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UBC Theses and Dissertations

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

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SAND SOURCES, VOLUMES AND MOVEMENT PATTERNS ON WRECK BEACH, VANCOUVER, BRITISH COLUMBIA by MERIDITH INES POOL B.Sc. University of Oklahoma, U.S.A., 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the Department of Civil Engineering We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1975 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written pemiission. Department of t/ The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1WS Date /7 /975 / ABSTRACT Along Wreck Beach the existing headland cliffs are eroding and 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 1974 to halt wave erosion along the cliff base. A rock groin and sand—gravel protective beach scheme was only partially success ful during the following year. To design an adequate protection system for the cliffs wind and wave effects need to be deter mined to fully understand the resulting sand movement patterns. Understanding the processes affecting Wreck Beach is the first step in controlling them. Methods used to investigate sand movement included field coverage of the study area in photographic form as well as instrument cross—sectioning over a two year period. These data were correlated with historical wind records and predictions from wave refraction diagrams to determine seasonal movement onto and off the beach face and the cyclic progression of sandbars in the longshore current direction. Annual sand trans port volumes, sand supply sources and amounts contributed are outlined. ii In designing a protection scheme in which longshore trans port requirements must be considered the information and calcu lations suggests that the Fraser River North Arm could amply provide the longshore transport supply requirements. However, some means in addition to the present natural processes must be available to bring this sand into a range where wind gen erated wave activity can incorporate it into the existing Wreck Beach system. iii TABLE OF CONTENTS ABSTRACT TABLE OF CONTENTS . LIST OF FIGURES LIST OF TABLES ACKNOWLEDGEMENT Page ii iv vi vii ix CHAPTER I INTRODUCTION 1 CHAPTER II RECENT HISTORY OF EROSION 5 2.1 Geology . 2.2 Erosion Mechanisms 2.3 Remedial Measures . . CHAPTER III WIND CONDITIONS 13 3.1 General Wind Patterns 3.2 Annual Meteorological and Beach Cycles 3.3 Wind Directions of Primary Importance CHAPTER IV WAVE CONDITIONS • • . 13 • . • . 16 • • • . 22 24 4.1 4.2 4.3 4.4 4.5 4.6 CHAPTER V 5.1 5.2 5.3 24 32 42 43 44 46 50 50 55 75 77 78 5710 Determination of Effective Fetches Refraction Diagrams Waves from SW Sector Waves from NW Sector Waves from West Sector Waves from March 25, 1975 High Winds SAND MOVEMENT Limits of the Littoral Zones . • . . Compilation of Data Sand Movement on the West Beach . . . 5.4 Sand Movement on the Tower Beach and East End 5.5 Sandbar Movement iv Page CHAPTER VI SUMMARY 81 6.1 Calculation of Volumes Capable of Being Moved by Wreck Beach Longshore Transport System . . 81 6.2 Fraser River North Arm as a Sand Source . . . 98 6.3 Wreck Beach Cliffs as a Sand Source 104 6.4 Conclusions . 105 BIBLIOGRAPHY 106 V LIST OF TABLES NUMBER TABLE PAGE I Wind scales and sea descriptions 17 II High wind period information 19 III Wind, fetch and deep water wave data 33 IV Limits of the Wreck Beach littoral zones 53 V Directional hourly wind frequencies 83 VI Annual longshore transport volume toward the NE 92 VII Annual longshore transport volume toward the SW 93 VIII Freshet longshore transport volume toward the NE 94 IX Fraser River North Arm dredging records 99 vi LIST OF FIGURES NUMBER FIGURE PAGE 1 Wreck Beach study area map 4 2a Regional surface wind patterns of the northeastPacificOcean 15 2b Local surface wind patterns of the Strait of Georgia 15 3 NW wind direction effective fetch diagram 27 4 WNW wind direction effective fetch diagram 28 5 West wind direction effective fetch diagram 29 6 WSW wind direction effective fetch diagram 30 7 SW wind direction effective fetch diagram 31 8 NW wind direction wave refraction diagram 37 9 WNW wind direction wave refraction diagram 38 10 West wind direction wave refraction diagram 39 11 WSW wind direction wave refraction diagram 40 12 SW wind direction wave refraction diagram 41 13 Photograph sequence showing NE longshore transport waves breaking at an angle to Wreck Beach . 45 * ., + ? 14 Enlarged WNW wave refraction diagram pàket 15 Photograph sequence at photograph location 1, East End, prior to construction activities . 56 16 Photograph sequence at photograph locations 1 & 2, East End, following construction activities 57 vii NUMBER FIGURE PAGE 17 Photograph sequence at photograph location 6, Towers Beach, prior to construction activities... 59 18 Photograph sequence at photograph location 6, Towers Beach, following construction activities.. 60 19 Photograph sequence at photograph location 10, West Beach groin, following construction act 61 20 Photograph sequence at photograph location 13, West Beach, following construction activities.... 62 21 Photograph sequence at photograph location 18, West Beach, following construction activities..., 63 22 Photograph sequence at photograph location 19, Towers Beach, following construction activities.. 64 23 Chart of photograph sequences prior to construction activities . 67 24 Chart of photograph sequences following constructionactivities ...... 68 25 Chart correlating photograph information with cross—sectioning data on upper beach face 70 26 Chart correlating photograph information with cross—sectioning data at groins 71 27 Chart correlating photograph information with cross-sectioning data on sandbars 72 28 Annual Wreck Beach summer-winter beach cycle 74 29 Annualsandbarmovernent 80 30 Vancouver International Airport ten year qind rose 84 31 Fraser River North Arm and Wreck Beach area soundings chart 102 viii ACKNOWLEDGEMENT The author is very grateful to her supervisor, Dr. Peter R.B. Ward, for his guidance and encouragement during this study. The author is also grateful for the help and assistance received from Vancouver Board of Parks and Recreation and from Swan—Wooster Engineering Company Limited. This study was supported financially by a National Research Council grant to Dr. Ward. ix CHAPTER I U’TRODUCTION This thesis describes a study of erosion and sand move ment patterns on the Wreck Beach section of beach below the Point Grey headlands in Vancouver, British Columbia. Point Grey occupies the tip of Burrard Peninsula projecting into the Strait of Georgia. Wreck Beach is located just below the old Fort Camp military base on University of British Columbia Endowment Lands. Figure 1 shows the map of the Wreck Beach study area. This beach is under the jurisdiction of the Van couver Board of Parks and Public Recreation. Along Wreck Beach the headland cliffs are receding rapid ly under attack from terrestrial and marine erosion agents. At this time there is considerable concern for the buildings and structures within a few hundred feet of the cliff brim such as the new Museum of Anthropology with a 1973 contract price of $3,070,000.00 not to exceed $4,297,000.00 and Cecil Green Park purchased by the University in 1964 for $100,000.00. Remedial measures for cliff stabilization were proposed by Swan-Wooster Engineering Co. Ltd., 1973 and Robert Wiegel Consulting Engineer, 1973. Prime consideration was given to maintaining a natural beach appearance. In the summer of 1974 construction work was undertaken to implement some of these measures. 1 2The period of this study covers the year preceding con struction and the year following. The study considers the pro cesses of winds, waves and effects of waves on the cliff, beach and sand movement. To try and understand these processes and sources of sediment photographs were taken, wind records studied, wave patterns predicted and longshore transport vol umes calculated. Understanding these processes is the first step in controlling them. Chapter 2 describes the study area and reviews the geology and erosion mechanisms. A brief description of the remedial measures proposed and undertaken is outlined as well as comments concerning the success of the stabilization project. Chapter 3 describes the regional and local wind patterns affecting the Wreck Beach area. An abstract of high wind per iods during the study period is related to the erosion-deposi tion patterns derived from photographic evidence to determine the annual—summer winter cycles. Chapter 4 describes the wave conditions affecting Wreck Beach. Effective fetches are derived and wave refraction dia grams used to predict modified wave forces, longshore movement and erosion—deposition patterns. 3Chapter 5 describes the extent and direction of the long- shore transport system resulting from various wind and wave conditions, and describes the seasonal onshore—offshore move ment of sediment on Wreck Beach. Data from photographic records monitored during the study period are compiled in graphic form. Chapter 6 presents the conclusions of the study. Sand volumes capable of being transported JDy the longshore system are calculated. The sources of sand which supply the system are identified together with the relative magnitude of the volumes. The influence and extent of the Fraser River North Arm sediment with seasonal freshet effects are outlined. 4I WRECK -BEACH STUDY AREA —4’--.. Hydrographic contour linE 13 Photograph location and direction Map Scale: 1” = 330’ I / / / -I / I I 1 d I I I I I I I I I I I I I \ \ I // / / I.. ci \ I j 4 I I / I. I —— I / 7— / / \ \ \ I I I I’ /I I // 0 / I II \ \- I I I I I I I I I 1 ‘I FIGURE 1. Wreck Beach study aremap_ CHAPTER II RECENT HISTORY OF EROSION 2.1 GEOLOGY Eisbacher, 1973, Madsen, 1974, Backler, 1969, Carswell, 1955, and others have determined that geologically the Point Grey formation is a result of recurring glacial periods. The greatest contribution was laid down as river deposition during the last interglacial period, the Olympian Interglaciation between 50,000 and 25,000 years ago. Carbon-14 methods have dated peat from the cliffs at 25,000 years old according to Eisbacher, 1973. Rising 200 feet above sea level the cliffs are composed of alternating layers of sand, silt and clay sediments overlain by cross—bedded clean sands and gravel lenses. A 15 to 20 foot thick wave-worked gravel till layer was deposited by the last glaciation, the Fraser Glaciation between 20,000 and 15,000 years ago. Along the 3000 foot length of Wreck Beach erosion has exposed cliffs of unconsolidated sediments. These cliffs apparently have been receding since the last lowering of the sea level. Glaciated rocks ranging in size from cobbles to boulders litter the beach from the present cliff base to the outer slope of Spanish Banks. These rocks, originating in 5 6the till layer atop the cliff, have been deposited on the beach as underlying supporting soil was removed. Well-founded estimates as to the actual rate of recession are vague. Sur veys prior to 1937 do not exist for which control has been positively and accurately recovered or relocated. 72.2 EROSION MECHANISMS That these cliffs are presently highly unstable and easily degradeable is obvious from the general appearance of the area: slough and slide material collects as sand slump piles, clay blocks, toppled trees, tension cracks, the near vertical cliff face, and the absence of accumulated cliff material at the cliff base. The composition of the sea cliffs and characteristic pro perties as well as the erosion mechanisms have been thoroughly investigated, documented and explained by Carswell, 1955, Backler, 1960, Madsen, 1974, Waslenchuk, 1973, Lum, 1975, and McLean, 1975. The agents acting to erode the cliffs are the following: wave action at the cliff base; precipitation within and atop the cliffs; rain, wind, and people activity act directly on the cliff face to dislodge and move particles; and it is also suspected that earthquake activity in the past has served to destabilize the cliffs according to R.A. Spence Limited, 1967. Of these, wave action and precipitation are the most important erosion mechanisms. On Wreck Beach the cliff base is readily undercut by wave action especially during higher tides and onshore wind periods. McLean, 1975, found during 1974-75 that at times waves were capable of moving stones at least 0.03 ft.3 in size 8more than 100 feet eastward in the beach surf zone. At the same times stones 0.20 ft.3 and greater remained stationary. Wave action also removes accumulated toe material which other wise would eventually provide an undisturbed base for stabil izing the cliff at its natural angle of repose. An angle es timated by Piteau Gadsby McLeod Limited, 1972, to be a 30-35° slope with the horizontal. Precipitation, mostly as rain, aver ages 60 inches per year in the Burrard Inlet area. In the area draining to the Wreck Beach cliffs Carswell, 1955, determined that some 400 x io6 gallons of water (a net quantity: total precipitation in all forms less the amount lost through evap oration—transpiration) are available annually as erosion agents in the form of runoff and infiltration. Of that, an estimated 60 x 106 gallons per year infiltrate into the ground water system and eventually emerge from the cliff along seepage lines. Continued excavations into and below the surface till layer provide additional catchment basins where moisture can pond and move immediately into the groundwater system. Plant cover provides protection against surface runoff, sheetwash, and removes moisture by way of evapo—transpiration processes. With the development of the Endowment Lands forest and vegeta tion has been removed from the cliff top and slopes introducing additional water into the drainage basin and exposing unpro tected ground surfaces. Extrapolating from this estimate the 36” diameter storm drain from the drainage basin outfalls at sea level and carries some 300 x 106 gallons annually. Presumably 9the remaining 40 x io6 gallons is water directly available as surface runoff and pours over the cliff edge during the year. Gullying by surface runoff is an highly effective and rapid means of eroding the cliffs. Carswell, 1955, estimated that the present Campus Canyon was formed during a very short time by the washout of 100,000 cubic yards of cliff material during a 1935 flash flood. Temperatures seldom fall below freezing and rarely stay that 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 where it did occur, the thickness of the spalled slab was observed to vary between 3/8 inch to 1 inch. During severe winters with long periods of cold temperatures calculations indicate that retreats of 5 inches might be expected just by spalling. Fur ther, the freeze—thaw process was estimated to contribute from 1 percent to 6 percent of the total cliff material lost annually. 