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Sand sources, volumes and movement patterns on Wreck Beach, Vancouver, British Columbia Pool, Meridith Ines 1975-12-31

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SAND SOURCES, VOLUMES AND MOVEMENT PATTERNS ONWRECK BEACH, VANCOUVER, BRITISH COLUMBIAbyMERIDITH INES POOLB.Sc. University of Oklahoma, U.S.A.,1971A THESIS SUBMITTED IN PARTIAL FULFILMENTOFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF APPLIED SCIENCEin the DepartmentofCivil EngineeringWe accept this thesis as conformingto therequired standardTHE UNIVERSITY OF BRITISH COLUMBIASeptember, 1975In presentingthis thesis in partial fulfilment of the requirementsforan advanceddegree at the Universityof British Columbia,I agree thatthe Libraryshall make it freely available for reference and study.I furtheragree that permissionfor extensive copying ofthis thesisfor scholarlypurposes may be granted by the Head of my Department orby his representatives.It is understood that copying or publicationof this thesis forfinancial gain shall not be allowed without mywritten pemiission.Department of t/The University of British Columbia2075 Wesbrook PlaceVancouver, CanadaV6T 1WSDate /7 /975/ABSTRACTAlong Wreck Beach the existing headland cliffs are erodingand receding under attack from terrestrial and marine agents.Valuable property is being lost and nearby structures endangered.Remedial measures were undertaken in the summer of 1974to halt wave erosion along the cliff base. A rock groin andsand—gravel protective beach scheme was only partially successful during the following year. To design an adequate protectionsystem for the cliffs wind and wave effects need to be determined to fully understand the resulting sand movement patterns.Understanding the processes affecting Wreck Beach is the firststep in controlling them.Methods used to investigate sand movement included fieldcoverage of the study area in photographic form as well asinstrument cross—sectioning over a two year period. These datawere correlated with historical wind records and predictionsfrom wave refraction diagrams to determine seasonal movementonto and off the beach face and the cyclic progression ofsandbars in the longshore current direction. Annual sand transport volumes, sand supply sources and amounts contributed areoutlined.iiIn designing a protection scheme in which longshore transport requirements must be considered the information and calculations suggests that the Fraser River North Arm could amplyprovide the longshore transportsupply requirements. However,some means in addition to the present natural processes mustbe available to bring this sand into a range where wind generated wave activity can incorporate it into the existingWreck Beach system.iiiTABLE OF CONTENTSABSTRACTTABLE OF CONTENTS .LIST OF FIGURESLIST OF TABLESACKNOWLEDGEMENTPageiiivviviiixCHAPTER I INTRODUCTION1CHAPTER II RECENT HISTORY OF EROSION52.1 Geology .2.2 Erosion Mechanisms2.3 Remedial Measures . .CHAPTER III WIND CONDITIONS 133.1 General Wind Patterns3.2 Annual Meteorological and Beach Cycles3.3 Wind Directions of Primary ImportanceCHAPTER IV WAVE CONDITIONS• •. 13• . •. 16• • • . 22244. V5.15.25.32432424344465050557577785710Determination of Effective FetchesRefraction DiagramsWaves from SW SectorWaves from NW SectorWaves from West SectorWaves from March 25, 1975 High WindsSAND MOVEMENTLimits of the Littoral Zones . • . .Compilation of DataSand Movement on the West Beach . . .5.4 Sand Movement on the Tower Beach and East End5.5 Sandbar MovementivPageCHAPTER VI SUMMARY816.1 Calculation of Volumes Capable of Being Movedby Wreck Beach Longshore Transport System . . 816.2 Fraser River North Arm as a Sand Source . . .986.3 Wreck Beach Cliffs as a Sand Source 1046.4 Conclusions .105BIBLIOGRAPHY106VLIST OF TABLESNUMBERTABLEPAGEI Wind scalesand sea descriptions17II High wind periodinformation19III Wind, fetchand deep waterwave data33IV Limits ofthe Wreck Beachlittoral zones53V Directionalhourly wind frequencies83VI Annual longshoretransport volumetoward the NE92VII Annuallongshore transportvolume toward theSW 93VIII Freshet longshoretransport volume towardthe NE94IX Fraser RiverNorth Arm dredgingrecords99viLIST OF FIGURESNUMBER FIGUREPAGE1 Wreck Beach study area map 42a Regional surface wind patternsof thenortheastPacificOcean 152b Local surface wind patterns of theStraitof Georgia 153 NW wind direction effectivefetch diagram 274 WNW wind direction effectivefetch diagram 285 West wind direction effective fetchdiagram 296 WSW wind direction effectivefetch diagram 307 SW wind direction effectivefetch diagram 318 NW wind direction wave refractiondiagram 379 WNW wind direction wave refraction diagram 3810 West wind direction wave refraction diagram 3911 WSW wind direction wave refraction diagram 4012 SW wind direction wave refraction diagram 4113 Photograph sequence showing NE longshoretransport waves breaking at an angle toWreck Beach . 45* .,+?14 Enlarged WNW wave refraction diagram pàket15 Photograph sequence at photograph location 1,East End, prior to construction activities . 5616 Photograph sequence atphotograph locations 1 & 2,East End, following constructionactivities 57viiNUMBER FIGUREPAGE17 Photographsequence at photographlocation 6,Towers Beach, priorto construction activities...5918 Photographsequence at photographlocation 6,Towers Beach, followingconstruction activities..6019 Photograph sequenceat photograph location10,West Beach groin, followingconstruction act6120 Photograph sequenceat photograph location13,West Beach, followingconstruction activities....6221 Photograph sequence atphotograph location 18,West Beach, followingconstruction activities...,6322 Photograph sequenceat photograph location19,Towers Beach, followingconstruction activities..6423 Chart of photographsequences prior toconstruction activities.6724 Chart ofphotograph sequencesfollowingconstructionactivities...... 6825 Chartcorrelating photographinformation withcross—sectioningdata on upper beachface7026 Chart correlatingphotograph information withcross—sectioningdata at groins7127 Chart correlatingphotograph informationwithcross-sectioning dataon sandbars7228 Annual WreckBeach summer-winter beachcycle7429 Annualsandbarmovernent8030 Vancouver InternationalAirport ten yearqind rose8431 Fraser River North Arm and Wreck Beach areasoundings chart102viiiACKNOWLEDGEMENTThe author is verygrateful to her supervisor, Dr.PeterR.B. Ward, for his guidanceand encouragement during thisstudy. The author is alsograteful for the helpand assistancereceived from VancouverBoard of Parks and Recreationandfrom Swan—Wooster EngineeringCompany Limited.This study was supportedfinancially by a NationalResearch Council grant to Dr.Ward.ixCHAPTER IU’TRODUCTIONThis thesis describes a study of erosion and sand movement patterns on the Wreck Beach section of beach below thePoint Grey headlands in Vancouver, British Columbia. PointGrey occupies the tip of Burrard Peninsula projecting into theStrait of Georgia. Wreck Beach is located just below the oldFort Camp military base on University of British ColumbiaEndowment Lands. Figure 1 shows the map of the Wreck Beachstudy area. This beach is under the jurisdiction of the Vancouver Board of Parks and Public Recreation.Along Wreck Beach the headland cliffs are receding rapidly under attack from terrestrial and marine erosion agents.At this time there is considerable concernfor the buildingsand structures within a few hundredfeet of the cliff brimsuch as the new Museum of Anthropologywith a 1973 contractprice of $3,070,000.00 not to exceed$4,297,000.00 and CecilGreen Park purchased by the Universityin 1964 for $100,000.00.Remedial measures for cliff stabilization wereproposedby Swan-Wooster Engineering Co. Ltd.,1973 and Robert WiegelConsulting Engineer, 1973. Prime considerationwas given tomaintaining a natural beach appearance. Inthe summer of 1974construction work was undertaken to implementsome of thesemeasures.12The period of this study covers the year preceding construction and the year following. The study considers theprocesses of winds, waves and effects of waveson the cliff, beachand sand movement. To try and understand these processesandsources of sediment photographs were taken, wind recordsstudied, wave patterns predicted andlongshore transport volumes calculated. Understanding these processes isthe firststep in controlling them.Chapter 2 describes the study area andreviews thegeology and erosion mechanisms. A briefdescription of theremedial measures proposed andundertaken is outlined aswell as comments concerning thesuccess of the stabilizationproject.Chapter 3 describes the regionaland local wind patternsaffecting the Wreck Beach area.An abstract of high wind periods during the study periodis related to the erosion-deposition patterns derived fromphotographic evidence to determinethe annual—summer winter cycles.Chapter 4 describes the waveconditions affecting WreckBeach. Effective fetches arederived and wave refractiondiagrams used to predict modifiedwave forces, longshore movementand erosion—deposition patterns.3Chapter 5 describes the extent and direction of the long-shore transport system resulting from variouswind and waveconditions, and describes the seasonal onshore—offshore movement of sediment on Wreck Beach. Data from photographicrecords monitored during the study period are compiled ingraphic form.Chapter 6 presents the conclusions ofthe study. Sandvolumes capable of being transportedJDy the longshore systemare calculated. The sources of sandwhich supply the systemare identified togetherwith the relative magnitude of thevolumes. The influence and extent ofthe Fraser River NorthArm sediment with seasonal freshet effectsare outlined.4IWRECK -BEACH STUDY AREA—4’--..Hydrographic contour linE13Photograph location anddirectionMap Scale: 1” = 330’I///-I/II1dIIIIIIIIIIIII\\I////I..ci\Ij4II/I.I ——I/7—//\\\IIII’ /II //0/III\\-IIIIIIIII1‘IFIGURE 1. Wreck Beach study aremap_CHAPTER IIRECENT HISTORY OF EROSION2.1 GEOLOGYEisbacher, 1973, Madsen, 1974, Backler, 1969, Carswell,1955, and others have determined that geologically the PointGrey formation is a result of recurring glacial periods. Thegreatest contribution was laid down as river deposition duringthe last interglacial period, the Olympian Interglaciationbetween 50,000 and 25,000 years ago. Carbon-14 methodshavedated peat from the cliffs at 25,000 yearsold according toEisbacher, 1973. Rising 200 feet above sea level the cliffsare composed of alternating layers of sand, silt and claysediments overlain by cross—bedded clean sands and gravellenses. A 15 to 20 foot thick wave-worked gravel till layerwas deposited by the last glaciation, the Fraser Glaciationbetween 20,000 and 15,000 years ago.Along the 3000 foot length of Wreck Beach erosion hasexposed cliffs of unconsolidated sediments. These cliffsapparently have been receding since the last lowering ofthesea level. Glaciated rocks ranging in size from cobblestoboulders litter the beach from the present cliff base to theouter slope of Spanish Banks. These rocks, originating in56the till layer atop the cliff, have been deposited on thebeach as underlying supporting soil was removed. Well-foundedestimates as to the actual rate of recession are vague. Surveys prior to 1937 do not exist for which control has beenpositively and accurately recovered or relocated.72.2 EROSION MECHANISMSThat these cliffs are presently highly unstable and easilydegradeable is obvious from the general appearance of the area:slough and slide material collects as sand slump piles, clayblocks, toppled trees, tension cracks, the near vertical cliffface, and the absence of accumulated cliff material at thecliff base.The composition of the sea cliffs and characteristic properties as well as the erosion mechanisms have been thoroughlyinvestigated, documented and explained by Carswell, 1955,Backler, 1960, Madsen, 1974, Waslenchuk,1973, Lum, 1975,and McLean, 1975. The agents acting to erode the cliffs arethe following: wave action at the cliff base; precipitationwithin and atop the cliffs; rain, wind, andpeople