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

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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 FULFILMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF APPLIED SCIENCEin the DepartmentofCivil EngineeringWe accept this thesis as conforming to therequired standardTHE UNIVERSITY OF BRITISH COLUMBIASeptember, 1975In presenting this thesis in partial fulfilment of the requirements foran advanced degree at the University of British Columbia, I agree thatthe Library shall make it freely available for reference and study.I further agree that permission for extensive copying of this thesisfor scholarly purposes may be granted by the Head of my Department orby his representatives. It is understood that copying or publicationof this thesis for financial 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 transport supply 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• • • . 22244.14.24.34.44.54.6CHAPTER 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 SUMMARY 816.1 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 . 105BIBLIOGRAPHY 106VLIST OF TABLESNUMBER TABLE PAGEI Wind scales and sea descriptions 17II High wind period information 19III Wind, fetch and deep water wave data 33IV Limits of the Wreck Beach littoral zones 53V Directional hourly wind frequencies 83VI Annual longshore transport volume toward the NE 92VII Annual longshore transport volume toward the SW 93VIII Freshet longshore transport volume toward the NE 94IX Fraser River North Arm dredging records 99viLIST OF FIGURESNUMBER FIGURE PAGE1 Wreck Beach study area map 42a Regional surface wind patterns of thenortheastPacificOcean 152b Local surface wind patterns of the Straitof Georgia 153 NW wind direction effective fetch diagram 274 WNW wind direction effective fetch diagram 285 West wind direction effective fetch diagram 296 WSW wind direction effective fetch diagram 307 SW wind direction effective fetch diagram 318 NW wind direction wave refraction diagram 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 at photograph locations 1 & 2,East End, following construction activities 57viiNUMBER FIGURE PAGE17 Photograph sequence at photograph location 6,Towers Beach, prior to construction activities... 5918 Photograph sequence at photograph location 6,Towers Beach, following construction activities.. 6019 Photograph sequence at photograph location 10,West Beach groin, following construction act 6120 Photograph sequence at photograph location 13,West Beach, following construction activities.... 6221 Photograph sequence at photograph location 18,West Beach, following construction activities..., 6322 Photograph sequence at photograph location 19,Towers Beach, following construction activities.. 6423 Chart of photograph sequences prior toconstruction activities . 6724 Chart of photograph sequences followingconstructionactivities ...... 6825 Chart correlating photograph information withcross—sectioning data on upper beach face 7026 Chart correlating photograph information withcross—sectioning data at groins 7127 Chart correlating photograph information withcross-sectioning data on sandbars 7228 Annual Wreck Beach summer-winter beach cycle 7429 Annualsandbarmovernent 8030 Vancouver International Airport ten yearqind rose 8431 Fraser River North Arm and Wreck Beach areasoundings chart 102viiiACKNOWLEDGEMENTThe author is very grateful to her supervisor, Dr. PeterR.B. Ward, for his guidance and encouragement during thisstudy. The author is also grateful for the help and assistancereceived from Vancouver Board of Parks and Recreation andfrom Swan—Wooster Engineering Company Limited.This study was supported financially 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 concern for the buildingsand structures within a few hundred feet of the cliff brimsuch as the new Museum of Anthropology with a 1973 contractprice of $3,070,000.00 not to exceed $4,297,000.00 and CecilGreen Park purchased by the University in 1964 for $100,000.00.Remedial measures for cliff stabilization were proposedby Swan-Wooster Engineering Co. Ltd., 1973 and Robert WiegelConsulting Engineer, 1973. Prime consideration was given tomaintaining a natural beach appearance. In the summer of 1974construction work was undertaken to implement some of thesemeasures.12The period of this study covers the year preceding construction and the year following. The study considers the processes of winds, waves and effects of waves on the cliff, beachand sand movement. To try and understand these processes andsources of sediment photographs were taken, wind recordsstudied, wave patterns predicted and longshore transport volumes calculated. Understanding these processes is the firststep in controlling them.Chapter 2 describes the study area and reviews thegeology and erosion mechanisms. A brief description of theremedial measures proposed and undertaken is outlined aswell as comments concerning the success of the stabilizationproject.Chapter 3 describes the regional and local wind patternsaffecting the Wreck Beach area. An abstract of high wind periods during the study period is related to the erosion-deposition patterns derived from photographic evidence to determinethe annual—summer winter cycles.Chapter 4 describes the wave conditions affecting WreckBeach. Effective fetches are derived and wave refraction diagrams used to predict modified wave forces, longshore movementand erosion—deposition patterns.3Chapter 5 describes the extent and direction of the long-shore transport system resulting from various wind 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 of the study. Sandvolumes capable of being transported JDy the longshore systemare calculated. The sources of sand which supply the systemare identified together with the relative magnitude of thevolumes. The influence and extent of the Fraser River NorthArm sediment with seasonal freshet effects are outlined.4IWRECK -BEACH STUDY AREA—4’--.. Hydrographic contour linE13 Photograph 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 