10 2.3 REMEDIAL MEASURES Since 1962 Swan-Wooster Engineering Co. Ltd. has been involved in the erosion problems and protection schemes at Wreck Beach. Retained by the Vancouver Board of Parks and Recreation in 1973, Swan—Wooster proposed a protective beach— groin system to stabilize the 3200 foot length of upper beach and 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. Modifications were made to meet the demands of the many public factions inter ested in Wreck Beach area. The final design accepted by the Provincial Government included a rubble—mound groin system with a 60 to 100 foot wide gravel core and coarse sand overlay protective beach built to above high tide levels at the cliff base, all to have as natural an appearance as possible. (For construction details see Dave McLean’s, 1975, thesis or Swan— Wooster Construction Plans, 1973). Construction Cartage con structed the system in the spring of 1974. Project cost was $350,000.00. The protective beach was to provide protection and sta bilization in a number of ways: an area of energy dissipation for incoming breaking waves, a substitute for cliff material as a supply source for the longshore drift process, it was built above high tide elevation so erosion material could 11 accumulate undisturbed at the toe and the cliffs could begin to stabilize at their natural angle of repose. The groin system was to help maintain the protective beach by trapping part of the material already in the littoral transport system, to retard the erosion of the existing beach and 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 to avoid abruptly offsetting the shore alignment which occurs with impermeable groins. Theoretically the permeable groin permits part of the longshore forces and materials to pass through the structure which triggers deposition on both sides of the groin. An exception to the permeable groin concept was the extension of the existing storm drain outfall -- a solid 36 inch diameter concrete conduit which serves as an impermeable groin at that location. In addition certain measures have been suggested which would halt or retard cliff erosion from above and within. These suggestions as urged by Swan—Wooster, 1973, as well as by Wiegel, 1973, Backler, 1960, Carswell, 1955, Bain, 1970, and others included: storm drainage away from the cliffs, not to ward or along it; drains or wells to intercept subsurface drainage layers; revegetation of the cliff face; elimination of access to the cliff face; and future construction well away from the edge of the cliff. 12 To determine the success of the protective beach—groin system McLean, 1975, documented the extent and rate of marine erosion 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 fill and cobble core berm and groin system was constructed at Towers Beach, University of British Columbia to prevent marine erosion along Point Grey cliffs. During the following winter the berm was partially successful in protecting the cliff base, however, along the western beach the sand fill was severely eroded by W and NW storm waves. By the end of February the berm had failed over a 1500 foot length allowing storm waves to undercut the cliff base during high tides. Throughout the study period the groins were very ineffective in stabilizing the sand fill, allowing a large amount of material to move eastward by littoral drift. The useful life of the berm is probably less than two years. Remedial measures will probably be required in the future.” CHAPTER III WIND CONDITIONS 3.1 GENERAL WIND PATTERNS The general surface wind patterns in the northwest Pacific Ocean are summarized in Figure 2a. The summer pattern is direct ly influenced by a semi—permanent high pressure cell near the Hawaiian Islands. The cell created from this North Pacific high controls the region so that northwest and westerly winds prevail along the Canadian Pacific coast. The winter pattern emerges when the North Pacific cell weakens and migrates southward while a low pressure cell in the Gulf of Alaska intensifies. Along the Pacific coast this causes a reversal of prevailing wind directions so that south easterly to southwesterly winds moving nearly parallel to the coast dominate. Within the Strait of Georgia the general regional wind patterns are frequently and strongly modified by the presence of mountains and the altered winds from the Juan de Fuca Strait, Puget Sound and Fraser Valley. The Strait of Georgia wind patterns are summarized in Figure 2b. The winter pattern is closed and counterclockwise in the southern part of the Strait including Point Grey. 13 14 The spring pattern shows a general shift to easterly and southeasterly winds. The summer pattern loses the distinct closed circulation cell. In the southern part of the Strait southwesterly to south easterly winds prevail. In the northern part northwesterly winds prevail. On Wreck Beach wave effects and the ensuing beach sedi ment distribution moves primarily in response to the Strait of Georgia wind conditions. 15 (1) CANADA • (I) winter (ii) summer FIGURE 2a. Regional surface wind patterns of the northeast Pacific Ocean. (ii’) / I (ii) * ;• (1) (11) (ii) spring transition, April-May iii) summer, June—September FIGURE. 2b. Local surface wind patterns of the Strait of Georgia. 16 3.2 ANNUAL METEOROLOGICAL AND BEACH CYCLES From time to time periods of high velocity winds occur in the Strait of Georgia. Occasionally sustained winds (one hour or more) of up to 40 miles per hour (35 knots) occur. At rare time gusts of 70 miles per hour (61 knots) are recorded at the Vancouver International Airport. However, sustained winds of 23 to 25 miles per hour (20 to 22 knots) are suffi cient to create extensive white-capping in the Strait of Georgia. A 22 knot velocity is classified on the Seaman’s Wind Descrip tion as a Strong Breeze and on the Beaufort Scale as a 6 as shown in Table I. 17 WIND SCALES AND SEA DESCRIPTIONS Beaufort International Inter- Seaman’s Wind . . . scale sea nationalscale description velocity Estimating wind velocities description code for of wind knots on sea and wave state of heights sea 0 Calm Less than Calm; sea like a mirror. 1 knot Calm glassy 0 1 Light air 1 to 3 Light air; ripples—no foam crests. 0 knots 2 Light 4 to 6 Light breeze; small wavelets, crests have Rippled 1 breeze knots glassy appearance and do not break. 0 to 1 foot 3 Gentle 7 to 10 Gentle breeze; large wavelets, crests begin Smooth 2 breeze knots to break. Scattered whitecaps. 1 to 2 feet 4 Moderate 11 to 16 Moderate breeze; small waves becoming Slight 3 breeze knots longer. Frequent whitecaps. 2 to 4 feet 5 Fresh 17 to 21 Fresh breeze; moderate waves taking a Moderate 4 breeze knots more pronounced long form; mainly 4 to 8 feet whitecaps, some spray. 6 Strong 22 to 27 Strong breeze; large waves begin to form Rough 5 breeze knots extensive whitecaps everywhere, some 8 to 13 feet spray. 7 High wind 28 to 33 Moderate gale; sea hcaps up and white 6(Moderate knots foam from breaking waves begins to be gale) blown in streaks along the direction of the wind. 8 Gale 34 to 40 Fresh gale; moderately high waves of (Fresh knots greater length; edges of crests break into gale) spindrift. The foam is blown in well- Very roughl3to20feetmarked streaks along the direction of the wind. 9 Strong 41 to 47 Strong gale; high waves, dense streaks of gale knots foam along the direction of the wind. Spray may affect visibility. Sea begins to roll. 10 Whole 48 to 55 Whole gale; very high waves. The surface 7 gale knots of the sea takes on a white appearance. High The rolling of sea becomes heavy and 20 to 30 feet shocklike. Visibility affected. 11 Storm 56 to 63 Storm; exceptionally high waves. Small Very high 8 knots and medium-sized ships are lost to view 30 to 45 feet long periods. 12 Hurricane 64 and Hurricane; the air is filled with foam and Phenomenal 9 above spray. Sea completely white with driv- over 45 feet ing spray; visibility very seriously af fected. TABLE I. Wind scales and sea descriptions. 18 Listed in Table II is information related to high wind periods during the Wreck Beach study. Wind information is de rived from wind records monitored hourly at the Vancouver In ternational Airport by Environment Canada. Typical wind directions, strengths and frequencies are assumed the same for Wreck Beach as for the Vancouver International Airport located a few miles south of the study area. Selection criteria is based on winds having one hour or more of 23 miles per hour (20 knots) sustained velocities with a minimum of three success ive hours of 20 miles per hour (17.5 knots). Duration of a high wind is the time of blow exceeding and returning to a minimum 15 mile per hour velocity. Also listed for reference in Table II are the dates when photographs of Wreck Beach were taken during the study period. 19 HIGH WIND PERIOD INFORMATION High Maximum Wind Photograph Direction Duration Sustained Gust Date Date Velocity A1..N 1973 March 18 E—ESE 9 20 38 SE April5 W 15 25 35W April 27 WSW-WNW 18 21 31 W May 17-18 W-WNW 12 21 29 W May 18—19 WSW—WNW 18 24 33 WNW May 30—31 W—WNW 22 27 40 W June NONE -. July4 July 13—14, WNW—NW 34 21 27 WNW July 15 WNW-NW 16 19 26 WNW July 16 WNW-NW 13 22 28 WNW July_19 August NONE Aug._24 Sept. 24—25 W—WNW 21 22 31 WNW Sept. 26 ,___________ - Oct. 6 WNW 7 22 28 WNW Oct. 9 Oct. 18 Oct.30 W 8 22 32W Nov.’ 13 SE—SSE 11 20 32 SSE Nov. 18 Nov. 19-20 E—SE ‘ 12 20 33 E Dec. 7 W 12 28 44W Dec. 11—12 E—SE 31 26 50 SE Dec. 13 SE-SSE 16 20 30 SE Dec. 14 Dec. 15—16 E—SSE 16 20 36 SE 1974 , . . Jan. 13 Jan. 15 SSE—SSW 20 20 41 S Jan. 18-19 S—W 13 20 37 W Jan. 20 W—WNW 10 21 32 WNW Jan. 25 W-WNW 6 22 35 WNW Jan. 29 SSW—WNW 9 20 36 SW Jan. 29-30 W—WNW 15 22 25 W Feb. 4 W-NW 18 26 45 WNW Feb. 19 W—WNW 8 24 32 W Feb. 28 SE—SSE 8 20 33 E March 1—3 W—WNW 36 24 39 WNW March 2 March 5 W—WNW 9 20 35 WNW March 8-9 E—SE 38 21 31 SE April 11-12 WSW-WNW 14 31 44 WNW April 12 April 23 WNW-NW 13 24 30 WNW TABLE II. High wil2d period information. 20 Bigh Maximum Wind Photograph Direction Duration Sustained Gust Date Date Velocity HO UPS 4?PH MPH May NONE June 18 WNW 11 21 25 WNW July NONE August NONE • August 1 • August 15 August_28 Sept. 25—26 W—WNW 12 35 51 WNW Sept._26 Oct. 3—4 V W—WNW 27 26 37 WNW Oct. 10 Oct.20 W 13 20 31W Oct. 22 V Oct. 28—29 . WNW—NW 26 20 33 NW Nov. 12 Nov. 20—21 . W—WNW 24 20 30 W Nov. 24 Nov. 25 W .13. 25 36 W V Nov.26 Dec. 17 V W—WNW 9 22 37 S Dec. 18 E—SE 6 20 31 ESE Dec. 21—22 W—NW 27 27 55 W Dec. 27 W—NW 11 4 34 WNW Dec. 29 SE 5 23 36 SE 1975 V V Jan.2 SE 4 25 42SE Jan. 4 V W—WNW 12 -25 42 WNW Jan. 8-9 WSW—WNW 24 23 50 NW Jan. 10 V Jan. 20 W—WNW 12 27 39 W Jan. 25 W—WNW 18 22 28 WNW Jan.31 E 18 33E Feb. 4 Feb.10 W 7 25 38W Feb. 16 Feb. 19-20 WNW 26 37 57 WNW V March 18 March 24 WNW 10 21 30 WNW March 25 WNW .14 28 42 WNW March 25 March 30 V V 24 38 67 WNW March_31 April 19 W—WNW 15 29 39 WNW Apr. 27—28 W—WNW 22 29 45 WNW TABLE II continued, 21 By further examining the wind parameters given in Table II during only peak extreme conditions cyclic or annual meteorological patterns might be determined. This information is correlated in Figure 28 for conditions of wind durations in excess of 20 hours, maximum sustained velocities above 24 miles per hour, and gusts of at least 35 miles per hour. From this evidence cyclic patterns are apparent. Figure 28 also includes certain representative erosion—deposition patterns at select locations on Wreck Beach for the periods shown. The erosion—deposition information is derived from Figures 25, 26 and 27. The duration, maximum sustained velocity and gusts criteria suggests that distinct phases occur. Well—defined summer periods commenced about the month of May. Correspond ingly, winter phases evolved around October to November. In general, an average annual cycle for the Wreck Beach area would include a summer period from June to October, and a winter period from November to May. The 1973 summer period included a number of lower velocity wind periods while in the 1974 summer period these were con spicuously absent. The 1973-74 winter phase included several easterly winds of major strength both in duration and velocity. In the following 1974-75 winter phase winds from the east were the exception and were also the winds of shortest durations and lower maximum sustained velocities. 