activityact directly on the cliff face to dislodgeand move particles;and it is also suspected that earthquake activity inthe pasthas served to destabilize the cliffs according to R.A. SpenceLimited, 1967. Of these, wave actionand precipitation arethe most important erosion mechanisms.On Wreck Beach the cliff base is readily undercut bywave action especially during higher tidesand onshore windperiods. McLean, 1975, found during1974-75 that at timeswaves were capable of moving stones at least0.03 ft.3 in size8more than 100 feet eastward in the beach surf zone. At thesame times stones 0.20 ft.3 and greater remained stationary.Wave action also removes accumulated toe material which otherwise would eventually provide an undisturbed base for stabilizing the cliff at its natural angle of repose. An angle estimated by Piteau Gadsby McLeod Limited, 1972, to be a 30-35°slope with the horizontal. Precipitation, mostly as rain, averages 60 inches per year in the Burrard Inlet area. In theareadraining to the Wreck Beach cliffs Carswell,1955, determinedthat some 400 xio6gallons of water (a net quantity: totalprecipitation in all forms less the amount lost through evaporation—transpiration) are availableannually as erosion agentsin the form of runoff and infiltration. Ofthat, an estimated60 x106gallons per year infiltrate into the ground watersystem and eventually emerge from the cliffalong seepagelines. Continued excavations into andbelow the surface tilllayer provide additional catchmentbasins where moisture canpond and move immediately into thegroundwater system. Plantcover provides protection againstsurface runoff, sheetwash,and removes moisture by way ofevapo—transpiration processes.With the development of the EndowmentLands forest and vegetation has been removed fromthe cliff top and slopes introducingadditional water into the drainage basinand exposing unprotected ground surfaces. Extrapolating from this estimate the 36”diameter storm drain from the drainagebasin outfalls at sealevel and carries some 300 x106gallons annually. Presumably9the remaining 40 xio6gallons is water directly available assurface runoff and pours over the cliff edge during the year.Gullying by surface runoff is an highly effective andrapid means of eroding the cliffs. Carswell, 1955, estimatedthat the present Campus Canyon was formed during a very shorttime by the washout of 100,000 cubic yards of cliff materialduring a 1935 flash flood.Temperatures seldom fall below freezing and rarely staythat low for any length of time. On these occasions the freeze—thaw cycle affects the outer few inches of exposed soil. Lum,1975, studied the freeze-thaw action of the cliff face in 1974-75. Slabbing on a daily basis was not widespread. But whereit did occur, the thickness of the spalled slab was observedto vary between 3/8 inch to 1 inch. During severe winters withlong periods of cold temperatures calculations indicate thatretreats of 5 inches might be expected just by spalling. Further, the freeze—thaw process was estimated to contribute from 1percent to 6 percent of the total cliff material lost annually.102.3 REMEDIAL MEASURESSince 1962 Swan-Wooster Engineering Co. Ltd. has beeninvolved in the erosion problems and protection schemes atWreck Beach. Retained by the Vancouver Board of Parks andRecreation in 1973, Swan—Wooster proposed a protective beach—groin system to stabilize the 3200 foot length of upper beachand prevent further recession of the cliffs by wave attack.The Provincial Government retained Dr. Robert L. Wiegel,Consulting Engineer, Acting Dean, University of California,Berkeley, 1973, to review the proposed design. Modificationswere made to meet the demands of the many public factions interested in Wreck Beach area. The final design accepted by theProvincial Government included a rubble—mound groin system witha 60 to 100 foot wide gravel core and coarse sand overlayprotective beach built to above high tide levels at the cliffbase, all to have as natural an appearance as possible. (Forconstruction details see Dave McLean’s, 1975, thesis or Swan—Wooster Construction Plans, 1973). Construction Cartage constructed the system in the spring of 1974. Project cost was$350,000.00.The protective beach was to provide protection and stabilization in a number of ways: an area of energy dissipationfor incoming breaking waves, a substitute for cliff materialas a supply source for the longshore drift process, it wasbuilt above high tide elevation so erosion material could11accumulate undisturbed at the toe and the cliffscould begin tostabilize at their natural angle of repose.The groin system was to help maintain the protectivebeach by trapping part of the material already in the littoraltransport system, to retard the erosion ofthe existing beachand new protective beach, and to dissipateincoming wave energies.The groins are the low-profile permeable type and of rubble-mound construction. The permeable type of groin was usedtoavoid abruptly offsetting the shore alignmentwhich occurs withimpermeable groins. Theoretically the permeable groin permitspart of the longshore forces and materialsto pass through thestructure which triggers deposition onboth sides of the groin.An exception to the permeable groin conceptwas the extensionof the existing storm drain outfall --a solid 36 inch diameterconcrete conduit which serves as animpermeable groin at thatlocation.In addition certain measures havebeen suggested whichwould halt or retardclifferosion fromabove and within. Thesesuggestions as urged by Swan—Wooster, 1973,as well as byWiegel, 1973, Backler, 1960, Carswell,1955, Bain, 1970, andothers included: storm drainage awayfrom the cliffs, not toward or along it; drains or wells tointercept subsurfacedrainage layers; revegetation of the cliffface; elimination ofaccess to the cliff face; and futureconstruction well away fromthe edge of the cliff.12To determine the success of the protective beach—groinsystem McLean, 1975, documented the extent and rate of marineerosion from construction in 1974 through the winter to April,1975. His findings are given in summary.“During the summer of 1974 a 3200 foot sand filland cobble core berm and groin system was constructedat Towers Beach, University of British Columbia toprevent marine erosion along Point Grey cliffs. Duringthe following winter the berm was partially successfulin protecting the cliff base, however, along the westernbeach the sand fill was severely eroded by W and NWstorm waves. By the end of February the berm had failedover a 1500 foot length allowing storm waves to undercutthe cliff base during high tides. Throughout the studyperiod the groins were very ineffective in stabilizingthe sand fill, allowing a large amount of material tomove eastward by littoral drift. The useful life ofthe berm is probably less than two years. Remedialmeasures will probably be required in the future.”CHAPTER IIIWIND CONDITIONS3.1 GENERAL WIND PATTERNSThe general surface wind patterns in the northwest PacificOcean are summarized in Figure 2a. The summer pattern is directlyinfluenced by a semi—permanent high pressure cell near theHawaiian Islands. The cell created from this North Pacifichigh controls the region so that northwest and westerly windsprevail along the Canadian Pacific coast.The winter pattern emerges when the North Pacific cellweakens and migrates southward while a low pressure cell inthe Gulf of Alaska intensifies. Along the Pacific coast thiscauses a reversal of prevailing wind directions so that southeasterly to southwesterly winds moving nearly parallel to thecoast dominate.Within the Strait of Georgia the general regional windpatterns are frequently and strongly modifiedby the presence ofmountains and the altered winds from the Juan de Fuca Strait,Puget Sound and Fraser Valley. The Strait of Georgiawindpatterns are summarized in Figure 2b. The winter pattern isclosed and counterclockwise in the southern part ofthe Straitincluding Point Grey.1314The spring pattern shows a general shift to easterly andsoutheasterly winds.The summer pattern loses the distinct closed circulationcell. In the southern part of the Strait southwesterly to southeasterly winds prevail. In the northern part northwesterlywinds prevail.On Wreck Beach wave effects and the ensuing beach sediment distribution moves primarily in response to the Strait ofGeorgia wind conditions.15(1)CANADA• (I)winter(ii)summerFIGURE 2a. Regional surface windpatterns of thenortheast Pacific Ocean.(ii’)/I(ii)* ;•(1)(11)(ii)spring transition, April-Mayiii) summer, June—SeptemberFIGURE. 2b. Local surface wind patterns of the Straitof Georgia.163.2 ANNUAL METEOROLOGICAL AND BEACH CYCLESFrom time to time periods of high velocity winds occurin the Strait of Georgia. Occasionally sustained winds (onehour or more) of up to 40 miles per hour (35 knots) occur.At rare time gusts of 70 miles per hour (61 knots) are recordedat the Vancouver International Airport. However, sustainedwinds of 23 to 25 miles per hour (20 to 22 knots) are sufficient to create extensive white-capping in the Strait of Georgia.A 22 knot velocity is classified on the Seaman’s Wind Description as a Strong Breeze and on the Beaufort Scale as a 6 asshown in Table I.17WIND SCALES AND SEA DESCRIPTIONSBeaufort International Inter-Seaman’s Wind . .. scale sea nationalscaledescription velocityEstimating wind velocitiesdescription code forof wind knotson seaand wave state ofheights sea0 CalmLess than Calm; sea like a mirror.1 knot Calm glassy 01 Light air1 to 3 Light air; ripples—no foam crests. 0knots2 Light4 to 6 Light breeze; small wavelets, crests have Rippled 1breeze knotsglassy appearance and do not break. 0 to 1 foot3 Gentle 7 to 10Gentle breeze; large wavelets, crests begin Smooth 2breeze knotsto break. Scattered whitecaps. 1 to 2 feet4 Moderate 11 to 16 Moderate breeze; smallwaves becoming Slight 3breeze knots longer. Frequent whitecaps. 2 to 4 feet5 Fresh 17 to 21 Fresh breeze; moderatewaves taking a Moderate 4breeze knots more pronounced long form;mainly 4 to 8 feetwhitecaps, some spray.6 Strong 22 to 27 Strong breeze; largewaves begin to form Rough 5breeze knots extensive whitecaps everywhere, some 8 to 13 feetspray.7 High wind 28 to 33 Moderate gale;sea hcaps up and white6(Moderate knots foamfrom breaking waves beginsto begale) blown instreaks along the directionofthe wind.8 Gale 34 to 40 Freshgale; moderately highwaves of(Fresh knots greater length;edges of crests break intogale) spindrift. Thefoam is blown in well-Very roughl3to20feetmarked streaks alongthe direction ofthe wind.9 Strong 41 to 47 Strong gale; highwaves, dense streaks ofgale knots foam alongthe direction of thewind.Spray may affect visibility. Seabeginsto roll.10 Whole 48 to 55 Whole gale;very high waves.The surface 7gale knots of the sea takeson a white appearance. HighThe rolling of sea becomes heavyand 20 to 30 feetshocklike. Visibility affected.11 Storm 56 to 63 Storm; exceptionallyhigh waves. Small Very high8knots and medium-sizedships are lost to view 30 to 45 feetlong periods.12 Hurricane 64 and Hurricane; the air isfilled with foam and Phenomenal9above spray. Sea completelywhite with driv- over 45 feeting spray; visibility very seriouslyaffected.TABLE I. Wind scales and sea descriptions.18Listed in Table II is information related to highwindperiods during the Wreck Beach study. Wind information isderived from wind records monitored hourly at the VancouverInternational Airport by Environment Canada. Typicalwinddirections, strengths and frequencies are assumed thesame forWreck Beach as for the Vancouver International Airportlocateda few miles south of the study area. Selection criteria isbased on winds having one hour or more of 23 miles per hour(20 knots) sustained velocities with a minimumof three successive hours of 20 miles per hour (17.5 knots). Duration of a highwind is the time of blow exceeding and returning to a minimum15 mile per hour velocity. Also listed for reference in TableII are the dates when photographs of Wreck Beach were takenduring the study period.19HIGH WIND PERIOD INFORMATIONHighMaximumWind Photograph Direction DurationSustained GustDate DateVelocityA1..N1973March 18 E—ESE 9 2038 SEApril5 W 15 2535WApril 27 WSW-WNW 18 2131 WMay 17-18 W-WNW 12 2129 WMay 18—19 WSW—WNW 18 24 33WNWMay 30—31 W—WNW 22 27 40WJune NONE-. July4July 13—14, WNW—NW 34 21 27WNWJuly 15 WNW-NW 16 19 26 WNWJuly 16 WNW-NW 13 22 28 WNWJuly_19August NONEAug._24Sept. 24—25 W—WNW 21 22 31 WNWSept. 