methods havedated peat from the cliffs at 25,000 years old 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 of thesea level. Glaciated rocks ranging in size from cobbles toboulders 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, and people activityact directly on the cliff face to dislodge and move particles;and it is also suspected that earthquake activity in the pasthas served to destabilize the cliffs according to R.A. SpenceLimited, 1967. Of these, wave action and precipitation arethe most important erosion mechanisms.On Wreck Beach the cliff base is readily undercut bywave action especially during higher tides and onshore windperiods. McLean, 1975, found during 1974-75 that at timeswaves were capable of moving stones at least 0.03 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 the areadraining to the Wreck Beach cliffs Carswell, 1955, determinedthat some 400 x io6 gallons of water (a net quantity: totalprecipitation in all forms less the amount lost through evaporation—transpiration) are available annually as erosion agentsin the form of runoff and infiltration. Of that, an estimated60 x 106 gallons per year infiltrate into the ground watersystem and eventually emerge from the cliff along seepagelines. Continued excavations into and below the surface tilllayer provide additional catchment basins where moisture canpond and move immediately into the groundwater system. Plantcover provides protection against surface runoff, sheetwash,and removes moisture by way of evapo—transpiration processes.With the development of the Endowment Lands forest and vegetation has been removed from the cliff top and slopes introducingadditional water into the drainage basin and exposing unprotected ground surfaces. Extrapolating from this estimate the 36”diameter storm drain from the drainage basin outfalls at sealevel and carries some 300 x 106 gallons annually. Presumably9the remaining 40 x io6 gallons 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 cliffs could 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 of the existing beachand new protective beach, and to dissipate incoming wave energies.The groins are the low-profile permeable type and of rubble-mound construction. The permeable type of groin was used toavoid abruptly offsetting the shore alignment which occurs withimpermeable groins. Theoretically the permeable groin permitspart of the longshore forces and materials to pass through thestructure which triggers deposition on both sides of the groin.An exception to the permeable groin concept was the extensionof the existing storm drain outfall-- a solid 36 inch diameterconcrete conduit which serves as an impermeable groin at thatlocation.In addition certain measures have been suggested whichwould halt or retard cliff erosion from above and within. Thesesuggestions as urged by Swan—Wooster, 1973, as well as byWiegel, 1973, Backler, 1960, Carswell, 1955, Bain, 1970, andothers included: storm drainage away from the cliffs, not toward or along it; drains or wells to intercept subsurfacedrainage layers; revegetation of the cliff face; elimination ofaccess to the cliff face; and future construction 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 directly influenced 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 modified by the presence ofmountains and the altered winds from the Juan de Fuca Strait,Puget Sound and Fraser Valley. The Strait of Georgia windpatterns are summarized in Figure 2b. The winter pattern isclosed and counterclockwise in the southern part of the 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 wind patterns 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 nationalscale description velocity Estimating wind velocities description code forof wind knots on sea and wave state ofheights sea0 Calm Less than Calm; sea like a mirror.1 knot Calm glassy 01 Light air 1 to 3 Light air; ripples—no foam crests. 0knots2 Light 4 to 6 Light breeze; small wavelets, crests have Rippled 1breeze knots glassy appearance and do not break. 0 to 1 foot3 Gentle 7 to 10 Gentle breeze; large wavelets, crests begin Smooth 2breeze knots to break. Scattered whitecaps. 1 to 2 feet4 Moderate 11 to 16 Moderate breeze; small waves becoming Slight 3breeze knots longer. Frequent whitecaps. 2 to 4 feet5 Fresh 17 to 21 Fresh breeze; moderate waves taking a Moderate 4breeze knots more pronounced long form; mainly 4 to 8 feetwhitecaps, some spray.6 Strong 22 to 27 Strong breeze; large waves 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 white 6(Moderate knots foam from breaking waves begins to begale) blown in streaks along the direction ofthe wind.8 Gale 34 to 40 Fresh gale; moderately high waves of(Fresh knots greater length; edges of crests break intogale) spindrift. The foam is blown in well- Very roughl3to20feetmarked streaks along the direction ofthe wind.9 Strong 41 to 47 Strong gale; high waves, dense streaks ofgale knots foam along the direction of the wind.Spray may affect visibility. Sea beginsto roll.10 Whole 48 to 55 Whole gale; very high waves. The surface 7gale knots of the sea takes on a white appearance. HighThe rolling of sea becomes heavy and 20 to 30 feetshocklike. Visibility affected.11 Storm 56 to 63 Storm; exceptionally high waves. Small Very high 8knots and medium-sized ships are lost to view 30 to 45 feetlong periods.12 Hurricane 64 and Hurricane; the air is filled with foam and Phenomenal 9above spray. Sea completely white with driv- over 45 feeting spray; visibility very seriously affected.TABLE I. Wind scales and sea descriptions.18Listed in Table II is information related to high windperiods during the Wreck Beach study. Wind information is derived from wind records monitored hourly at the Vancouver International Airport by Environment Canada. Typical winddirections, strengths and frequencies are assumed the same forWreck Beach as for the Vancouver International Airport locateda 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 minimum of 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 INFORMATIONHigh MaximumWind Photograph Direction Duration Sustained GustDate Date Velocity A1..N1973March 18 E—ESE 9 20 38 SEApril5 W 15 25 35WApril 27 WSW-WNW 18 21 31 WMay 17-18 W-WNW 12 21 29 WMay 18—19 WSW—WNW 18 24 33 WNWMay 30—31 W—WNW 22 27 40 WJune NONE-. July4July 13—14, WNW—NW 34 21 27 WNWJuly 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 16 20 30 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 10 21 32 WNWJan. 