22 3.3 WIND DIRECTIONS OF PRIMARY IMPORTANCE During the months covered by Table II the winds of major importance occurred out of the WNW to WSW sector. From the percentage frequency records listed in Table V for this period and the longshore transport capabilities deter mined in Chapters V and VI winds from this sector predominate. It is significant that no major winds occurred out of the NW to NE quadrant. A representative historical wind rose re veals that maximum velocities out of the north are around 10 knots. Under these conditions from Table III the greatest wavelength that normally could be expected would be 35 feet long after five hours of 10 knot winds. Sand transport cap acities to the south associated with waves of this size are small and function in water depths less than 2.2 feet. The limits of this zone would be near the one fathom contour on a Canadian Hydrographic Chart. In addition, these winds occur so seldom as to have little influence on the sand transport in the headlands area as outlined in Chapter V. Winds from the SE quadrant have little effect on the headlands and Wreck Beach due to the protection afforded by the surrounding landforms and structures. Highly influencial winds out of the northern quadrant are not common. The infre quency of high winds and waves from these directions limit their influence on the headlands longshore transport process. 23 Resulting is a longshore transport system largely restricted to movement toward the northeast. CHAPTER IV WAVE CONDITIONS 4.1 DETERMINATION OF EFFECTIVE FETCHES Waves approaching the Point Grey headlands are the most important and persistent forces taking part in the beach fore- shore activities. The nature of a particular wave field is a result of the interrelated characteristics of the wind regime generating the wave field and the physical shape of the area over which the wind and resulting waves move. Wind direc tions, durations, and velocities are restricted and limited by the surrounding landforms. In order for these potential winds to produce wave fields that are self—sustaining (i.e. waves are removing energy equal to 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 Beach are “fetch—limited”; in which case wave dimensions depend upon fetch rather than wind generation time (duration). Point Grey is surrounded by water on three sides as shown in Figure 3. So easterly winds will produce waves having minimal effect on Wreck Beach. Winds out of the south generate waves that are largely impeded from striking Wreck Beach by the Fraser Delta 24 25 and the North Arm jetty. Winds from the north produce wave fields of very small dimensions due to the extremely restricted fetch areas and rare periods of high velocity winds from that direction. Therefore, winds from the westerly directions, SW through NW, have the larger fetch-generation areas. In addi tion as discussed in Chapter III, wind conditions for the head lands area are such that predominating high-velocity winter winds blow out of the west and northwest as opposed to smaller winds prevailing out of the south and southeast during the summer. Fetch dimensions for five westerly wind directions are derived in Figures 3 through 7 and include the associated com putations and graphic procedures. This method of “effective fetch computation for irregular shorelines” is outlined in the 1973 “Shore Protection Manual” of the U.S. Corps of Army Engineers. This method is based on the following assumptions: i) wind moving over a water surface transfers energy to the water surface in the direction of the wind and in all directions within 45° on either side of the wind direc tion; ii) the wind transfers a unit amount of energy to the water along the central radial in the direction of the wind and along any other radial an amount modified by the cosine of the angle between the radial and the wind direction; 26 iii) waves are completely absorbed by shorelines. The larger fetch distances occur in the range between WSW through WNW as would be expected from visual estimations on charts. More specifically, a first observation would indicate that the due west direction has by far the greatest fetch when taken as a point to point measurement (i.e. the greatest un obstructed straight line distance from Point Grey westward.) However, the WSW direction has a greater fetch dimension which is due to the wind acting as a field over the fetch area rather than as a point source. The method for “effective fetch compu tation for irregular shorelines” takes this phenomenon into con sideration and is a closer approximation to the true physical situation. NW W IN D D IR EC TI O N i4 a( 42 36 30 24 18 12 6 0 6 12 18 24 30 36 42 C os cc . 74 3 . 80 9 . 86 6 . 91 4 . 95 1 . 97 8 . 99 5 1. 00 0 . 99 5 . 97 8 . 95 1 . 91 4 . 86 6 . 80 9 . 74 3 13 .5 12 x i 8.9 15 .0 16 .9 12 .3 10 .1 . 5. 1 2. 2 2 .0 2 .0 1 .9 2. 1 2 .3 2 .3 1. 6 1. 1 X1C o s” < 6. 61 12 .1 4 14 .6 4 11 .2 4 9 6 1 4. 99 2. 19 2 .0 0 1 .9 9 1 • 86 2 .0 0 2. 10 1. 99 1 .2 9 0. 82 75 .4 7 0 0 1 F = Z X 4C O B ‘ /‘ Z C os IC an ad ia n H y dr og ra ph ic C ha rt Fe . i4 13 .5 12 = 5. 59 m _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I e w he re 1 cm = 3. 26 2 m il es LN at u ra l S ca le 1 t5 25 ,0 00 Fe = 18 .2 2 s ta tu te m il es _ _ _ _ _ * w \ N . 85 2 9 c m o n i P t . 7 M t.D r.w fl / ‘ . \ ‘ % r 14 4 2 V in in ci . 9 )% ç, k ç 60 69 ,JN ar ro w s I . 1 n 1 e t . 12 4 18 3 66 6 / 4 . I 0 . 1 . \‘ / 1l 30 \ 17 S N 7 2 N or ih e. jt Pt . 3 (I8 ’ 15 1 D S O \i ,1 10 05 \ \ 9 2 i o 7 R I 8 o 8 5 T E X i: L A N I) 2 O ) c L T ISO 13 5 M ou at I, % 3. S 2 0 . 04 80 • . . Pt M 86 181 58 . 70 . . IN LE T R . 12 2 • 7 . - . 17 3 I6 .4 S ‘ ‘ 117 2, M c N .u 0h t o n Pt 11 87 6 0 % ‘ 6 2A . f A hl Ii ., 6a nh . . 8 I S S . 10 3 ‘ 6 85 . 7 . 20 1 64 . J D e n m .n . 64 : . • M l.S h. ph .r I I 7 S c ,. tC r 121 \ n d \ 7 H or nb y ‘ \ ( J S 0 29 00 ! 2 o n a y ‘ I 2 9 i e r 0 : . • : . . . . . . . • ‘ . . . ‘ . - L . 25 I ip Pt 2 9 \ 5 7 9 1 0 I0 I 7 S C h I 9 6 6 5 ‘ \ 191 76 14 z4 . . 81 4 ib .o I 41 10 49 30 77 18 3 • !.. / . . I 4 % 4 6 Q O r ,C e l - 17 6 14 5 I MM 27 • 2 I M *r k ‘ — 5 - r 54 21 DU MP IN G I 2 Q ua lIc r B c. ch o RE A - , 20 7 . • - • 8 •- .. • . . • N p 2 4 ) V . c P. rk sv II l 1 2 — — 94 8 ( W in c h l. e a 22 2 . . . . , . . N or th w ii B a y . . + r 20 3 - 5 - - . . . . ::.. : I b e r n , A r .w ,m 0 0 + x : : : k e 2 7 ’ 19 2 :0 - : :9 - 10 8 C ER FI G U R E 3. NW w in d d ir ec ti o n e ff e c ti v e fe tc h di ag ra m . T o ta ls 17 6 C ar ia d. ia n H yd ro gr ap hi ó C ha rt #3 00 1 N at u ra l S ca le li 5 2 5 ,0 0 0 ) M 6 • i2 2 ‘ ° \. . 81 :: M M ar k ( 42 s ;4 5 IT2 Qu ali cu m Be ac ho . .•. 7 \ • 3 9 — — . $69 9 M t. W re ne l2 ey IN LE T ‘ . 16 H O W E II 8 . M cN au gh to n Pt . . . 10 4 L. ..? I t8 . . 41 4• . tc sw f’ M e lL o n r - t Q I 2I M oi ,ta u • H al fm oo n Ba y . . 21 30 6 M Ck an a.1 • •‘ 1 . _ . . — ‘ 29 G am W er I. Iru niw Ick M t.. ía’ II . • • 4 / • . 55 5$ — I. . r 7 Se ch el t Mt .U ph Ia at on . . SO JN D • . \2 1 48 / “ ° 4 . \ 35 540 1 1Fh . Li on i — o W ils on C ec k 31 13 7 I9 ’: 6 ’ 6 — • 7 ç • • 8 ;G ;o n i. . • : ‘ “ • ISI JSE D M G . . : _ j7 0 MU NI TIO N 96 : 27 • . . 4 9. an 24 6k Fl nr se ah ni B uy (‘ DU M Pl G : . • • . • • • T .4 3 2 Bowe n $ AR EA / 20 7 — . . . :. •• . 3 14 5 - ‘ ‘ 2 . . . . A R D 2 4 )’ ... lea 22 2 c P •• • . • - 1-— • . \. N . E 7 8 46 — 6 / L ’ 4 ii P N an oo tc Ba y 14 . — 62 211 20 2 — t Gr ey 4 - - I Y ,A N C O . ?- : e k e 2 7 De pa rtu re Ba y . . ‘ 2Q ,— i • 1 • .. . . . . . . . — 92 0 Se a! N A N A IM O G ab rio la 8 82 — II? L U L U IS ) Is la nd • . . ‘ • • • • . — — II 6 , a rio la Pa 3s ae 71 64 , ,. . • , • . 44 40 t’ d e s . 38 Sa nd H e id i/ , ? . ‘ Ye llo w :: :;R ;;: ak :d9 : p M < I W h m a . r ” — , 39 WN W W IN D D IR EC TI O N “ < C os o’ X j X jC os °< 42 . 74 3 4 .8 3. 57 36 . 80 9 5. 2 4. 21 30 . 86 6 6. 1 5. 28 24 . 91 4 7. 1 6. 49 18 . 95 1 8 .9 8. 46 12 . 97 8 11 .5 11 .2 5 6 . 99 5 15 .0 14 .9 3 0 1. 00 0 21 .4 21 .4 0 6 . 99 5 13 .1 13 .0 3 12 . 97 8 10 .2 9. 98 18 . 95 1 6. 8 6. 47 24 . 91 4 2 .2 2. 01 30 . 86 6 1 .8 1. 56 36 . 80 9 1. 6 1, 29 42 . 74 3 1 .5 . 1. 11 T o ta ls 13 .5 12 11 1. 04 Fe = Z X 1C o s ‘ /. C o s Fe 11 1. 04 /. 13 .5 12 = 8, 22 cm w he re 1 cm = 3. 26 2 m il es Fe = 26 .8 1 s ta tu te m il es F IG U R E 4. W NW w in d d ir ec ti o n e ff e c ti v e fe tc h di ag ra m . W ES T W IN D D IR EC TI O N / 4 c C os c( x l X jC og c( + 71 < 4\ w nc he l ea W ES T W IN D D IR E C T IO N “ Np j ° N an oo ic a y 4 I - , . . • • . . 16 2 21 20 2 7 . .,:, . :Y c pc Sn k e 2 18 D ep or iu re Ba y J2 , . ML N A N A IM O C ab rio la 8 82 8 1 1 1 7 42 . 74 3 1. 5 1. 11 33 44 In la nd LU LL ) IS 36 • 80 9 1 • 9 1 • 54 5 171 116 64 14 Sc ev ei w n 30 . 86 6 6. 1 5. 28 . d 8 S an d H ea d ,. , . ; . . 24 . 91 4 9. 5 8. 68 _ s - S _ _ . I 5 I ‘ 18 . 95 1 12 ,5 11 .8 9 l 9 ÷ c c l. 12 . 97 8 20 . 7 20 • 24 “ \ ° ‘ ‘ 6 • 99 5 1 5 .0 14 .9 3 . . Y e Il Pt . “ “ • i3 ° I0 6 16 3 0 1. 00 0 11 .7 11 .7 0 . 41 40 % f 2 3 18 2 2 \ + ’ . . . ‘ I2 5 _ L : . - • : 6 . 99 .5 9. 4 9. 35 - \ / L ad y. m kh N . 9 6 1 . 6 6 .4 O ‘ . 12 . 97 8 7. 6 7. 43 \ \ — . . . . ‘ I 3 9 68 P t R 0b . r t 1 8 6 6 M I. W hy m pi r 2c - . . . . . C] 03 6 36 - - F = Z X C os /. Z C os 42 . — — = 1 0 .8 5 ‘ /• i1 ,9 6 = 9. 10 cm C an ad ia n H yd ro gr ap hi c C ha rt #3 00 1 w he re 1 cm = 3. 26 2 m il es Fe = 29 ,6 9 s ta tu te m il es N at ur al S ca le 1: 52 5, 00 0 C T o ta l 11 .9 60 10 8. 85 FI G U R E 5. W es t w in d d ir e c ti o n e ff e c ti v e fe tc h d ia g ra m . < C os c ’ X j W SW W IN D D IR EC TI O N 42 36 30 24 18 12 6 0 6 12 18 24 30 36 42 T o ta ls , 74 3 . 80 9 . 86 6 . 91 4 . 95 1 . 97 8 . 99 5 1 • 00 0 . 99 5 . 97 8 9. 22 9 7 9 10 .9 17 ,1 16 • 5 11 .3 9. 4 9. 1 7. 3 6. 4 6 5 X jC os o< 5. 87 8. 82 14 .8 1 15 .0 8 10 .7 5 9. 19 9. 05 7 .3 0 6. 37 6. 36 93 ,6 0 C an ad ia n H yd .r og ra ph ic C ha rt #3 00 1 Fe = X jC os /Z C o s _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ F = 93 .6 0 •/. 9, 22 9 = 10 .1 4 cm N at u ra l S ca le ls 5 2 5 ,0 0 0 . e w he re 1 c n = 3. 26 2 m il es _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Fe 3 3 S a U E i h p 2 2 7 4 L O 8 I i 5 8 7 j ’ 1 N 1 ( ’ : 4 b 1 ; 8 e B ay ‘ ‘ : i1 La sq iie ti I. 2 5 2 C, . . / Si si Ii 4 . 9b % 9 ’ 101 - , _ Se ch el t M I. EI pf lIn ht oi ie . 87 79 - . 41 60 ) i . 63 — . 48 95 * 66 . . c 11 9 N W ils on Cr ce k \.• 91 17 6 ‘ !4 ” s 3 ! 4 2 , ‘ \ ‘ 5 . . ‘ . ‘ . . — — s . , , ( W h ie — S L d g - “ / • . . . • 18 3 / DI SU SE D \ 4 — 5 — . 21 3 \ Q _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ • 66 17 6 45 - A g6 12 7 “ Qu s cu B ei ch o — 42 27 2 DU MP IN G I _ _ _ _ _ _ _ _ _ _ _ — Pa rk .v lll : 3 s\ 12 3 $4 “ AR EA 20 7 — i:’ ‘ - ‘ - I 4 R D 2 4 v c o u ’ 1e , . , . , ? 9 N or tlw .a a B .y . 22 2 ‘ J . . . . N ar oo s.N a, bo u 46 ” 21 7 Pt .G re y Po rt ) N .ri ào se 14 • 16 2 211 2 — — • V A N C O J V E P 5 — A — ç • • • . , ,f, . M I. A ils im It l * ? 2 7 _ V 0 pa.fla ireB ay . 2Q , J - ‘ — I 3 _ _ l 19 0 Sc . I. M il . N A N A IM + 4 6 Ga 6 87 8 15 8 L U L U IS L A N D la la nd A s- .’ I / . & . 44 40 — • 30 I S H . . ’ C ltO fl 11 14 c— 96 . (C’ 117 I b, “ : : , , f . . ,, c. M L G s L: dy ,m lth I r 0 ? 1 3 3 I 2 5 F IG U R E 6. W SW w in d d ir ec ti o n e ff e c ti v e fe tc h di ag ra m . . I.- ) C SW W IN D D IR E C T I0 N 4: 0< C os X I X jC os < 5 65 6 • 07 . 5. 54 5, 39 6 . ‘ 09 6. 36 6. 57 6. 70 48 .3 7 I 7 ? 0 ) • . i 7 e t M L E I p h I n ,t o n . r u M c : : 18 3 7 6 21 1 / : s : 9 7 Q4 ? I’ /’ Q u ai l B e a c h o 14 2 4 12 1 D U M PI N G I (,8 — 94 1l J ( 1 3 (7 2 ‘ p 9 5 1 tø ° ° IC J 4 ’ . . ;, . 12 3’ , B a I 0. T . \ I AR EA , ‘ 2 0 7 ‘ > i . . . . . . . 2 I \ • . . . . . 5)C ..l’ . , . . 4 ’ P. rk iv lll 2 14 9 “ . . _ 0 3 14 5 _ > 20 84 35 . e 7_ _” _ — 9r c h C A R D 24 ) V . c 1V or iA io e: 22 2 . . . . . . • 9& .• “ D I . N E7’ N ar .o ,. H rb ea + 3 : 03 _ _ : I 4 — — / ( 4 ‘ 6 8 c o y 7 N a n o o c e B ay 4 1 - 6 2 21 1 P L .C re y ;• .. . . ) . . V 4 N C O V V E R , - . . . . N e w W e s m (n ar er M L. A rr ia lm Il k . 4 . S n ak e , . . . . . . ML : l 2 7 ) . i 2 i 18 ‘ ‘ / I . . , _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ • ,. 41 - — , 4 : L U L U 0 — I a’ . ab c’ a s e / /. : a’ • Se vc ito n k . 13 8 d , 4 90 : “ 3N • Z( 0 ° 20 , :? ? . . 1: ,,. ... . :. Ye lT bw ‘I’ , 9’\ \ * 61 ‘ ‘ 61 . 1 0 k : . : f. 14 15 % / 2 3 ‘ 2 2 \ +r l 0 3 ‘ \% , ‘ 2 2 4 1 4 • . . “ çl- . . . . • . 38 — . . . :. : L ad ys m ih 6 :. .. .4 : . . (7 &J : 60 I M * S o _ _ c z : ; ’ o : 7,, . 11 1 CH A N N EL L ’ - . 96 N Fe X jC o s ‘ /• Z C os Fe 48 .3 7 i / 7. 25 6 6 .6 6 i C az ia .d ia fl H yd ro gr ap hi c C ha rt #3 00 1 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ w he re 1 cm = 3. 