26 ,___________ -Oct. 6 WNW 7 22 28 WNWOct. 9Oct. 18Oct.30 W 8 22 32WNov.’ 13 SE—SSE 11 20 32 SSENov. 18Nov. 19-20 E—SE ‘ 12 20 33 EDec. 7 W 12 28 44WDec. 11—12 E—SE 31 26 50 SEDec. 13 SE-SSE 162030 SEDec. 14Dec. 15—16 E—SSE 16 20 36 SE1974 , .. Jan. 13Jan. 15 SSE—SSW 20 20 41 SJan. 18-19 S—W 13 20 37 WJan. 20 W—WNW 1021 32WNWJan. 25 W-WNW 62235 WNWJan. 29 SSW—WNW 920 36SWJan. 29-30 W—WNW 1522 25WFeb. 4 W-NW 1826 45WNWFeb. 19 W—WNW 8 24 32 WFeb. 28 SE—SSE 820 33EMarch 1—3 W—WNW 36 24 39 WNWMarch 2March 5 W—WNW 9 20 35 WNWMarch 8-9 E—SE 382131 SEApril 11-12 WSW-WNW 14 31 44 WNWApril 12April 23 WNW-NW 13 24 30WNWTABLE II. High wil2d periodinformation.20BighMaximumWindPhotograph DirectionDurationSustained GustDateDateVelocityHO UPS 4?PHMPHMayNONEJune 18 WNW11 21 25 WNWJulyNONEAugust NONE• August 1• August 15August_28Sept. 25—26 W—WNW 12 3551 WNWSept._26Oct. 3—4 VW—WNW 27 26 37 WNWOct. 10Oct.20 W 13 20 31WOct. 22VOct. 28—29 . WNW—NW 26 2033 NWNov. 12Nov. 20—21 . W—WNW 24 2030 WNov. 24Nov. 25 W .13. 2536 WVNov.26Dec. 17 V W—WNW 9 22 37SDec. 18 E—SE 6 2031 ESEDec. 21—22 W—NW 27 27 55WDec. 27 W—NW 11 434 WNWDec. 29 SE 5 23 36SE1975V VJan.2 SE 4 25 42SEJan. 4VW—WNW 12 -25 42 WNWJan. 8-9 WSW—WNW 24 23 50NWJan. 10VJan. 20 W—WNW 12 27 39WJan. 25 W—WNW 18 22 28WNWJan.31 E 18 33EFeb. 4Feb.10 W 7 25 38WFeb. 16Feb. 19-20 WNW 26 37 57 WNWVMarch 18March 24 WNW 10 2130 WNWMarch 25 WNW .14 28 42WNWMarch 25March 30VV24 38 67 WNWMarch_31April 19 W—WNW 15 29 39 WNWApr. 27—28 W—WNW 22 29 45WNWTABLE II continued,21By further examiningthe wind parameters given inTable II during only peakextreme conditions cyclic orannualmeteorological patterns might be determined.This informationis correlated inFigure 28 for conditions of winddurationsin excess of 20 hours,maximum sustained velocities above24miles per hour, and gustsof at least 35 miles per hour. Fromthis evidence cyclic patterns are apparent.Figure 28 alsoincludes certain representative erosion—depositionpatterns atselect locations on WreckBeach for the periods shown. Theerosion—deposition information isderived from Figures 25, 26and 27.The duration, maximumsustained velocity and gustscriteria suggests that distinct phasesoccur. Well—definedsummer periods commenced about the month of May.Correspondingly, winter phases evolved aroundOctober to November. Ingeneral, an average annual cycle for the WreckBeach areawould include a summer period from June to October,and awinter period from November to May.The 1973summer period included a number of lower velocitywind periods while in the 1974 summer period these were conspicuously absent. The 1973-74 winter phase included severaleasterly winds of major strength both in durationand velocity.In the following 1974-75 winter phase winds from the east werethe exception and were also the winds of shortestdurations andlower maximum sustained velocities.223.3 WIND DIRECTIONS OF PRIMARY IMPORTANCEDuring the months covered by Table II the winds ofmajor importance occurred out of the WNW to WSW sector.From the percentage frequency records listed in Table Vforthis period and the longshore transport capabilities determined in Chapters V and VI winds from this sector predominate.It is significant that no major winds occurred out of the NWto NE quadrant. A representative historical wind rosereveals that maximum velocities out of the north are around 10knots. Under these conditions from Table III the greatestwavelength that normally could be expected would be 35 feetlong after five hours of 10 knot winds. Sand transport capacities to the south associated with waves of this size aresmall and function in water depths less than 2.2 feet. Thelimits of this zone would be near the one fathom contour on aCanadian Hydrographic Chart. In addition, these winds occurso seldom as to have little influence on the sand transport inthe headlands area as outlined in Chapter V.Winds from the SE quadrant have little effect on theheadlands and Wreck Beach due to the protection afforded bythe surrounding landforms and structures. Highly influencialwinds out of the northern quadrant are not common. The infrequency of high winds and waves from these directions limittheir influence on the headlands longshore transport process.23Resulting is alongshore transportsystem largely restrictedto movement towardthe northeast.CHAPTER IVWAVE CONDITIONS4.1 DETERMINATION OFEFFECTIVE FETCHESWaves approaching thePoint Grey headlands are the mostimportant and persistentforces taking part in the beachfore-shore activities. The natureof a particular wave field is aresult of the interrelated characteristicsof the wind regimegenerating the wave field and the physicalshape of the areaover which the wind and resultingwaves move. Wind directions, durations, and velocities arerestricted and limitedby the surrounding landforms.In order for these potential winds to producewave fieldsthat are self—sustaining (i.e.waves are removing energy equalto that introduced by the wind) a minimum sized bodyof water(fetch) must be available over which the wind actioncan operate.Under conditions of this sort wave fields actingon Wreck Beachare “fetch—limited”; in which case wave dimensions dependuponfetch rather than wind generation time (duration).Point Grey is surrounded by water on three sides as shownin Figure 3. So easterly winds will produce waves having minimaleffect on Wreck Beach. Winds out of the south generate waves thatare largely impeded from striking Wreck Beach by the Fraser Delta2425and the North Arm jetty. Windsfrom the north produce wavefields of very small dimensionsdue to the extremely restrictedfetch areas and rare periodsof high velocity winds from thatdirection. Therefore,winds from the westerly directions, SWthrough NW, have the larger fetch-generationareas. In addition as discussed in ChapterIII, wind conditions for the headlands area are such thatpredominating high-velocity winterwinds blow out of the west andnorthwest as opposed to smallerwinds prevailing out of the southand southeast during thesummer.Fetch dimensions for five westerly wind directionsarederived in Figures 3 through 7 and include the associatedcomputations and graphic procedures. This method of“effectivefetch computation for irregular shorelines” is outlined inthe1973 “Shore Protection Manual” of the U.S. Corps of ArmyEngineers. This method is based on the following assumptions:i) wind moving over a water surface transfers energy to thewater surface in the direction of the wind and in alldirections within 45° on either side of the wind direction;ii) the wind transfers a unit amount of energy to the wateralong the central radial in the direction of the windand along any other radial an amount modified by thecosine of the angle between the radial and the winddirection;26iii) waves are completelyabsorbed by shorelines.The larger fetch distancesoccur in the range between WSWthrough WNW as would be expectedfrom visual estimations oncharts. More specifically, afirst observation would indicatethat the due west directionhas by far the greatest fetch whentaken as a point to pointmeasurement (i.e. the greatest unobstructed straight line distancefrom Point Grey westward.)However, the WSW direction has a greater fetchdimension whichis due to the wind acting as a field over thefetch area ratherthan as a point source. The method for “effectivefetch computation for irregular shorelines” takes this phenomenon intoconsideration and is a closer approximation to the truephysicalsituation.NWWINDDIRECTIONi4a(4236 30 24 18 126 0 612 18 24 30 36 42Coscc.743.809 .866 .914.951.978 .9951.000.995 .978.951.914.866 .809 .74313.512xi8.915.0 16.9 12.3 2.0 2.0 1.9 2.1 2.3 2.3 1.6 1.1X1Cos”<6.6112.14 14.64 11.24961 4.99 2.19 2.00 1.99 1•862.00 2.10 1.99 1.29 0.8275.47001F=ZX4COB‘/‘ZCosICanadianHydrographicChartFe.i413.512=5.59m_________________________Iewhere1cm=3.262milesLNaturalScale1t525,000Fe=18.22statutemiles__________________*w\N.8529cmoniPt.7Mt.Dr.wfl/‘.\‘%r1442Vininci.9)%ç,kç6069,JNarrowsI.1n1et.124183666/4.I0.1.\‘/1l30\17SN72Norihe.jtPt.3(I8’151DSO\i,11005\\92io7RI8o85TEXi:LANI)2O)cLTISO135MouatI,%3.S20.0480•..PtM8618158.70..INLETR.122•7.-.173I6.4S‘‘1172,McN.u0htonPt118760%‘62A.fAhlIi.,6anh..8ISS.103‘685.7.20164.JDenm.n.64:.•Ml.Sh.ph.rII7Sc,.tCr121\nd\7Hornby‘\(JS02900!2onay‘I29ier0:.•:.......•‘...‘.-L.25IipPt29\57910I0I7SChI9665‘\1917614z4..814ib.oI4110493077183•!../..I4%46QOr,Cel-176145IMM27•2IM*rk‘—5-r5421DUMPINGI2QualIcrBc.choREA-,207.•-•8•-..•..•Np24)V.cP.rksvIIl12——948(Winchl.ea222....,..NorthwiiBay..+r203-5--....::..:Ibern,Ar.w,m00+x:::ke27’192:0-::9-108CERFIGURE3.NWwinddirectioneffectivefetchdiagram.Totals176Cariad.ianHydrographióChart#3001NaturalScaleli525,000)M6•i22‘°\..81::MMark(42s;45IT2QualicumBeacho..•.7\•39——.$699Mt.Wrenel2eyINLET‘.16HOWEII8.McNaughtonPt...104L...?It8..414•.tcswf’MelLonr-tQI2IMoi,tau•HalfmoonBay..21306MCkana.1••‘1._..—‘29GamWerI.IruniwIckMt..ía’II.••4/•.555$—I..r7SecheltMt.UphIaaton..SOJND•.\2148/“°4.\3554011Fh.Lioni—oWilsonCeck31137I9’:6’6—•7ç••8;G;oni..•:‘“•ISIJSEDMG..:_j70MUNITION96:27•..49.an246kFlnrseahniBuy(‘DUMPlG:.••.•••T.432Bowen$AREA/207—...:.••.3145-‘‘2....ARD24)’...lea222cP•••.•-1-—•.\.N.E7846—6/L’4iiPNanootcBay14.—62211202—tGrey4--IY,ANCO.?-:eke27DepartureBay..‘2Q,—i•1•.........—920Sea!NANAIMOGabriola882—II?LULUIS)Island•..‘••••.——II6,ariolaPa3sae7164,,..•,•.4440t’des.38SandHeidi/,?.‘Yellow:::;R;;:ak:d9:pM<IWhma.r”—,39WNWWINDDIRECTION“<Coso’XjXjCos°<42.7434.83.5736.8095.24.2130.8666.15.2824.9147.16.4918.9518.98.4612.97811.511.256.99515.014.9301.00021.421.406.99513.113.0312.97810.29.9818.9516.86.4724.9142.22.0130.8661.81.5636.8091.61,2942.7431.5.1.11Totals13.512111.04Fe=ZX1Cos‘/.CosFe111.04/.13.512=8,22cmwhere1cm=3.262milesFe=26.81statutemilesFIGURE4.WNWwinddirectioneffectivefetchdiagram.WESTWINDDIRECTION/4cCosc(xlXjCogc(+71<4\wncheleaWESTWINDDIRECTION“Npj°Nanooicay4I-,..••..162212027..,:,.:YcpcSnke218DeporiureBayJ2,.MLNANAIMOCabriola8828111742.7431.51.113344InlandLULL)IS36•8091•91•5451711166414Sceveiwn30.8666.15.28.d8SandHead,.,.;..24.9149.58.68_s-S__.I5I‘18.95112,511.89l9÷ccl.12.97820.720•24“\°‘‘6•99515.014.93..YeIlPt.““•i3°I0616301.00011.711.70.4140%f231822\+’...‘I25_L:.-•:\/Lady.mkhN.961.66.4O‘.12.9787.67.43\\—....‘I3968PtR0b.rt1866MI.Whympir2c-.....C]03636--F=ZXCos/.ZCos42.——=10.85‘/•i1,96=9.10cmCanadianHydrographicChart#3001where1cm=3.262milesFe=29,69statutemilesNaturalScale1:525,000CTotal11.960108.85FIGURE5.Westwinddirectioneffectivefetchdiagram.<Cosc’XjWSWWINDDIRECTION4236 30 2418 126 0 612 18 24 30 36 42Totals,743.809 .866 .914 .951 .978 .9951•000.995 .9789.2297910.9 17,1 16•511.39.4 9.1 7.3 6.4 65XjCoso<5.87 8.8214.81 15.08 10.759.19 9.05 7.30 6.37 6.3693,60CanadianHyd.rographicChart#3001Fe=XjCos/ZCos_______________________F=93.60•/.9,229=10.14cmNaturalScalels525,000.ewhere1cn=3.262miles_________________Fe33SaUEihp2274LO8Ii587j’1N1(’:4b1;8eBay‘‘:i1LasqiietiI.252C,../SisiIi4.9b%9’101-,_SecheltMI.EIpflInhtoiie.8779-.4160)i.63—.4895*66..c119NWilsonCrcek\.•91176‘!4”s3!42,‘\‘5..‘.‘..——s.,,(Whie—SLdg-“/•...•183/DISUSED\4—5—.213\Q_________________________________________•6617645-Ag6127“QuscuBeicho—42272DUMPINGI___________—Park.vlll:3s\123$4“AREA207—i:’‘-‘-I4RD24vcou’1e,.,.,?9Nortlw.aaB.y.222‘J....Naroos.Na,bou46”217Pt.GreyPort)N.riàose14•1622112——•VANCOJVEP5—A—ç•••.,,f,.MI.AilsimItl*?27_V0pa.flaireBay.2Q,J-‘—I3__l190Sc.I.Mil.NANAIM+46Ga6878158LULUISLANDlalandAs-.’I/.&.4440—•30ISH..’CltOfl1114c—96.(C’117Ib,“::,,f..,,c.MLGsL:dy,mlthIr0?133I25FIGURE6.WSWwinddirectioneffectivefetchdiagram..I.-) CSWWINDDIRECTI0N4:0<CosXIXjCos<5656•07.5.54 5,39 6.‘096.36 6.57 6.7048.37I7?0)•.i7etMLEIphIn,ton.ruMc::18376211/:s:97Q4?I’/’QuailBeacho1424121DUMPINGI(,8—941lJ(13(72‘p951tø°°ICJ4’..;,.123’,BaI0.T.\IAREA,‘207‘>i.......2I\•.....5)C..l’.,..4’P.rkivlll2149“.._03145_>208435.e7__”_—9rchCARD24)V.c1VoriAioe:222......