25 W-WNW 6 22 35 WNWJan. 29 SSW—WNW 9 20 36 SWJan. 29-30 W—WNW 15 22 25 WFeb. 4 W-NW 18 26 45 WNWFeb. 19 W—WNW 8 24 32 WFeb. 28 SE—SSE 8 20 33 EMarch 1—3 W—WNW 36 24 39 WNWMarch 2March 5 W—WNW 9 20 35 WNWMarch 8-9 E—SE 38 21 31 SEApril 11-12 WSW-WNW 14 31 44 WNWApril 12April 23 WNW-NW 13 24 30 WNWTABLE II. High wil2d period information.20Bigh MaximumWind Photograph Direction Duration Sustained GustDate Date VelocityHO UPS 4?PH MPHMay NONEJune 18 WNW 11 21 25 WNWJuly NONEAugust NONE• August 1• August 15August_28Sept. 25—26 W—WNW 12 35 51 WNWSept._26Oct. 3—4 V W—WNW 27 26 37 WNWOct. 10Oct.20 W 13 20 31WOct. 22 VOct. 28—29 . WNW—NW 26 20 33 NWNov. 12Nov. 20—21 . W—WNW 24 20 30 WNov. 24Nov. 25 W .13. 25 36 WV Nov.26Dec. 17 V W—WNW 9 22 37 SDec. 18 E—SE 6 20 31 ESEDec. 21—22 W—NW 27 27 55 WDec. 27 W—NW 11 4 34 WNWDec. 29 SE 5 23 36 SE1975 V VJan.2 SE 4 25 42SEJan. 4 V W—WNW 12 -25 42 WNWJan. 8-9 WSW—WNW 24 23 50 NWJan. 10VJan. 20 W—WNW 12 27 39 WJan. 25 W—WNW 18 22 28 WNWJan.31 E 18 33EFeb. 4Feb.10 W 7 25 38WFeb. 16Feb. 19-20 WNW 26 37 57 WNWV March 18March 24 WNW 10 21 30 WNWMarch 25 WNW .14 28 42 WNWMarch 25March 30 V V 24 38 67 WNWMarch_31April 19 W—WNW 15 29 39 WNWApr. 27—28 W—WNW 22 29 45 WNWTABLE II continued,21By further examining the wind parameters given inTable II during only peak extreme conditions cyclic or annualmeteorological patterns might be determined. This informationis correlated in Figure 28 for conditions of wind durationsin excess of 20 hours, maximum sustained velocities above 24miles per hour, and gusts of at least 35 miles per hour. Fromthis evidence cyclic patterns are apparent. Figure 28 alsoincludes certain representative erosion—deposition patterns atselect locations on Wreck Beach for the periods shown. Theerosion—deposition information is derived from Figures 25, 26and 27.The duration, maximum sustained velocity and gustscriteria suggests that distinct phases occur. Well—definedsummer periods commenced about the month of May. Correspondingly, winter phases evolved around October to November. Ingeneral, an average annual cycle for the Wreck Beach areawould include a summer period from June to October, and awinter period from November to May.The 1973 summer 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 duration and velocity.In the following 1974-75 winter phase winds from the east werethe exception and were also the winds of shortest durations 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 V forthis 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 rose reveals 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 a longshore transport system largely restrictedto movement toward the northeast.CHAPTER IVWAVE CONDITIONS4.1 DETERMINATION OF EFFECTIVE FETCHESWaves approaching the Point Grey headlands are the mostimportant and persistent forces taking part in the beach fore-shore activities. The nature of a particular wave field is aresult of the interrelated characteristics of the wind regimegenerating the wave field and the physical shape of the areaover which the wind and resulting waves move. Wind directions, durations, and velocities are restricted and limitedby the surrounding landforms.In order for these potential winds to produce wave fieldsthat are self—sustaining (i.e. waves are removing energy equalto that introduced by the wind) a minimum sized body of water(fetch) must be available over which the wind action can operate.Under conditions of this sort wave fields acting on Wreck Beachare “fetch—limited”; in which case wave dimensions depend uponfetch 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. Winds from the north produce wavefields of very small dimensions due to the extremely restrictedfetch areas and rare periods of high velocity winds from thatdirection. Therefore, winds from the westerly directions, SWthrough NW, have the larger fetch-generation areas. In addition as discussed in Chapter III, wind conditions for the headlands area are such that predominating high-velocity winterwinds blow out of the west and northwest as opposed to smallerwinds prevailing out of the south and southeast during thesummer.Fetch dimensions for five westerly wind directions arederived in Figures 3 through 7 and include the associated computations and graphic procedures. This method of “effectivefetch computation for irregular shorelines” is outlined in the1973 “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 completely absorbed by shorelines.The larger fetch distances occur in the range between WSWthrough WNW as would be expected from visual estimations oncharts. More specifically, a first observation would indicatethat the due west direction has by far the greatest fetch whentaken as a point to point measurement (i.e. the greatest unobstructed straight line distance from Point Grey westward.)However, the WSW direction has a greater fetch dimension whichis due to the wind acting as a field over the fetch area ratherthan as a point source. The method for “effective fetch computation for irregular shorelines” takes this phenomenon into consideration and is a closer approximation to the true physicalsituation.NWWINDDIRECTIONi4a( 42 36 30 24 18 12 6 0 6 12 18 24 30 36 42Coscc.743.809.866.914.951.978.9951.000.995.978.951.914.866.809.74313.512xi 8.9 15.016.912.310.1.5.12.22.02.01.92.12.32.3 1.61.1X1Cos”<6.6112.1414.6411.249614.992.192.001.991 •862.002.101.991.290.8275.47001F=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\17SN 72Norihe.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:.-•:6.99.59.49.35-\/Lady.mkhN.961.66.4O‘.12.9787.67.43\\—....