26 2 m Il es Fe = 21 .7 5 s ta tu te m il es N at u ra l S ca le 1 :5 25 ,0 00 42 36 30 24 18 12 6 0 6 12 18 24 30 36 42 T o ta l . 74 3 . 80 9 . 86 6 . 91 4 . 95 1 . 97 8 . 99 5 1. 00 0 7. 25 6 7. 6 7. 5 6. 4 5. 9 6. 4 6. 5 6. 6 6. 7 1W .) I- I FI G U R E 7. SW w in d d ir ec ti o n e ff e c ti v e fe tc h di ag ra m . 32 4.2 REFRACTION DIAGRAMS Wave fields assume their individual characteristics from the nature of the generating wind regime. Wind regimes are identified by velocity, direction, duration and fetch aspects. Wave fields are commonly typified in terms of their significant wave height, significant wave period, deep water wave length and deep water wave velocity characteristics. Table III lists the deep water wave characteristics for the given wind regimes. Minimum durations, significant wave heights and signifi cant wave periods were interpolated from the Sverdrup—Munk— Bretschneider curves contained in the 1973 “Shore Protection Manual” of the U.S. Corps of Army Engineers, Volume I, Chapter 3 for the given fetches and wind velocities. Theoretical deep water wave lengths and velocities were computed using linear theory equations. The method of determining wave breaking heights, wave breaking depths and longshore current velocities is given in Chapter V1 Section 5.1. W IN D , FE TC H AN D D EE P W AT ER W AV E DA TA w w F et ch E ff e c ti v e F et ch , Fe W in d V el o ci ty , U M in im um S ig n if ic a n t S ig n if ic a n t D ir ec ti o n D u ra ti o n , tm W av e H ei g h t, H0 W av e P er io d , T0 N au ti ca l S ta tu te M il es M il es K no ts H ou r H ou rs F ee t S ec on ds NW 15 .8 3 18 .2 2 10 11 .5 5. 2 1 .4 2. 6 20 23 .0 3. 5 3. 5 4. 0 30 34 .5 2. 8 5. 6 5. 2 40 46 .0 2 .5 7 .8 6. 0 50 57 .5 2. 2 10 .3 6. 8 60 69 .0 2 .0 13 .0 7 .5 W NW 23 .3 0 26 .8 1 10 11 .5 7 .0 1. 6 2. 7 20 23 .0 4. 6 3. 8 4. 3 30 34 .5 3. 7 6. 4 5. 5 40 46 .0 3. 3 9. 0 6. 5 50 57 .5 2. 9 12 .0 7. 4 60 69 .0 2 .6 15 .0 8. 2 W ES T 25 .8 0 29 .6 9 10 11 .5 7 .5 1. 6 2. 8 20 23 .0 5. 2 4 .1 4. 4 30 34 .5 4. 1 6. 6 5. 6 40 46 .0 3. 5 9. 5 6. 6 50 57 .5 3. 1 12 .3 7. 5 60 69 .0 2 .7 15 .6 8. 5 W SW 28 .7 5 33 .0 8 10 11 .5 8. 5 1. 7 2. 8 20 23 .0 5. 6 4. 2 . 4 .5 30 34 .5 4. 5 7 .0 5. 8 . 40 46 .0 . 3. 8 10 .0 6. 8 50 57 .5 3. 4 13 .0 7 .7 60 69 .0 3. 2 16 .0 8. 7 SW 18 .9 0 21 .7 5 10 11 .5 6. 0 1. 5 2. 7 20 23 .0 4. 0 3. 6 4. 2 30 34 .5 3. 3 6. 0 5. 3 40 46 .0 2 .8 8. 4 6. 2 50 57 .5 2 .5 11 .0 7. 0 60 69 .0 2. 2 13 .5 7 .5 T A B L E I I I . W in d , fe tc h a n d d ee p w a te r w a v e d a ta , 34 U) -Ii 0 Dr-oo,-4 occ. C I i-I Lfl,-4 a)l C) WIG) V.- V.- 0. V.4 rr1V.4 4-, 4) a) — 4C) 00 U)GJ 0 ‘.D 0 V.4 fl V.- at 0 r1 r -f -4 - .D at r4 C’4’.D.-4Lt 0000..- IriV.4 4, U) a) U > Cd 0 at C) V.- V.4 Ot. Co (‘1 U) D 0 V. fl V. at CN( ;V.;C;C; Cr-,-1.-f,-lr-4 0 0 0 0 Q Lfl 0 C., Co b c’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,O Cd 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’4 a) 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 4 bt : •1f )4 - Cd -. ‘3tflOCoC’)0 VCoJ000 V.-V.40000 ‘D00CtC g r—oc’, J’D0tCNtf) 1•t—om’o cOi-f U 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.tatOtLflcD 04 a) C” C” U> UCd c C U >1 ‘f -P r •r4 0 140 0 e.) 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’1 04a) a) U> r14 a)Cd c f: 0 i Q Cl) z • - Cd U :1 r4 4-) 0 C) H H H rxl 35 Wave fields generated by identifiable wind regimes are modified by the underwater topography over which they move. The effects of topography on wave fields moving inshore toward Wreck Beach is captured graphically in the refraction diagrams shown in Figures 8 through 12 The refraction diagrams help to predict the distribution of modified wave forces and wave heights through the shallow water area which vary from the deep water distribution. And the diagrams aid in the assessment of erosion—deposition patterns of Wreck Beach sediments. The assumptions generally made in the use of refraction diagrams are the following: i) wave energy between orthogonals remains constant; ii) direction of wave advance is perpendicular to the wave crest and in the direction of the orthogonals; iii) speed of a wave of a given period at a particular location depends 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 consi dered negligible. All of the diagrams were prepared using the 30 knot wind velocity and corresponding wave data of Table III with still 36 water level at higher high water of 16.2 feet. Winds of this velocity and duration occur occasionally throughout the year and typify rough sea conditions in the Strait of Georgia. I NW is - - - - - - \ \ J r \ Jr \ 5 4 J r : \ - - - - / 70 X 4 8 ) B U R R A2 6 R D N 84 . . . . \ 28 \ I - - - - - - - - - \ • • . . • _ \ \ \ I \ \ \ - - lo J’ \ - - \ 1c J ’ \ \ 2 7 jr \ . . . . . . / _ \. i H 4 \ a , . F IR - \ 8Z B n \ 4 N ‘ ‘ , 7 - - - - : \. .. B A N K + S 3 4 I \ ç1/> \\ 4 \ / 1 f _ _ _ _ \ \ : 8 4 3 : M •. \f j8 iI \ 2 W R EC K BE A CH \ \ \ ST U D Y A R EA \ \ \ ). \ I _ _ _ _ _ — 08 / ‘ 48 s \c 9 z / / \ I L . 0 P oi nt I 2 S \ Th : • : 4 : NW W IN D D IR EC TI O N W AV E RE FR A CT IO N DI AG RA !1 W av e R eg im e Ho = 5. 6 fe e t To = 5. 2 s e c o n ds Co = 26 .6 ft /s e c Lo = 13 8. 4 fe e t = 23 .1 fa th om s W in d R eg im e Fe = 18 .2 2 sm = 15 .8 3 rim U = 34 .5 m ph = 30 k n o ts tm = 2. 8 ho ur s W av e S ca le S = 50 ,0 00 n = 0. 00 81 5 S /T o 2 = 15 w a v e le ng th s t = 0. 00 81 5 S/ T o = 78 s e c o n ds C an ad ia n H yd ro gr ap hi c C ha rt i # 34 80 , 19 71 N at u ra l S ca le 1 :5 0, 00 0 1 cm = 0. 31 s ta tu te m il es = 0, 27 n a u ti ca l m il es FI G U RE 8. NW w in d d ir ec ti o n w a v e r e fr a c ti o n di ag ra m . 75 . / — — — • 84 I • I L -— , £ 3 I— 4 5 I’” I — I I I _ _ I-, -’- ._ .._ I _ . _ I_ .o u I • - - I ‘ I I r .’ - i — i i • 1.•., •,•— ,—. .-•I , . . , i— i /•[ 4 I / . % / . . / i /: I I’ ’4 _ _ I I I 1 > ’ t ’ . . i g I A I / L J 4 r - i’ 8 e 1 , 7 . w L j i i- r 7 ’7 4 /s r .‘.‘•— • ‘ • ‘ 1 / 4 c o / - J J I I • ‘ — I I • - — I 21 Cd ,! J J . , j I6 t— I I I-m • I •:: hI , t I \I I I) I 1’ - . - - - - . . - \ : 1 / / I l. / I- • 1. . I I l 6 8 l\ Gp F /‘ _ • - • — . — — — — . 75 \ /çT \3 9 W !M W IN D D IR EC TI O N W AV E R EF R A CT IO N DI AG RA M W av e R eg im e H o = 6. 4 fe e t T o = 5. 5 s e c o n ds Co = 28 .2 ft /s e c Lo = 15 4. 0 fe et . = 25 .8 fa th om s W in d R eg im e F e = 26 .8 1 s = 23 .3 0 rim U = 34 .5 m ph = 30 k n o ts tm = 3• 7 ho ur s W av e S ca le S = 50 ,0 00 n = 0. 00 81 5 S /T o 2 = 1+ w a v e le ng th s t = 0. 00 81 5 S/ T o = 74 s e c o n ds 36 28 27 I_ •r I % s ç 5 A N II ( • ‘ . _ I - i 4 4 2 u / z / / ÷ y w E A c H 3 . V ’ 57 . . . 1 s J / ST U D Y A RE A jY J • :i ... iI W ( Pt rey R 51 1 CO LU M BI A H f ‘ _ _ _ • po )( • L — n : N C an ad ia n H yd ro gr ap hi o C ha rt #3 48 0, 19 71 N at u ra l S ca le 1 i5 0, 00 0 1 cm 0. 31 s ta tu te . m il es = 0. 27 n a u ti c a l m il es : w FI G U R E 9. W NW w in d d ir ec ti o n w a v e r e fr a c ti o n di ag ra m . I I I> 26 IC . 1. - — — g — :; . ‘ I> ’% , 2 / — . . :7 IH I: 2 34 j : Iz \ 9 ( 39 )\ — - r - • 7 T ” Os 3 2_ i41 \ S / ,‘ c: / / / 3 7 — — 8 W ES T W IN D D1 RE CT IO !b T W AV E R EF R A CT IO N DI AG RA M W av e R eg im e - HO = 6. 6 fe e t T o = 5. 6 s e c o n d s Co = 28 ..? ft /s e c Lo = 16 0. 6 fe e t = 26 .8 fa th om s W in d. R eg im e Fe = 29 .6 9 sm = 25 .3 0 n m U 34 .5 m ph = 30 k n o ts t = 4 .1 ho ur s W av e S ca le S = 50 ,0 00 = 0. 00 81 5 S /T o 2 = 13 w a v e le ng th s = 0. 00 81 5 S /T 0 = 73 s e c o n ds 2 — - , — • 1 - , 75 4 . W E S rW . >)) >> N 68 / / /• 27 / • • % . 18 17 ‘ ‘ % _ . . • - . . _ _ M • ‘ • • - - . 9i 11 \ SP IS H SA N K 4 I 4 • . . . . • 28 9 - / / j811 I I 3) 12 — z r / — — - i 4 A / pF I? UN IV E ? : : i 9 R : u l A - . • — — — 4 • — ‘ : ;• — 10 8 • / / (9 i • Il ) : I / ‘ : . , • . . :• :: • . P o in t - - ‘ I1 - z / / , • 75 9 C an ad ia n H yd ro gr ap hi c C ha rt #3 48 0, 19 71 N at u ra l S ca le 1 :5 0, 00 0 1 cm = 0. 31 s ta tu te m il es = 0. 27 n a u ti c a l m il es \. .. :• , , : 4 FI G U R E 1 0. W es t w in d d ir ec ti o n w a v e r e fr ac ti Q n di ag ra m . W av e R eg im e = 7. 0 fe et = 5. 8 s e c o n ds 29 .7 ft /s e c 17 2. 2 fe et = 28 .7 fa th om s W in d R eg im e Fe = 33 .0 8 sin = 28 .7 5 nm U = 34 .5 m ph 30 kn ot s t = 4. 5 ho ur s W av e S ca le 73 V) 3 4 \ // // _ _ _ _ \ , , 75 / 3 9 \— --1 ‘ (w 1 i 69 1 i ’ 4 W SW W IN D D IR EC TI O N W AV E RE FR A CT IO N DI AG RA M H o To Co Lo — — - - — . le I ‘ — — — . — . I - . . — . . . . Ix I‘ ‘ 4 7 — — — — — . . . — . . I l LL. i . . . - 3 \ 69 / j - . . — , . . . j , — . — 41 — 27 - . - . . . . - - . . — . . . - . . — . . - - “ - / — ‘ 9 . . . . — FI IT • . . . . 7 / — — — - 1 - ‘ . . — - • - ‘ i . : — 4— u — / — — — G j - t S % 1I 4 37 •. .— - •. . . - . . • ‘ “ . , _ L . r V / . — - 4 , - . , . ? / — . . 3 1 P IS H BA N K - \ . . - . . ç i . I - • . . . — . 71 8 / 4 , , r I! f’ (_ __ • M . “ — a - . / • ‘ jW R E C K B E A % s .\ A . . ‘ o5j ) / ) ST U D Y A R E A . I + ((f \ ø j \ ; ‘ : r : : u M e I A 8 = = 50 ,0 00 0. 00 81 5 S /T o 2 12 w a v e le ng th s 0. 00 81 5 S/ T o 70 s e c o n ds 7 . 89 :___ ___ ___ ___ _ nJ / C an ad ia n H yd ro gr ap hi c C ha rt #3 48 0, 19 71 N at u ra l S ca le 1: 50 ,0 00 1 cm = 0. 31 s ta tu te m il es 0. 27 n a u ti ca l m il es . . ‘ Ij. • L . — — I \‘ -. -1 ’ ‘ Ii ,: I I . C FI G U R E 11 . W SW w in d d ir ec ti o n w a v e r e fr a c ti o n di ag ra m . , “ 6 / ‘ K I, .‘• c: , / 27 L _ 7 iS f/ i \i .X & ;: v z ‘ I: + :. 1 BE A CH :. J/7 ,) ST UD Y A RE A 2 4 Y \ k R c :L u M B IA 3 0 I ; (\,> ( ‘ s; : ‘ n t — — - SW W IN D D IR EC TI O N W AV E RE FR A CT IO N D IA GR AN W av e R eg im e H o = 6. 0 fe e t T o = 5. 3 s e c o n ds Co = 27 .1 ft /s e c Lo = 14 3. 8 fe e t = 24 .0 fa th om s W in d R eg im e F e = 21 .7 5 sm = 18 .9 0 tim U 34 .5 m ph = 30 k n o ts t = 3. 3 ho ur s W av e S ca le ’ S = 50 ,0 00 n = 0. 00 81 5 S /T o 2 = 15 w a v e le ng th s t = 0. 00 81 5 S/ T o 77 s e c o n ds •. . 12 6 ‘ 4 : “ ‘ ; / - , . ‘ - I• •/• • :t s1 :. C an ad ia n H yd ro gr ap hi c. C ha rt #3 48 0, 19 71 ’ N at u ra l S ca le 1* 50 ,0 00 1 cm 0. 31 s ta tu te m il es = 0. 27 n a u ti ca l m il es FI G U R E 1 2 . SW w in d d ir ec ti o n w a v e r e fr a c ti o n di ag ra m . 42 4.3 WAVES FROM THE SW SECTOR Waves from the SW sector in general diverge around the headlands. The South Arm jetty absorbs most of the direct energy. Increasing wave heights through the shallow area are due mostly to shoaling influences while wave diverging effects would tend to decrease wave heights and forces The wide angle of wave attack from this direction creates a large littoral drift component toward the NE throughout the area. Fetches from the SW are relatively small and high wind velocities are not common from this direction. However, a large percentage of low 10 knot and under winds come from the SW sector as indicated in Chapter V. Resulting are waves not very effective in eroding the cliffs but highly important in transporting sediment in the nearshore zones during extended times of the year when mild winds prevail. 43 4.4 WAVES FROM THE NW SECTOR Waves from the NW sector tend to converge throughout the headlands area. The wave attack angle from the NW tends to be minimal. The small littoral components produced appear to move NE around the Towers Beach area with some slight movement toward the SE from the west tower. Fetches from the NW sector are the most restricted of those under consideration and winds of all velocities occur rarely. Waves from these winds are small in both erosion and longshore transport capacities. The most northerly winds will have a greater longshore component but will have extremely reduced fetch and frequencies. 