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

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SAND SOURCES, VOLUMES AND MOVEMENT PATTERNS 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  Page  ii  ABSTRACT TABLE OF CONTENTS  iv  .  vi  LIST OF FIGURES  vii  LIST OF TABLES  ix  ACKNOWLEDGEMENT  CHAPTER I  INTRODUCTION  CHAPTER II  RECENT HISTORY OF EROSION  2.1 2.2 2.3  Geology . Erosion Mechanisms Remedial Measures  CHAPTER III 3.1 3.2 3.3  4.1 4.4 4.5 4.6  13  WIND CONDITIONS •  •  .  •  .  •  .  •  •  •  .  13 16 22 24  WAVE CONDITIONS  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  CHAPTER V 5.1 5.2 5.3 5.4 5.5  .  General Wind Patterns Annual Meteorological and Beach Cycles Wind Directions of Primary Importance  CHAPTER IV  4.2 4.3  .  SAND MOVEMENT  24 32 42  43 44 46 50  Limits of the Littoral Zones . • . . Compilation of Data Sand Movement on the West Beach . . . Sand Movement on the Tower Beach and East End Sandbar Movement  iv  50 55 75  77 78  Page  CHAPTER VI 6.1 6.2 6.3 6.4  SUMMARY  81  Calculation of Volumes Capable of Being Moved by Wreck Beach Longshore Transport System . . Fraser River North Arm as a Sand Source . . . Wreck Beach Cliffs as a Sand Source Conclusions .  BIBLIOGRAPHY  81 98 104 105 106  V  LIST OF TABLES  TABLE  NUMBER  I II III IV V  PAGE  Wind scales and sea descriptions  17  High wind period information  19  Wind,  fetch and deep water wave data  33  Limits of the Wreck Beach littoral zones  53  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  vi  99  LIST OF FIGURES  NUMBER  PAGE  FIGURE  1  Wreck Beach study area map  2a  Regional surface wind patterns of the northeastPacificOcean  15  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  2b  14  Enlarged WNW wave refraction diagram  15  Photograph sequence at photograph location 1, East End, prior to construction activities  16  4  *  .  56  Photograph sequence at photograph locations 1 & 2, 57 East End, following construction activities  vii  + .,  pàket  ?  NUMBER  PAGE  FIGURE  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  viii  102  ACKNOWLEDGEMENT  The author is very grateful to her supervisor, Dr. Peter R.B. Ward, study.  for his guidance and encouragement during this  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. study area.  Figure 1 shows the map of the Wreck Beach  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., Consulting Engineer, 1973.  1973 and Robert Wiegel  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  2  The 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, and erosion—deposition patterns.  longshore movement  3  Chapter 5 describes the extent and direction of the longshore 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.  / I..  /  /  I  I / I I 1  4 WRECK -BEACH STUDY AREA —4’--.. Hydrographic contour linE  d  ci  13 Photograph location and direction  I  I  Map Scale: 1”  I I I I I I  \  I  =  -I  /  /  I /  /  330’  I I I I  I \  \  I  \ \  I  \  /  I I I  j  ——  /  7—  /  4  I’ I  I  I  /  / I.  /  /  I  0  /  I II  \  \-  I  I I  1  I  I  ‘I  I  I  I 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  6  the 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.  7  EROSION MECHANISMS  2.2  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,  and McLean,  1975.  the following:  1974, Waslenchuk,  1973, Lum,  1975,  The agents acting to erode the cliffs are  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  8  more 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. draining to the Wreck Beach cliffs Carswell, 1955, that some 400 x io6 gallons of water  In the area determined  (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. cover provides protection against surface runoff,  Plant  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  9  the 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. that the present Campus  Carswell,  1955, estimated  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 197475.  Slabbing on a daily basis was not widespread.  it did occur,  But where  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. ther,  Fur  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.  construction details see Dave McLean’s, Wooster Construction Plans,  1973).  1975,  (For  thesis or Swan—  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 rubblemound 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. suggestions as urged by Swan—Wooster, Wiegel,  1973, Backler,  others included:  1960, Carswell,  These  1973, as well as by 1955, Bain,  1970, and  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; access to the cliff face; the edge of the cliff.  elimination of  and future construction well away from  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 I  /  CANADA  (1)  (ii)  • (I) winter (ii) summer FIGURE 2a. Regional surface wind patterns of the northeast Pacific Ocean.  (1)  * ;• (11)  (ii) spring transition, April-May  (ii’)  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. hour or more)  Occasionally  of up to 40 miles per hour  At rare time gusts of 70 miles per hour at the Vancouver International Airport. winds of 23 to 25 miles per hour  sustained winds (35 knots) (61 knots)  (one  occur. are recorded  However, sustained  (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  Beau fort scale  Seaman’s description of wind  0  Calm  1  Light air  2  3  Wind velocity knots  .  .  .  Estimating wind velocities on sea  Light  Light breeze; small wavelets, crests have  breeze Gentle breeze  knots 7 to 10 knots  glassy appearance and do not break. Gentle breeze; large wavelets, crests begin to break. Scattered whitecaps.  