•9&.•“DI.NE7’Nar.o,.Hrbea+3:03__:I4——/(4‘68coy7NanooceBay41-62211PL.Crey;•....)..V4NCOVVER,-....NewWesm(narerML.ArrialmIlk.4.Snake,......ML:l27).i2i18‘‘/I..,__________________________________________•,.41-—,4:LULU0—Ia’.abc’ase//.:a’•Sevcitonk.138d,490:“3N•Z(0°20,:??..1:,,.....:.YelTbw‘I’,9’\\*61‘‘61.10k:.:f.1415%/23‘22\+rl03‘\%,‘22414•..“çl-....•.38—...:.:Ladysmih6:....4:..(7&J:60IM*So__cz:;’o:7,,.111CHANNELL’-.96NFeXjCos‘/•ZCosFe48.37i/7.2566.66iCazia.diaflHydrographicChart#3001________________________where1cm=3.262mIlesFe=21.75statutemilesNaturalScale1:525,00042 36 30 24 18 126 0 612 18 24 30 3642Total.743.809 .866 .914 .951.978 .9951.0007.2567.6 7.5 6.45.9 6.4 6.5 6.6 6.71W.) I-IFIGURE7.SWwinddirectioneffectivefetchdiagram.324.2 REFRACTION DIAGRAMSWave fields assume their individual characteristics fromthe nature of the generating wind regime. Wind regimes areidentified by velocity, direction, duration and fetch aspects.Wave fields are commonly typified in terms of their significantwave height, significant wave period, deep water wave lengthand deep water wave velocity characteristics. Table III liststhe deep water wave characteristics for the given wind regimes.Minimum durations, significant wave heights and significant wave periods were interpolated from the Sverdrup—Munk—Bretschneider curves contained in the 1973 “Shore ProtectionManual” of the U.S. Corps of Army Engineers, Volume I, Chapter3 for the given fetches and wind velocities. Theoretical deepwater wave lengths and velocities were computed using lineartheory equations.The method of determining wave breaking heights, wavebreaking depths and longshore current velocities is given inChapter V1 Section 5.1.WIND,FETCHANDDEEPWATERWAVEDATAw wFetchEffectiveFetch,FeWindVelocity,UMinimumSignificantSignificantDirectionDuration,tmWaveHeight,H0WavePeriod,T0NauticalStatuteMilesMilesKnotsHourHoursFeetSecondsNW15.8318.221011.,fetchanddeepwaterwavedata,34U)-Ii0Dr-oo,-4occ. C Ii-ILfl,-4a)lC)WIG)V.- V.- 0. V.4rr1V.44-,4)a) —4C)00U)GJ0‘.D 0 V.4 fl V.-at0 r1 r -f -4 -.D at r4C’4’.D.-4Lt0000..-IriV.44,U)a)U>Cd0at C) V.- V.4 Ot. Co (‘1 U) D 0 V. fl V. atCN( ;V.;C;C; Cr-,-1.-f,-lr-40 00 0QLfl 0C.,Cobc’1r.-ooc-1 at0DCV.4r-,--fo ‘.Dtflafl.—Io C’DP)O.-4r-•I—f . . . •4 Co(’4 V.4tflOtUCoC) D0’jbOhI.J. CN’DOLflOr-f C)NC,OCd r-f .4 V.4 r-1.-f V.4 r-l i-f i-f (‘4 i-I r-f (‘4 (‘1 i—I —4 V.4W1C)4,I—f (1) 111111111111 111111 311111 131111- a)C (Z4 Oti-1.D 0LflCr-f 0-ftOtCo t0C’4a) 4) . . . . .>04 atcqD -4Lnat Coc’lLnat )CoCNO0 NOV.Cd 0) 4 r - i-ii-f .-4 r-4 r- r-j 1-4 V.4 r4 ,-4 4bt:•1f)4 -Cd-.‘3tflOCoC’)0VCoJ000V.-V.40000 ‘D00CtCgr—oc’,J’D0tCNtf) 1•1t—om’o cOi-fU bti-I i4 .-4 r4> --4‘dO)0:I.144-i$‘.DV.-0 CC.i r-fi-I’.0000’i CNC-.’.oLfl“coco oj:c;-cC. 0at0CoOt0c’4Cflt- N0C’i’DOCo-‘rc-.ooc’1ao ‘0F-c’)0Co C.tatOtLflcD04 a)C” C”U>UCdcCU>1 ‘f-P r•r40140 0e.) Co O V.- Co Co Lfl V.4 Ct 0 U) V.- CO Lfl V.1 0 V.- Co Lfl Co LC1 r-4 N Co‘UW ‘-..4CoC’1V.-C’4 C’4CoV.tCoC’1 atCt:>- CC1C’) CflC C1C.1 C1C’104a) a)U> r14a)Cdcf:0iQCl)z • -CdU:1r44-)0C)HHHrxl35Wave fields generated by identifiable wind regimes aremodified by the underwater topography over which they move.The effects of topography on wave fields moving inshore towardWreck Beach is captured graphically in the refraction diagramsshown in Figures 8 through 12 The refraction diagrams helpto predict the distribution of modified wave forces and waveheights through the shallow water area which vary from the deepwater distribution. And the diagrams aid in the assessment oferosion—deposition patterns of Wreck Beach sediments. Theassumptions generally made in the use of refraction diagrams arethe following:i) wave energy between orthogonals remains constant;ii) direction of wave advance is perpendicular to the wavecrest and in the direction of the orthogonals;iii) speed of a wave of a given period at a particular locationdepends only on the water depth at that location;iv) changes in bottom topography are gradual;v) waves are long—crested, constant period, small amplitude,and monochromatic;vi) effects of currents, winds and reflections from beaches,and minor underwater topographic variations are considered negligible.All of the diagrams were prepared using the 30 knot windvelocity and corresponding wave data of Table III with still36water level at higher high water of16.2 feet. Winds of thisvelocity and duration occur occasionally throughout theyearand typify rough sea conditions in the Strait of Georgia.INWis------\\Jr\Jr\54Jr:\----/70X48)BURRA26RDN84....\28\I---------\••..•_\\\I\\\--loJ’\--\1cJ’\\27jr\....../_\.iH4\a,.FIR-\8ZBn\4N‘‘,7----:\...BANK+S34I\ç1/>\\4\/1f____\\:843:M•.\fj8iI\2WRECKBEACH\\\STUDYAREA\\\).\I_____—08/‘48s\c9z//\IL.0PointI2S\Th:•:4:NWWINDDIRECTIONWAVEREFRACTIONDIAGRA!1WaveRegimeHo=5.6feetTo=5.2secondsCo=26.6ft/secLo=138.4feet=23.1fathomsWindRegimeFe=18.22sm=15.83rimU=34.5mph=30knotstm=2.8hoursWaveScaleS=50,000n=0.00815S/To2=15wavelengthst=0.00815S/To=78secondsCanadianHydrographicCharti#3480,1971NaturalScale1:50,000 1cm=0.31statutemiles=0,27nauticalmilesFIGURE8.NWwinddirectionwaverefractiondiagram.75./———•84I•IL-—,£3I—45I’”I—III__I-,-’-._.._I_._I_.ouI•--I‘IIr.’-i—ii•1.•.,•,•—,—..-•I,..,i—i/•[4I/.%/../i/:II’’4__III1>’t’..igIAI/LJ4r-i’8e1,7.wLjii-r7’74/sr.‘.‘•—•‘•‘1/4co/-JJII•‘—II•-—I21Cd,!JJ.,jI6t—III-m•I•::hI,tI\III)I1’-.----..-\:1//Il./I-•1..IIl68l\GpF/‘_•-•—.————.75\/çT\39W!MWINDDIRECTIONWAVEREFRACTIONDIAGRAMWaveRegimeHo=6.4feetTo=5.5secondsCo=28.2ft/secLo=154.0feet.=25.8fathomsWindRegimeFe=26.81s=23.30rimU=34.5mph=30knotstm=3•7hoursWaveScaleS=50,000n=0.00815S/To2=1+wavelengthst=0.00815S/To=74seconds362827I_•rI%sç5ANII(•‘._I-i442u/z//÷ywEAcH3.V’57...1sJ/STUDYAREAjYJ•:i...iIW(PtreyR511COLUMBIAHf‘___•po)(•L—n:NCanadianHydrographioChart#3480,1971NaturalScale1i50,000 1cm0.31statute.miles=0.27nauticalmiles:wFIGURE9.WNWwinddirectionwaverefractiondiagram.II I>26IC.1.-——g—:;.‘I>’%,2/—..:7IHI:234j:Iz\9(39)\—-r-•7T”Os32_i41\S/,‘c:///37——8WESTWINDD1RECTIO!bTWAVEREFRACTIONDIAGRAMWaveRegime-HO=6.6feetTo=5.6secondsCo=28..?ft/secLo=160.6feet=26.8fathomsWind.RegimeFe=29.69sm=25.30nmU34.5mph=30knotst=4.1hoursWaveScaleS=50,000=0.00815S/To2=13wavelengths=0.00815S/T0=73seconds2—-,—•1-,754.WESrW.>))>>N68///•27/••%.1817‘‘%_..•-..__M•‘••--.9i11\SPISHSANK4I4•....•289 -//j811 II3)12—zr /——-i4A/ pFI?UNIVE?::i9R:ulA-.•———4•—‘:;•—108•//(9i•Il):I/‘:.,•..:•::•.Point--‘I1-z//,• 759CanadianHydrographicChart#3480,1971NaturalScale1:50,000 1cm=0.31statutemiles=0.27nauticalmiles\...:•,,:4FIGURE10.WestwinddirectionwaverefractiQndiagram.WaveRegime=7.0feet=5.8seconds29.7ft/sec172.2feet=28.7fathomsWindRegimeFe=33.08sin=28.75nmU=34.5mph30knotst=4.5hoursWaveScale73V)34\////____\,,75/39\—--1‘(w1i691i’4WSWWINDDIRECTIONWAVEREFRACTIONDIAGRAMHo To Co Lo——--—.leI‘———.—.I-..—....IxI‘‘47—————...—..IlLL.i...-3\69/j-..—,...j,—.—41—27-.-....--..—...-..—..--“-/—‘9....—FIIT•....7/———-1-‘..—-•-‘i.:—4—u—/———Gj-tS%1I437•..—-•...-..•‘“.,_L.rV/.—-4,-.,.?/—..31PISHBANK-\..-..çi.I-•...—.718/4,,rI!f’(___•M.“—a-./•‘jWRECKBEA%s.\A..‘o5j)/)STUDYAREA.I+((f\øj\;‘:r::uMeIA8==50,000 0.00815S/To212wavelengths0.00815S/To70seconds7.89:_____________nJ/CanadianHydrographicChart#3480,1971NaturalScale1:50,000 1cm=0.31statutemiles0.27nauticalmiles..‘Ij.•L.——I\‘-.-1’‘Ii,:II.CFIGURE11.WSWwinddirectionwaverefractiondiagram.,“6/‘KI,.‘•c:,/27L_7iSf/i\i.X&;:vz‘I:+:.1BEACH:.J/7,)STUDYAREA24Y\kRc:LuMBIA30I;(\,>(‘s;:‘nt——-SWWINDDIRECTIONWAVEREFRACTIONDIAGRANWaveRegimeHo=6.0feetTo=5.3secondsCo=27.1ft/secLo=143.8feet=24.0fathomsWindRegimeFe=21.75sm=18.90timU34.5mph=30knotst=3.3hoursWaveScale’S=50,000n=0.00815S/To2=15wavelengthst=0.00815S/To77seconds•..126‘4:“‘;/-,.‘-I••/••:ts1:.CanadianHydrographic.Chart#3480,1971’NaturalScale1*50,000 1cm0.31statutemiles=0.27nauticalmilesFIGURE12.SWwinddirectionwaverefractiondiagram.424.3 WAVES FROM THE SW SECTORWaves from the SW sector in general diverge around theheadlands. The South Arm jetty absorbs most of the directenergy. Increasing wave heights through the shallow area aredue mostly to shoaling influences while wave diverging effectswould tend to decrease wave heights and forcesThe wide angle of wave attack from this direction createsa large littoral drift component toward the NE throughout thearea.Fetches from the SW are relatively small and high windvelocities are not common from this direction. However, alarge percentage of low 10 knot and under winds come from theSW sector as indicated in Chapter V.Resulting are waves not very effective in eroding thecliffs but highly important in transporting sediment in thenearshore zones during extended times of the year when mildwinds prevail.434.4 WAVES FROM THE NW SECTORWaves from the NW sector tend to converge throughout theheadlands area. The wave attack angle from the NW tends tobe minimal. The small littoral components produced appear tomove NE around the Towers Beach area with some slight movementtoward the SE from the west tower.Fetches from the NW sector are the most restricted ofthose under consideration and winds of all velocities occurrarely.Waves from these winds are small in both erosion andlongshore transport capacities. The most northerly winds willhave a greater longshore component but will have extremelyreduced fetch and frequencies.444.5 WAVES FROM THEWEST SECTORWaves from the west sectorare most important in erosionand have considerable longshoretransport components. Convergingwaves tend to strike the westbeach straight on. But in theTowers Beach area the waves begin adiverging pattern whichcontinues to the NE.Typically high winter waves out of the westsectorapproach Wreck Beach at anangle across the wide shallow offshore sandbank. The waves are refracted and shoaled bythetopography such that the breaking of any one wavecrest on theupper beach area will be progressively delayedtoward the easterly end of the area. For example,Figure 13 shows a wavebreaking at the outfall location that is still 5 to7 wavelengths seaward of the beach breaking area near theeasttower. Longshore drift from these waves is toward theNE andis most effective from the west tower eastward.Fetches from the WSW through WNW directions areconsiderably greater than the NW and SW sector fetches. Also highwind frequencies and velocities are most common from this sector.I,WNW-__ __u4 &S-.—4,____4-‘4,r:45West BeachMarch 25, 1975Photographlocation 18FIGURE 13. Photograph sequence showing NElongshoretransportwavesbreaking at an angle toWreck Beach.WNWTowersBeacharchphotograph- cations22March 25, 1975Photographlocation 19464.6 WAVES FROM THE MARCH 25, 1975 HIGH WINDSThe most important wind directions on Wreck Beach arefrom the WNW and W. Although neither has the greatest fetch,WNW-27 miles and W-30 miles compared with WSW-33 miles, theirfrequency at all velocities covers a much larger percentage thando the other wind directions as shown in Table V. At lowervelocities W winds prevail and at extreme high velocities WNWwinds predominate.Typically a high wind period will begin by blowing out ofthe southern part of the Strait of Georgia. As it gains instrength and intensity it will swing counter-clockwise aroundthe Strait of Georgia having its greatest speeds and gusts outof the WNW. Such a period of wind conditions occurredon March25, 1975. Winds of 28 knots from the WNW with gusts of 39 milesper hour blew for several hours. Figure 13 ofMarch 25, 1975photographs show the physical appearance of the wave field onWreck Beach. Tidal elevation at the timeof the photographswas 13.7 feet (2.5 feet below Refraction Diagramdatum). Thedeep water wave dimensions from this stormcan be predicted asgiven in Table III. But it is usefulto anticipate their altered height in the nearshore regions. As these wave crestheights begin to change due to the influences of shoaling andrefraction, their characteristics and dimensions will change.These influences occur whenever the waves begin “to feel the47bottom” at depths generally accepted as being one-half the deepwater wave length.Representing the March 25, 1975 storm is the enlarged WNWrefraction diagram and accompanying information of Figure 14. Todetermine the anticipated wave height, H, at any location on WreckBeach