44 4.5 WAVES FROM THE WEST SECTOR Waves from the west sector are most important in erosion and have considerable longshore transport components. Converging waves tend to strike the west beach straight on. But in the Towers Beach area the waves begin a diverging pattern which continues to the NE. Typically high winter waves out of the west sector approach Wreck Beach at an angle across the wide shallow off shore sandbank. The waves are refracted and shoaled by the topography such that the breaking of any one wave crest on the upper beach area will be progressively delayed toward the easter ly end of the area. For example, Figure 13 shows a wave breaking at the outfall location that is still 5 to 7 wave lengths seaward of the beach breaking area near the east tower. Longshore drift from these waves is toward the NE and is most effective from the west tower eastward. Fetches from the WSW through WNW directions are consi derably greater than the NW and SW sector fetches. Also high wind frequencies and velocities are most common from this sec tor. I,WNW - _ _ _ _ u4 & S _ -. — 4, _ __ 4- ‘4, r : 45 West Beach March 25, 1975 Photograph location 18 FIGURE 13. Photograph sequence showing NE longshore transport waves breaking at an angle to Wreck Beach. WNW Towers Beach arch photograph - cations 22 March 25, 1975 Photograph location 19 46 4.6 WAVES FROM THE MARCH 25, 1975 HIGH WINDS The most important wind directions on Wreck Beach are from the WNW and W. Although neither has the greatest fetch, WNW-27 miles and W-30 miles compared with WSW-33 miles, their frequency at all velocities covers a much larger percentage than do the other wind directions as shown in Table V. At lower velocities W winds prevail and at extreme high velocities WNW winds predominate. Typically a high wind period will begin by blowing out of the southern part of the Strait of Georgia. As it gains in strength and intensity it will swing counter-clockwise around the Strait of Georgia having its greatest speeds and gusts out of the WNW. Such a period of wind conditions occurred on March 25, 1975. Winds of 28 knots from the WNW with gusts of 39 miles per hour blew for several hours. Figure 13 of March 25, 1975 photographs show the physical appearance of the wave field on Wreck Beach. Tidal elevation at the time of the photographs was 13.7 feet (2.5 feet below Refraction Diagram datum). The deep water wave dimensions from this storm can be predicted as given in Table III. But it is useful to anticipate their al tered height in the nearshore regions. As these wave crest heights begin to change due to the influences of shoaling and refraction, their characteristics and dimensions will change. These influences occur whenever the waves begin “to feel the 47 bottom” at depths generally accepted as being one-half the deep water wave length. Representing the March 25, 1975 storm is the enlarged WNW refraction diagram and accompanying information of Figure 14. To determine the anticipated wave height, H, at any location on Wreck Beach the deep water wave height, H0, is modified by the shoaling effect, K, and by the refraction effect, KR; that is H=HOKSKR. The H0 is related to wind velocity and fetch as listed in Table III. The shoaling coefficient, K5, represents the effect of a change in water depth on a wave height and results from a wave moving into progressively shallower water. The K5 value depends upon the wave length and water depth at the desired location. The Ks values were derived from common tables which are available in the 1973 “Shore Protection Manual” of the U.S. Corps of Army Engineers, Volume III. These values and corresponding water depths are listed on Figure 14 in the Refraction Diagram Information Block. The K5 values for the March 25, 1975 storm are shown at various locations on the refraction diagram. The shoaling coefficient, KR, is related to the wind direction and reflects the change in height and direction of a wave moving over the underwater contours at an angle causing the wave energy to either converge or to diverge. In practice the KR value is determined by the square root of the ratio of the deep water orthogonal spacing to the orthogonal spacing at the 48 shallow water depth desired; the spacings are measured directly from the refraction diagrams. The KR values for the March 25, 1975 storm are shown at various locations around Wreck Beach on the refraction diagram. The effect of changes in wavelengths is reflected in the ratio of the wave length, L, at the desired location to the deep water length, L0. The values of the shallow water wave length, L, are listed in the Refraction Diagram Information Block of Figure 14 corresponding to the water depth contour and are derived from the tables available in the 1973 “Shore Protection Manual”. The L values for the March 25, 1975 storm are shown at various locations around Wreck Beach on the refraction diagram. The altered wave heights resulting in the March 25, 1975 incoming storm waves seen in the Wreck Beach photographs of Figure 13 are shown on the refraction diagram of Figure 14 at various locations. Sand volumes moved by the wind period are calculated in Chapter VI. 49 In summary: K5 - shoaling coefficient (Listed in Refraction Diagram Infor mation Block, shown on the refraction diagram) KR - refraction coefficient (Shown on the refraction diagram between orthogonals) T0 - wave period in deep water (significant wave period Table III) L0 - wave length in deep water (Table III) L — wave length in nearshore region (Listed in Refraction Diagram Information Block, and shown on the refraction diagram) H0 - wave height in deep water (significant wave height Table III) H - wave height in nearshore region (H = HOKSKR and shown on the refraction diagram) CHAPTER V SAND MOVEMENT 5.1 LIMITS OF THE LITTORAL ZONES From fetch and weather considerations the littoral trans port system must presently originate at the Point Grey head lands and move downcurrent towards Spanish Banks. Clearly waves are the most effective and important agent acting to move sediment in the nearshore region of Wreck Beach. Their ability to transport material is closely related to their height, period, and direction of approach to the beach. Waves approach Wreck Beach shoreline across the shallow submerged sandbank, extending about a mile offshore at an average slope of 0.1 percent to a depth of 5 fathoms along the outer rim. At that point the slope increases suddenly dropping off quickly into the Strait of Georgia depths. Waves first feel the bàttom effectively when the water depth is equal to half the wave length, but it is not until the depth is much shallower that any appreciable amount of sand is transported. The transport of sand along Wreck Beach takes place primarily in two zones: the swash zone and the surf zone. Beach—drifting occurs along the upper limit of wave action and is related to the swash and backwash of waves. Its action is most effective when waves approach at a considerable angle to 50 51 the shore. The other major zone of the longshore movement is in the surf and breaker zone. Here the largest quantity of material is moved, part in suspension and part along the bed, and sand can be moved by relatively weak longshore currents. The location at which a wave regime approaching Wreck Beach enters the breaking zone delineates the extent of the zone of transport seaward from the swash zone on the upper beach. This location, called the breaking point, is the point where foam first appears on the wave crest. The breaking point is an intermediate point in the breaking process between the first stages of instability and the area of complete breaking. That waves do not break in deep water in this area is due to wave dimension limitations imposed by the restricted fetch generation areas. In shallow water regions the breaking point is identi fied in terms of the breaking depth, db, the water depth be low still water level at which breaking is initiated; and the breaking height, Hb, the crest to trough dimension when break ing is initiated. At the breaking point a longshore current direction and velocity is established which is sensitive to both crest angle and wave height. Listed in Table III are wave breaking depths and heights for the range of wind and unrefracted wave regimes noted. These values were interpolated from the dimensionless breaking wave curves contained in the 1973 “Shore 52 Protection Manual” of the U.S. Corps of Army Engineers, Volume II, Chapter 7 for the range of wind and wave regimes listed. Also listed are the corresponding theoretical longshore current velocities that would result from the given conditions. Long- shore current velocities were derived using the energy approach which depends upon wave height, period, angle of approach, beach slope, sand surface texture and hydraulic roughness of the beach. Correlations of the parameters have been determined by King et al., 1959. During the course of a tidal cycle water heights may vary over an elevation range as much as 16 feet between lower low water and higher high water. Because of this areas from 800 feet seaward of the west beach cliff base to 1800 feet seaward at the east end are alternately exposed and inundated during the large tidal cycles. Wave attack then that covers a six hour period or more effectively increases its breaking depth by as much as 16 feet; depending on the tidal range in that period. As a result the region around the headlands of longshore trans port activities is considerably extended. Table IV lists di mensions of transport zones at select areas of Wreck Beach for a variety of wave regimes. Wind categories and volumes of sand transported are derived in Chapter VI, Section 6.1. Breaker heights and depths are compiled from Table III. 53 _____________ LIMITS OF THE WRECK BEACH LITTORAL ZONES Wind Breaker Breaker Elevation Width of Breaker Zone Volume Transported Velocity Height Depth Range of U TMb db Breaker West Tower’s East 1973—74 1974—75 Zone Beach Beach End Feet Feet Feet Feet Feet Feet c.y/year c.y/year A Peak Extreme 5.1 6.5 — 8.0 12 2300 2200 2500 6,150 10,581 Winds B General High 3.8 4.8 — 6.0 10 2000 2000 2300 12,023 17,507 Winds C Other 1.6 2.0 — 2.5 6 1000 1300 2000 17,759 16,717Winds Data for determining deep end depth of Elevation Range: Chart Datum: “The Canadian Hydrographic Service has adopted the plane of lowest normal tides as Chart Datum”.(p. 4 Canadian Tide and Current Tables) Chart 13481: Average Tides Mean Water Level Large Tides HHW LLW HHW LLW 14.4’ 4.1’ 10.1’ 16.2’ 0.3’ Contour datum on Chart 43481: 16.0’— .l6.2’-Lge.HBW-- :‘ - 4.1’ Av .LLW 3 8 0 fathom (0’) contour 0.0’— .. . ge.LLW 0.63 fathom (3.8’) contour —2.0’— . . . 1 fathom (6’) contour Therefore, 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. 54 Wave requirements to move sand at the outer edge of the sand bank, 26 feet below low low water, into the longshore transport system necessitate a generating 2—3 hour wind of 60 knot velocity. Winds of this speed are very near those classified as Hurricanes on the Seaman’s Wind Description pre sented in Table I. These conditions are not likely to occur near Vancouver. However, extended extremely high wind periods of 36 to 40 knots do occur on occasion. During the period covered by the information contained in Table II such winds occurred on February 19 and 20, 1975 and on March 30, 1975. Both winds were from the WNW direction, each had at least 3 hours of sus tained 37 to 38 knot velocities, and the duration of their entire storms covered two complete tidal cycles. Tidal cycles for each covered ranges of about 3 to 14 feet. It is likely that waves generated from these winds moved sands at depths 10 to 15 feet below normal lower low water (near the 2.5 fathom contour line on a Canadian HydrOgraPhiC chart such as Figure 31) and as far seaward as 3200 feet. 55 5.2 COMPILATION OF DATA That sand in the Wreck Beach area moves in response to cyclic weather activities is evident from the sand movement records available. Historically, continuous and common base records covering this are limited. Data used for this study are sequential photographic records available for the months listed 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-sectioning data courtesy of Vancouver Board of Parks and Recreation and Mr. 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 and cross—sectioning form. For simplicity and ease of presentation not all photographs taken at the locations may be included in the sequences shown in Figures 15 through 22. However, information covering all the photographic sequences and locations as shown on Figure 1 is compiled in Figures 23 and 24. 56 July 4, 1973 January 13, 1974 A ¶1 FIGURE 1. Photograph sequence at photograph location 1, East End, prior to construction activities. November 18, I — 4 July 19, 1973 March 2, 1974 57 FIGURE l6. Photograph sequence at photograph locations 1 & 2, East End, following construction activities. 30, 1974 August 28, 1974 September 26, 1974 November 26, 1974 January (0, (975 58 February 4, 1975 March 31, (975 May 12, 1975 : -— an — -. FIGURE 16 continued 59 -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 - I 61 ‘ .,. ‘—.-— : FIGURE 19. Photograph sequence at photograph location 10, West Beach groin, following construction activities. j February 4, 1975 1975 . -- —9 • 2 F 62 FIGtJR 20. Photograph sequence at photograph location 13, West Beach, following construction activities. Auqust 15. 1974 - February 4, 1975 Auqust 28, 1974 February 16, 1975 September 26, 1974 November 26. 1974 August 28. 1974 September 26 1974 March 31. 1975 63 May 12, 1975 FIGURE 21 Photöraph sequence at photógrap? location 18, West Beach, following construction activities. -.- — (- -:1 .- — --— - - March (8, (975 October (0, 1974 August 15. 1974 February 10. 1975 64 FIGURE 22. Photbgraph sequence at photograph location 19, Towers Beach, following construction activities. September 26, 1974 October 10, 1974 ‘vember 26, 1974 65 The charts in Figures 23 and 24 are graphic summaries of the information observed in the photograph sequences. The chart in Figure 23 covers the period of study prior to the disturbance of Wreck Beach by the construction project during the summer of 1974; Figure 24, the period following the disturbance. The construction activities considerably altered the upper beach face throughout the length of the study area. The alignment was changed along a 200 foot wide strip at the cliff base as well as replacing the composition and arrangement of the surface beach face. In addition, the placement of the protective beach fill served to make some 70,000 cubic yards of easily assimi lated material available to wave action and longshore transport. This method of presentation permits sand and gravel movement patterns to be determined over the area and associated with time and weather conditions. The points on the lines are relative and a gross approximation for that particular location. The lines indicate a change in the amount of sand and gravel accumulated or lost during subsequent photographs as compared with the initial photograph. The intent is not to suggest that exact heights and quantities have been determined from the photographs but rather that the photographs have shown how, re lative to themselves, a net amount of material has changed. The dot indicates the approximate position of sand and gravel on that photograph with the position on the first August photograph of each chart (initial August position is plotted as 66 the baseline). The dotted lines indicate the date of the high wind periods listed in Table II. FI G U R E 2 3. C h ar t o f p h o to g ra p h s e q u en ce s p ri o r to c o n s tr u c ti o n a c ti v it ie s . - J D A T E . % c c39’ IC ... • + ‘ H 1 n • - • ± .I .. . W es t T ow e r f jr : ‘ — 1 I U pp er S ea h F a e t . : . : : : . : : I: fl II W es t B ea ch : . U pp er G ro i E nd : :1. — . 