‘I3968PtR0b.rt1 866MI.Whympir2c-.....C]03636--F=ZXCos/.ZCos42.——=10.85‘/•i1,96=9.10cmCanadianHydrographicChart#3001where1cm=3.262milesFe=29,69statutemilesNaturalScale1:525,000CTotal11.960108.85FIGURE5.Westwinddirectioneffectivefetchdiagram.<Cosc’XjWSWWINDDIRECTION42 36 30 24 18 12 6 0 6 12 18 24 30 36 42Totals,743.809.866.914.951.978.9951•000.995.9789.2297910.917,116•511.3 9.49.17.36.465XjCoso<5.878.8214.8115.0810.759.199.057.306.376.3693,60CanadianHyd.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•07.5.545,396 .‘096.366.576.7048.37I7?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 12 6 0 6 12 18 24 30 36 42Total.743.809.866.914.951.978.9951.0007.2567.67.56.45.96.46.56.66.71W.)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,T0NauticalStatuteMilesMilesKnotsHourHoursFeetSecondsNW15.8318.221011.55.21.42.62023.03.53.54.03034.52.85.65.24046.02.57.86.05057.52.210.36.86069.02.013.07.5WNW23.3026.811011.57.01.62.72023.04.63.84.33034.53.76.45.54046.03.39.06.55057.52.912.07.46069.02.615.08.2WEST25.8029.691011.57.51.62.82023.05.24.14.43034.54.16.65.64046.03.59.56.65057.53.112.37.56069.02.715.68.5WSW28.7533.081011.58.51.72.82023.05.64.2.4.53034.54.57.05.8.4046.0.3.810.06.85057.53.413.07.76069.03.216.08.7SW18.9021.751011.56.01.52.72023.04.03.64.23034.53.36.05.34046.02.88.46.25057.52.511.07.06069.02.213.57.5TABLEIII.Wind,fetchanddeepwaterwavedata,34U)-Ii0Dr-oo,-4occ. C I i-ILfl,-4a)l C)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 0 0 0Q Lfl 0C., Cobc’1r.-ooc-1 at0DC V.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) 111111 111111 111111 311111 131111- a)C (Z4 Oti-1.D 0LflCr-f 0-ft OtCo t0C’4a) 4) . . . . .>04 atcqD -4Lnat Coc’lLnat )CoCNO0 NOV.Cd 0) 4 r - i-i i-f .-4 r-4 r- r-j 1-4 V.4 r4 ,-4 4bt:•1f)4 -Cd-.‘3tflOCoC’)0 VCoJ000 V.-V.40000 ‘D00CtCg r—oc’, J’D0tCNtf) 1•t—om’o cOi-fU bt i-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. 0at0CoOt 0c’4Cflt- N0C’i’DOCo-‘rc-.ooc’1ao ‘0F-c’)0Co C.tatOtLflcD04 a) C” C”U>UCdcCU>1 ‘f-P r•r4 0140 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:0iQ Cl)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 of 16.2 feet. Winds of thisvelocity and duration occur occasionally throughout the yearand 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#3480,1971NaturalScale1:50,0001cm=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.wLj ii-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#3480,1971NaturalScale1i50,0001cm0.31statute.miles=0.27nauticalmiles:wFIGURE9.WNWwinddirectionwaverefractiondiagram.II I>26IC.1.- ——g—:;.‘I>’%,2/—..:7IHI:234j:Iz\9(39)\—-r-•7T”Os3 2_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//,• 75 9CanadianHydrographicChart#3480,1971NaturalScale1:50,0001cm=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‘(w1i691 i’4WSWWINDDIRECTIONWAVEREFRACTIONDIAGRAMHoTo 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= =50,0000.00815S/To212wavelengths0.00815S/To70seconds7.89:_____________nJ/CanadianHydrographicChart#3480,1971NaturalScale1:50,0001cm=0.31statutemiles0.27nauticalmiles..‘Ij.•L.——I\‘-.-1’‘Ii,:II.CFIGURE11.WSWwinddirectionwaverefractiondiagram.,“6/‘KI,.‘•c:,/27 L_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*50,0001cm0.31statutemiles=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 THE WEST SECTORWaves from the west sector are most important in erosionand have considerable longshore transport components. Convergingwaves tend to strike the west beach straight on. But in theTowers Beach area the waves begin a diverging pattern whichcontinues to the NE.Typically high winter waves out of the west sectorapproach Wreck Beach at an angle across the wide shallow offshore sandbank. The waves are refracted and shoaled by thetopography such that the breaking of any one wave crest on theupper beach area will be progressively delayed toward the easterly end of the area. For example, Figure 13 shows a wavebreaking at the outfall location that is still 5 to 7 wavelengths seaward of the beach breaking area near the easttower. Longshore drift from these waves is toward the NE andis most effective from the west tower eastward.Fetches from the WSW through WNW directions are considerably 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 NE longshore transportwaves breaking at an angle to Wreck Beach.WNWTowers Beacharchphotograph- 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 occurred on March25, 1975. Winds of 28 knots from the WNW with gusts of 39 milesper hour blew for several hours. Figure 13 of March 25, 1975photographs show the physical appearance of the wave field onWreck Beach. Tidal elevation at the time of the photographswas 13.7 feet (2.5 feet below Refraction Diagram datum). Thedeep water wave dimensions from this storm can be predicted asgiven in Table III. But it is useful to 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 is H=HOKSKR.The H0 is related to wind velocity and fetch as listedin Table III.The shoaling coefficient, K5, represents the effect of achange 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. TheKs values were derived from common tables which are available inthe 1973 “Shore Protection Manual” of the U.S. Corps of ArmyEngineers, Volume III. These values and corresponding water depthsare listed on Figure 14 in the Refraction Diagram Information Block.The K5 values for the March 25, 1975 storm are shown at variouslocations on the refraction diagram.The shoaling coefficient, KR, is related to the winddirection and reflects the change in height and direction of awave moving over the underwater contours at an angle causing thewave energy to either converge or to diverge. In practice the KRvalue is determined by the square root of the ratio of the deepwater orthogonal spacing to the orthogonal spacing at the48shallow water depth desired; the spacings are measured directlyfrom the refraction diagrams. The KR values 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 water depth contour andare derived from the tables available in the 1973 “ShoreProtection Manual”. The L values for the March 25, 1975 