Moderate breeze Fresh breeze  11 to 16 knots 17 to 21 knots  6  Strong breeze  22 to 27 knots  Moderate breeze; small waves becoming longer. Frequent whitecaps. Fresh breeze; moderate waves taking a more pronounced long form; mainly whitecaps, some spray. Strong breeze; large waves begin to form extensive whitecaps everywhere, some spray.  7  High wind  28 to 33 knots  5  (Moderate gale) 8  Gale (Fresh gale)  34 to 40 knots  9  Strong gale  41 to 47 knots  10  Whole gale  48 to 55 knots  Storm  56 to 63  11  knots 12  Hurricane  64 and above  Light air; ripples—no foam crests.  Moderate gale; sea hcaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. Fresh gale; moderately high waves of greater length; edges of crests break into spindrift. The foam is blown in wellmarked streaks along the direction of the wind. Strong gale; high waves, dense streaks of foam along the direction of the wind. Spray may affect visibility. Sea begins to roll. Whole gale; very high waves. The surface of the sea takes on a white appearance. The rolling of sea becomes heavy and shocklike. Visibility affected. Storm; exceptionally high waves. Small and medium-sized ships are lost to view long periods. Hurricane; the air is filled with foam and spray. Sea completely white with driv-  ing spray; visibility very seriously af fected.  TABLE I.  International code for state of sea  Calm glassy  0  Calm; sea like a mirror.  Less than 1 knot 1 to 3 knots 4 to 6  4  International scale sea description and wave heights  Wind scales and sea descriptions.  0  Rippled 0 to 1 foot Smooth 1 to 2 feet Slight 2 to 4 feet Moderate 4 to 8 feet Rough 8 to 13 feet  1 2 3  4  5  6  Very rough l3to20feet  7 High 20 to 30 feet Very high 30 to 45 feet  8  Phenomenal over 45 feet  9  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 Wind Date  Photograph Date  Direction  Duration  Maximum Sustained Velocity  Gust A1..N  1973 9  20  38 SE  W WSW-WNW  15 18  25 21  35W 31 W  May 17-18 May 18—19  W-WNW  May 30—31  W—WNW  12 18 22  21 24 27  29 W 33 WNW 40 W  34 16 13  21 19 22  27 WNW 26 WNW 28 WNW  22  31 WNW  March 18  E—ESE  April5 April 27  WSW—WNW NONE  June July4  -.  WNW—NW  July 13—14, July 15 July 16  WNW-NW  WNW-NW July_19 NONE  August Aug._24 Sept. 24—25  21  W—WNW Sept.  26  Oct. 6  ,___________  -  WNW  7  22  28 WNW  W  8  22  32W  11  20  32 SSE  12  20  33 E  Oct. 9 Oct. 18 Oct.30  SE—SSE  Nov.’ 13 Nov. 18 Nov. 19-20  E—SE  Dec. 7 Dec. 11—12 Dec. 13  W E—SE SE-SSE  12 31 16  28 26 20  44W 50 SE 30 SE  E—SSE  16  20  36 SE  SSE—SSW S—W  20 13 10 6 9 15  20 20 21 22 20 22  41 37 32 35 36 25  SE—SSE  18 8 8  26 24 20  45 WNW 32 W 33 E  W—WNW  36  24  39 WNW  W—WNW  E—SE  9 38  20 21  35 WNW 31 SE  WSW-WNW  14  31  44 WNW  WNW-NW  13  24  30 WNW  ‘  Dec. 14 Dec. 15—16 1974  ,  .  Jan. 13  .  