella@coastaltechcorp.com

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~hOIe& a..GBeaC11VOL.70 NO.1, January 2002

JOURNAL OFTHE AMERICAN SHORE AND BEACHPRESERVATION ASSOCIATION

American Shore and Beach Preservation Association

1724 Indian WayOakland, California 94611-1221

Front Cover: Manasquan Inlet, New Jersey, an urban beach. (Photograph courtesy of U.S.Army Corps of Engineers, Philadelphia District)

CONTENTS

FROM THE EDITOR'S DESK: ASBPA WEB PAGE AND THIS ISSUENicholas C. Kraus

2

ROLE OF ANTECEDENT WAVE CONDITIONS IN PREDICTINGBEACH EROSION AND ACCRETIONJohn P. Ahrens, Jane McKee Smith, Edward B. Hands

3

COASTAL OBSERVATIONS:

PHOTOGRAPHS OF VENICE, ITALYAndrew Morang

8

THE ECONOMIC VALUE OF BEACHES - A 2002 UPDATEJames R. Houston

9

COASTAL FORUM:NSBPA CONFEREES EXPLORE CRITICAL NEED FORURBAN SHORELINE REVITALIZATION

13

COASTAL FORUM:CSBPAfCALCOAST YEAR 2000ANNUAL CONFERENCE:

CALIFORNIANS SEEK COMMON GROUND ON BEACHRESTORATION PROGRAM AT ANNUAL CONFERENCE

IS

SEAWALLS, SEACLIFFS, BEACHROCK:WHAT BEACH EFFECTS? PART 1Robert L. Wiegel

17

COASTAL FORUM:YEAR 2001 JOE JOHNSON AWARD PRESENTED BY CSBPA TO

PAWKA, GUZA, O'REILLYReinhard E. Flick

28

ORGANIZED 1926 - SEVENTY-SIXTH YEARSHORE- & BEACH is published four times per year by tbe American Sbore and Beach Preservation Association,

ASBPA, 1724 Indian Way, Oakland, California, 94611. The views expressed and the data presented by the contributors

are not to he coostrued as having the endorsement of the Association, unless specifically stated. SHORE- & BEACH is

a refereed journal.

Shore & Beach Website: http://www.asbpa.org

Claims for missing issues should be made to tbe Membership Office. Sucb claims will be honored up to sixmonths after pnblication.

American Shore and Beach Preservation Association is a tax- exempt non-profit organization under a taxexemption letter from the commissioner of the Internal Revenue, September 14. 1950. Articles appearingin this journal are indexed in ENVIRONMENTAL PERIODICALS BIBLIOGRAPHY. - ISSN 0037-4237

Seawalls, Seacliffs, Beachrock: What Beach Effects?By

Part 1

Robert L. Wiegel, Professor EmeritusDepartment of Civil & Environmental Engineering

410 O'Brien Hall, MC 1718, University of CaliforniaBerkeley, CA 94720-1718

ABSTRACT

Most seawalls are built to protect property after erosion/recession hasoccurred. Some have been built on coasts with no chronic erosion, inconjunction with a quay, a promenade, or other infrastructure to assure itssafety during severe coastal wave, tide, and surge events. Debate continuesabout the interaction of seawalls and beaches, with differences of opinion in

articles in the press and the conclusions of carefully done engineering andscience studies. In the author's judgment, seawalls do not cause erosion,except in the special circumstances of where they prevent erosion of anupland source of sand for a beach downdrift, or are so situated that they act asa groin. In some locations seawalls can decrease erosion of beaches bypreventing transport of sand inland by a hurricane, a tsunami, some othermajor event, or even ordinary strong winds. Whether a shore is stable,eroding, or accreting depends on many factors - some natural, and somecaused by human works. It is necessary to distinguish between long term(chronic) and cyclic erosion. It is important to deterruine iflong-term erosionis occurring, and if so, what is causing it - and what might be done to halt ormitigate it. Many of the problems result from multiple use of the coast, oftenconflicting. Whether or not seawalls are perruitted at a site is often a legaland/or political decision, not an engineering, scientific, or economic one.With reliable technical knowledge (not just information), and hopefullywisdom, it is more likely that good decisions can be made in establishing andimplementing zoning regulations and construction codes. Some members ofregulatory and perruitting agencies prefer uniform simple regulations thatallow them to make easy decisions when thorough site-specific data collec-tion and analyses should be made for complex conditions and problems. Inmy judgment, some coastal zone management agencies have poorly thought-out policies regarding seawalls and revetments - prohibition in some cases.There are sites where such structures would be inappropriate (functionallyand/or aesthetically), certainly; but there are other situations where they areappropriate, and probably the best solution, considering physical, economic,public use, and public safety aspects. If properly placed, constructed andmaintained, seawalls are useful as "insurance" during intervals of large cyclicerosion. Short descriptions are given of a variety of case studies from whichwe can learn. This paper is the first of a three-part series reviewing anddiscussing the functioning of seawalls.

Additional Keywords: Accretion, alongshore transport, beach, beachnourishment, Bruun rule, bulkheads, coastal policy, coastal zone manage-ment, dams, datum (vertical), erosion, harbors (shoreline), insurance (physi-cal), mining beaches, pocket beaches, property rights, revetments, sandbypassing, sand rights, sand trapping, sand waves, sea level change, shoreprotection, shore types, shoreline recession, shorelines, subsidence, tidalinlets

CONTENTS OF SERIES

Part 1. Prologue; Introduction; Seawall classification according to locationon beach profile; Beach profile and beach width variability; Seawalls atpersistently eroding (receding) beaches; Structure "footprint" - loss of usablebeach; Seawall or revetment at a persistently eroding (receding) seacliff; Twolong-term quantitative studies.Part 2. Erosion of upland as sand source for beaches; Cause and effect; Uselogic, not blind correlation; Find cause(s) and cure it (them) if feasible - ormitigate; Downdrift erosion caused by updrift works - including sand mining;

Examples of cases only partially discussed in some papers; Compositeprojects.Part 3. Seawalls or revetments as insurance; Seacliffs with pocket beaches;Beachrock; Sea level rise/land subsidence; Pocket beaches - eroding?;Contrarian's view - vertical wall or revetment; Review of simplistic policies -change where unsubstantiated.