the deep water wave height, H0, is modified by the shoalingeffect,K,and by the refraction effect,KR;that isH=HOKSKR.The H0 is related to wind velocity and fetch as listedin Table III.The shoaling coefficient, K5, represents the effect ofachange in water depth on a wave height and results from a wavemoving into progressively shallower water.The K5 value dependsupon the wave length and water depth at the desired location. TheKsvalues were derived from common tables which are available inthe 1973 “Shore Protection Manual” of theU.S. Corps of ArmyEngineers, Volume III. These values and corresponding waterdepthsare listed on Figure 14 in the RefractionDiagram Information Block.The K5 values for the March 25, 1975storm are shown at variouslocations on the refraction diagram.The shoaling coefficient,KR,is related to the winddirection and reflects the change in heightand direction of awave moving over the underwater contoursat an angle causing thewave energy to either converge or to diverge.In practice theKRvalue is determinedby the square root of the ratio of the deepwater orthogonal spacing to the orthogonalspacing at the48shallow water depth desired; the spacings are measured directlyfrom the refraction diagrams. TheKRvalues for the March 25,1975 storm are shown at various locations around Wreck Beach onthe refraction diagram.The effect of changes in wavelengths is reflected in theratio of the wave length, L, at the desired location to thedeep water length, L0. The values of the shallow water wavelength, L, are listed in the Refraction Diagram InformationBlock of Figure 14 corresponding to the waterdepth contour andare derived from the tables available in the1973 “ShoreProtection Manual”. The L values for the March25, 1975 stormare shown at various locations around Wreck Beach on therefraction diagram.The altered wave heights resulting in the March25,1975 incoming storm waves seen in the WreckBeach photographsof Figure 13 are shown on the refractiondiagram of Figure 14at various locations.Sand volumes moved by the wind periodare calculatedin Chapter VI.49In summary:K5 - shoaling coefficient (Listed in Refraction Diagram Information Block, shown on the refraction diagram)KR- refraction coefficient (Shown on the refraction diagrambetween orthogonals)T0 - wave period in deep water (significant wave periodTable III)L0 - wave length in deep water (Table III)L — wave length in nearshore region (Listed in RefractionDiagram Information Block, and shown on the refractiondiagram)H0 - wave height in deep water (significant wave heightTable III)H - wave height in nearshore region (H= HOKSKRand shown onthe refraction diagram)CHAPTER VSAND MOVEMENT5.1 LIMITS OF THELITTORAL ZONESFrom fetch and weatherconsiderations the littoral transport system must presentlyoriginate at the Point Grey headlands and move downcurrent towardsSpanish Banks. Clearlywaves are the most effectiveand important agent acting tomovesediment in the nearshore regionof Wreck Beach. Their abilityto transport material isclosely related to their height, period,and direction of approach tothe beach. Waves approach WreckBeach shoreline across theshallow submerged sandbank, extendingabout a mile offshore at anaverage slope of 0.1 percent to adepth of 5 fathoms along the outerrim. At that point theslope increases suddenly droppingoff quickly into the Straitof Georgia depths.Waves first feel the bàttom effectivelywhen the waterdepth is equal to half the wave length, but it is notuntilthe depth is much shallower that any appreciable amountof sandis transported. The transport of sand alongWreck Beach takesplace primarily in two zones: the swash zoneand the surf zone.Beach—drifting occurs along the upper limit of waveaction andis related to the swash and backwash of waves.Its action ismost effective when waves approach at aconsiderable angle to5051the shore. The other major zone of the longshore movementis in the surf and breaker zone. Here thelargest quantityof material is moved, part in suspensionand part along thebed, and sand can be moved by relativelyweak longshore currents.The location at which a wave regime approaching WreckBeach enters the breaking zone delineates the extent of thezone of transport seaward from the swash zone on the upperbeach. This location, called the breakingpoint, is the pointwhere foam first appears on the wavecrest. The breakingpoint is an intermediate point in the breakingprocess betweenthe first stages of instability and the area of completebreaking. That waves do not break in deepwater in this area isdue to wave dimension limitations imposedby the restrictedfetch generation areas.In shallow water regions the breaking pointis identified in terms of the breakingdepth,db,the water depth below still water level at which breakingis initiated; and thebreakingheight,Hb,the crest to trough dimension when breaking is initiated. At the breakingpoint a longshore currentdirection and velocity is establishedwhich is sensitive toboth crest angle and wave height. Listedin Table III are wavebreaking depths and heights forthe range of wind and unrefractedwave regimes noted. These values wereinterpolated from thedimensionless breaking wave curves contained inthe 1973 “Shore52Protection Manual” of the U.S. Corps of Army Engineers, VolumeII, Chapter 7 for the range of wind and wave regimes listed.Also listed are the corresponding theoretical longshore currentvelocities that would result from the given conditions. Long-shore current velocities were derived using the energy approachwhich depends upon wave height, period, angle of approach,beach slope, sand surface texture and hydraulic roughness ofthe beach. Correlations of the parameters have been determinedby King et al., 1959.During the course of a tidal cycle water heights mayvary over an elevation range as much as 16 feet between lowerlow water and higher high water. Because of this areas from 800feet seaward of the west beach cliff base to 1800 feet seawardat the east end are alternately exposed and inundated during thelarge tidal cycles. Wave attack then that covers a six hourperiod or more effectively increases its breaking depth by asmuch as 16 feet; depending on the tidal range in that period.As a result the region around the headlands of longshore transport activities is considerably extended. Table IV lists dimensions of transport zones at select areas of Wreck Beach fora variety of wave regimes. Wind categories and volumes of sandtransported are derived in Chapter VI, Section 6.1. Breakerheights and depths are compiled from Table III.53_____________LIMITS OF THE WRECK BEACH LITTORAL ZONESWind Breaker Breaker Elevation Width ofBreaker Zone Volume TransportedVelocity Height Depth Range ofUTMb dbBreaker West Tower’sEast 1973—74 1974—75Zone Beach Beach EndFeet Feet FeetFeet Feet Feet c.y/yearc.y/yearAPeakExtreme 5.1 6.5— 8.0 12 2300 22002500 6,150 10,581WindsBGeneralHigh 3.8 4.8— 6.0 10 2000 20002300 12,023 17,507WindsCOther 1.6 2.0— 2.5 6 1000 1300 200017,759 16,717WindsData for determiningdeep end depth of ElevationRange:Chart Datum: “The CanadianHydrographic Servicehas adopted theplane of lowest normaltides as Chart Datum”.(p. 4 Canadian Tide andCurrent Tables)Chart 13481: AverageTides Mean Water LevelLarge TidesHHW LLWHHW LLW14.4’ 4.1’10.1’ 16.2’0.3’Contour datum on Chart43481:16.0’— .l6.2’-Lge.HBW--:‘- 4.1’ Av .LLW3 80 fathom (0’) contour0.0’— .. .ge.LLW 0.63 fathom(3.8’) contour—2.0’— . .. 1 fathom(6’) contourTherefore, Datum for determiningdeep end depthof ElevationRange is 3.8 feetdepth (0.63 fathoms) plusdb.TABLE IV. Limitsof the Wreck Beachlittoral zones.54Wave requirements to move sand at the outer edge of thesand bank, 26 feet below low low water, intothe longshoretransport system necessitate a generating2—3 hour wind of60 knot velocity. Winds of this speed are very near thoseclassified as Hurricanes on the Seaman’s Wind Description presented in Table I. These conditions are not likely to occurnear Vancouver.However, extended extremely high wind periods of 36to40 knots do occur on occasion. During the period coveredbythe information contained in Table II suchwinds occurred onFebruary 19 and 20, 1975 and on March 30,1975. Both windswere from the WNW direction, each had at least3 hours of sustained 37 to 38 knot velocities, and the duration of theirentire storms covered two complete tidalcycles. Tidal cyclesfor each covered ranges of about3 to 14 feet. It is likelythat waves generated from thesewinds moved sands at depths10 to 15 feet below normal lower low water (near the 2.5 fathomcontour line on aCanadian HydrOgraPhiCchart such as Figure31)and as far seaward as 3200 feet.555.2 COMPILATION OF DATAThat sand in the Wreck Beach area moves in response tocyclic weather activities is evident from the sand movementrecords available. Historically, continuous and common baserecords covering this are limited. Data used for this studyare sequential photographic records available for the monthslisted in Table II and periodic beach cross-sectioning profiles.The July, 1973 through Mayf 1974 photographs courtesy of Dr.P.R.B. Ward, Assistant Professor of Civil Engineering,University of British Columbia. The June, 1974 through May,1975 photographs taken by the author. The cross-sectioningdata courtesy of Vancouver Board of Parks and Recreation andMr. Dave McLean, B.Sc., Geology, University of British Columbia.The information available from July, 1973 through May,1974 covers the east end beach. The June, 1974 through May,1975 covers the entire study area in both photographic andcross—sectioning form. For simplicity and ease of presentationnot all photographs taken at the locations may be included in thesequences shown in Figures 15 through 22. However, informationcovering all the photographic sequences and locations as shownon Figure 1 is compiled in Figures 23 and 24.56July 4,1973January 13,1974A¶1FIGURE 1. Photographsequenceat photographlocation1,East End, priorto constructionactivities.November 18,I—4July 19, 1973March 2,197457FIGURE l6. Photograph sequence at photographlocations1 & 2, East End, followingconstructionactivities.30, 1974August 28, 1974September 26, 1974November 26, 1974January (0, (97558February 4, 1975March 31,(975May 12, 1975:-—an — -.FIGURE 16 continued59-I- - -S• ,—••• -• .••- -••I. ---I..__ __FIGURE 17. Photograph sequence at photographlocation 6,Towers Beach, prior to construction activities,60---FIGURE 18, Photograph sequence. at photograph.location 6,Towers Beach, following constructionactivities.August 19.(97A-I61‘.,. ‘—.-— :FIGURE 19. Photographsequence at photograph location10,West Beach groin, following construction activities.jFebruary 4, 1975 1975. --—9• 2F62FIGtJR 20. Photograph sequenceat photograph location 13,West Beach, following constructionactivities.Auqust 15. 1974-February 4, 1975Auqust 28, 1974February 16, 1975September 26, 1974November 26. 1974August 28. 1974September 261974March 31. 197563May 12, 1975FIGURE 21 Photöraphsequenceat photógrap?location18,West Beach,followingconstructionactivities.-.- —(--:1.- —--—--March (8, (975October(0, 1974August 15. 1974February10. 197564FIGURE 22. Photbgraph sequence at photographlocation 19,Towers Beach, followingconstruction activities.September 26, 1974October 10, 1974‘vember 26, 197465The charts in Figures 23 and 24 are graphic summaries ofthe information observed in the photograph sequences. The chartin Figure 23 covers the period of study prior to the disturbanceof Wreck Beach by the construction project during the summerof 1974; Figure 24, the period following the disturbance.The construction activities considerably altered the upper beachface throughout the length of the study area. The alignmentwas changed along a 200 foot wide strip at the cliff base aswell as replacing the composition and arrangement of the surfacebeach face. In addition, the placement of the protective beachfill served to make some 70,000 cubic yards of easily assimilated material available to wave action and longshore transport.This method of presentation permits sand and gravelmovement patterns to be determined over the area and associatedwith time and weather conditions. The points on the lines arerelative and a gross approximation for that particular location.The lines indicate a change in the amount of sand and gravelaccumulated or lost during subsequent photographs as comparedwith the initial photograph. The intent is not to suggest thatexact heights and quantities have been determined from thephotographs but rather that the photographs have shown how, relative to themselves, a net amount of material has changed.The dot indicates the approximate position of sand and gravelon that photograph with the position on the first Augustphotograph of each chart (initial August position is plotted as66the baseline). The dotted lines indicate thedate of the highwind periods listed in TableII.FIGURE23.Chartofphotographsequencespriortoconstructionactivities.