stormare shown at various locations around Wreck Beach on therefraction diagram.The altered wave heights resulting in the March 25,1975 incoming storm waves seen in the Wreck Beach photographsof Figure 13 are shown on the refraction diagram of Figure 14at various locations.Sand volumes moved by the wind period are 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= HOKSKR and shown onthe refraction diagram)CHAPTER VSAND MOVEMENT5.1 LIMITS OF THE LITTORAL ZONESFrom fetch and weather considerations the littoral transport system must presently originate at the Point Grey headlands and move downcurrent towards Spanish Banks. Clearlywaves are the most effective and important agent acting to movesediment in the nearshore region of Wreck Beach. Their abilityto transport material is closely related to their height, period,and direction of approach to the beach. Waves approach WreckBeach shoreline across the shallow submerged sandbank, extendingabout a mile offshore at an average slope of 0.1 percent to adepth of 5 fathoms along the outer rim. At that point theslope increases suddenly dropping off quickly into the Straitof Georgia depths.Waves first feel the bàttom effectively when the waterdepth is equal to half the wave length, but it is not untilthe depth is much shallower that any appreciable amount of sandis transported. The transport of sand along Wreck Beach takesplace primarily in two zones: the swash zone and the surf zone.Beach—drifting occurs along the upper limit of wave action andis related to the swash and backwash of waves. Its action ismost effective when waves approach at a considerable angle to5051the shore. The other major zone of the longshore movementis in the surf and breaker zone. Here the largest quantityof material is moved, part in suspension and part along thebed, and sand can be moved by relatively weak 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 breaking point, is the pointwhere foam first appears on the wave crest. The breakingpoint is an intermediate point in the breaking process betweenthe first stages of instability and the area of completebreaking. That waves do not break in deep water in this area isdue to wave dimension limitations imposed by the restrictedfetch generation areas.In shallow water regions the breaking point is identified in terms of the breaking depth, db, the water depth below still water level at which breaking is initiated; and thebreaking height, Hb, the crest to trough dimension when breaking is initiated. At the breaking point a longshore currentdirection and velocity is established which is sensitive toboth crest angle and wave height. Listed in Table III are wavebreaking depths and heights for the range of wind and unrefractedwave regimes noted. These values were interpolated from thedimensionless breaking wave curves contained in the 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 of Breaker Zone Volume TransportedVelocity Height Depth Range ofU TMb db Breaker West Tower’s East 1973—74 1974—75Zone Beach Beach EndFeet Feet Feet Feet Feet Feet c.y/year c.y/yearAPeakExtreme 5.1 6.5— 8.0 12 2300 2200 2500 6,150 10,581WindsBGeneralHigh 3.8 4.8— 6.0 10 2000 2000 2300 12,023 17,507WindsCOther 1.6 2.0— 2.5 6 1000 1300 2000 17,759 16,717WindsData for determining deep end depth of Elevation Range:Chart Datum: “The Canadian Hydrographic Service has adopted theplane of lowest normal tides as Chart Datum”.(p. 4 Canadian Tide and Current Tables)Chart 13481: Average Tides Mean Water Level Large TidesHHW LLW HHW LLW14.4’ 4.1’ 10.1’ 16.2’ 0.3’Contour datum on Chart 43481:16.0’— .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 determining deep end depth of ElevationRange is 3.8 feet depth (0.63 fathoms) plus db.TABLE IV. Limits of the Wreck Beach littoral zones.54Wave requirements to move sand at the outer edge of thesand bank, 26 feet below low low water, into the longshoretransport system necessitate a generating 2—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 36 to40 knots do occur on occasion. During the period covered bythe information contained in Table II such winds occurred onFebruary 19 and 20, 1975 and on March 30, 1975. Both windswere from the WNW direction, each had at least 3 hours of sustained 37 to 38 knot velocities, and the duration of theirentire storms covered two complete tidal cycles. Tidal cyclesfor each covered ranges of about 3 to 14 feet. It is likelythat waves generated from these winds moved sands at depths10 to 15 feet below normal lower low water (near the 2.5 fathomcontour line on a Canadian HydrOgraPhiC chart such as Figure 31)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. Photograph sequence at photograph location 1,East End, prior to construction activities.November 18,I—4July 19, 1973March 2, 197457FIGURE l6. Photograph sequence at photograph locations1 & 2, East End, following construction activities.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 photograph location 6,Towers Beach, prior to construction activities,60---FIGURE 18, Photograph sequence. at photograph. location 6,Towers Beach, following construction activities.August 19. (97A-I61‘.,. ‘—.-— :FIGURE 19. Photograph sequence at photograph location 10,West Beach groin, following construction activities.jFebruary 4, 1975 1975. --—9• 2F62FIGtJR 20. Photograph sequence at photograph location 13,West Beach, following construction activities.Auqust 15. 1974-February 4, 1975Auqust 28, 1974 February 16, 1975September 26, 1974November 26. 1974August 28. 1974September 26 1974March 31. 197563May 12, 1975FIGURE 21 Photöraph sequence at photógrap? location 18,West Beach, following construction activities.-.- —(--:1.-—--—- -March (8, (975October (0, 1974August 15. 1974 February 10. 197564FIGURE 22. Photbgraph sequence at photograph location 19,Towers Beach, following construction 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 the date of the highwind periods listed in Table II.FIGURE23.Chartofphotographsequencespriortoconstructionactivities.-JDATE.%cc39’IC...