PROLOGUE

In arecentbookreview,GerardStoddard(1999)com-ments on land-useproblems/coastalpolicy:

Shore & Beach Vol. 70, No.1, January 2002, pp.17 - 27

"The conflictis familiarto thoseinvolvedin the debateover coastal policy. The [Cornelia] Dean version, how-ever, fails to distinguish between "politics" and law.What usually dictates the decision to allow an owner toprotect property is a judge who has been convinced thatnot to allow it is to deprive him or her of well-establishedrights incident to property ownership. As with allnettlesome policy issues, the facts of individual cases arelikely to vary widely; decisions based on different factsituations will vary as well. Generalized rules that mustcover a host of different fact situations tend to run into

problems. But land-use problems are settled by the law,not political popularity, at the coast as well as everywhereelse."

Considering both the "different fact situations" mentioned byStoddard, the site-specific coastal processes and environmentalconditions I have seen or read about during more than 50 years ofstudy and practice, and trips to more than 50 countries with oceanshores, led me to give a lecture on the subject of this paper in thegraduate-level Ocean Engineering Seminar at the University ofCalifornia at Berkeley during Spring 2000. I prepared writtennotes as a handout to the students to accompany the lecture. Thiswas then expanded into a technical report (Wiegel 2000). Thispaper is an outgrowth of those notes and report, with a fewchanges and additions based on information received subse-quently. I did not want to be repetitious, but found some wasneeded to set the stage for students and laypersons, as well ascoastal engineers and scientists. Owing to its length, this paperwill be published in three parts. I have not addressed the structuraldesign or performance of seawalls, revetments, or bulkheads; forinformation on these subjects see the Shore Protection Manual(1984), CIRIA (1986), and Griggs (1999). Nor have I addressedaesthetic design. Where possible, I have used situations of which Ihave personal knowledge.

INTRODUCTION

Seawalls, revetments, and bulkheads are built to protectbuildings, infrastructure, and uplands (dunes, bluffs, cliffs,wetlands), and not to protect beaches (e.g., Kraus 1988,

Griggs 1999). Some are built where there are no beaches, andothers where there are beaches. For example, some have beenbuilt to protect a promenade; perhaps for today's lifestyle toprotect a shoreline path used for aerobic walking and runningwhile enjoying the seascape. An example of a type of aesthetic useis in Kailua-Kona, HI, a restaurant and seawall where: "Theupstairs dining room. . . its ocean front location - an open-airdining room with lanai seating, ocean views, and the rhythmicsound of the surf slapping against Ali'i Drive's lava rock walls"(McCullough and McCullough 2000). At some sites they can beuseful in decreasing erosion by preventing sand from beingtransportedinland during inundation,or blown inland by a hurri-cane (Heron Island, on the Great Barrier Reef, Australia - Tropical

17

Cyclone Simon, 24-27 February 1980; Poipu, Kauai, HI - Hurri-cane Iniki, 11 September 1992), or by a tsunami. Photographs ofsand transported inland and lost to the beach during hurricanes areshown in Figures la and lb.

Evidence continues to mount that although many seawalls areassociated with eroding beaches and shoreline recession, they areseldom the cause, and then only under special circumstances -suchas the prevention of the erosion of dunes or sandy bluffs thatsupply downdrift beaches, or so situated that they act as a groinwith resulting shoreline accretion updrift and recession downdrift(e.g., Dean 1987a). Most have been built in response.to erosion(for examples in Hawaii, see Hwang 1981). However, debatecontinues about the interaction of seawalls/revetments andbeaches. For some background on the debate, see Pilkey et al.(1982); O'Brien (1982a); Kraus (1988); Weggel (1988); Basco(1991, 1992); Thieler, Young, and Pilkey (1992); and Kraus andMcDougal (1996). An extensive literature survey of papers andreports on the effects or non-effects of seawalls on beaches hasbeen made by Kra:us (1987, 1988 - about 100 papers and reports)and Kraus and McDougal (1996). The findings are not summa-rized herein, as the review was so extensive; it is important tostudy the papers. Few quantitative field studies have been made;the reasons are discussed by Kraus (1988) - perhaps the mostimportant being the large cost of a long-term comprehensivemonitoring program. For some studies, see Basco, Bellano, andPollock (1993); Basco et al. (1997a, 1997b); Griggs, Tait, andCorona (1994); Griggs et al. (1997); and Griggs (1999). Reliancemust be placed on field observations as there are some funda-mental problems with movable bed - wave hydraulic model studiesof waves, sediment, structures, although they are useful and muchcan be learned from them, especially if done in a large facility(e.g., Kraus 1988; McDougal, Kraus, and Ajiwibowo 1996).Kraus commented that there was almost always insufficient dataon waves, beach profiles, shore configuration, etc., in field datasets and in reports and papers - what Morrough P. O'Brien termedan "incomplete experiment" or an "incomplete study". Kraus(1988) has listed the requirements for a good field-monitoringprogram.

I am aware of only two long-term quantitative field studies ofseawalls and beach effects. They are by Gary B. Griggs and hiscolleagues (Griggs, Tait, and Corona 1994; Griggs et al. 1997;Griggs 1999) on a beach with no chronic erosion near the northend of Monterey Bay, CA, and by David R. Basco and hiscolleagues at Sandbridge, on the southern Atlantic Coast ofVirginia, a beach chronically eroding (Basco et al. 1997a, 1997b).The study by Griggs et al. (1997) consists of carefully documentedsurvey data made for 8 years for seawalls, stone revetments, andcontiguous "control" beaches without structures. The study ofBasco et al. (1997a, 1997b) includes carefully documented sur-veys of subaerial beach and dune profIles for 5 years by his group(which is continuing), and surveys for 15 years by the City ofVlfginia Beach, and surveys for 1 year by another organization - atsections with seawalls and at sections without seawalls, with sanddunes. It includes as background, data of others from the results ofshoreline (Mean High Water, MHW) survey data maps of 1859,1925 and 1980, and changes obtained from a study of aerialphotographs, 1937 through 1984. I have read that another studyhas been, or is being made, at the Great Lakes, but I have noinformation on it.