-JDATE.%cc39’IC...•+‘H1n•-•±.I...WestTowerfjr:‘—1IUpperSeahFaet.:.:::.::I:flIIWestBeach:.UpperGroiEnd::1.—.1!— —-I,.I————————II-PHOTOGRAPH LOCATIONEasFEnd UpperBeocI1—1—120•V1<Q,F..rVFt.HT1lThfftf4II—Iii6-.--—--——————rt—!aaceUj-fl:44r4WHTi-....IH14--HEastEnd.•.I—.-.,.•UpperGroi_-—Li’i-EastTower........•j....LowerGroin_j.-—__T•_-.—+—---j:iI-——EastTower.H[EJ’,H1’Hh:1LiftUpperGroinEnd,i4—I1Lj.41r,.rTFace14:ostTowerFacetHIt1p=TowersBea.h—-:r-r-;-Ir*r.rz::jtr1::zr..i!L7-i_Lttt..-d—.rUpdnftSideOutf.a.II.:.....E1.:4iJ.L±r+J+j1.fTrlTrTowersBeeDowndrift7. 8I..IdeOuttaIi_._!H—----r--IIIITi.-ri[]1,1LM—fr-rr’—r,1i*f—..—..—..1r—1———————r—j——ii.!IiI•i..II;•Ijl::rTTE-ttT::fLh1i+h1![j’:?11-—.-————.————.——..—..————.—._..I*•...11:1Il_!IIil_f..--H’-—hnt’4’JJ4-::—U——...;;IiiI—iI1.1II..-..7.,II.WestBeoc.••I.1...iiILowerBechFace.—..-—.-.I--.:.IiiI..11.‘iiWesiBeac,.....,.•,.iIJ}iIi[Il1IIjIf:[ILowerBeachFace.1.::i.!.:;.lrHill•-zrt-Tp—II.ee..I——••.•_.,.———-rzt!iII.I_lIIfl..t..lI.j.I.fl--,;: -..4..i.;.:H-’-i44—.*-•i;•—F-F-+H—H—.4’;—:1 :•L,.UiJJ..L!ii.JiI-IILi-FIGURE24.Chartofphotographsequencesfollowingconstructionactivities.69The charts ofFigures 25, 26 and 27 are compiledfromthe photographicsummaries charted in Figures23 and 24 andfrom correspondinginformation derived fromcross—sectioningdata. The S,-, and+ symbols represent the activityof thebeach at thatlocation during thatparticular time period.UPPERBEACHFACEWestWestLOCATIONTowerTowerWestLookingLookingEastTowerEastTowerBeachWestEastLookingWestLookingEastEastEndDATE1974—751974—751974—751973—741974—751973—741974—751973—741974—75Aug.1-Aug.15---+S+S-SAug.15-Aug.28-——+S+S-SAug.28-Sept.26——-+S+S—sSept.26—Oct.22———+—+S+sOct.22-Nov.26---++-+-Nov.26-Jan.6-+-----+-Jan.6-Jan.1O-++-—--+-Jan.1D-Feb..4-----.--++Feb.4-Feb.16---——--++Feb.16-Mar.18——————+—Mar..18-Mar.25———-———+-Mar.25-Mar.31+++----+SMar.31-May12—+—000—0S+accumulationofmaterial-erosionofmaterialSnochange0no:infomationFIGURE25.Chartcorrelatingphotographinformationwithcross-sectioningdataonupperbeachfaces.-1 cDGROINSLOCATIONWestWestOutfallEastEastBeachBeachOutfallDown—TowerTowerEast•UpperLowerUpdriftdriftUpperLowerEndDATE1974—751974—751974—751974—751974—751974—751974—75Aug.l—Aug.150000000Aug.15-Aug.28-SS+S++Aug.28-Sept.26+++-S++Sept.26-Oct.22+—+—-++Oct.22-Nov.26--++-++Nov.26—Jan..6————-—+Jari.6—Jan.lO—-————+Jan.l0—Feb.4—-—-—-Feb.4-Feb.l6-+-----Feb.16-Mar.18-—-—+—+Mar.l8-Mar.25--+++++Mar.25—Mar.31+——+-÷+Mar.31-May12-+--00++accumulationofmaterial-erosionofmaterialSnochange0noinformationFIGURE26.Chartcorrelatingphotographinformationwithcross-sectioningdataatgroins.SANDBARSLOCATIONWestEastEastTowerTowerTowerWestLookingLookingLookingBeachEastWestEastEastEndDATE1974—751974—751973—741973—741974—75‘1973—74‘1974—75July7-July19++-July19-Aug.1++-Aug.l-Aug.15+-+++--Aug.15-Aug.28+-+++--Aug.28-Sept.26+-+++++Sept.26-Oct.22+++++++Oct.22-Nov.26+++++++Nov.26-Jan.6-+--S+Jan.6-Jn.1O-+—--++Jan.1O-Feb.4-+--++Feb.4—Feb.16-+-——++Feb.16—Mar.18-+--—+—Mar.18-Mar.25‘—+——-——Mar.25—Mar.31—+—————Mar.3l—May12++-—+sandbarmovinginorupbeachface.—sandbarmovingoutordownbeachfaceSnochangeonoinformationFIGURE27.Chartcorrelatingphotographinformationwithcross-sectioningdataonsandbars.73Figure 28 shows the annual summer—winter beachcyclesat several sections of the beach.These cycles are derivedfrom the correlation of annual peak extreme windperiods withbeach deposition—erosion patternsevident from Figures 25, 26, 27.Selection criteria for peak extreme wind periodsis outlined inSection 3.2 of ChapterIII.I•rJ H 0 tn0w‘1aCDCCD:,:‘P’Pp0 C0 C,—4..•0.•.U,,3’-iE.•.4‘6L4-perBa.c.h.-Ei.4EotEast EastIit.tndIindSTower‘1 CD Fw -30 z4OYI’O•ATIVIIESCD C,0.ndbarQpperBeac1--1-Zo“c..0CDC:crp÷‘.0 -4 0-.4.GD pJ I-1 CD U t:L1 CD pJC) J. (n CD ri CD II CD a3’ -4 rn:4-SondUppe-H-—4--—rBea-r HEE+4---H--i444.•.I.h.!East West West WestTower(.TowerToweBeocLLt LI-I•--H.LU4-±.H-t i4LL..1..SonF--f-1Uppbar ><—-rBec‘-+4+.4. it.-.jEtL4:1:1T4’.4—i-----0t4zrJ4±.r:r;NTEl4..L!.WestIIrt-T.it+LI-[1H-Li---4------4--i---+±.-t-4.-tm 3’ C-) = 3’ C-) -4 -4 -<3tSM1Ii_I__!__[.ELDUFER:th7NG AT/ER:4f-J-’.14-J-H!H•..,4I-.4.4-i--4-4-4--H-4--4.L4.4..1.4-...oc.:i:;:-F:;::4jL9/-1c RA4jJzt44.tFl:1i••.SLfir-DLRT•,CI4.LLLL.i_LR—4-;slj.L.CiJR-—I_I.’. GE4 TI-C±ii:.:t±tri:t.ittl-tSHRTb---rrNSIOQ 30 oc (DC 3’ -4 0 zEL.)CIIE4VL.C/T/1$4ça/EL)C/IEVLCITIESt11i-z:.4::1.z:.,::.-::-..L.’.j:::::j::-:.H.:....:::--.:L.L::14:LLHit..:..flT——7-.-.HIH‘.:--L014‘&.1-IGHR6’x-LCWEd’II.,-.,..-.I,-0-.-‘EL7C/IES:..VLOITlS.::IEL)CIIES-IVL.Oirirs-3Zhzz‘Z_*LLH-J755.3 SAND MOVEMENT ONTHE WEST BEACHSand movement on the west beach is directlyinfluencedby both velocity and durationconsiderations. There appears tobe certain minimum duration requirements over arange of suitably high wind velocities neededfor the seasonal transitionfrom onshore movement of sand to offshore movement.Highwinds of long duration are necessary to move the westbeachsand into the offshore sand bar configuration typicalof beachareas exposed to waves approaching at little or noangle.Waves necessary to accomplish this must retain enoughenergy orsand—carrying capacity during the downslopebackrush to consistently move sand seawardinto the offshore bars. High windperiods of at least 23 miles perhour maximum sustained velocities (Refer to ChapterIII, Section 3.2 for definitioncriteria) with miiiimum 24 hour durations appear to bethenecessary conditions for the west beach to bein its winter offshore bar configuration. Periodic higher velocitywind periodsof this duration provide exposure of the beach face to waveattack over a period of two tidal cycles. Waves generated bythese wind conditions approach the headlands withminimum deepwater wave heights of 4.1 feet and periods of 4.4 seconds. Conditions are appropriate from November through Mayfor offshorebar building on the west beach. The remaining part oftheyear durations and velocitiesare lower and sand moves inshoreand up the beach face.76At the extreme higher endof the beach the protectivebeach fill was eroded andremoved seaward throughout the yearwith the exception of theMarch 25 to 31, 1975 period. OnMarch 30, 1975 occurred the highest winds onrecord for tenyears as given in TableII. These waves, approaching from theWNW, were of such size as to throw large sand andpea gravelup onto the upper beachin berm-building action. As a resultthis storm refaced the extreme upper sideof the entire westbeach with sand and gravel. Following the storm thisbermmaterial proceeded to be removed also.775.4 SANDMOVEMENT ON THE TOWERSBEACH AND EAST ENDThe west tower marksa dramatic alterationfrom the westbeach alignmentand exposure (Referto Figure 1 forWreckBeach configuration).Here the upper shorelineand cliffmakes a sharp turn,forming an angle withincoming wave attack,and a corner is exposedto wave forces.As can be seenfromthe refraction diagramsin Figures 8 through 12wave crestsfrom the westerlydirections begin anaccelerated bending toward an alignment withthe upper shorelinealong the lengthof this section of WreckBeach. As a result waveenergiestend to converge andconcentrate at the westtower corner,thereby increasing theirerosive powers. Downcurrentthoughtoward the east wave energiesspread as indicated bythe diverging orthogonals onthe refraction diagrams.Like the west beachthe protective berm fillcontinuallyeroded through the yearexcept for the refacingduring theMarch 30, 1975 storm.Near the west tower erosionof the protective fill commencedimmediately following constructionandcontinued during the summerperiod. With the transitionintohigher velocity and longerduration winter winds erosionproceeded faster at the westtower and commenced inthe more protected east end.785.5 SANDBAR MOVEMENTFrom the west tower eastward sandbars as distinct unitsappear to migrate along the length of the beach in the directionof their long axes.The information presented in Figures 28 and 29 summarizesthe movement of sand in the nearshore region of Wreók Beach. Theevidence suggests that sand moves up and down as well as alongthe shorelines in definite rhythmic patterns in response to cyclic weather activities. The orderly progression of sedimentdown the beach is indicated by the solid lines connecting thetransition dates between summer—winter cycles in Figure 29.Beach building and sand removal activities are indicated by +and - signs. They suggest the arrival and passage of the bulkof a sandbar.On the basis of this data it is reasonable to concludethat sandbars near the intertidal zones progress the length ofthe beach from the west tower area to the east end annually.That is, during the course of a summer—winter cycle sand movesup, down and along the shoreline in the basic form of sandbars.For example, with reference to Figure 29 the head of a sandbarapproached the west tower area on September 26, 1973 after havingmoved inshore across the west beach during the summer season. ByMay 1, 1974 the tail of the sandbar had passed the west towerI-.’Pi.)0.øiU)<—JcJU)CDCDçjrtrtI-’.CDCDCDr1‘<0rtCD0P.)ir1H F-’CDctP)J•’CDp.)HP.)jU)U) rt-P.)FlP.)I-’FlIICDU)HCDi0<P.)CDI551P.)p.)P.)I-’I-5U):U)CDU)CDo.)JCDP.)•.51IIr1rtl<CDCDCDCDP.)P.)P.)).<U)U)rtrtF-’.ftçt00F-’ ‘..DCDCD-.1I-5Fl01P.)ft51CD P.)CD0i-i. i—’CDCD P.)P.)51CD51FlP.)k)51EASTTOWER75—UPPERBEACH1974-EASTEND74SANDBAR—EASTENDSANDBAR974-75---I-WESTBEACHSANDBAR1974-75—-rn°—-;-WESTTOWERSANDBAR1974-75%C.‘0efr<e.1I.IIiLOIIIEASTTOWERSANDBAR1973-74—EASTTOWERSANDBAR1974-75—u-ri-i-iTTi-r‘wTiu.1iI-‘I(.111LTTjFLTirfl-TrI_LIIlEASTTOWERUPPERBEACH1973-741’I’EASTENDUPPERBEACH1973-74rI\FIGURE29.Annualsandbarmovement.CHAPTER VI$UMMARY6.1 CALCULATION OF VOLUMES CAPABLE OFBEING MOVEDBY WRECK BEACH LONGSHORE TRANSPORT SYSTEMThe volume of sand capable of being movedif availableby the Wreck Beach longshoretransport system is dependent uponthe size of wave attack, frequency, duration, angleof approach,sediment characteristics and beach slope. Correlations of theseparameters have been determined by Castanho. Any calculationsofthe amounts of littoral drift are subjectto a large uncertaintyand few methods are available which are suitable to theWreckBeach study area. Castanho’s calculations havenot been widelypublished or tested but are suitably applicable to the studyareaand are likely good to within a factor of 2. Wreck Beachfitswell into the typical characteristics suggested by Castanhointhe use of the sandy shores equation. Some valuable conclusionscan be made about sand transport on Wreck Beach even thoughaprecise calculation is impossible.Castanho’s method is outlined in “Coastal Engineering”,Volume II, Chapter I by Richard Silvester together with thenecessary graphs and coefficients. Using the Castanhoequationsuggested for sandy shores estimates of longshore transportvolumes were determined for the annual summer—winter cyclesof81821973—74 and 1974—75, Tables VI and VII, and for the 1973-74 and1974-75 freshet seasons, Table VIII. The volumes given in TablesVI, VII and VIII are quantities of sand which if available arecapable of being moved north and south annually, and during thebrief Fraser River freshet period by the Wreck Beach longshoretransport system.The equation for sandy shores,7GT/wH02L= Ersino(bcoso(owhere w = specific weight of sea water= 64 pounds per cubic footS = specific weight of dry sand= 100 pounds per cubic footis solved for G, the volume of sediment moved per hour acrossa