•+‘H1n•-•±.I...WestTowerfjr:‘—1IUpperSeahFaet.:.:::.::I:flIIWestBeach:.UpperGroiEnd::1.—.1!— —-I,.I————————II-PHOTOGRAPHLOCATIONEasFEndUpperBeocI1—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 of Figures 25, 26 and 27 are compiled fromthe photographic summaries charted in Figures 23 and 24 andfrom corresponding information derived from cross—sectioningdata. The S, -, and + symbols represent the activity of thebeach at that location during that particular 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 beach cyclesat several sections of the beach. These cycles are derivedfrom the correlation of annual peak extreme wind periods withbeach deposition—erosion patterns evident from Figures 25, 26, 27.Selection criteria for peak extreme wind periods is outlined inSection 3.2 of Chapter III.I•rJH 0 tn0w‘1aCDCCD:,:‘P’Pp0 C0 C,—4..•0.•.U,,3’-iE.•.4 ‘6L4-perBa.c.h.-Ei.4 EotEastEastIit.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 pJ C) J. (n CD ri CD II CD a3’ -4 rn:4-SondUppe-H-—4--—rBea-r HEE+4---H--i444.•.I.h.!EastWestWestWestTower(.TowerToweBeocLLt LI-I•-- H.LU 4-±.H-ti4LL..1..SonF--f-1Uppbar><—-rBec‘-+4+.4.it.-. jEtL4:1:1T4’. 4—i-----0t4zrJ4±.r:r;NTEl4..L!.WestIIrt-T.it+L I-[1H-Li---4------4--i---+±.-t-4.-tm 3’ C-)= 3’ C-)-4-4-<3tSM1 Ii_I__!__[.ELDUFER:th7NGAT/ER:4f-J-’.14-J-H!H•..,4 I-.4.4-i--4-4-4--H-4--4.L4.4..1.4-...oc.:i:;:-F:;::4jL9/-1cRA4jJzt44.tFl:1i••.SL fir-DLRT•,CI4.LLLL.i_LR—4-;slj.L.CiJR-—I_I.’.GE4TI-C±ii:.:t±tri:t. ittl-tSHRTb---rrNSIOQ30oc(DC 3’ -4 0 zEL.) CII E4VL.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 ON THE WEST BEACHSand movement on the west beach is directly influencedby both velocity and duration considerations. There appears tobe certain minimum duration requirements over a range of suitably high wind velocities needed for the seasonal transitionfrom onshore movement of sand to offshore movement. Highwinds of long duration are necessary to move the west beachsand into the offshore sand bar configuration typical of beachareas exposed to waves approaching at little or no angle.Waves necessary to accomplish this must retain enough energy orsand—carrying capacity during the downslope backrush to consistently move sand seaward into the offshore bars. High windperiods of at least 23 miles per hour maximum sustained velocities (Refer to Chapter III, Section 3.2 for definitioncriteria) with miiiimum 24 hour durations appear to be thenecessary conditions for the west beach to be in its winter offshore bar configuration. Periodic higher velocity wind 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 with minimum deepwater wave heights of 4.1 feet and periods of 4.4 seconds. Conditions are appropriate from November through May for offshorebar building on the west beach. The remaining part of theyear durations and velocities are lower and sand moves inshoreand up the beach face.76At the extreme higher end of the beach the protectivebeach fill was eroded and removed seaward throughout the yearwith the exception of the March 25 to 31, 1975 period. OnMarch 30, 1975 occurred the highest winds on record for tenyears as given in Table II. These waves, approaching from theWNW, were of such size as to throw large sand and pea gravelup onto the upper beach in berm-building action. As a resultthis storm refaced the extreme upper side of the entire westbeach with sand and gravel. Following the storm this bermmaterial proceeded to be removed also.775.4 SAND MOVEMENT ON THE TOWERS BEACH AND EAST ENDThe west tower marks a dramatic alteration from the westbeach alignment and exposure (Refer to Figure 1 for WreckBeach configuration). Here the upper shoreline and cliffmakes a sharp turn, forming an angle with incoming wave attack,and a corner is exposed to wave forces. As can be seen fromthe refraction diagrams in Figures 8 through 12 wave crestsfrom the westerly directions begin an accelerated bending toward an alignment with the upper shoreline along the lengthof this section of Wreck Beach. As a result wave energiestend to converge and concentrate at the west tower corner,thereby increasing their erosive powers. Downcurrent thoughtoward the east wave energies spread as indicated by the diverging orthogonals on the refraction diagrams.Like the west beach the protective berm fill continuallyeroded through the year except for the refacing during theMarch 30, 1975 storm. Near the west tower erosion of the protective fill commenced immediately following construction andcontinued during the summer period. With the transition intohigher velocity and longer duration winter winds erosion proceeded faster at the west tower and commenced in the 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(.111LTTjFLirfl-TrI_LIIlEASTTOWERUPPERBEACH1973-741’ I’EASTENDUPPERBEACH1973-74rI\FIGURE29.Annualsandbarmovement.CHAPTER VI$ UMMARY6.1 CALCULATION OF VOLUMES CAPABLE OF BEING MOVEDBY WRECK BEACH LONGSHORE TRANSPORT SYSTEMThe volume of sand capable of being moved if availableby the Wreck Beach longshore transport system is dependent uponthe size of wave attack, frequency, duration, angle of approach,sediment characteristics and beach slope. Correlations of theseparameters have been determined by Castanho. Any calculations ofthe amounts of littoral drift are subject to a large uncertaintyand few methods are available which are suitable to the WreckBeach study area. Castanho’s calculations have not been widelypublished or tested but are suitably applicable to the study areaand are likely good to within a factor of 2. Wreck Beach fitswell into the typical characteristics suggested by Castanho inthe use of the sandy shores equation. Some valuable conclusionscan be made about sand transport on Wreck Beach even though aprecise 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 Castanho equationsuggested for sandy shores estimates of longshore transportvolumes were determined for the annual summer—winter cycles of81821973—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.DIRECTIONAL HOURLY WIND FREQUENCIESWIND - A B CDFREQ Annual Annual Annual AnnualAverageWIND\ 1973—74 