Sometimes I may have inadvertently used the terms erosion andrecession interchangeably. This is common; however, they aredifferent (Basco 1992, p.34). They are defined in the NationalResearch Council's Committee on Beach Nourishment and Protec-

18

Figure 1a. Sand transported Inland by Tropical Cyclone (Hurri-cane) Simon, 24-27 February 1980, Herron Island on the GreatBarrier Reef, Australia, by Robert L.Wiegel, 21 March 1980(#2950)

7,\ : '~1't..~'.~'~';Mf'.~"':!..-'~~-':r-~~-_4'~"-~f~~r'~7fJljt~t

Figure 1b. Sand transported inland by Hurricane Iniki, Poipu,Kauai, Hawaii (Hurricane on 11 September 1992). One of theground units of the Sheraton Hotal at Poipu Beach. Photographby Mike Critchfield, 2 November 1992 (#7632)

tion report (1995, p. 24): "erosion - a volumetric measure of theamount of sand removed from a beach by waves, currents, or otherprocesses; recession - a linear measure of the landward movementof the shoreline." They are usually associated, but not always.Recession also occurs with subsidence (tectonic, earthquake in-duced consolidation or lateral spreading, or caused by withdrawalof ground water, oil, gas), or a rise in mean sea level.

I have recommended that seacliffs with pocket beaches at theirbase be studied to learn more about the complicated processesinvolved, and use this to increase our understanding of seawall andbeach interactions (Wiegel 1999). Why do the beaches exist forvery long times at the base of seacliffs (seacliffs are "highseawalls") even where there is little sand supply, if seawalls reallywere to cause erosion? Seacliff erosion processes are complicated,e.g., Benumof and Griggs (1999). After writing these notes, I alsorecommend the study of pocket beaches with a cobble backshoreand sand foreshore, to see what we can learn from them.

I have seen hundreds of beaches, rocky shores, and coastalwetlands in about 55 countries during 54 years of professionalinvolvement in coastal engineering and science (engineering -conception, development or management of a device or system;science - systematized knowledge of nature), and have read a greatnumber of papers and reports about the subject. 'The generalcoastal processes are similar, but their mix and environmental

.....

W;

Shore & Beach Vol.70, No.1, January 2002, pp.17 - 27

".-.

.dgE"i~.

Figure 2a. Barrier Island Beach, West of Peridodo Pass, AL.Aerial photograph by Robert L.Wiegel, 4 November 1976 (#1881)

'-,-

Figure 2b. Seacliff, narrow beach, natural groin (trapped sand)- a little northwest of Santa Barbara, CA, October 1985, fromJames R. (UKimo")Walker (#5457)

conditions are site specific. Shores are a dynamic system as areother natural systems, always changing in response to varyingforcings, One can transfer ideas learned from one site to another,but it must be done with care. The more we learn about a specificsite the more likely a reliable decision can be made about whatshould be done. The variability of beach profiles with space andtime, and the location of a seawall relative to the profile and localwater levels and waves are of paramount importance. Majordifferences in sites are the amount of sand along the shore; whetherthe sand layer is thick, or only a veneer on top of bedrock; thecharacteristics of the sediment For example, there is a greatamount of sand, and barrier islands are the dominant coastallandform from New Jersey (Wicker 1951) to Florida, and Texas(e.g., Committee on Coastal Erosion Zone Management 1990)(Figure 2a). On the other hand, along the Santa Barbara Countycoast in southern California there is little sand; the beach berm isnarrow and backed by vertical bluffs, and the thickness usuallydoes not exceed a lO-ft covering of the underlying cobbles, shaleand sedimentary rock, and is frequently removed by storms(Figure 2b). It has been estimated there is only about 1 millioncu yd of sand in the 13 miles of shore between Santa Barbara andCarpenteria (O'Brien 1939). Another example is the island ofMaui, HI, which has a variety of shores, with most of the beachesbeing pocket beaches. Nearly every pocket beach on this, and onthe other Hawaiian Islands differs in composition from its neigh-bors (Moberly, Baver, and Morrison 1965). Some have fringingreefs and others do not, some have beachrock, rocky headlands,

seacliffs, and different wave and wind climates although only afew miles apart, or less (e.g., Clark 1985a). An example of the

Shore & Beach Vol.70, No.1, January 2002, pp. 17 - 27

Figure 3a. Beach in front of Polo Beach Club, Wailea, Maui, Ha-waii, looking south along lava/coral rubble cobble beach. Fromsame location as Figure 4b, on top of low rocky point, 17 Janu-ary 2000 (#9819)

Figure 3b. Beach in front of Polo Beach Club, Wailea, Maui, Ha-waii, looking north along calcium carbonate beach. From samelocation as Figure 4a, on top of low rocky point, 17 January2000 (#9820)

variability are the pocket beaches on either side of the low smalllava point at the Polo Beach Club in Wailea, Maui. The beachsouth of the point consists of lava cobbles and coral rubble, and tothe north the beach is carbonate sand (Figures 3a and 3b).

SEAWALL CLASSIFICATION ACCORDING TOLOCATION ON BEACH PROFILE

Coastal engineers and scientists have noted the importance ofthe location on beaches of a seawall, revetment, or bulkheadrelative to local water levels and wave action (e.g., O'Brien andJohnson 1980; Macdonald and Patterson 1985; Weggel 1988;Griggs, Tait, and Corona 1994; Griggs et al. 1997). Weggel (1988)recommends a classification of seawalls according to their locationon the beach profIle relative to local water levels and wave action,and thus their effects on local coastal processes. He suggests sixtypes (Figure 4); I have modified some of the descriptions a little:(a) Type 1. Base of seawall is located landward of the level ofmaximum wave setup and runup during times of maximum tideand storm surge, (b) Type 2. Base of seawall is located abovewater level that occurs at time of maximum combined tide andstorm surge, but below level of maximum combined wave setupand runup, (c) Type 3. Base of seawall is above spring high tides,but below storm surge plus tide level, (d) Type 4. Base of seawallis located within normal tide range, and thus the base is underwater duringpart of the nonnal tidal cycle, (e) Type5. Base ofseawall is located seaward of the mean lower low water shoreline;

19

Type

MTL

e = angle incident wave crest makes with the seawall(dimensionless), and

a =angle between incident wave crest and shoreline.

Assuming that the site is subject to both astronomicaland storm tides, water levels affecting the processesnear a seawall are given by:

Z, = astronomical half-tide range, (L).Z, = storm surge elevation, (L).