Jan. Jan. Jan. Jan. Jan. Jan.  15 18-19 20 25 29 29-30  W—WNW  W-WNW SSW—WNW W—WNW  Feb. 4 Feb. 19 Feb. 28  W-NW W—WNW  March 1—3  S W WNW  WNW SW W  March 2 March 5 March 8-9 April 11-12 April 12 April 23  TABLE II.  High wil2d period information.  20  Bigh Wind Date  Duration  Maximum Sustained Velocity  Gust  HO UPS  4?PH  MPH  11  21  25 WNW  W—WNW  12  35  51 WNW  W—WNW  27  26  37 WNW  W  13  20  31W  Direction  Photograph Date  May  NONE  June 18  WNW  July  NONE  NONE  August • August 1 August 15 August_28  • Sept. 25—26  Sept._26 Oct. 3—4  V  Oct. 10 Oct.20 Oct. 22 Oct. 28—29  V  .  WNW—NW  26  20  33 NW  W—WNW  24  20  30 W  .13.  25  36 W  9 6 27 11 5  22 20 27 4 23  37 31 55 34 36  SE W—WNW WSW—WNW  4 12 24  25 -25 23  42SE 42 WNW 50 NW  W—WNW  12 18  27 22 18  39 W 28 WNW 33E  7  25  38W  WNW  26  37  57 WNW  WNW WNW  10 .14  21 28  30 WNW 42 WNW  24  38  67 WNW  15 22  29 29  39 WNW 45 WNW  Nov. 12 Nov. 20—21  .  Nov. 24 W  Nov. 25 V  Dec. Dec. Dec. Dec. Dec.  Nov.26  17 18 21—22 27 29  W—WNW  V  E—SE W—NW  W—NW SE  1975  WNW  SE  V  V  Jan.2 Jan. 4 Jan. 8-9  S ESE W  V  Jan. 10 V  20 25 Jan.31  Jan.  W—WNW E  Jan.  Feb. 4 W  Feb.10 Feb. 16 Feb. 19-20 March 18  V  March 24 March 25 March 25 March 30  V  V  March_31 April 19 Apr. 27—28  TABLE II continued,  W—WNW W—WNW  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,  From  and gusts of at least 35 miles per hour.  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 26  erosion—deposition information is derived from Figures 25, 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 foreshore 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. i)  This method is based on the following assumptions:  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.  Natural Scale  1t525,000  183  66  6  N 72  I  ‘  Pt  0  6  .  .  Hornby  2A  86 R  ‘  \  -  :.•:  ..  (  FIGURE  117  •7  ‘—5-  191  9  \  64  AhlIi., 6anh  Bc.cho  103 f ‘6  .122  Mouat I,  QualIcr  0.  /  7  r  ..  76  P.rksvIIl  77  ..  .  -.  . .  0480•  8  .  I0  :.•  .  181  2O  (I8’  4  Northwii  183  Bay  1 2  176  4 14 z  .•‘  .  151  54  145  •!..  D  58  I  /  I  SO  .\‘/  ton Pt McN.u h 0  203  21  REA  DUMPING  MM  10I0  -L  !  +x:: :  -,  I 207  27  81  ‘  60%  S  .  ..  4  7SCh  ke27’  222  ..  I  ay  .  S  135  192  ...., -5--  rJ  1005  /  1n1et  1187  %3.  2on  64S Sc,.tC  INLET  ISO  fl  6069,JNarrows  Mt.Dr.w  17 \i,1  1l30\  kç  Pt.7  )cLT  ç,  r  9cmoni  —— Winchl.ea r  .  2,  .. I6.4  .70  1  )%  %  II7  ..+  ...‘  201  173  .  Ml.Sh.ph.r 2900 (JS0  85  .  .  .  2  ‘/‘ZCos F =ZX4COB .i4 Fe 13.512 = 5.59 m e where 1 cm = 3.262 miles Fe = 18.22 statute miles  3. NW wind direction effective fetch diagram.  Ar.w,m00  M*rk  ‘  29\57  S  M  :Ibern,  ip  7 \nd\  Denm.n.  ‘  Pt  ‘‘  2  3  9  i:LA N I)  Norihe.jt Pt.  .\  \\92io7RI8o85 TEX  S  .124  14 42Vininci.  .85  ‘  Canadian Hydrographic Chart 001  *w\N  L  I I  :0  .•-•  .  743  .809  .866  8 94  .  .  •.  2  .•  2  -:  •-..  •  I966 I  29ier  :9  .  .  -  I4%46Q  ib.o  I  108  Totals 13.512  42  36  .  .  978 951 . 914  .995  6 12 18 24 30  1.000  .978 .995  914 951  0  6  .  .  .866  .809  30 24 18 12  .  36  743  Cos cc  42  i4a(  I  N  4110  8  C  4930  ER  V. c  75.47  1.29 0.82  1.99  2.00 2.10  1 • 86  2.00 1.99  4.99 2.19  6.61 12.14 14.64 11.24 961  os”< X C 1  p24)  ..::..  Or,Cel  5  25 I  121  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  xi  NW WIND DIRECTION  (  6  .743 .809 .866 .914 .951 .978  .995  42 36 30 24 18 12  6  FIGURE  3.57  4.8 5.2 6.1 7.1 8.9 11.5 15.0 21.4 13.1 10.2 6.8 2.2 1.8 1.6 1.5. 111.04  4.21 5.28 6.49 8.46 11.25 14.93 21.40 13.03 9.98 6.47 2.01 1.56 1,29 1.11  XjCos°<  Xj  176  81  .4440  Nanootc Bay  .  42  \..  14  .•.  .  Wh  s;45  13  II.  • •‘1  lea  ?-  62  3  =  .‘2Q  —,  NANAIMO  .  AREA  DUMPlG  ..  II8  •39  cP  Yellow  4  ._..—‘  7  /  8  4  • 8  145  •..‘  .  82 ——  0  38  \  —  46  M  L...?  6  .  6  246k  .  31  II?  —  .  .  .  --  I  ,  —  ,.  ..  .  . ...  ‘  <I  LULU IS)  Sea!  •  / Y,ANCO.  .E78 6 P t Grey  ARD24)’...  (‘  •  Natural Scale  li525,000  Cariad.ian Hydrographió Chart #3001  39  •:‘“  5401 1 Fh. Lioni  SOJND  555$  IruniwIck Mt..  Ckana.1  Flnrseahni Buy  \. N  ‘‘2  HOWE  Moi,tau  64, .•, ,?. Sand Heidi/  II6  ..  35  16  j70  .  •.  Bowen $  pM  71  -1-—•  ••.  an  .2130  GamWer I.  T.432  9.  .:_  104  I 2 r-tQI  It8  Mt. Wrenel2ey  I9’:6’  4.  29  ‘.  ;G;oni.  “°  a riola Pa3sae  ••••  202  t’des.  92  .  :::;R;;:ak:d9:  211  ••• .•  ••.••• :. .. :.. -  ••  .  MelLon  $699  / Mt. UphIaaton.  f’ o Wilson C eck  Sechelt  —.  MG.  48  7  —  Island  ii  —  •..  —  — Gabriola  4  207  27  ç  I. .r  :eke2 7 ,—i •1  /  222  •7  • .\21  —  ••  • Halfmoon Bay  .tcsw  MUNITION 96:  ISIJSED  Departure Bay  ma.r”  —  L’ 4  7  2 IT \  —  ía’  ..414•  McNaughton Pt.  INLET  =ZX C os ‘/.Cos Fe 1 111.04 /. 13.512 8,22 cm Fe where 1 cm = 3.262 miles Fe = 26.81 statute miles  ‘°  4. WNW wind direction effective fetch diagram.  Totals 13.512  .978 .951 .914 .866 .809 .743  .995  1.000  Coso’  “<  0 6 12 18 24 30 36 42  Qualicum Beacho  :  •i22  WNW WIND DIRECTION  MMark  )M  .  15.0  • 995  .99.5 .978  6 12 18  •  108.85  —  -  9.4 7.6 6  -  9.35 7.43 6  11.7  —  4  ..  ..••..  / C]  NANAIMO  .4140  3344  \ \ —....‘ MI. Whympir  \  ML  -,  Deporiure Bay  I  j°  71<4\wnchel ea  162  Lady.mkh  %  F  21  .  2c  8  N.  •i3°I06  cl.  82  18  22\+’.  ““  c  d8  202  -..  163  .  6414  ..  I39  .  ‘I25  ‘  °‘‘  .;..  ,  cpc  Sceveiwn  LULL) IS  .  . .:Y  03  68  ‘.  Natural Scale  1:525,000  C  6  .rt PtR b 0  66.4O  _L:.-•:  “\  SandHead,.,  961  ..  I5I  171  116  1117  7  Canadian Hydrographic Chart #3001  f23  5  8  J2  18  l9÷  Inland  YeIl Pt.  Cabriola  Sn ke 2  = ZX Cos /.ZCos = 10.85 ‘/•i1,96 = 9.10 cm where 1 cm = 3.262 miles 29,69 statute miles = Fe  -  8.68 _s-S__.  