1974—75 1973—74 1974—75 1973—74 1974—75 YearlyDIRECT\.. % hr % hr % hr % hr % hr % hrhrNE — — — — — — — — 5.0 438 5.0 438 5.0 438NNE — — — — — — — — 1.0 88 1.0 88 1.088N — — — — — — — — 1.0 88 1.0 88 1.0 88NNW — — — — — — — — 1.0 88 1.0 88 1.0 88NW — — — — 0.5 47 — — 4.0 350 3.5 303 4.0 350WNW 0.9 81 2.2 192 0.5 44 1.0 89 4.6 401 2.8 244 6.0 526N 0.7 57 0.7 64 0.4 33 0.2 13 8.0 698 8.1 711 9.0 788wsw — — — — — — — — 4.0 350 4.0 350 4.0 350SW — — — — — — — — 3.5 307 3.5 307 3.5 307DIRECTIONAL HOURLY WIND FREQUENCIESWIND A B CFREQUENCY Freshet Freshet FreshetWIND 1973 1974 1973 1974 1973 1974DIRECTION, % hr % hr % hr % hr % hr % hrNE -: -----------NNE - - - - - - - - - - -N - - - - - - - - - - - -NNW - - - - - - - - - - - -NW — — — — 0.2 13 0.1 1 0.7 57 0.2 19WNW 0.1 8 — — 0.5 41 0.4 37 1.2 103 1.5 129W 0.1 3 — — 0.3 22 0.1 8 0.5 47 0.7 59wSw — — — — 0.1 4 — — 0.5 40 0.5 41SW — — — — 0.1 6 — — 0.3 23 0.2 16TABLE V. Directional hourly wind frequencies.I•rJ H w 0 p) 0 0 CD II H r1 CD 3 rt I-i. 0 I-J.II 0 rt CD CD p) Ii Fl 0 cn CDco85Volumes according to wind velocities or wind strengthshave been derived by grouping winds of all direction 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 Wind Periods, 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. Included arewinds 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 blowing times between groupsA,B and C is as follows:- of the wind periods included in Group A, 25 percentof the blowing time was spent near the 25 knot velocity, 75percent of the time was spent at lower velocities so addedinto Group B;- of the wind periods included in Group B, 75 percentof the blowing time was spent near the 20 knot velocity, 25percent of the time was spent at lower velocities so addedinto Group C.Winds during the months of the Fraser River freshet,mid-May through mid-July, are distributed into the A,B, and Cgroups also and derived from daily meteorological recordsmonitored at the Vancouver International Airport by CanadaAtmospheric Environment Service.Typical wave characteristics for these groups are theaveraged values given in Table III.87Group A. Peak Extreme Wind Periods:Average maximum sustained velocity = 28 mph = 25 knotsH0 = 5.1 feetT0 = 4.9 secondsL0 = 123 feetGroup B. General High Wind Periods:Average maximum sustained velocity = 22 mph = 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 sustained velocity = 11.5 mph = 10 knotsAverage fetch = 6.5 milesH0 = 1.0 feetT0 = 2.2 secondsL0 = 25 feet88Examples in the uses of Tables VI, VII and VIII.Example 1.What total volume of sand was transported by waves generatedby winds from the west during the 1974-75 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)(Table VIII)(Table VI)(Table VIII)(Table VI)(Table VIII)(Table VII)During the year 1974-75 winds of all velocities from thewest moved a total of 16,908cy toward the NE.During the freshet period of that year these winds moved2031cy of the total 16908cy in the same direction. That is,12% of the yearly volume transported by winds from the westcould have moved during freshet.Winds from the west did not contribute to movement of sandin the opposite direction (see Table VII).= 3477cy0 cy= 4907cy1280 cy8524cy751cy= Ocy2031cy 16908cy89Example 2.What volume of sand was transported by waves generated by25 knot winds during the 1973-74 year?Winds of 25 knot velocities are included in Group A.NE movement by Group A winds = 6150cy (Table VI)includes freshet volume of 2567cy (Table VIII)SW movement by Group A winds = 0 cy (Table VII)2567cy 6l5OcyDuring the year 1973-74 waves from winds of 25 knot velocitiestransported a total of 6150 cy of sand, all of it toward the NE.No 25 knot winds occurred which were effective in moving sandin the opposite direction. (All sand transported toward the SWwas accomplished by waves from winds of Group D (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 would waves from a 10 hour WNW wind of20 knot velocity be capable of moving on Wreck Beach?In what zone of the beach would this movement likely takeplace?A 20 knot velocity wind is included in Group B winds.From Table VI WNW winds of Group B have an Hourly TransportRate of 1944 cubic feet per hour. During a 10 hour period19,440 cubic feet (720 cubic yards) of sand could be transportedtoward the NE. Table VII indicates that WNW winds are noteffective in moving sand in the opposite direction.From Table IV movement of sand by these waves takes placein water depths of up to 10 feet. A 10 hour period coversalmost an entire tidal cycle. If it coincides with a largetide then sand would be moving as far seaward of the cliffbase as 2000 to 2300 feet which would be near the 2 fathomcontour line on a Canadian Hydrographic Chart (see Figure 31).91Example 4.How often do winds blow out of the NE that are capable oftransporting sand on Wreck Beach?From Table VII winds from the NE direction are effectiveonly in moving sand toward the SW. These winds are of Group Dhaving an average velocity of 10 knots. (Higher velocity windsof Groups C,B and A do not occur with respect to Wreck Beachcalculations) . These winds occur approximately 438 hours peryear, 18¼ total days, and could contribute 503 cy to the SWlittoral drift. (NE winds do not contribute to movement ofsand in the opposite direction, see Table 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 transport estimates predictthat typically volumes of 40,000 cubic yards ± 20,000 cubicyards (see Table VI) are transported to the NE annually pasta plane that could be extended perpendicular to the beachshoreline. Because of the uncertainties associated withsediment transport problems particularly coastal situationsa fairly large error is assigned to the estimates. An indication of the scatter of data from field tests and laboratorytests in the range of a general solution is outlined by Sil—vester, “Coastal Engineering”, Volume II, Chapter 1. Thevolumes computed from the Castanho calculations should beconsidered no more accurate than to be within a factor of 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 