R =height of runup on the beach/seawall system, (L).

6

-Hi

mous Pebble Beach GolfCourse. O'Brien (1936) ob-served that the beach width: "...varies from zero in some yearsduring the winter season to asmuch as 200 ft in August andSeptember." I have seen thebedrock exposed during the EINino winters of 1982/1983 and1997/1998, and seen it recoverfrom these events, Figures 9a and9b. How do we measure these

quantities; what are their meansand variances (Anders andByrnes 1991, Bokuniewicz 1981,Flick and Elwany 1997,Grosskopf and Kraus 1994,Johnson 1971, Dolan et al. 1980,O'Brien 1982b, Smith and Jack-son 1992)? How can we evaluatethe reliability and accuracy ofshore recession or growth ratesfrom a few sets of aerial photos,usually taken at random times(e.g" relative to storms, months oflight seas, tides), and variously

using a 'wetted bound,' base ofseacliffs, or vegetation line as thebeach boundary? Information on defi-nition of shoreline is contained in the

Appendix of this paper.

Morrough P. O'Brien (1982b) dis-cusses some of the problems that engi-neers, planners and officials have inregard to the shoreline in his note: OurWandering High-tide Lines! He says:

"One of the questions facingcommunities on sandy coasts iswhether or not progressive,long-term erosion underlies theannual cycle. It is clear fromFigure 7 that comparison oftwo surveys, made at randomtimes during the year, mightshow almost any rate of ero-sion or accretion. For ex-ample, if the first survey weremade in August 1966, whenthe beach was 260 ft wide, andthe comparative survey in May1970, when it was 160 ft wide,one might conclude that ero-sion amounted to 100ft - and it

really had er~ded - but the fig-ure is not only irrelevant, be-cause the dates of the compara-tive surveys were improperlychosen, but it would be grosslymisleading to report this ero-sion rate at 25 ft/year. Thechange in width is not really afunction of the month of the

yearbut ratheraconsequenceof preceding storm conditions,

Figure 4. Variables that define the behavior of a typical seawall, and definition of a seawall byits location with respect to prevailing water levels (profile view), from J. Richard Weggel (1988).Courtesty, Journal of Coastal Research

it is subject to breaking and brokenwaves, and (f) Type 6. Base ofseawalilocated in water so deep thatincident waves do not normally breakbefore reaching it.

BEACH PROFILE ANDBEACH WIDTHVARIABILITY

The variability of beach profIlesmust be considered, the subaerial partof which, the visible beach, is whatmost people think of as the beach.There is cyclic erosion and accretionof beaches, depending on wave con-ditions during "winter/ summer"wave seasons, mild/severe years ormulti-year intervals, episodic events(EI Nino winters, hurricanes, north-easters) followed by recovery. Thevariations are superimposed onchronic erosional, accretional, orstable beaches. Well-known earlysurveys of cyclic changes are byShepard (1950), Bascom (1954),Johnson (1971) (Figures 5-7). Thereare more recent data sets (e.g., at theOuter Banks, Duck, NC, Figures 8aand 8b, which are surveys of thesubaerial beach and through thesurfzone - Birkemeier (1985) andStauble (1992). The profiles inFigure 8a are an update of the data inBirkemeier (1985).1 Bascom's datawere of the south end of CarmelBeach, CA, a pocket beach a littlemore than I-mile long, contiguous tothe rocky coast along the world-fa-

Variables that describe the seawall are:

1= shore-parallel length of the seawall, (L).d =water depth at the base of the wall (measured from the mean

tide level), (L).Xw= distance from the mean tide level shoreline to the base of the

seawall, (L).

Variables that describe the water and sediment are:

w =fall velocity of sediment, (L)/(T).

p =mass density of water, (M)/(L)'.

SIX 'fEARS OF SEASONAL CUT AND FILLALONG SCRIPPS PIER

(~rom She.pard, 1950)

"OR'ZO"TAL S"-'L£ ,. FEETc"

Figure 5. Six years of seasonal cut and fillalong Scripps Institution of OceanographyPier, La Jolla, CA, from Shepard (1950) (#8823)

201 Birkemeier, William A. 2000. personal communication, letter to R. L. Wiegel, June 2000, .

Shore & Beach Vol.70, No.1, January 2002, pp. 17 - 27

CAR"EL. CAL'"

STA1"s-GOOWT.'__n RETR£AT

...

~...

'0 .". '--~-'"'00 Fee t

Figure 6. Growth and retreat of a beach berm, Carmel, CA,south end of beach, from Bascom (1951) (#8821)

- 300..-..c

'~1969

.....z 250e1

UPPER ENVELOPE, ~~196B

1\/948\ 1\

~~67\\~66

/

uc

.. 200-'! \

\ Ij'9681:'":::c0"e 150

'0..ucl!..a II

Aug septOtt Noy Dee

Month

Figure 7. Seasonal variation of the position of the mean high-tide line, Stinson Beach Spit (seadrift), CA, 1948-1970, fromJohnson (1971) (#8822). (Data compiled by the California StateLands Commission)

which vary greatly from year to year. Comparisons yearto year at the end of the quiet season appear to be the bestmeans of establishing the long-term trend."

An important measure of a beach is its "width." Smith andJackson (1992) made 85 measurements during a 3-month intervalof "visible beach width" of the Gold Coast Beach, Queensland,Australia. They measured this "width" along the beach slope froma benchmark or permanent mark set in the back beach dune crest,to the last high tide maximum incursion line since the previousevening (similar to the 'wetted bound'). They found that a Weibulldistribution fit their data points. I am not aware of other statisticalanalyses of beach width measurements, but it would be useful forthis to be done routinely. The fit of data to a type of distributionfunction is found empirically. Brillinger (1989, p.255) states agenerality:

"In statistical work with data, a central concern is choosingan appropriate distribution to employ. Probability plottingis one technique for discerning a reasonable family. Inprobability plotting one graphs on special graph paper anestimate of the distribution function versus a member of a

contemplated family. If the family is reasonable, the pointsplotted will lie near a straight line."