plane perpendicular to the beach, and is listed in the Tablesas the Hourly Transport Volume. The Hourly Transport Volumerepresents the ability of wavesof that particular regime totransport sand. The Average Rates are based on actual winddirections and wind frequencies occurring during the given timeperiods and the volumes which could be moved on Wreck Beach bythe resulting wave fields.Volumes attributed to winds from various direction are determined from directional wind frequency information given in TableV. Table V presents the hourly values of wind blowing times fromthe percentage frequency data derived from Table II and the windrose of Figure 30.83. DIRECTIONALHOURLY WIND FREQUENCIESWIND -AB CDFREQAnnualAnnualAnnualAnnualAverageWIND\ 1973—741974—75 1973—741974—75 1973—741974—75YearlyDIRECT\.. %hr % hr %hr % hr% hr %hrhrNE —— — —— — — —5.0 438 5.0438 5.0438NNE —— — —— — — —1.0 88 1.088 1.088N —— — —— — — —1.0 88 1.088 1.088NNW —— — —— — —— 1.0 88 1.088 1.088NW —— — —0.5 47 —— 4.0 3503.5 3034.0 350WNW 0.981 2.2 192 0.544 1.0 894.6 401 2.8244 6.0526N 0.7 570.7 64 0.433 0.213 8.0 698 8.1 7119.0 788wsw —— — —— — — — 4.0350 4.0 3504.0 350SW —— — —— — — —3.5 307 3.5 3073.5 307DIRECTIONAL HOURLYWIND FREQUENCIESWINDA B CFREQUENCYFreshet FreshetFreshetWIND 19731974 1973 19741973 1974DIRECTION,% hr % hr % hr% hr % hr % hrNE-: - -- - -- - -- - -NNE- - -- - -- - -- -N- - -- - -- - -- - -NNW- - -- - -- - -- - -NW— — — — 0.2 13 0.1 1 0.757 0.2 19WNW 0.1 8— — 0.5 41 0.4 371.2 103 1.5 129W 0.13 — — 0.3 22 0.18 0.5 47 0.7 59wSw— — — — 0.1 4 — — 0.540 0.5 41SW— — — — 0.1 6 — — 0.3 23 0.216TABLE V. Directionalhourly wind frequencies.I•rJ H w 0p) 0 0 CDII H r1 CD3 rt I-i. 0 I-J.II 0 rt CD CDp) Ii Fl 0 cn CDco85Volumes according to wind velocitiesor wind strengthshave been derived by grouping winds of alldirection into GroupsA,B,C and D with the average wind regime characteristics givenas follows.Winds used in determining NE transport for the entire yearare divided into three groups. The Peak Extreme WindPeriods, A,are those defined in Section 3.2, Chapter III selected fromTable II. Included are all winds having maximum sustainedvelocities above 24 miles per hour.The General High Wind Periods, B, are those winds remaining in Table II except those entered in Group A. Includedarewinds having maximum sustained velocities in the range 17 to 24miles per hour. Groups A and B contain all the wind periodslisted in Table II.The Other Winds of the year, C, are derived from the his—torical 10—year record less those periods entered in A and B.Included are winds having maximum sustained velocities in therange 8 to 16 miles per hour.The Northern Wind Periods, D, for the year used in determining the SW transport are the average 10—year winds givenin the wind rose of Figure 30. Included are the winds from theNE to NW sector which affect the southwesterly movement of sandon Wreck Beach.86The distribution of wind blowingtimes between groupsA,B and C is as follows:- of the wind periods included inGroup A, 25 percentof the blowing time was spent near the25 knot velocity, 75percent of the time was spent at lowervelocities so addedinto Group B;- of the wind periods includedin Group B, 75 percentof the blowing time was spentnear the 20 knot velocity, 25percent of the time was spent at lowervelocities so addedinto Group C.Winds during the months of theFraser River freshet,mid-May through mid-July, are distributed intothe A,B, and Cgroups also and derived from dailymeteorological recordsmonitored at the Vancouver InternationalAirport by CanadaAtmospheric Environment Service.Typical wave characteristics for these groupsare theaveraged values given in Table III.87Group A. Peak Extreme Wind Periods:Average maximum sustained velocity = 28mph = 25 knotsH0 = 5.1 feetT0 = 4.9 secondsL0 = 123 feetGroup B. General High Wind Periods:Average maximum sustained velocity = 22mph = 20 knotsH0 = 3.8 feetT0 = 4.3 seconds= 95 feetGroup C. Other Wind Periods:Average maximum sustained velocity= 11.5 mph = 10 knotsH0 = 1.6 feetT0 = 2.7 secondsL0 = 37 feetGroup D. Northern Wind Periods:Average maximum sustainedvelocity = 11.5 mph = 10 knotsAverage fetch = 6.5 milesH0 = 1.0 feetT0 = 2.2 secondsL0 = 25 feet88Examples in the uses of TablesVI, VII and VIII.Example 1.What total volume ofsand was transported bywaves generatedby winds from the west during the1974-75 year?NE movement by Groupincludes freshetNE movement by Groupincludes freshetNE movement by Groupincludes freshetSW movement by GroupA windsvolume ofB windsvolume ofC windsvolumeD winds(Table VI)(TableVIII)(Table VI)(Table VIII)(Table VI)(TableVIII)(TableVII)During the year 1974-75 windsof all velocities from thewest moved a total of16,908cy toward the NE.During the freshet period of that yearthese winds moved2031cy of the total 16908cy in the samedirection. That is,12% of the yearly volume transported bywinds from the westcould have moved during freshet.Winds from the west did not contributeto movement of sandin the opposite direction (seeTable VII).= 3477cy0 cy= 4907cy1280 cy8524cy751cy= Ocy2031cy 16908cy89Example 2.What volume of sand wastransported by waves generated by25 knot winds during the 1973-74year?Winds of 25 knot velocitiesare included in Group A.NE movement by Group A winds = 6150cy (TableVI)includes freshet volume of 2567cy (TableVIII)SW movement by Group A winds = 0 cy (Table VII)2567cy 6l5OcyDuring the year 1973-74 waves from windsof 25 knot velocitiestransported a total of 6150 cy of sand, all of ittoward the NE.No 25 knot winds occurred which were effective in moving sandin the opposite direction. (All sand transported toward theSWwas accomplished by waves from winds of GroupD (see Table VII)which have an average velocity of 10 knots.)During freshet period of that year 25 knot winds could havemoved 2567 cy of the total 6150 cy in the same direction. That is,42% of the annual volume transported during the 1973-74 year by25 knot winds could have occurred during freshet.90Example 3.What volume of sand wouldwaves from a 10 hour WNW wind of20 knot velocity be capable of movingon Wreck Beach?In what zone of the beach would this movement likelytakeplace?A 20 knot velocity wind is included in GroupB winds.From Table VI WNW winds of Group B have anHourly TransportRate of 1944 cubic feet per hour. During a10 hour period19,440 cubic feet (720 cubic yards) of sand couldbe transportedtoward the NE. Table VII indicatesthat WNW winds are noteffective in moving sand in the opposite direction.From Table IV movement of sand by these wavestakes placein water depths of up to 10 feet. A 10 hourperiod coversalmost an entire tidal cycle. If it coincides witha largetide then sand would be moving as far seawardof the cliffbase as 2000 to 2300 feet which would be near the2 fathomcontour line on a Canadian Hydrographic Chart(see Figure31).91Example 4.How often do winds blow outof the NE that are capable oftransporting sand on Wreck Beach?From Table VII windsfrom the NE direction are effectiveonly in moving sand towardthe SW. These winds are of Group Dhaving an average velocity of 10 knots. (Highervelocity windsof Groups C,B and A do not occur with respectto Wreck Beachcalculations) . These winds occur approximately438 hours peryear, 18¼ total days, and could contribute 503cy to the SWlittoral drift. (NE winds do notcontribute to movement ofsand in the opposite direction, seeTable VI).ANNUALLONGSHORETRANSPORTVOLUMETOWARDTHENE.Hourly1973i9741974—1975WaveTranspOrtWindYearlyWindYearlyDirectionVolumeFrequencyVolumeFrequencyVolumec.f./hr.hours-c.y.hoursc.y.A.NW504----WNW3996213108487104W5868143042163477WSW5724————SW1728————SUBTOTALS35--61506410581AVERAGERATES175cy/hr.165cy/hr.B.NW25235327——WNW194478561617512600W2880576080464907WSW2808———SW828————SUBTOTALS1701202322117507AVERAGERATES71cy/hr.-79cy/hr.C.NW29362389303325WNW23442737013022617W31771784187268524WSW32035041483504148SW9730711033071103SUBTOTALS2163177591988--16717AVERAGERATES8cy/hr.8cy/hr.TOTALS2368hours35932cy.2273hours44805c.y.TABLEVI.AnnuallongshoretransportvolumetowardtheNqE,ANNUALLONGSHORETRANSPORTVOLUMETOWARDTHES.W.HourlyAverageAverageWaveTransportWindYearlyDirectionVolumeFrequencyVolumec.f./hr.hoursc.y.D.NE31438503NNE10488339N10388336NNW7588244NW10350130AVERAGERATE1.5cy/hr.TOTAL1052hours1552c.y.TABLEVII.AnnuallongshoretransportvolumetowardtheS.W..0FRESHETLONGSHORETRANSPORTVOLUMETOWARDTHEN.E.Hourly1973—19741974—1975WaveTransportWindYearlyWindYearlyDirectionVolumeFrequencyVolumeFrequencyVolumec.f./hr.hoursc.y.hoursc.y.A.NW504----WNW3996101480——W586851087——WSW5724————SW1728————SUBTOTALS15256700AVERAGERATES171cy/hr.0cy/hr.B.NW25216149437WNW1944443168412952W2880262773121280WSW28087728——SW8289276——SUBTOTALS1027094574269AVERAGERATES70cy/hr.75cy/hr.C.NW2960642527WNW2341059101351170W3175058764751WSW3204351046545SW9726932072SUBTOTALS28421642902565AVERAGERATES8cy/hr.9cy/hr.TOTALS401hours11825c.y.347hours6834c.y.TABLEVIII.FreshetlongshoretransportvolumetowardtheN.E.95The Wreck Beach longshore transportestimates predictthat typically volumes of 40,000cubic yards ± 20,000 cubicyards (see Table VI) are transportedto the NE annually pasta plane that could be extendedperpendicular to the beachshoreline. Because of the uncertaintiesassociated withsediment transport problems particularly coastalsituationsa fairly large error is assigned to the estimates. An indication of the scatter of data from field testsand laboratorytests in the range of a general solution is outlined bySil—vester, “Coastal Engineering”, Volume II, Chapter1. Thevolumes computed from the Castanho calculationsshould beconsidered no more accurate than to be within a factorof 2.Wave activity is also capable of moving to the SW smallvolumes of about 1550 cubic yards (see Table VII) in a relatively narrow beach width confined mostlyto the intertidalexposure areas. This minor amount of sandconstitutes only3 to 4 percent of the total volume transportedannually. Thisquantity is roughly equivalent to a 5 yard truck movingsouthwest along the beach once a day, while transport tothe northeast is approximated by a 5 yard truck movingalong the beachin that direction once every hour.Throughout the year information presented in Table VIsuggests that winds of Group C with velocitiesfrom 8 to 16miles per hour move some 17,000 cubicyards of sand annuallyor 40 to 50 percentof the total volume transported. Theselow96velocity winds occupy thegreatest portion, 90 percent, ofthewind frequency blowingtimes under consideration. Thesewindsapparently are responsiblefor a sizable and constant yearlymovement of sand in theWreck Beach longshore transportsystem.That is, about one-halfof the sand volume carried by theaforementioned 5 yard truckmoving northeast each hour isproduced by 16 mile perhour winds and under.On the other hand, when the highwinds of Groups A and Bdo occur large volumesare moved in brief time intervals:compare in Table VI the average rateof 170 cubic yards perhour for A winds with 75 and 8 cubicyards per hour for B andC winds respectively. As indicatedinTable IV the width andextent of the zone in which sand isactively moved by wavesgenerated from winds ofGroups A and B ranges up to twice asfar seaward and in depth as theactive zone produced by lowvelocity winds of Group C.Using the derived Hourly TransportRates presented inTable VI sand volumes moved duringindividual storms can beestimated. From Table II four highwind periods were selectedwith two of these havingextremely high winds.Hourly directions and velocities weretaken from meteoro—logical records monitoredhourly at the Vancouver InternationalAirport. Rough estimatesof the volumes moved toward the NE97during these periods and the longshorecurrent velocitiesgenerated at the wave breaking pointare listed below.January 8-9, 1975February 19-20, 1975March 25, 1975March 30, 19752500 cubic yards4700 cubic yards1500 cubic yards3300 cubic yards1.7 to 2.2 ft/sec2.2 to 2.6 ft/sec1.7 to 2.2 ft/sec2.2 to 2.6 ft/secBoth the February 19-20, 1975and the March 30, 1975 stormshad several hours of 35 to 40 mileper hour WNW winds withthe associated longshore transportvelocities given in Table III.The January 