1! — — - I , . I — — — — — — — — I I- PH O TO G R A PH L O C A T IO N E as F E nd U pp er B eo c I 1—1 —1 2 0• V 1<Q , F . . rV Ft .H T1 lTh fftf 4 I I — I i i 6 - . - - — - - — — — — — — r t — ! a a c e U j - f l: 4 4 r4 W H T i - . . . . I H 1 4 -- H E as tE n d . • . I — . - . , . • U pp er G ro i _ - — L i’ i - E as t To w er . . . . . . . . • j. . . . L ow er G ro in _ j . - — _ _ T •_ -. — +— -- - j : i I - — — E a s tT o w e r .H [ E J ’ , H 1 ’ H h : 1 Lif t U pp er G ro in E nd , i 4— I 1Lj. 41 r , . r T F a c e 1 4 : o s t To w er F a c e t H I t1 p = T o w er sB ea .h — - : r - r - ; - I r * r . r z : : j t r 1: : z r. .i !L 7 - i_ L tt t . . - d— . r U pd nf t Si de O ut f. a. II .:. . . . . E 1 . :4 iJ . L ±r +J +j 1 . f T r l T r T ow er s B ee D ow nd ri ft 7. 8 I . . Id e O ut ta I i _ . _ ! H — - - - - r- - I I I I Ti . - r i [ ] 1, 1 LM — f r- rr ’— r, 1 i * f — . . — . . — . . 1 r— 1— —— —— —— r—j— — ii .! Ii I • i.. I I ; • I j l : : r T T E -t t T : : fL h 1 i + h 1 ! [j’ :?1 1 - — . - — — — — . — — — — . — — . . — . . — — — — . — . _ . . I * • . . . 11 :1 I l _ ! I I il _ f .. - - H ’- — hn t’ 4 ’ J J 4 - : : — U — — . . . ;; Iii I — i I 1.1 II . . - . . 7 . , I I. W es t B eo c . • • I. 1 . . . ii I L ow er B e c h F ac e . — . . - — . - . I - - . : . Ii i I . . 1 1 . ‘ ii W es iB ea c , . . . . . , . • , . i I J } i I i [I l1 I I j I f : [ I L o w e r B e a c h F a c e . 1 . : : i. ! .: ;. lr H i l l • - z rt -T p— I I. e e . . I— — • • . • _ . , . — — — - r zt !i II .I _ lI If l. .t .. lI .j .I .f l - - , ;: - . . 4. .i. ;.: H -’ -i 44 — . * - • i; • — F-F - +H — H — . 4’; — :1 : •L,. UiJ J..L!i i.Ji I - I ILi- FI G U R E 24 . C h ar t o f p h o to g ra p h s e q u en ce s fo ll o w in g c o n s tr u c ti o n a c ti v it ie s . 69 The charts of Figures 25, 26 and 27 are compiled from the photographic summaries charted in Figures 23 and 24 and from corresponding information derived from cross—sectioning data. The S, -, and + symbols represent the activity of the beach at that location during that particular time period. U PP ER BE A CH FA CE W es t W es t LO C A TI O N T ow er T ow er W es t L o o k in g L o o k in g E a st T ow er E a st T ow er B ea ch W es t E a st L o o k in g W es t L o o k in g E a st E a st E nd D A TE 19 74 — 75 19 74 — 75 19 74 — 75 19 73 — 74 19 74 — 75 19 73 — 74 19 74 — 75 19 73 — 74 19 74 — 75 A u g .1 -A u g .1 5 - - - + S + S - S A u g .1 5 -A u g .2 8 - — — + S + S - S A u g .2 8 -S ep t. 2 6 — — - + S + S — s S ep t. 2 6 — O ct .2 2 — — — + — + S + s O ct . 2 2 -N o v .2 6 - - - + + - + - N o v .2 6 -J an .6 - + - - - - - + - Ja n .6 -J an .1 O - + + - — - - + - Ja n .1 D -F eb .. 4 - - - - - . - - + + F e b .4 -F eb .1 6 - - - — — - - + + F eb .1 6 -M ar .1 8 — — — — — — + — M ar .. 1 8 -M ar .2 5 — — — - — — — + - M ar .2 5 -M ar .3 1 + + + - - - - + S M ar .3 1- M ay 12 — + — 0 0 0 — 0 S + a c c u m u la ti o n o f m a te ri a l - e r o s io n o f m a te ri a l S n o c h an g e 0 n o :i n fo m a ti o n FI G U R E 25 . C h ar t c o r r e la ti n g p h o to g ra p h in fo rm a ti o n w it h c r o s s - s e c ti o n in g d a ta o n u p p er b ea ch fa c e s. - 1 cD G R O IN S LO C A TI O N W es t W es t O u tf a ll E a st E a st B ea ch B ea ch O u tf a ll D ow n— T ow er T ow er E a st • U pp er L ow er U p d ri ft d ri ft U pp er L ow er E nd D A TE 19 74 — 75 19 74 — 75 19 74 — 75 19 74 — 75 19 74 — 75 19 74 — 75 19 74 — 75 A ug .l — A ug .1 5 0 0 0 0 0 0 0 A u g .1 5 -A u g .2 8 - S S + S + + A u g .2 8 -S ep t. 2 6 + + + - S + + S e p t. 2 6 -O c t. 2 2 + — + — - + + O ct .2 2 -N o v .2 6 - - + + - + + N ov .2 6— Ja n. .6 — — — — - — + Ja ri .6 — Ja n .l O — - — — — — + Ja n .l 0 — F eb .4 — - — - — - F e b .4 -F e b .l 6 - + - - - - - F eb .1 6 -M ar .1 8 - — - — + — + M ar .l 8 -M ar .2 5 - - + + + + + M ar . 25 — M ar .3 1 + — — + - ÷ + M ar .3 1- M ay 12 - + - - 0 0 + + a c c u m u la ti o n o f m a te ri a l - e r o s io n o f m a te ri a l S n o c h an g e 0 n o in fo rm a ti o n FI G U R E 2 6. C h ar t c o r r e la ti n g p h o to g ra p h in fo rm a ti o n w it h c r o s s - s e c ti o n in g d a ta a t g ro in s. SA N D BA RS LO C A TI O N W es t E a st E a st T ow er T ow er T ow er W es t L o o k in g L o o k in g L o o k in g B ea ch E a st W es t E a st E a st E nd D A TE 19 74 — 75 19 74 — 75 19 73 — 74 19 73 — 74 19 74 — 75 ‘ 19 73 — 74 ‘ 19 74 — 75 Ju ly 7 -J u ly 19 + + - Ju ly 19 -A ug .1 + + - A u g .l -A u g .1 5 + - + + + - - A u g .1 5- A ug .2 8 + - + + + - - A u g .2 8 -S ep t. 2 6 + - + + + + + S ep t. 2 6 -O ct .2 2 + + + + + + + O ct . 22 -N ov . 26 + + + + + + + N o v .2 6 -J an .6 - + - - S + Ja n .6 -J n .1 O - + — - - + + Ja n .1 O -F eb .4 - + - - + + F eb .4 — F eb .1 6 - + - — — + + F eb .1 6— M ar .1 8 - + - - — + — M ar .1 8 -M ar .2 5 ‘ — + — — - — — M ar .2 5— M ar .3 1 — + — — — — — M ar .3 l— M ay 12 + + - — + s a n d b ar m o v in g in o r u p b ea ch fa ce . — s a n d b ar m o v in g o u t o r do w n b ea ch fa ce S n o c ha ng e o n o in fo rm at io n FI G U R E 27 . C h ar t c o r r e la ti n g p h o to g ra p h in fo rm at io n w it h c r o s s - s e c ti o n in g d at a o n s a n d b ar s. 73 Figure 28 shows the annual summer—winter beach cycles at several sections of the beach. These cycles are derived from the correlation of annual peak extreme wind periods with beach deposition—erosion patterns evident from Figures 25, 26, 27. Selection criteria for peak extreme wind periods is outlined in Section 3.2 of Chapter III. I•r J H 0 tn 0 w ‘ 1 a CD C CD :, :‘ P’ P p 0 C 0 C, — 4 .. • 0 . • . U , , 3’ - i E. • . 4 ‘ 6 L 4 - pe r B a. c. h. - Ei. 4 E o t E as t E as t Ii t.t n d Ii n d S To w er ‘ 1 CD F w - 3 0 z 4 O Y I’ O • A TI V I IE S CD C, 0 . n d ba r Qp pe r B ea c 1 - - 1 - Z o “ c. . 0 CD C :c r p ÷ ‘ .0 - 4 0 - . 4. GD pJ I-1 CD U t:L1 CD pJ C) J. (n CD ri CD II CD a 3’ -4 rn : 4 - S on d U pp e - H - — 4- -— r B ea - r HE E + 4- - - H - - i 44 4. • . I. h .! E as t W es t W es t W es t T ow er ( . T ow er To w e B eo c LL t LI - I • - - H . LU 4 - ± .H -t i4L L. . 1. . So n F- -f- 1 U pp ba r > < — - r B ec ‘ - + 4 + . 4 . it . - . jEtL 4:1:1 T 4’ . 4 — i - - - - - 0 t4z rJ 4 ± . r: r ;N TE l4 .. L !. W es t I I r t - T . it +L I-[1 H- L i - - - 4 - - - - - - 4- -i- -- + ± . - t- 4.- t m 3’ C- ) = 3’ C- ) - 4 - 4 - < 3tS M 1 I i_ I _ _ ! _ _ [ . E L D U F E R :t h 7N G A T / E R : 4f -J- ’.1 4- J-H !H • . . , 4 I - . 4 .4 - i-- 4- 4- 4- - H -4 -- 4 .L 4 . 4 .. 1 .4 -. . . o c . :i :; : - F :;: :4 jL 9/ -1 c R A 4j J z t4 4. t F l : 1 i • • . SL f ir - D L R T • , C I 4 .L L L L .i _ L R — 4- ; s lj . L. C i J R - — I_ I. ’. G E4 T I- C ± ii :. :t± tr i:t . i t tl- t S H R T b - - - rr N S I O Q 3 0 o c (D C 3’ -4 0 z E L . ) C I I E 4 V L. C /T /1 $ 4ç a /E L ) C / IE V L C I T I E S t 1 1 i- z : . 4 : : 1 . z : . , : : . - : : - . . L .’ . j : : : : : j: : - :. H . : . . . . : : : - - . : L . L: :1 4 : L L H it . . : . . fl T — — 7 - . - . H I H ‘ . : - - L 01 4 ‘ & . 1- IG H R 6’x - L C W E d’ I I . , - . , . . - . I, - 0 - . - ‘ E L 7C / IE S : . . V L O IT l S . : : IE L )C I IE S - I V L .O i r i rs - 3 Zh z z ‘ Z _ * LL H - J 75 5.3 SAND MOVEMENT ON THE WEST BEACH Sand movement on the west beach is directly influenced by both velocity and duration considerations. There appears to be certain minimum duration requirements over a range of suit ably high wind velocities needed for the seasonal transition from onshore movement of sand to offshore movement. High winds of long duration are necessary to move the west beach sand into the offshore sand bar configuration typical of beach areas exposed to waves approaching at little or no angle. Waves necessary to accomplish this must retain enough energy or sand—carrying capacity during the downslope backrush to consis tently move sand seaward into the offshore bars. High wind periods of at least 23 miles per hour maximum sustained velo cities (Refer to Chapter III, Section 3.2 for definition criteria) with miiiimum 24 hour durations appear to be the necessary conditions for the west beach to be in its winter off shore bar configuration. Periodic higher velocity wind periods of this duration provide exposure of the beach face to wave attack over a period of two tidal cycles. Waves generated by these wind conditions approach the headlands with minimum deep water wave heights of 4.1 feet and periods of 4.4 seconds. Con ditions are appropriate from November through May for offshore bar building on the west beach. The remaining part of the year durations and velocities are lower and sand moves inshore and up the beach face. 76 At the extreme higher end of the beach the protective beach fill was eroded and removed seaward throughout the year with the exception of the March 25 to 31, 1975 period. On March 30, 1975 occurred the highest winds on record for ten years as given in Table II. These waves, approaching from the WNW, were of such size as to throw large sand and pea gravel up onto the upper beach in berm-building action. As a result this storm refaced the extreme upper side of the entire west beach with sand and gravel. Following the storm this berm material proceeded to be removed also. 77 5.4 SAND MOVEMENT ON THE TOWERS BEACH AND EAST END The west tower marks a dramatic alteration from the west beach alignment and exposure (Refer to Figure 1 for Wreck Beach configuration). Here the upper shoreline and cliff makes a sharp turn, forming an angle with incoming wave attack, and a corner is exposed to wave forces. As can be seen from the refraction diagrams in Figures 8 through 12 wave crests from the westerly directions begin an accelerated bending to ward an alignment with the upper shoreline along the length of this section of Wreck Beach. As a result wave energies tend to converge and concentrate at the west tower corner, thereby increasing their erosive powers. Downcurrent though toward the east wave energies spread as indicated by the di verging orthogonals on the refraction diagrams. Like the west beach the protective berm fill continually eroded through the year except for the refacing during the March 30, 1975 storm. Near the west tower erosion of the pro tective fill commenced immediately following construction and continued during the summer period. With the transition into higher velocity and longer duration winter winds erosion pro ceeded faster at the west tower and commenced in the more pro tected east end. 78 5.5 SANDBAR MOVEMENT From the west tower eastward sandbars as distinct units appear to migrate along the length of the beach in the direction of their long axes. The information presented in Figures 28 and 29 summarizes the movement of sand in the nearshore region of Wreók Beach. The evidence suggests that sand moves up and down as well as along the shorelines in definite rhythmic patterns in response to cyc lic weather activities. The orderly progression of sediment down the beach is indicated by the solid lines connecting the transition 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 bulk of a sandbar. On the basis of this data it is reasonable to conclude that sandbars near the intertidal zones progress the length of the beach from the west tower area to the east end annually. That is, during the course of a summer—winter cycle sand moves up, down and along the shoreline in the basic form of sandbars. For example, with reference to Figure 29 the head of a sandbar approached the west tower area on September 26, 1973 after having moved inshore across the west beach during the summer season. By May 1, 1974 the tail of the sandbar had passed the west tower I-. ’ Pi . ) 0 . ø i U) < — J c J U) CD CD ç j rt rt I-’ . CD CD CD r1 ‘ < 0 rt CD 0 P.) i r1 H F- ’ CD c t P) J• ’ CD p. ) H P.) j U) U) rt- P.) Fl P.) I-’ Fl II CD U) H CD i 0 < P.) CD I5 51 P.) p. ) P.) I-’ I-5 U) : U) CD U) CD o . )J CD P.) • . 51 II r1 r t l< CD CD CD CD P.) P.) P.) ).< U) U) rt rt F- ’ . ft çt 0 0 F-’ ‘..D CD CD - . 1 I-5 Fl 01 P.) ft 51 CD P.) CD 0 i- i. i— ’ CD CD P.) P.) 51 CD 51 Fl P.) k) 51 E A ST TO W ER 75 — U PP E R B EA CH 19 74 - E A ST EN D 74 SA N D B A R — E A ST EN D SA N D B A R 97 4- 75 -- - I- W E ST B EA CH SA N D B A R 19 74 -7 5— - r n° — -; - W ES T TO W ER SA N D B A R 19 74 -7 5 % C . ‘ 0ef r < e . 1 I. I I iL O I I I E A ST TO W ER SA N D B A R 19 73 -7 4— E A ST TO W ER SA N D B A R 19 74 -7 5— u - ri- i- iT T i- r ‘ w T iu . 1 i I - ‘ I (. 