The variance of beach width can be extreme - the entiresubaerial beach. A small pocket beach of this type, only about100 m long, which fascinates me is variously called Magic SandsBeach, White Sands Beach, Disappearing Sands Beach. It is on

Shore & Beach Vol.70, No.1, January 2002, pp. 17 - 27

I

10t

\

4

, "'''-'

Profile Line 188214$urveys17 Jul 81 to 21 Dee 88

- Envelope Height- -.. Std. Dev. of DepthMeas.

4.0

.5

0.0

3.0 E'"

2.0 ~>Q)

1.0 [j

a>CJz

E 0g-'"~Q)[j

~......._-.._------..., .- -----------

.10P

t-'900

t200

t300

t700

,500400 860100 600

Distance, m

Figure 8a. Envelope of 214 surveys of Profile Line 188, col-lected between 17 July 1981 to 21 December 1988, Duck, NC.Envelope height and standard deviation from WilliamBirkemeier (personnal communication, 22 June 2000)

'I/I

I II I

J

'00 's '

Olsr",-c: F ~Oo '"I/04f8€J." 0 00;,

c,,''''1/1( r",)

Figure 8b. Prospective view of Profile 62 morphology changesthrough the study period (mid 1984 - mid 1985), Duck, NC, fromStauble (1992)

the Kona Coast of Hawaii, HI, and I have seen it many times.Clark (l985b) describes how high surf, usually during winter,erodes the beach down to bedrock: "causing the beach literally todisappear overnight." Then, when the wave action is light again,the sand is gradually moved back onto the beach, which might takeseveral months.

During my visit in February 2000, there was a visible beachwith many people using it. The sand had not moved offshore ontothe fringing reef, as up to then during the 1999/2000 winter therehad been very light wave action. I have seen it on a number ofoccasions when there was little or no sand on it. Photographs ofthe beach, with and without sand are shown in Figures lOa, lOb.For several miles or more on each side of this beach there is a lowrocky lava shore. This is another example of a beach, with itsfringing reef and small supply of sand, which is greatly differentthan the barrier island beaches with extensive sand, such as the

Carolina coast. At the upland edge of the beach, there is a verticalseawall along the road - Ali'i Drive. I have never seen waves reach

21

~.. -----

Figure 9a. Carmel Beach, CA,south end. Eroded down to bed-rock, south end, during EI Nino winter of 1997/1998. 20 April1998, about 10:30 a.m., looking southerly, by Robert L.Wiegel(#9249)

,I

Figure 10a. White sand beach ("Magic Sands Beach"), Kailua-Kona, Hawaii, Hawaii. All of the sand has been transported offthe visible beach to the reef by waves. Photograph by RobertL.Wiegel, 27 January 1997 (#8610)

this wall, and I have been there when there were very large wavesalong this coast, generated by "kona" stonns. It is probably a Type1 seawall ofWeggel's classification, but perhaps it is Type 2.

SEAWALL AT PERSISTENTLY ERODING(RECEDING) BEACHES

Experience at persistently eroding beaches, with shoreline re-cession, verifies the expectation that a seawall will becomesituated relatively nearer to the sea on the beach profile - eventu-ally there may be no subaerial beach (e.g., Macdonald andPatterson 1985, p. 1537; Basco et al. 1997a, 1997b). Its classifica-tion can change from Type 1 to Type 2, or Type 2 to Type 3, orType 3 to Type 4, etc.

As will be described in some detail subsequently, there areplaces and times where economic and social considerations lead toremedying a persistently erosional situation. One is Santa Bar-bara, CA; the natural alongshore transport of sand was interruptedby a harbor built in the littoral (shoreline harbor), with sandtrapped updrift, along the breakwater, and within the harborentrance - and the beach downdrift eroded. There are two aerialphotographs on the cover of the July 1939 issue of Shore andBeach. The one taken in December 1936 shows the erosion!

recession, together with a seawall to protect the highway, and inthe background a series of groins. The aerial photograph taken in

22

Figure 9b. Carmel Beach, CA,south end. Recovering from EINino winter of 1997/1998. South end, looking northerly, 23 July1999. Photograph by Robert L.Wiegel (#9622)

Figure 10b. White sand beach ("Magic Sands Beach"), Kailua-Kona, Hawaii, Hawaii. The sand has not been transported offthe visible beach to the reef, as the wave action this winter hasbeen small. Photograph by Robert L.Wiegel, 1 February 2000(#9887)

June 1939 shows the same location about 2 years after beachrestoration by sand bypassing had been started. Details of thislong-tenn project (sand bypassing is still being perfonned) will begiven subsequently.

A second example is also in southern California. A shorelineharbor was built during World War n as part of an amphibioustraining base, U.S. Marine Corps Base Camp Pendleton justnorthwest of Oceanside. The military harbor works (Del Mar BoatBasin) were expanded in 1958 and again in 1962-1963, togetherwith the construction of a civilian small craft harbor (e.g., Wiegel1994). Two rivers enter the ocean here, the Santa Margarita andthe San Luis Rey, one northwest of and the other southeast of theharbor - formerly major sand sources; but dams have been built onthem. Wave direction and alongshore sediment transport isbimodal here. Waves from westerly directions transport sand tothe southeast, and the "southern swell" transports littoral sedimentto the northwest, with the net transport toward the southeast. I givethis example for several reasons, one of which is that I spent mostof 1949 there studying. waves, currents, beaches and amphibiousoperations for the U.S. Marine Corps/Office of Naval Research,and have followed what has happened there since, including manyvisits. Oceanside was founded in 1888as a coastalresort(Bagleyand Whitson 1982). With its beach and pier, it is a popular

Shore & Beach Vol.70, No.1, January 2002, pp. 17 - 27

...~,."t'~',;"

'::::'~',,'::'~':':'<':'::: /<.: <':. ~'.::'< :":':".::.:. :'. ::'.,: ';'.", ,'.'

(A) Beach without any coastal protection structures.