8-9, 1975 and March25, 1975 storms had lower continuous WNW winds of about25 miles per hour. Other informationassociated with the March 25, 1975storm is presented in Chapter IV, Section 4.6.986.2 FRASER RIVER NORTH ARM AS A SAND SOURCENet sediment transport around the Point Grey headlandsis to the NE so the large submerged sandbank extending offshore SW seen in Figure 31 must have an important relationshipwith the transport system. The Point Grey headlandsmarks theupstream beginning of a transport systemwhich evidently continues well into Burrard Inletvia the shoreline. As such thesandbank extending from the northern bankof the North Armmouth is an area of considerable activitywhere Fraser Riversand is absorbed into the system atthe outer limits of thetransport zone.The Fraser River freshet reaches a maximumfrom mid—Maythrough mid—July. During this shorttime a great deal ofmaterial is added to the sedimentbudget of the area. Theseevents coincide briefly butprovide a mechanism for movingsediment available during its mostabundant period from theriver channel onto the Wreck Beachoffshore sandbanks. ThePublic Works dredging records forthe past ten years is contained in Table IX. The dredging recordsand theoretical volumes are courtesy of Mr. Woo, Departmentof Public Works, Vancouver, British Columbia throughpersonal telephone communication in August, 1975.99FRASER RIVER NORTHARM DREDGING RECORDSAnnual Volumes Enteringthe NorthArm:(Average theoreticalvolume)Bed load-materialwithin 8 inches of bottom:sands and gravels= 90,000 cy.Suspended load—material above8 inches ofbottom and largerthan 0.065 mm.:sands and gravels= 240,000 cy.Wash load-material 0.065mm. and smaller:silts and clays= 1,000,000 cy.Average volume entering:Total = 1,330,000 cy.Annual Dredging Quantities:North Arm MouthApril to March VolumesDredgedCubic Yards1964 196533,6001965 1966164,0001966 1967354,0001967 1968 416,0001968 1969 286,0001969 1970347,0001970 1971142,3001971 1972 397,1001972 1973211,0001973 1974 196,0001974 197593,300 (incomplete)Average volume dredged:sands and gravelsTotal = 240,000 cy.TABLE IX. FraserRiver North Armdredging records100The North Arm mouth is dredged each yearimmediatelyfollowing freshet to maintain an open navigation channelup todepths of 20 feet below lower low water. Some 1,330,000cubicyards of material of all sizes enters the North Arm each year.At the mouth an average of 240,000 cubic yards is removed byyearly dredging. Leaving the North Arm mouth is the wash loadfaction consisting of silts and clays and the sand andgravelvolume less the dredged quantity. The silts and clays are washedquickly seaward and do not contribute significantly to theheadlands sand transport system. Therefore 90,000 cubic yards isavailable annually for introduction into the headlands process.Winds from the SW through the Nw continue through thefreshet season of sufficient velocity to generate wave fieldscapable of moving sand from the North Arm mouth shoreward toWreck Beach. Referring to the breaking depth,db,column ofTable III delineates the breaker zones for the given wind directions and wind velocities where for practical purposes mostof the active movement occurs. For the winds which did occurduring the freshets, Table VIII, movement from waves of Group Acould have taken place in depths up to 12 feet below the zerocontour depth; from Group B, up to 10 feet; and from Group C, upto 6 feet. Figure 31 is an hydrographic chart of the study areashowing contour lines and sounding depths at the mouth of theNorth Arm river channel and the offshore region of the Wreck Beacharea. From Figure 31 it appears that throughout the channel there101are areas of depths 12 feet and less where sandwould be availableto wave transport activities and subsequent introduction intotheWreck Beach longshore system. The large area outlined by the 6foot contour (1 fathom) would be a region where winds of Group C(8 to 16 mph) would be capable of transporting sandand wherewinds of Group A and Group B would be particularly effective.Further, the shape of the underwater topography at the NorthArm mouth and headlands seen in Figure 31 suggests that river sandis influenced by the winds and waves under consideration. Ratherthan a fan-shaped delta common of undisturbed deposition the contours are distinctly skewed toward the north indicating wave-sweptmovement of sand.The volumes of sand capable of being moved by winds and wavesduring the 1973 and 1974 freshets were estimated using Castanh&smethod and presented in Table VIII. The quantities range from7,000 to 12,000 cubic yards. The freshet transport activitiesare capable of moving into the headlands longshore system about10 percent of the 90,000 cubic yards of sand reaching the NorthArm mouth providing it were in depths less than 12 feet at lowerlow water. However, part of the sediment is in depths greaterthan 12 feet. As well winds might occur during the higher watersof a tidal cycle which with respect to the North Arm supply movesthe sediment out of the range of wave actions.HDiP) iu.1CD z 0 r1 I-1 Di CD C) CD Di C) Di CD Dl (n 0 U)-U)ctC)I-Li3Pa).-1_a.I•-’cDP)—‘CooQJ.)1_ac4\Qom%I•11111_a\OOooaa‘-)‘-‘)OC)(DCD0 (DCDO ç+ct0)10—--.------.-----IDr)00ci)0cU)—.U)ccc‘—••cL-.cc-..Z3I’J—..J.-F’)/—=—f.,_j—“0F’)“Liq01=— 0)FL)-.1\_01•••U)U)01=ac..-OwF’)•I-.\•-1U)F’)-\ Is)FL) 0C.)==U)F’) “301)/0)F)...?C.)0103Waslenchuk, 1973, found limited amounts of sand on the outerbank which he determined to be of the same origin as sand foundnear the mouth of the North Arm. In the nearshore and on thebeaches the sediment proved to be exclusively of cliff origin.Significantly, his work does not concentrate on this crucialthough brief time of freshet. Instead the work was done in November and February and the importance of the sediment supply peakwith accompanying sand movement mechanism are lost over the winter.By winter the bulk of the freshet sand will have already movedaround the headlands. This is evidenced by the sandbar progressiondescribed in Section 5.5 of Chapter V and by the building of thebeaches in the summer, then the loss of sand and exposure of rocksby winter described in Sections 5.3 and 5.4.1046.3 WRECK BEACHCLIFFS AS A SAND SOURCEIf, as Waslenchuk suggests andlongshore transport calculations indicate, theFraser River is not presently theonlymajor source of sand supply to thelongshore transport systemin the Wreck Beach area then theheadlands themselvesmust besupplying a large portion of the sedimentto maintain thesystem. In the area of most activeerosion, just below the newMuseum of Man, 1200 feet of near-verticalcliffs 200 feet highare estimated to be receding atabout one foot per year.Atthis rate 8900 cubic yards annually (1 cubicyard per hour) ofsediment is supplied from this area alone.If the remaining2200 feet of eroding and susceptible cliff face alongWreckBeach is receding at a much slower rate ofone—half foot peryear then an additional 8200 cubic yards (about 1 cubicyard perhour) also becomes available annually. Under these conditionsthe cliffs appear to be supplying a volumeof about 17,000cubic yards of sand each year to the longshoretransport system.The Wreck Beach cliffs appear to be eroded by wave attackin a cyclic pattern which may be as follows:- vigorous attack at the base of the cliffs during the wintermonths at times when higher tides and high wind periods coincide,- movement of part of the sand to help build up the offshore sandbar and part of the sand moves northeast out of the study area,— during the summer months sand moves from the offshore sandbaronshore,- erosior of the onshore accumulation during thefollowing winter.1056.4 CONCLUSIONSThe information and calculations suggests that the NorthArm could amply supply the longshore transport nourishment requirements. However, some means in addition to the presentnatural processes must be available to bring this sand into arange where wind generated wave activity can incorporate itinto the existing headlands transport system.LiC)WbJWC)P3CDHH-P3HP3P3P3IICl)I-iCl)H-C)CDCl)Cl)C)P3P3CDP30H0aCDCDCDcw-.Od-’W(DtzIO.b-’C)C)fl00)—’C)’t)HWOh)j(D-tçtOOCDt-1[1)--’H-’0CDP3t-Hi’.J<CDc4H-I-’-CiCDqH-H-’j•cLaCD’i•C)H-HkCD—’•<ct-P30•<ci-P3Li’•<‘<CDH-1-<ct-’ct-Wi-HCDH-<CDlQ(DH-ti-HCDH--i-Cn•F-IF-’CDCDH-3’•.I-ICJCDO•hCl)t-)cl-Ci)P3i-HH-•HP’LI1Ci)CDLiIH-’.Cl)’HP3’W0b-’H--Ht-rtW’-P3•C))ct-CDCflCDH-0HCl)CDH-00iCD•H-.•-•[1H-ci-H-Li‘HP3b-1ci-flQt-ci-0HCflh)CDHhCflC1)’Qj1OCtc-i-flhci-t-1‘<OP3<P3-<0O-i-CDP30C)CD<0OP3ci-Hi-)P3HO—.i••2CDI-’-I—’Cl)‘CDOH-OHOj.(.jC)P3c-t-‘DOH0CI)hI-h.Cfr)-hSOI-hP3.•Cfl•OCDctd-P3:r:t-1lOCDb-h<P3CD’HCD.t.<CDbiOCDP3WH-H-H-WH-.btC)CD0Fl-)•CD‘.QWH-P3CIQIIP3L’i<Cl)IlP3ç-l-CDCDçt<Cl)hP3Cl)0I1P3Hpj<I-)H--FlCDH-O<CDP3I-’-)))H-OHctCl)I1I-’•’I:2jI-I’ci-0t-PJOci-CDl-’P3Cl)C)0F-’-Cl)0P3(-I-ct-ci-rI-OH-C%)Cflct-H)H-OC)P3’IidH[-hC4Cl).H-H-Cfl.C)P3CD‘0CDLHci-Ci).0P3WCD•CI)Oci-F-tCl)Q<0Cl)t)Cl)QHOI)btci-LC)‘-<0OF---P30<—‘(DpiOC)HCDHt•fl•CDfl•<1C)P3CDCDdct-OCD<(Th.CD[l0CD’0P3OCD0ci-CCDCflOFl(JiP3CDFllP3HP300OH-ci-F-hI1<HI-3t-1P3HiFlt-1C)P3()LCHFP3(nP3H-’‘-<•0.ç-i-CD5’C)(DCDI—)CDt-)<C)CDSP3CflHCD‘WoOCDH0P3CnOI-lb:IH-tYCnCDCDC)O0-‘CDCl)-bCl)CDH-I-’H-H-HCDP3H-H-’-<IIII0P3Cl)H-<H-H-‘tiCl)0OP3Cl)CDctP3ci-P3CflCflI-’-Q•Cl)Cl)Qci-HCDP3Cl)OOHCD-IIH-C)I—’-Cl)H-ci-<ci--D•P3I-IOCl)Cl)QCDd-H-CDCl)C)<OCD—.3iI-IcI-flH1HDP3‘<Cl)EH”’[-hHt’JC)OiHCtH-•‘-.ØCDWDCDC)(D‘0Ci)p3•H-OCD--.-i’dCDflO--.iH0(tOtH0Ci)a’t0CDP).U1P3P30F-h(-flP3H-I-hC)ci-LDiH-CDCDHI‘-DFloP31OI-_J1-•tIC)HCJ)•-)F-hOCfl•OC!)0H-Q-j.tICD(-l-C).IJ(tfrhWI—’P3HP3CtP3Cl)CDP3•CDCñ[lPI-)0OLi0HOC)ct-iCDIICDH-act-Ct-I.QtICl)0.DF-h(DO))-’H-H-F3ctb’I—hri-<0c’—-..iCDC)(DOç-i-P3ZCDH-H-ct-‘Cl)Cl)a’tJçtpiCl)H-•CDP3Cl)P3I—iC)0H--•P3C)C)0<Cfl3OH-Y”CDP3OH-110fl)-CCDcI-0I-hCDH-H-H-i<0H-H,F-’liCl)CDIICflHCDflWC/)HP3H-H-0Cl)-.CDCD0Cl)H-0h0.01CD<0Cl)0HiCDCDH-ci-CDCl)HCfl3(D[-h(ib’P3Or-b-)’-<OH-C)c-t-i-ICDHOCflcICDHci-tiCñ’tJIICDHH-0‘t3O’-<H-O0LOP3H-tQH-I-3C1)P3cl-H•0P3P3CflCD.‘-<F-hI-Id-‘-<0P3I—’‘-<Iii-h‘-<‘-<rid-Fl’‘H-,-(DOHIci--H-—H-Cl)HCl)0CDHF--CD ‘-DCl)CDci-—J’II Cl)U)U)U)P3H-H-HCOCDC!)P3CDHctP3H•CDIlCDCDC)CDP30HC)CDCOt!)HiOIrl-Wc-I-H’(ThOP3P3P3P3P3b0()U)Hi’ctW(Th00CDIl(DO(DOOIlIi(DOOCDOCD•OOF-tiCT)C)P3OIIIIC)P30-i0-.0-iIlCflHH-Ilb11flHCOP30.•0COCOCOr-I-CO••CDQWFi-(DIlCDIl-c-I-CDH-lL.ç-I-COHOHOCDP30OIlbHIlC)(Dc-I-(Dc-I-HIlHHibI-hIiC)OP3H-ZH-‘<c-I-P3CDCD.‘-<CD‘-<CD‘.DctI—’HHHHtiP3ri-C)OP3OH-’U)-‘C)C)iH-H-HH-H-c-I-Ii‘i0H-1<‘HiCOCD-lC)C)C)C)C)0COc-I-OP)CDC)0-iIl-3..CDH-HI-CD0.iIlOvCI-P3w’‘H-H-.C)C)jCO0.b(DP3CDflHiCOCOCDIlOIOCDCDCDCDCDCDoC1)--‘CD000CDCDH-H-C)H-CCDCDC)C)C)C)C)OCD-.JCflIlc-I-0.iH•0PiI-HCDC)CDCDIlIIIIIlIIH-I-I•(DHOC)CD1i(Dc-I-‘c-I-<‘CDIlIlCDCDCDCDCDIH-ICO00C)01-CO•OPJH-H-P3H-Cl)P3P3P3P3P3c-I-H<•P3HJF1HH<H-HH0(DHOCDc-I-c-I-c-I-c-I-c-I-IT101CD‘CO‘DrtSH-CD0OP3<‘-DIlcDIl0‘-QH-H-H-H-H-0OCDCOc-I-—.jH-H-P3COhh‘-QCDCO-JCD--.3CDU)000•00IlC)IlrtPJMC)C)c-I-H‘<C)IlH-w’-<Ow’-<OI-I(DOc-I-C)HCDH•P3P3CDCOc-I-‘0-Cl)•Hi•HiP)(DOCOCOCOCOCO‘<.CDcHS01H’C)C)COIl-----‘(ThCOP3-‘-.0CDC4P3HHCDCDLxH-lpc-I-I-<l:1C)CD0.H-IlH-IlH-P3‘iU)I-Ic-I-P’H-C)‘-00Cl)MCDC)H-IlH-0-iHiOH,0C)I-I’tJP3CDCDCD001‘CJQIlH-H-•CDF-htYHitTP3C)Il‘tC)CO.01COCDc-ICDctflCOHCOHHOciIl’ctCD’CD’H-’‘CDPJCDI-Ic-IIlW0CDCDc-I-P3CD0IlU)0CDHc-I-IlCOøIlL’JC)CDIlP3H(Dc-I-I-hHIlc-I-ciHP3H-H-IlI-IciciCDC)‘-<CDIlCDb’CDwCDCDCDCDP33‘-OH-CDHrtc-I-CDCDP3pcd<dCD-IIlt5CVd-bi—I-<‘-<I-’-.HH-iH-lH-c-I-H-0‘0Il00‘000H-04-LClc-i-<1CDc-i-P3COP3<01l(DOHIlIl-IlHIlIlIlciI—•-‘COCDCO0C)ctCDCDCDIlDc-I-Hc-I-ri-‘.OctHc-I-ctH--‘c-I-001I--hHH-IlIlCD—3‘.DH‘-.0H-H-c-I-COH-HiCOIlCOIlI-Li.c-l-—..1ri-‘.D(t‘-.Dctic-I-ri-ri-<1’-<P3HH-i.QClWOHH-0H-0H-HP3•0MO-.10•0—JOc-I-OCDctCOOCtPJ00IlHH,rl-’-CIIi‘.0•0•CDIlOH-CDIl’-<c-I-CDH-COO‘-<0‘-<0i.0-.1tnW•WWCDC)COHi0ctH-Octr-i-HiCOCO‘WP300000‘HH-0OH-P3OCDOCD•HP3P3P3P3P3P3c-I-C)CDHiiOCDCOH•CI)Hi01Hi(1-IlIlIlIlIIJH-‘-<HC)IlcQj1P301CDIl010101QiCDIlH-OP3W-01C)U)flU)CDci0HiU)IlIl-C)H-P30P30•00000IlP3HiHi01C)C)H-0U)OWCDHHHHc-I-Cl)HiHiHiHiHiH-H-0d-H.P3CDH-iH-H-•P3Wc-I-CDH-0IlHic-i-Hic-i-C)‘dIlP3Il0H-<COCOC)c-I-OH-OH-CDP3P3P3P3P3‘-<H-PJOc-I-CDCD<Hty•CDCOIlOIlOIlIlIlIlI-IIl-01c-I-H-F-’-Il01CDc-IHCOH-COHi-IlP3I-H-COH-COP3‘-<COCl)COCOCOHCOCOI-’-COO‘P3P3P3H.iØ(Dc-I-C)H-HiMI


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