1 1 1 L T T j F L i r fl - T r I _ L I I l E A ST TO W ER U PP E R B EA CH 19 73 -7 4 1’ I’ E A ST EN D U PP ER BE A CH 19 73 -7 4 rI \ FI G U R E 2 9. A n n u al s a n d b ar m o v e m e n t. CHAPTER VI $ UMMARY 6.1 CALCULATION OF VOLUMES CAPABLE OF BEING MOVED BY WRECK BEACH LONGSHORE TRANSPORT SYSTEM The volume of sand capable of being moved if available by the Wreck Beach longshore transport system is dependent upon the size of wave attack, frequency, duration, angle of approach, sediment characteristics and beach slope. Correlations of these parameters have been determined by Castanho. Any calculations of the amounts of littoral drift are subject to a large uncertainty and few methods are available which are suitable to the Wreck Beach study area. Castanho’s calculations have not been widely published or tested but are suitably applicable to the study area and are likely good to within a factor of 2. Wreck Beach fits well into the typical characteristics suggested by Castanho in the use of the sandy shores equation. Some valuable conclusions can be made about sand transport on Wreck Beach even though a precise calculation is impossible. Castanho’s method is outlined in “Coastal Engineering”, Volume II, Chapter I by Richard Silvester together with the necessary graphs and coefficients. Using the Castanho equation suggested for sandy shores estimates of longshore transport volumes were determined for the annual summer—winter cycles of 81 82 1973—74 and 1974—75, Tables VI and VII, and for the 1973-74 and 1974-75 freshet seasons, Table VIII. The volumes given in Tables VI, VII and VIII are quantities of sand which if available are capable of being moved north and south annually, and during the brief Fraser River freshet period by the Wreck Beach longshore transport system. The equation for sandy shores, 7GT/wH02L = Ersino(bcoso(o where w = specific weight of sea water = 64 pounds per cubic foot S = specific weight of dry sand = 100 pounds per cubic foot is solved for G, the volume of sediment moved per hour across a plane perpendicular to the beach, and is listed in the Tables as the Hourly Transport Volume. The Hourly Transport Volume represents the ability of wavesof that particular regime to transport sand. The Average Rates are based on actual wind directions and wind frequencies occurring during the given time periods and the volumes which could be moved on Wreck Beach by the resulting wave fields. Volumes attributed to winds from various direction are de termined from directional wind frequency information given in Table V. Table V presents the hourly values of wind blowing times from the percentage frequency data derived from Table II and the wind rose of Figure 30. 83 . DIRECTIONAL HOURLY WIND FREQUENCIES WIND - A B C D FREQ Annual Annual Annual AnnualAverage WIND\ 1973—74 1974—75 1973—74 1974—75 1973—74 1974—75 Y early DIRECT\.. % hr % hr % hr % hr % hr % hr hr NE — — — — — — — — 5.0 438 5.0 438 5.0 4 38 NNE — — — — — — — — 1.0 88 1.0 88 1.0 88 N — — — — — — — — 1.0 88 1.0 88 1.0 88 NNW — — — — — — — — 1.0 88 1.0 88 1.0 88 NW — — — — 0.5 47 — — 4.0 350 3.5 303 4.0 3 50 WNW 0.9 81 2.2 192 0.5 44 1.0 89 4.6 401 2.8 244 6.0 526 N 0.7 57 0.7 64 0.4 33 0.2 13 8.0 698 8.1 711 9.0 788 wsw — — — — — — — — 4.0 350 4.0 350 4.0 350 SW — — — — — — — — 3.5 307 3.5 307 3.5 307 DIRECTIONAL HOURLY WIND FREQUENCIES WIND A B C FREQUENCY Freshet Freshet Freshet WIND 1973 1974 1973 1974 1973 1974 DIRECTION, % hr % hr % hr % hr % hr % hr NE -: - - - - - - - - - - - NNE - - - - - - - - - - - N - - - - - - - - - - - - NNW - - - - - - - - - - - - NW — — — — 0.2 13 0.1 1 0.7 57 0.2 19 WNW 0.1 8 — — 0.5 41 0.4 37 1.2 103 1.5 129 W 0.1 3 — — 0.3 22 0.1 8 0.5 47 0.7 59 wSw — — — — 0.1 4 — — 0.5 40 0.5 41 SW — — — — 0.1 6 — — 0.3 23 0.2 16 TABLE 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 CD c o 85 Volumes according to wind velocities or wind strengths have been derived by grouping winds of all direction into Groups A,B,C and D with the average wind regime characteristics given as follows. Winds used in determining NE transport for the entire year are divided into three groups. The Peak Extreme Wind Periods, A, are those defined in Section 3.2, Chapter III selected from Table II. Included are all winds having maximum sustained velocities above 24 miles per hour. The General High Wind Periods, B, are those winds remain ing in Table II except those entered in Group A. Included are winds having maximum sustained velocities in the range 17 to 24 miles per hour. Groups A and B contain all the wind periods listed 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 the range 8 to 16 miles per hour. The Northern Wind Periods, D, for the year used in de termining the SW transport are the average 10—year winds given in the wind rose of Figure 30. Included are the winds from the NE to NW sector which affect the southwesterly movement of sand on Wreck Beach. 86 The distribution of wind blowing times between groups A,B and C is as follows: - of the wind periods included in Group A, 25 percent of the blowing time was spent near the 25 knot velocity, 75 percent of the time was spent at lower velocities so added into Group B; - of the wind periods included in Group B, 75 percent of the blowing time was spent near the 20 knot velocity, 25 percent of the time was spent at lower velocities so added into Group C. Winds during the months of the Fraser River freshet, mid-May through mid-July, are distributed into the A,B, and C groups also and derived from daily meteorological records monitored at the Vancouver International Airport by Canada Atmospheric Environment Service. Typical wave characteristics for these groups are the averaged values given in Table III. 87 Group A. Peak Extreme Wind Periods: Average maximum sustained velocity = 28 mph = 25 knots H0 = 5.1 feet T0 = 4.9 seconds L0 = 123 feet Group B. General High Wind Periods: Average maximum sustained velocity = 22 mph = 20 knots H0 = 3.8 feet T0 = 4.3 seconds = 95 feet Group C. Other Wind Periods: Average maximum sustained velocity = 11.5 mph = 10 knots H0 = 1.6 feet T0 = 2.7 seconds L0 = 37 feet Group D. Northern Wind Periods: Average maximum sustained velocity = 11.5 mph = 10 knots Average fetch = 6.5 miles H0 = 1.0 feet T0 = 2.2 seconds L0 = 25 feet 88 Examples in the uses of Tables VI, VII and VIII. Example 1. What total volume of sand was transported by waves generated by winds from the west during the 1974-75 year? NE movement by Group includes freshet NE movement by Group includes freshet NE movement by Group includes freshet SW movement by Group A winds volume of B winds volume of C winds volume D 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 the west moved a total of 16,908cy toward the NE. During the freshet period of that year these winds moved 2031cy of the total 16908cy in the same direction. That is, 12% of the yearly volume transported by winds from the west could have moved during freshet. Winds from the west did not contribute to movement of sand in the opposite direction (see Table VII). = 3477cy 0 cy = 4907cy 1280 cy 8524cy 751cy = Ocy 2031cy 16908cy 89 Example 2. What volume of sand was transported by waves generated by 25 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 6l5Ocy During the year 1973-74 waves from winds of 25 knot velocities transported a total of 6150 cy of sand, all of it toward the NE. No 25 knot winds occurred which were effective in moving sand in the opposite direction. (All sand transported toward the SW was 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 have moved 2567 cy of the total 6150 cy in the same direction. That is, 42% of the annual volume transported during the 1973-74 year by 25 knot winds could have occurred during freshet. 90 Example 3. What volume of sand would waves from a 10 hour WNW wind of 20 knot velocity be capable of moving on Wreck Beach? In what zone of the beach would this movement likely take place? A 20 knot velocity wind is included in Group B winds. From Table VI WNW winds of Group B have an Hourly Transport Rate of 1944 cubic feet per hour. During a 10 hour period 19,440 cubic feet (720 cubic yards) of sand could be transported toward the NE. Table VII indicates that WNW winds are not effective in moving sand in the opposite direction. From Table IV movement of sand by these waves takes place in water depths of up to 10 feet. A 10 hour period covers almost an entire tidal cycle. If it coincides with a large tide then sand would be moving as far seaward of the cliff base as 2000 to 2300 feet which would be near the 2 fathom contour line on a Canadian Hydrographic Chart (see Figure 31). 91 Example 4. How often do winds blow out of the NE that are capable of transporting sand on Wreck Beach? From Table VII winds from the NE direction are effective only in moving sand toward the SW. These winds are of Group D having an average velocity of 10 knots. (Higher velocity winds of Groups C,B and A do not occur with respect to Wreck Beach calculations) . These winds occur approximately 438 hours per year, 18¼ total days, and could contribute 503 cy to the SW littoral drift. (NE winds do not contribute to movement of sand in the opposite direction, see Table VI). A N N U A L LO N G SH O RE TR A N SP O R T V OL UM E TO W AR D TH E N E . H o u rl y 1 9 7 3 i9 7 4 19 74 — 19 75 W av e T ra n sp O rt W in d Y ea rl y W in d Y ea rl y D ir e c ti o n V ol um e F re q u en cy V ol um e F re q u en cy V ol um e c . f. /h r. h o u rs - c .y . h o u rs c .y . A .N W 50 4 - - - - W NW 39 96 21 31 08 48 71 04 W 58 68 14 30 42 16 34 77 W SW 57 24 — — — — SW 17 28 — — — — SU B TO TA LS 35 - - 61 50 64 10 58 1 A V ER A G E R A TE S 17 5 c y /h r. 16 5 c y /h r. B . NW 25 2 35 32 7 — — W NW 19 44 78 56 16 17 5 12 60 0 W 28 80 57 60 80 46 49 07 W SW 28 08 — — — SW 82 8 — — — — SU BT O TA LS 17 0 12 02 3 22 1 17 50 7 A V ER A G E R A TE S 71 c y /h r. - 79 c y /h r. C . NW 29 36 2 38 9 30 3 32 5 W NW 23 4 42 7 37 01 30 2 26 17 W 31 7 71 7 84 18 72 6 85 24 W SW 32 0 35 0 41 48 35 0 41 48 SW 97 30 7 11 03 30 7 11 03 SU B TO TA LS 21 63 17 75 9 19 88 - - 16 71 7 A V ER A G E R A TE S 8 c y /h r. 8 c y /h r. TO TA LS 23 68 h o u rs 35 93 2 c y . 22 73 h o u rs 44 80 5 c .y . TA B LE V I. A n n u al lo n g sh o re tr a n s p o rt v o lu m e to w a rd th e N qE , A N N U A L LO N G SH O RE TR A N SP O R T V OL UM E TO W AR D TH E S. W . H o u rl y A v er ag e A v er ag e W av e T ra n sp o rt W in d Y ea rl y D ir e c ti o n V ol um e F re q u en cy V ol um e c . f. /h r. h o u rs c .y . D . N E 31 43 8 50 3 N N E 10 4 88 33 9 N 10 3 88 33 6 NN W 75 88 24 4 NW 10 35 0 13 0 A V ER A G E R A TE 1 .5 c y /h r. TO TA L 10 52 h o u rs 15 52 c .y . TA B LE V II . A n n u al lo n g sh o re tr a n s p o rt v o lu m e to w a rd th e S. W . . 0 FR E SH ET LO N G SH O RE TR A N SP O R T V O LU M E TO W AR D TH E N .E . H o u rl y 19 73 — 19 74 19 74 — 19 75 W av e T ra n sp o rt W in d Y ea rl y W in d Y e a rl y D ir e c ti o n V ol um e F re q u en cy V ol um e F re q u en cy V ol um e c . f. /h r. h o u rs c .y . h o u rs c .y . A .N W 50 4 - - - - W NW 39 96 10 14 80 — — W 58 68 5 10 87 — — W SW 57 24 — — — — SW 17 28 — — — — SU BT O TA LS 15 25 67 0 0 A V ER A G E R A TE S 17 1 c y /h r. 0 c y /h r. B . NW 25 2 16 14 9 4 37 W NW 19 44 44 31 68 41 29 52 W 28 80 26 27 73 12 12 80 W SW 28 08 7 72 8 — — SW 82 8 9 27 6 — — SU B TO TA LS 10 2 70 94 57 42 69 A V ER A G E R A TE S 70 c y /h r. 75 c y /h r. C . NW 29 60 64 25 27 W NW 23 4 10 5 91 0 13 5 11 70 W 31 7 50 58 7 64 75 1 W SW 32 0 43 51 0 46 54 5 SW 97 26 93 20 72 SU B TO TA LS 28 4 21 64 29 0 25 65 A V ER A G E R A TE S 8 c y /h r. 9 c y /h r. TO TA LS 40 1 h o u rs 11 82 5 c .y . 34 7 h o u rs 68 34 c .y . TA B LE V II I. F re sh e t lo n g sh o re tr a n s p o rt v o lu m e to w a rd th e N .E . 