~.~f.!:j,;;...~.~

(B) Beach impoundment due to construction of seawall and home,

FOOD"'",

J,":::'::'.::';::.::.:::: '.::.:y ;::: .:.:. '::':': '::""'.,

(C) Beach impou,rulment due.to constl;1ction. of revetment

Figure 11. "Footprints" of seawall, beach home, and revetment,from Griggs, Tate, and Corona. (1994)

recreational area for the local residents, the Marines, and visitors.There is a street with a low seawall in front of it along the base ofa reach of the seacliff that backs the beach. After construction ofthe fIrst harbor and the dams, serious beach erosion occurred; theseawall did not cause this. There has been extensive beachnourishment (e,g" Bagley and Whitson 1982, Wiegel 1994).However, to the southeast, in Carlsbad, there is a cobble backbeachat the foot of the seacliff (FlickI994, editor). It has beenhypothesized that much of the sand lost from the beach has beentransported offshore by rip currents generated at the rubblemoundbreakwaters, from either side, depending on the direction ofalongshore transport - the gross, not just the net. It has been furtherhypothesized that the sand is transported mostly in a southeasterlydirection and deposited in water 40 to 60 ft deep. This lineardeposit was discovered in a comparison study of the NationalOcean Survey Sheets for 1934 and 1971-1978, and fInding the S-mile-long (plus) accretion feature. The accretion in the portion inexcess of 2 ft deep was estimated to be about 4.4 million cu yd, anannual rate of 146,000 cu yd!year if it started when the Boat Basinwas built in 1942, or 440,000 cu yd!year if it started aftercompletion of the harbor complex in 1962 (Dolan et al. 1987),However, it is not clear how the linear feature forms.

STRUCTURE "FOOTPRINT" -LOSS OF USABLEBEACH

Where shore protection structures are built on a beach, there is aloss of useful beach - the "footprint" of the structure (e.g., Griggs,

Shore & Beach Vol.70, No.1, January 2002, pp. 17 . 27

Tait, and Corona 1994). Generally a vertical seawall has a smaller"footprint" than a revetment (Figure 11). There are exceptions, forexample where a beach has eroded down to bedrock and thestructure is built on it. The seawall "footprint" is much less thanthe impoundment, which includes a beach house; treat themseparately.

SEAWALL OR REVETMENT AT A PERSISTENTLYERODING (RECEDING) SEA CLIFF

At some places and times seawalls or revetments are theappropriate solution to an erosion/recession situation. I havedescribed briefly an example in another paper, with text andphotos, - Capitola, near the northern end of Monterey Bay, CA(Wiegel 1999, pp. 7-8). The coastal highway from Capitola toSanta Cruz is along the present edge of a seacliff for severalhundred feet, between it and a higher bluff a few hundred feetinland (Figure 12). There are homes on this bluff, some datingfrom the early 1900's. A railroad is between the highway and theinland bluff, and there is a highway bridge and a railroad trestleover Soquel Creek within a few hundred feet. Imagine the costand great inconvenience if a decision had been made to allow theerosion and recession to continue rather than design and constructa well-engineered stone revetment. It was constructed in 1962, Aninspection in 1988 (Magoon, Pope, and Treadwell 1989) indicatedit to be in good condition. I photographed it on 26 March 1998 atthe end of the El Nino winter of 1997/1998, and again on 8December 1999; it appeared to be in good condition. It has servedits purpose for the past 37 years.

TWO LONG TERM QUANTITATIVE STUDIES

The only long term quantitative field studies of which I amaware, to measure the effects on beaches, if any, of seawalls andrevetments are by Gary B. Griggs and his colleagues (Griggs, Tait,and Corona 1994; Griggs et al. 1997; Griggs 1999) and by DavidR. Basco and his colleagues (Basco et al. 1997a, 1997b),

Griggs, Tait, and Corona (1994) and Griggs et al. (1997) madeobservations, including surveys along a series of transects in frontof a seawall or a rock revetment, and along the beach on both sidesof the structures. This was done at several locations on the northshore of Monterey Bay, CA, at Rio del Mar, Aptos Seascape, andvicinity. I have walked along this beach many times, summer and!or winter, on nearly a yearly basis for about 70 years, and agreewith their observation that it is has no long term erosion, just cyclic

Figure 12. Aerial photograph of Capitola, CA, revetment, beach,pier, railroad, highway, groin, Soquel Creek, November 1977.Courtest of U.S. Army Engineer Division, South Pacific, OrvilleT. Magoon (#2189)

23

Compa~on of Winter Seawall &O>ntrol BeachProfdes

(curvature of shoreline removed)

2

"'"'

;:;{!g"0.",~ 0iii

-1

.2-40 -20 0 20 40 60

Cross-shoraDistance (lrieters).

80 100

Figure 13a. Aptos Seascape, Monterey Bay, CA. Comparison ofaveraged winter profiles (February) from seawall-backed andcontrol beach (Profile Lines 13 and 18), from Griggs et al. (1997)

(seasonal) erosion/recession/accretion - a broad beach in summerand fall in front of a seacliff. According to Griggs (1999, pp. 25,32):

"We recently completed an 8-year study monitoring theimpacts of several different types of seawalls and revet-ments on fronting and flanking beaches in northernMonterey Bay. Although local moderate-scale seasonalimpacts have [been - sic] documented (Griggs et al. 1997),there have been no permanent effects on the beachesstudied, which are along a coastline which has a highlittoral drift rate and is not undergoing any net long-termerosion but does undergo expected seasonal changes.Although rip-rap revetments have often been perceivedand judged by permitting agencies to be more permeableand therefore expected to have less impact on beaches than"impermeable" seawalls, this was not supported by fieldobservations and surveying."

"Surveys of the spring and summer accretionary phaseindicate that the berm advances seaward on the controlbeach until it reaches the seawall. At that point, a bermbegins to form in front of the seawall and subsequentaccretion occurs uniformly on both beaches. Thus, whilethe winter erosional phase is influenced to some degree bythe presence of a seawall, this is not the case for the bermrebuilding phase." . . . "Finally, of greatest significance, isthe comparison of time-averaged winter and summerprofiles for the seawall-backed and control beaches. Com-parison reveals no distinguishable differences between thewinter profile for the seawall and control beaches and thesummer profile for the seawall and control beaches." SeeFigures l3a and l3b.