Nanooic ay  “Np  FIGURE 5. West wind direction effective fetch diagram.  Total 11.960  36 42  1.000  0  6  1  5.28  54  c(  1.11  XjCog  /  11.89 20 • 24 14.93 11.70  9.5  1•9 6.1  12,5 20. 7  •  809 .866 .914 .951 . 978  30 24 18 12  36  1.5  xl  .743  c(  42  4c  Cos  WEST WIND DIRECTION  WEST WIND DIRECTION  +  )  MLGs  .  •  •...•  91  Park.vlll:  —  66  176  *  176  ‘!4”  42  95  3s\  183  . ..  123 $4  N.riàose  .4440  14 •  27  Mil.  .  45-  s3!  66  2 52 C, b% 9  Naroos.Na,bou  Nortlw.aa B.y  i  Lasqiieti I.  46”  “  /  2  63  9’  —  c  •  162  s.,,  +  •., *? 2Q .  AREA  DUMPING  Bay  A  -  DISUSED 213  ——  101  NANAIM  pa.flaire  ..  ,J  30  -‘  —  I  211  2  ‘-‘-  87  c—  As-.’  96  .(C’  158  ..  -  I  —  I  .978  .995  —  /  117  I  b,  •  Pt.Grey  65  7.3 6.4  9.1  .  v  ,,f  .. ,,c.  ISLAND CltOfl  LULU  Sc. I.  .  ••  9  —  Port)  e,.,.,? 1 cou’  93,60  6.37 6.36  9.19 9.05 7.30  10.75  15.08  14.81  8.82  5.87  XjCoso<  5 VA NCOJ VEP  4RD24  “::  .&  ,f,ç  SH..’  I  A  ——  .  Totals 9.229  42  36  12 18 24 30  6  1 • 000  .995  0  6  11.3 9.4  16 • 5  .951 .978  .914  10.9  79  Xj  17,1  743  c’  .809 .866  ,  Cos  WSW WIND DIRECTION  30 24 18 12  36  42  <  Ir0?133I25  8  V0  .  “  —  4160  SLdg  3__l 190  2,  6  —  —i:’  4  /  :  MI. EIpflInhtoiie.  Wilson Crcek  Sechelt  laland  217  Q  48 N Whie  ‘J  4  ,_  27_  207  Ga  222  (  —.  127  L:dy,mlth  46  I  \ g6  \  119  -.  1N1(’  Fe =XjCos /ZCos F.e =93.60 •/. 9,229 = 10.14 cm where 1 cn = 3.262 miles S a U Fe 33  6. WSW wind direction effective fetch diagram.  79  LO8Ii587j’  ls525,000  ‘‘:i1 Ii 4.  Beicho  MI. Ails imItl  Qus cu  5—  ‘.‘..  Sisi  FIGURE  1114  ‘5..  “/  ‘\  \.•  87  p2274  e Bay  4b1;8  Eih  Natural Scale  Canadian Hyd.rographic Chart #3001  I.-) C  Beacho  Total  42  36  30  12 18 24  6  0  42 36 30 24 18 12 6  4:0<  )  7  P.rkivlll  .;,  743  FIGURE 7.  7.256  1.000  .995  .914 .951 .978  .866  .809  .  Cos  2  149  48.37  6.70  .5.54 5,39 6 .‘09 6.36 6.57  •  6 07  5 65  XjCos<  4  •  1 -  \  AREA  DUMPING  03  (7  .4  :  62  I 222  .  207  •  %  ,  .111  .  ‘22\  CHANNEL  .  \  abc’  0  &J  9’\  ,.41-  __:  ......  °20  94  L’  ..  ‘‘  l0  61  ?  — —,  .  .  ,  /  a’ d  I  ‘\%,  :  •.  /. ,4  61  ‘  :  a’•  ..  38  ..  —..  2  .10k:  -. 96  60  ..  .:.:  0  ..,  .  Sevciton  LULU  .  6:....4:  ‘  .  ;•..  8  .  .  N  7,,  ..  V. c  rch 9  .:  I  f.  M  2  New Wes m(narer  coy  I’/’  .V4NCOVVER  6  .:.  ’ 7 E  -.  1:,,....  :  .  IC 4’  ARD24)  tø°°  PL.Crey  N  4  / (4  —  .  Natural Scale  1:525,000  Cazia.diafl Hydrographic Chart #3001  3  ,  DI  .e7__”_  .,.  ‘p951  ‘‘/I  —  —  C  35  “3N•.. Z(  e  ,:?  90:  as  18  I4  •9&.• “  84  +r “çl-.  *  138  13(72  •... ..5)C..l’  1 l J(  Fe XjCos ‘/•ZCos 7.256 6.66 i 48.37 Fe where 1 cm = 3.262 mIles Fe = 21.75 statute miles i/  ‘I’  211  —  ......2I\  (,8 20  /23  k. YelTbw  .  