95 The Wreck Beach longshore transport estimates predict that typically volumes of 40,000 cubic yards ± 20,000 cubic yards (see Table VI) are transported to the NE annually past a plane that could be extended perpendicular to the beach shoreline. Because of the uncertainties associated with sediment transport problems particularly coastal situations a fairly large error is assigned to the estimates. An indi cation of the scatter of data from field tests and laboratory tests in the range of a general solution is outlined by Sil— vester, “Coastal Engineering”, Volume II, Chapter 1. The volumes computed from the Castanho calculations should be considered no more accurate than to be within a factor of 2. Wave activity is also capable of moving to the SW small volumes of about 1550 cubic yards (see Table VII) in a rela tively narrow beach width confined mostly to the intertidal exposure areas. This minor amount of sand constitutes only 3 to 4 percent of the total volume transported annually. This quantity is roughly equivalent to a 5 yard truck moving south west along the beach once a day, while transport to the north east is approximated by a 5 yard truck moving along the beach in that direction once every hour. Throughout the year information presented in Table VI suggests that winds of Group C with velocities from 8 to 16 miles per hour move some 17,000 cubic yards of sand annually or 40 to 50 percent of the total volume transported. These low 96 velocity winds occupy the greatest portion, 90 percent, of the wind frequency blowing times under consideration. These winds apparently are responsible for a sizable and constant yearly movement of sand in the Wreck Beach longshore transport system. That is, about one-half of the sand volume carried by the aforementioned 5 yard truck moving northeast each hour is produced by 16 mile per hour winds and under. On the other hand, when the high winds of Groups A and B do occur large volumes are moved in brief time intervals: compare in Table VI the average rate of 170 cubic yards per hour for A winds with 75 and 8 cubic yards per hour for B and C winds respectively. As indicatedin Table IV the width and extent of the zone in which sand is actively moved by waves generated from winds of Groups A and B ranges up to twice as far seaward and in depth as the active zone produced by low velocity winds of Group C. Using the derived Hourly Transport Rates presented in Table VI sand volumes moved during individual storms can be estimated. From Table II four high wind periods were selected with two of these having extremely high winds. Hourly directions and velocities were taken from meteoro— logical records monitored hourly at the Vancouver International Airport. Rough estimates of the volumes moved toward the NE 97 during these periods and the longshore current velocities generated at the wave breaking point are listed below. January 8-9, 1975 February 19-20, 1975 March 25, 1975 March 30, 1975 2500 cubic yards 4700 cubic yards 1500 cubic yards 3300 cubic yards 1.7 to 2.2 ft/sec 2.2 to 2.6 ft/sec 1.7 to 2.2 ft/sec 2.2 to 2.6 ft/sec Both the February 19-20, 1975 and the March 30, 1975 storms had several hours of 35 to 40 mile per hour WNW winds with the associated longshore transport velocities given in Table III. The January 8-9, 1975 and March 25, 1975 storms had lower con tinuous WNW winds of about 25 miles per hour. Other information associated with the March 25, 1975 storm is presented in Chap ter IV, Section 4.6. 98 6.2 FRASER RIVER NORTH ARM AS A SAND SOURCE Net sediment transport around the Point Grey headlands is to the NE so the large submerged sandbank extending off shore SW seen in Figure 31 must have an important relationship with the transport system. The Point Grey headlands marks the upstream beginning of a transport system which evidently con tinues well into Burrard Inlet via the shoreline. As such the sandbank extending from the northern bank of the North Arm mouth is an area of considerable activity where Fraser River sand is absorbed into the system at the outer limits of the transport zone. The Fraser River freshet reaches a maximum from mid—May through mid—July. During this short time a great deal of material is added to the sediment budget of the area. These events coincide briefly but provide a mechanism for moving sediment available during its most abundant period from the river channel onto the Wreck Beach offshore sandbanks. The Public Works dredging records for the past ten years is con tained in Table IX. The dredging records and theoretical vol umes are courtesy of Mr. Woo, Department of Public Works, Van couver, British Columbia through personal telephone communica tion in August, 1975. 99 FRASER RIVER NORTH ARM DREDGING RECORDS Annual 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 of bottom 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 Mouth April to March Volumes Dredged Cubic Yards 1964 1965 33,600 1965 1966 164,000 1966 1967 354,000 1967 1968 416,000 1968 1969 286,000 1969 1970 347,000 1970 1971 142,300 1971 1972 397,100 1972 1973 211,000 1973 1974 196,000 1974 1975 93,300 (incomplete) Average volume dredged: sands and gravels Total = 240,000 cy. TABLE IX. Fraser River North Arm dredging records 100 The North Arm mouth is dredged each year immediately following freshet to maintain an open navigation channel up to depths of 20 feet below lower low water. Some 1,330,000 cubic yards of material of all sizes enters the North Arm each year. At the mouth an average of 240,000 cubic yards is removed by yearly dredging. Leaving the North Arm mouth is the wash load faction consisting of silts and clays and the sand and gravel volume less the dredged quantity. The silts and clays are washed quickly seaward and do not contribute significantly to the head lands sand transport system. Therefore 90,000 cubic yards is available annually for introduction into the headlands process. Winds from the SW through the Nw continue through the freshet season of sufficient velocity to generate wave fields capable of moving sand from the North Arm mouth shoreward to Wreck Beach. Referring to the breaking depth, db, column of Table III delineates the breaker zones for the given wind dir ections and wind velocities where for practical purposes most of the active movement occurs. For the winds which did occur during the freshets, Table VIII, movement from waves of Group A could have taken place in depths up to 12 feet below the zero contour depth; from Group B, up to 10 feet; and from Group C, up to 6 feet. Figure 31 is an hydrographic chart of the study area showing contour lines and sounding depths at the mouth of the North Arm river channel and the offshore region of the Wreck Beach area. From Figure 31 it appears that throughout the channel there 101 are areas of depths 12 feet and less where sand would be available to wave transport activities and subsequent introduction into the Wreck Beach longshore system. The large area outlined by the 6 foot contour (1 fathom) would be a region where winds of Group C (8 to 16 mph) would be capable of transporting sand and where winds of Group A and Group B would be particularly effective. Further, the shape of the underwater topography at the North Arm mouth and headlands seen in Figure 31 suggests that river sand is influenced by the winds and waves under consideration. Rather than a fan-shaped delta common of undisturbed deposition the con tours are distinctly skewed toward the north indicating wave-swept movement of sand. The volumes of sand capable of being moved by winds and waves during the 1973 and 1974 freshets were estimated using Castanh&s method and presented in Table VIII. The quantities range from 7,000 to 12,000 cubic yards. The freshet transport activities are capable of moving into the headlands longshore system about 10 percent of the 90,000 cubic yards of sand reaching the North Arm mouth providing it were in depths less than 12 feet at lower low water. However, part of the sediment is in depths greater than 12 feet. As well winds might occur during the higher waters of a tidal cycle which with respect to the North Arm supply moves the sediment out of the range of wave actions. HD iP ) iu .1 C D z 0 r1 I-1 Di CD C) CD Di C) Di CD Dl (n 0 U) - U ) c t C ) I- Li 3P a ) . - 1_ a. I•- ’ cD P) — ‘ Co o Q J .) 1_ ac 4 \ Q o m % I • 11 11 1_ a \O O o o a a ‘ - )‘- ‘)O C ) (D C D 0 (D C D O ç + c t 0 ) 10 — - - . - - - - - - . - - - - - ID r) 0 0 c i) 0c U ) — . U ) cc c ‘ — • • cL -.c c- ..Z 3 I’ J — . . J . - F’ ) / — = — f ., _ j — “ 0 F’ ) “ L i q 01 = — 0) FL ) - . 1 \ _ 0 1 • • • U ) U ) 01 = a c .. - O w F’ ) • I - . \ • - 1 U ) F’ ) - \ Is ) FL ) 0 C. ) = = U ) F’ ) “ 3 01 ) /0 ) F) . . . ? C. ) 0 103 Waslenchuk, 1973, found limited amounts of sand on the outer bank which he determined to be of the same origin as sand found near the mouth of the North Arm. In the nearshore and on the beaches the sediment proved to be exclusively of cliff origin. Significantly, his work does not concentrate on this crucial though brief time of freshet. Instead the work was done in Novem ber and February and the importance of the sediment supply peak with accompanying sand movement mechanism are lost over the winter. By winter the bulk of the freshet sand will have already moved around the headlands. This is evidenced by the sandbar progression described in Section 5.5 of Chapter V and by the building of the beaches in the summer, then the loss of sand and exposure of rocks by winter described in Sections 5.3 and 5.4. 104 6.3 WRECK BEACH CLIFFS AS A SAND SOURCE If, as Waslenchuk suggests and longshore transport cal culations indicate, the Fraser River is not presently the only major source of sand supply to the longshore transport system in the Wreck Beach area then the headlands themselves must be supplying a large portion of the sediment to maintain the system. In the area of most active erosion, just below the new Museum of Man, 1200 feet of near-vertical cliffs 200 feet high are estimated to be receding at about one foot per year. At this rate 8900 cubic yards annually (1 cubic yard per hour) of sediment is supplied from this area alone. If the remaining 2200 feet of eroding and susceptible cliff face along Wreck Beach is receding at a much slower rate of one—half foot per year then an additional 8200 cubic yards (about 1 cubic yard per hour) also becomes available annually. Under these conditions the cliffs appear to be supplying a volume of about 17,000 cubic yards of sand each year to the longshore transport system. The Wreck Beach cliffs appear to be eroded by wave attack in a cyclic pattern which may be as follows: - vigorous attack at the base of the cliffs during the winter months at times when higher tides and high wind periods coincide, - movement of part of the sand to help build up the offshore sand bar and part of the sand moves northeast out of the study area, — during the summer months sand moves from the offshore sandbar onshore, - erosior of the onshore accumulation during the following winter. 105 6.4 CONCLUSIONS The information and calculations suggests that the North Arm could amply supply the longshore transport nourishment re quirements. However, some means in addition to the present natural processes must be available to bring this sand into a range where wind generated wave activity can incorporate it into the existing headlands transport system. Li C) W bJ W C) P3 CD H H - P3 H P3 P3 P3 II Cl) I-i Cl) H - C) CD Cl) Cl) C) P3 P3 CD P3 0 H 0 a CD CD CD c w -. 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U 1P 3P 3 0 F - h (-f lP 3H - I- hC )c i- L D i H - CD CD H I ‘ - D Fl o P 3 1 O I- _ J1 - • tI C ) H C J) • - )F -h O C fl • O C !) 0 H - Q -j . t I C D (- l- C ) .I J (t fr h W I— ’ P3 H P3 Ct P3 Cl )C DP 3 • CD C ñ [ l P I-) 0 O L i 0 H O C )c t- i CD II CD H -a c t- C t- I . Q tI Cl) 0 . D F- h (D O )) -’ H - H -F 3 c tb ’ I— hr i- < 0 c ’ — - . . i C D C ) (D O ç -i - P 3Z C D H -H -c t- ‘ Cl) Cl) a ’ tJ çt p iC l) H - • C D P 3 C l) P 3 I—i C )0 H - - • P 3 C) C) 0 < C fl 3 O H - Y ”C D P 3 O H - 11 0 fl )- C C D cI -0 I-h CD H -H - H -i < 0 H - H ,F -’ li C l)C D II C fl H CD fl W C /) H P 3 H - H - 0 Cl) - . CD CD 0C l) H - 0 h 0 . 0 1C D < 0 Cl) 0H iC D C D H - ci- CD Cl ) H C fl 3 (D [-h (i b’ P3 O r- b- )’- < O H - C )c -t - i-I CD H O C fl cI CD H ci - ti C ñ’ tJ II CD H H - 0 ‘ t 3 O ’- < H -O 0 L O P3 H - tQ H -I -3 C 1) P3 c l- H • 0 P3 P3 C fl C D . ‘ - < F- h I- Id - ‘ - < 0 P 3 I— ’ ‘ - < Ii i-h ‘ - < ‘ - < r i d -F l’ ‘ H- , - (D O H I ci- - H - — H - C l)H Cl) 0 C D H F- -C D ‘ - DC l) CD ci- — J’ II Cl) U) U) U) P3 H - H - H CO CD C!) P3 CD H c t P3 H • CD Il CD CD C) CD P3 0 H C) CD CO t! )H iO Ir l- W c- I- H ’ (T hO P3 P3 P3 P3 P3 b 0 () U )H i’ c t W (T h 0 0 C D I l (D O (D O O Il Ii (D O O C D O C D • O O F- tiC T) C) P 3 O II II C ) P 3 0- i 0- . 0 -i Il C fl H H - I l b 1 1 fl H C O P 3 0 . • 0 CO CO CO r-I - C O • • C D Q W F i - (D Il C D Il - c- I- CD H - l L . ç -I -C O H O H O CD P 3 0 O Il b H Il C ) (D c-I - (D c-I - H Il H H i b I-h Ii C )O P3 H - Z H - ‘ < c- I-P 3 CD C D . ‘ - < CD ‘ - < CD ‘ . 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J C fl Il c -I -0 .i H • 0 P i I - H C D C) CD CD Il II II Il II H -I -I • (D H O C ) C D 1i (D c- I- ‘ c -I -< ‘ CD Il Il CD CD CD CD CD IH - IC O 0 0 C ) 0 1 - C O • O P J H - H- P3 H -C l) P3 P3 P3 P3 P3 c - I- H < • P3 H J F 1 H H < H -H H 0 (D H O C D c- I- c- I- c- I- c- I- c- I- IT 10 1C D ‘ C O ‘ D r t S H- CD 0 O P 3 < ‘ - D Il c D I l 0 ‘- Q H - H - H - H - H - 0 O C D C O c- I- — . jH - H - P3 C O hh ‘ - Q C D C O - JC D - - . 3C D U) 0 0 0 • 0 0 Il C ) I l r t P J M C )C )c -I - H ‘ < C )I lH - w ’ - < O w ’- < O I-I (D O c -I -C )H C D H • P3 P3 C D CO c- I - ‘ 0 -C l) • H i • H i P) (D O CO CO CO CO CO ‘ < . C D c H S 0 1 H ’ C) C) C O Il - - - - - ‘ (T hC OP 3 - ‘ - .0 CD C 4 P 3 H H CD CD L x H -l p c- I- I- <l :1 C) CD 0. H -I l H -I l H - P3 ‘ i U) I-I c- I- P’ H - C) ‘ - 0 0 Cl) M CD C) H -I lH -0 -i H iO H ,0 C) I- I’ tJ P3 CD CD CD 0 0 1 ‘ C J Q Il H - H - • C D F- ht Y H it T P3 C )I l ‘ t C) C O . 0 1 CO CD c- I CD c tf l C O H C O H H O ci Il ’ c t C D ’ C D ’ H -’ ‘ C D P JC D I- Ic -I Il W 0 CD CD c- I- P3 CD 0 Il U )0 CD H c -I -I l C O ø I l L’J C) CD I l P 3 H (D c- I-I -h H Il c -I -c iH P 3 H -H -I lI -I c i c i CD C) ‘ - < CD IlC D b’ CD w C D CD CD CD P 3 3 ‘ - O H - C D H rt c- I- C D C D P 3 p c d < d C D - I Il t5 C V d - b i — I - < ‘ - < I-’ - . H H - i H - l H- c- I- H - 0 ‘ 0 Il 0 0 ‘ 0 0 0 H - 0 4- LC l c- i- <1 CD c- i- P3 CO P3 < 0 1 l (D O H Il Il - Il H Il Il I l c iI — • - ‘ CO CD CO 0 C ) c t CD CD CD I l D c- I- H c- I- ri- ‘ . O ct H c- I- c t H - - ‘ c - I- 0 0 1 I-- h H H - I l I l CD — 3 ‘ .D H ‘ - .0 H - H -c -I - C O H - H i C O Il C O Il I- Li .c -l- — . . 1r i- ‘ . D (t ‘ - . 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