The second long-term study of which I am aware is by Bascoand his colleagues (Basco et al. 1997a, 1997b). It is at Sandbridge,a suburb of Virginia Beach, VA, about 15 miles south of theChesapeake Bay entrance, about half way between the entranceand the North Carolina border. It is at the north end of a 70-mile-long barrier strip. Rudee Inlet (with jetties) is at the south end ofVirginia Beach, and Dam Neck Naval Reservation (3.2 miles ofshore) is between Rudee Inlet and Sandbridge. As discussed byHeadland (1992), there is a major variation in the ocean bathym-

24

Comparison of SUJD]J).erSeawall &Control Beach Profiles

(curvature of shoreline removed)3

2.-

j~ 1,S§'"~ 0iii

-.1

-2-40 (j 20 40 60

<;rpss-shorcDistance(meters)80 100-20

Figure 13b. Aptos Seascape, Monterey Bay, CA. Comparisonof averaged summer profiles (June) from seawall-backed andcontrol beach (Profile Lines 13 and 18), from Griggs et al.(1997)

etry offshore this reach of coast. There is a shallow water deltaicfeature, part of the Chesapeake Bay ebb tide delta (shoal) north ofRudee Inlet. The bathymetry is deeper from Sandbridge south (seeFigure 14b). This alters the distribution of wave energy along theshore, and the direction and quantity of alongshore sand transport(Figure l4c). Everts, Battley, and Gibson (1983) concluded fromtheir shoreline study of the region from Cape Henry at the entranceto Chesapeake Bay, VA, to Cape Hatteras, NC, that there is adivergent alongshore sediment transport nodal zone at about36°41' north latitude (the north end of Back Bay, VA). The nettransport is toward the north, north of this, and toward the south,south of this. Sand is bypassed by dredging at Rudee Inlet, fromsouth to north (Everts, Battley, and Gibson 1983).

Historic data for 120 years prior to the first seawall, which wasbuilt in 1978, shows an average beach recession rate of about 2 m/year (several sources, as reported in Basco et al. 1997a, 1997b). Ithas been estimated that about 150,000 cu m/year of sand istransported alongshore toward the north, as reported by Bascoet al. (1997a, 1997b). Between 1978 and 1988 seawalls were builtalong about 10% of the 4-3/4-mile reach and by the start of thebeach monitoring project in 1990 there were seawalls along nearly60% of the reach (Basco et al. 1997a, 1997b). The structures werenot continuous, with substantial lengths of beach with no seawalls;this permitted the study of relative effects of walled and non-walled sections. The survey lines (transects) continued inlandthrough the first sand dune at the open beach sections, and over theseawalls and the same distance inland at the walled sections (overthe first dune).

The relative severity of each "wave year" (1 October - 30 Sep-tember of the following year), from 1981, was estimated fromwave gage measurements available from the U.S. Army Corps ofEngineers (USACE), Coastal Engineering Field Research Facility(FRF) at Duck, NC. The data used were from the gage at the endof the pier, which is about 35 miles south of Sandbridge, andwhich has a similar wave climate.

In August 1990, they began a 5-year program to survey 28subaerial beach profiles to just below mean low water (MLW),once a month and after significant coastal storms. Each profilenumber (between 0 and 252) is the distance in hundreds of feet

Shore & Beach Vol. 70, No.1, January 2002, pp. 17 - 27

a. SHORELINE CHANGE

LATITUDE36'55'

LEGEND T... :::::::::::::::;::::: ,-About1858 to about 1925 .,,::::l1'-"""'"'"About 1925 to 1980

1937 101984 (Aerial Photographs)

.;4 -3.5

'::::::::.'.'''.'.'.'''.'.'l :..::-.f~....,. .....

I36'30" .I

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5

AVERAGESHOREUNECHANGE RATES, M/YEAR

b. LOCATION (30' DEPTH) b. WAVE HEIGHT

AVERAGES FOR 1982

A

[

310

VIRGINIA 300BEACH

290

280RUOff INLET---

270CROATAN BEACH

260DAM NECK

a250240

SAHD8RIDGE[230

220

210

Figure 14. Composite of shoreline change rates (left), bathymetry (center), and breaking wave heights (right) and their variationalong the 25-mile Atlantic Ocean coastline of the city of Virginia Beach, VA, from Basco (1991)

south of the Dam Neck Naval Reservation. Other data were

available, many by the City ofVITginia Beach, with profile surveysstarting in October 1980. There were more than 2,700 profilesurveys in the data set for 53 profile locations from October 1980through September 1995; but for their report only 34 profilelocations were used as the others were not surveyed regularly orfor less than 1 year.

Three methods of analyzing the profiles were used to obtainmeasures of erosion rates, and a statistical analysis was made ofthe resulting data. Sand volumes per unit length of seawall/beach(cubic meters per meter of beach length) were calculated for thebeach seaward of a seawall or its hypothetical extension (they usedthe tenn "partition" for this) at non-wall sections; referred to asvolume seaward. Using the dune profiles, the volume landward ofthe walls or the "partitions"were calculated;referredto as duneprofile sand volume or wall profile sand volume. These data wereplotted as a function of time for the 5-year interval (1 October1990 - 30 September 1995).

Three questions were posed, and responded to:

a. Does the sand volume seaward of seawalls erode faster thanthe volume seaward of the 'partition' for non-walled locations?They found: "The results at three time scales and from the threeanalysis methods all supported the same conclusion, namely: thevolume erosion rates are not higher in front of seawalls."

b. Do seawalls delay beach recovery? They found:seawalled beaches recovered at about the same time as non-walledlocations." But, there were some complications, described in thepaper.

c. Is the sand volume landward of the "partition" at non-walledlocations eroding at a faster rate after construction of adjacent

Shore & Beach Vol. 70, No.1, January 2002, pp.17- 27

seawalls? The evidence was considered to be inconclusive.

These were the results of two mild winter seasons, two stonnywinter seasons, and a summer season without normal recovery.The study has been extended for an additional 5 years, and isnearly completed (Basco 2000)2. In addition, profile surveysthrough the surf zone to the depth of closure are being made atDam Neck for the U.S. Navy, and a wave gage is being operatedoffshore this section (Basco 2000).

Coastal engineers, scientists, planners, and regulators needstudies of this quality for other types of shores and coastaloceanographic conditions.

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Basco, D.R. 1991. Boundary Conditions and Long-Term ShorelineChange Rates for the Southern Virginia Ocean Coastline. Shore &Beach 59(4), 8-13.

Basco, D.R. 1992. Closure of: 'Boundary Conditions and Long-TermShoreline Change Rates for the Southern Virginia Ocean Coastline.'Shore & Beach 60(4),31-34.