mostly to the intertidalexposure areas. This minor amount of sand constitutes only3 to 4 percent of the total volume transported annually. Thisquantity is roughly equivalent to a 5 yard truck moving southwest along the beach once a day, while transport to the northeast is approximated by a 5 yard truck moving along the beachin that direction once every hour.Throughout the year information presented in Table VIsuggests that winds of Group C with velocities from 8 to 16miles per hour move some 17,000 cubic yards of sand annuallyor 40 to 50 percent of the total volume transported. These low96velocity winds occupy the greatest portion, 90 percent, of thewind frequency blowing times under consideration. These windsapparently are responsible for a sizable and constant yearlymovement of sand in the Wreck Beach longshore transport system.That is, about one-half of the sand volume carried by theaforementioned 5 yard truck moving northeast each hour isproduced by 16 mile per hour winds and under.On the other hand, when the high winds of Groups A and Bdo occur large volumes are moved in brief time intervals:compare in Table VI the average rate of 170 cubic yards perhour for A winds with 75 and 8 cubic yards per hour for B andC winds respectively. As indicatedin Table IV the width andextent of the zone in which sand is actively moved by wavesgenerated from winds of Groups A and B ranges up to twice asfar seaward and in depth as the active zone produced by lowvelocity winds of Group C.Using the derived Hourly Transport Rates presented inTable VI sand volumes moved during individual storms can beestimated. From Table II four high wind periods were selectedwith two of these having extremely high winds.Hourly directions and velocities were taken from meteoro—logical records monitored hourly at the Vancouver InternationalAirport. Rough estimates of the volumes moved toward the NE97during these periods and the longshore current velocitiesgenerated at the wave breaking point are 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, 1975 and the March 30, 1975 stormshad several hours of 35 to 40 mile per hour WNW winds withthe associated longshore transport velocities given in Table III.The January 8-9, 1975 and March 25, 1975 storms had lower continuous WNW winds of about 25 miles per hour. Other informationassociated with the March 25, 1975 storm 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 headlands marks theupstream beginning of a transport system which evidently continues well into Burrard Inlet via the shoreline. As such thesandbank extending from the northern bank of the North Armmouth is an area of considerable activity where Fraser Riversand is absorbed into the system at the outer limits of thetransport zone.The Fraser River freshet reaches a maximum from mid—Maythrough mid—July. During this short time a great deal ofmaterial is added to the sediment budget of the area. Theseevents coincide briefly but provide a mechanism for movingsediment available during its most abundant period from theriver channel onto the Wreck Beach offshore sandbanks. ThePublic Works dredging records for the past ten years is contained in Table IX. The dredging records and theoretical volumes are courtesy of Mr. Woo, Department of Public Works, Vancouver, British Columbia through personal telephone communication in August, 1975.99FRASER RIVER NORTH ARM DREDGING RECORDSAnnual Volumes Entering the North Arm:(Average theoretical volume)Bed load-material within 8 inches of bottom:sands and gravels = 90,000 cy.Suspended load—material above 8 inches ofbottom and larger than 0.065 mm.:sands and gravels = 240,000 cy.Wash load-material 0.065 mm. 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 Volumes DredgedCubic Yards1964 1965 33,6001965 1966 164,0001966 1967 354,0001967 1968 416,0001968 1969 286,0001969 1970 347,0001970 1971 142,3001971 1972 397,1001972 1973 211,0001973 1974 196,0001974 1975 93,300 (incomplete)Average volume dredged:sands and gravels Total = 240,000 cy.TABLE IX. Fraser River North Arm dredging records100The North Arm mouth is dredged each year immediatelyfollowing freshet to maintain an open navigation channel up todepths of 20 feet below lower low water. Some 1,330,000 cubicyards 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 and gravelvolume less the dredged quantity. The silts and clays are washedquickly seaward and do not contribute significantly to the headlands 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 sand would be availableto wave transport activities and subsequent introduction into theWreck 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 sand and 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.1 CD 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)—‘Co oQJ.)1_ac4\Qom%I•11111_a\OOooaa‘-)‘-‘)OC)(DCD0(DCDOç+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 BEACH CLIFFS AS A SAND SOURCEIf, as Waslenchuk suggests and longshore transport calculations indicate, the Fraser River is not presently the onlymajor source of sand supply to the longshore transport systemin the Wreck Beach area then the headlands themselves must besupplying a large portion of the sediment to maintain thesystem. In the area of most active erosion, just below the newMuseum of Man, 1200 feet of near-vertical cliffs 200 feet highare estimated to be receding at about one foot per year. Atthis rate 8900 cubic yards annually (1 cubic yard per hour) ofsediment is supplied from this area alone. If the remaining2200 feet of eroding and susceptible cliff face along WreckBeach is receding at a much slower rate of one—half foot peryear then an additional 8200 cubic yards (about 1 cubic yard perhour) also becomes available annually. Under these conditionsthe cliffs appear to be supplying a volume of about 17,000cubic yards of sand each year to the longshore transport 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 the following 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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