Basco, D.R., Bellamo, D.A., and Pollock, C.B. 1993. Statistically Signifi-cant Beach Profile Change With and Without the Presence of Sea-walls. Proc. 25" Coastal Engrg. Can[. 2, ASCE, NY, 1,924-1,937.

Basco, D.R., Bellomo, D.A., Hazelton, J.M., and Jones, B.N. 1997a. TheInfluence of Seawalls on Subaerial Beach Volumes with RecedingShorelines. Coastal Engrg. 30,203-233.

Basco, D.R., Bellomo, D.A., Hazelton, J.M., and Jones, B.N. 1997b. Influ-ence of Seawalls on Subaerial Beach Volumes with Receding Shore-lines, Final Report. Contract Report CHL-97-2, U.S. Army EngineerWaterways Experiment Station, Coastal Engineering Research Center,Vicksburg, MS, 176 pp.

Bascom, N.W. 1951. The Relationship Between Sand Zie and Beach-FaceSlope. Trans. American Geophys. Union 32(6), 866-874.

25

<: 200i1i HKIg 180\.)i:: FALSE170<:

CAPE0.5 0.7..;

<Hb> (m)

0 5 10I .. .

KILOMETERSISOBATHSIN METERS

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Griggs, G.B., Tait, J.F, Moore, L.J., Scott, K, Corona, W., and Pembrook,D. 1997. Interaction of Seawalls and Beaches: Eight Years of FieldMonitoring, Monterey Bay, CA. Contract Report CHL-97-1, U.S.Army Engineer Waterways Experiment Station, Vicksburg, MS, 34pp.

Griggs, G.B. 1999. The Protection of California's Coast: Past, Present,and Future. Shore & Beach 67(1), 18-28.

Grosskopf, WG., and Kraus, N.C. 1994. Guidelines for Surveying BeachNourishment Projects. Shore & Beach 62(2), 9-16.

Headland, J.R 1992. Design of Protective Dunes at Dam Neck, Virginia.Proc. Coastal Engr. Practice '92, S.A. Hughes, ed., ASCE, NY, 251-267.

Hwang, D. 1981. Beach Changes on Oahu as Revealed by Aerial Photo-graphs. University of Hawaii, Hawaii Inst. of Geophysics, TechnicalReport HIG-81-3, 146 pp.

Johnson, lW. 1971. The Significance of Seasonal Beach Changes in TidalBoundaries. Shore & Beach 39(1), 26-31.

Kraus, N.C. 1987. The Effects of Seawalls on a Beach: A Literature Re-

view. Proc. Coastal Sediments '87, ASCE, NY,945-960.

2 Basco, David R. 2000.26

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Zilkowski, D.B., Richards, I.H., and Young, G.M. 1992. Special Report:Results of the General Adjustment of the North American Datum of1988. Surveying and Land Information Systems 52(3), 133-149.

APPENDIX: DEFINITION OF THE SHORELINE

How is the shoreline defined? Shalowitz (1964), of theUSC&GS states, "The most important feature on a topographicsurvey is the high-water line." Shalowitz also states (1964,p. 174): "The mean high-water line along a coast is the intersec-tion of the plane of mean high water with the shore." This requiresthe determination of the tidal MHW from tide gage measurements.He says: "Obviously, for charting purposes, such precise methodswould not be justified, hence, the line is determined more from thephysical appearance of the beach. What the topographer actuallydelineates are the markings left on the beach by the last precedinghigh water, barring the drift cast up by storm waves." The use of,and the rationale for, the high-water line is discussed by Everts,Battley, and Gibson (1983, pp.44-50). They conclude: "... itwas the intention of all the agency's topographic surveys todetermine the line of mean high water for delineation on maps."They add "... that line at the time of the surveyor the date ofphotography." Thus, it would unlikely be the true mean high-water line. It probably is the 'wetted bound' observed by a personon the shore or on an aerial photograph. Moffatt & NicholEngineers (1995) used "'wetted bound' . . . to describe the bound-ary between sand saturated at high tide and drier sand furtherinland, and is analogous to a high water shoreline." Dolan et al.(1980) used the high water line, HWL, "identified as the landwardlimit of wetted sand (darker tone), and the water line of theprevious high tide." As a part of the field studies of amphibiousoceanography made by personnel of the College of Engineering,University of California at Berkeley, measurements were made ofwave uprush and wave backrush on several beaches with differentcharacteristics and wave conditions, to see if a reasonable relation-

ship with tide elevation could be determined (patrick 1950). Onemight expect the 'wetted bound' to be related to wave uprush limitat whatever was the existing tide stage. The results were quitevariable. One conclusion was: "The variabilities of the elevations

of limits of backrush and uprush are at best a very obscure functionof the tide stage." They were also an obscure function of the beachslope. Wave set-up must have been involved. There is consider-able uncertainty in reported shoreline changes and boundaries.Use the data with caution. On some beaches, a 'wetted bound' orsomething similar is not discemable on an aerial photograph.Steven Leatherman showed examples in his presentation at thesymposium Carbonate Beaches 2000.

The National Ocean Service (NOS) of the National Oceanicand Atmospheric Administration (NOS 1992) measures, ar-chives, and publishes values of mean higher high water(MHHW), mean high water (MHW) , mean sea level (MSL),mean tide level (MTL), mean low water (MLW), mean lower lowwater (MLLW), and other tidal data for a great many coastalsites. Mean sea level is obtained by averaging the hourly heightsof the tide while mean tide level (also called half-tide level) is theaverage of the high and low waters; usually less than 0.1 ftdifference between MSL and MTL (Meaney 1949). Note, thateffective 1 January 1989 NOS changed the chart datum and tidaldatum from MLW to MLLW along the U.S. east coast, toconform to the datum used on charts of other locations. NGVD(National Geodetic Vertical Datum) was used as a datum onmany surveys; this is useful, but is seldom the same value asmean sea level or mean tide level, although often close to them.NGVD has been replaced by the North American Vertical Datumof 1988 (NAVD 88) (FEMA 1992; U.S. Department Commerce1992; Zilkowski, Richards, and Young 1992). In addition toastronomical tides, there are other variations of water level, someof which are referred to as meteorological tides.3

3 An informative book on tides is Tides. A Scientific History, by David Edgar Cartwright (1999).

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