145 _>  ‘>i  Snake l27).i2i  1415  .  ,‘  Q4?  Ladysmih  “.._03  I  121  :s:97  *So  ML  414  ,BaI . 0 T.  /  •.i7etMLEIphIn,ton.  SW wind direction effective fetch diagram.  7.6 7.5 6.4 5.9 6.4 6.5 6.6 6.7  XI  123’  4  211  Nar.o,. H rbea+ 3:  .  Nanooce Bay  1VoriAioe:  4’.  142  76  SW WIND DIRECTI0N  ML. ArrialmIlk  J  Quail  183  I7?0)  ruMc::  I-I  1W.)  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 V 1  Section 5.1.  28.75  18.90  WSW  SW  .  21.75  33.08  29.69  26.81  18.22  10 20 30 40 50 60  10 20 30 40 50 60  10 20 30 40 50 60  10 20 30 40 50 60  10 20 30 40 50 60  11.5 23.0 34.5 46.0 57.5 69.0  11.5 23.0 34.5 46.0 57.5 69.0  11.5 23.0 34.5 46.0 57.5 69.0  11.5 23.0 34.5 46.0 57.5 69.0  11.5 23.0 34.5 46.0 57.5 69.0  .  6.0 4.0 3.3 2.8 2.5 2.2  8.5 5.6 4.5 3.8 3.4 3.2  7.5 5.2 4.1 3.5 3.1 2.7  7.0 4.6 3.7 3.3 2.9 2.6  5.2 3.5 2.8 2.5 2.2 2.0  Hours  Minimum Duration, tm  fetch and deep water wave data,  25.80  WEST  Wind,  23.30  WNW  TABLE III.  15.83  Hour  Knots  Nautical Miles Statute Miles  Wind Velocity, U  Effective Fetch, Fe  NW  Fetch Direction  WIND, FETCH AND DEEP WATER WAVE DATA  1.5 3.6 6.0 8.4 11.0 13.5  1.7 4.2 7.0 10.0 13.0 16.0  1.6 4.1 6.6 9.5 12.3 15.6  1.6 3.8 6.4 9.0 12.0 15.0  1.4 3.5 5.6 7.8 10.3 13.0  Feet  Significant Wave Height, H 0  2.7 4.2 5.3 6.2 7.0 7.5  2.8 .4.5 5.8 6.8 7.7 8.7  2.8 4.4 5.6 6.6 7.5 8.5  2.7 4.3 5.5 6.5 7.4 8.2  2.6 4.0 5.2 6.0 6.8 7.5  Seconds  Significant Wave Period, T 0  w w  34  U) -Ii  Dr-oo,-4  0  occ.  Lfl,-4  V.-  V.- 0. V.4  C I i-I  .D at  r4  rr1V.4  0000..-  4-,  4) a) —  a)l C) WIG)  ‘.D 0 V.4  fl V.- at  0 r1 r  -f -4 -  C’4’.D.-4Lt  at C) V.-  IriV.4 CN(  V.4 Ot. Co (‘1 U)  D 0 V. fl V.  at  ;V.;C;C;  Cr-,-1.-f,-lr-4  4C)  4, 00 U)  a)  U)GJ  0  b 4 Cd  C) 1 W I—f  C  at0DC  V.4r-,--fo  ‘.Dtflafl.—Io  V.4tflOtUCoC)  D0’jbOhI.J.  r-f .4 V.4  r-1 .-f V.4  r-l i-f i-f (‘4  CN’DOLflOr-f i-I r-f (‘4 (‘1  111111  .  .  111111  111111  Oti-1.D  0LflCr-f  0-ft  atcqD  -4Lnat - i-i i-f  (Z4  4) >04 Cd 0)  Co  Co(’4 4,  (1) a)  0  c’1r.-ooc-1  .  •I—f  Lfl  Q C.,  0  0  0  0  0  U > Cd  .  a)  .  4 r  311111 .  Coc’lLnat  .-4 r-4 r-  C’DP)O.-4r-  •  C)NC,O i—I —4 V.4  131111  OtCo  t0C’4  .  .  )CoCNO0 r-j 1-4 V.4  NOV.  r4 ,-4 4  bt  :  •1f  )4 Cd  -  ‘3tflOCoC’)0 -.  g  VCoJ000  r—oc’,  J’D0tCNtf)  U bt > --4 ‘dO)  V.-V.40000  ‘D00CtC  1• t 1 —om’o i-I i4  cOi-f  .-4 r4  0  :I .  144-i  $  “  -  ‘.DV.-0  CC.i  r-fi-I’.0000’i  CNC-.’.oLfl  coco ‘rc-  oj:c;-cC.  0at0CoOt  0c’4Cflt-  N0C’i’DOCo  .ooc’1ao  ‘0F-c’)0Co  C.tatOtLflcD  C”  a) U> UCd 04  C”  c C  U >1  -P  •r4  140  ‘f  r 0  0  Cd e.) Co O V.- Co  ‘UW :> 0 a 4 ) U> a)Cd  ‘-..  CC1C’)  -  Co Lfl V.4  U) V.- CO  Ct 0  4CoC’1V.-C’4 CflC  Lfl  V.1 0 V.- Co  Lfl  C’4CoV.tCoC’1  atCt  C1C.1  C1C’1  a) r14  Co LC1  r-4  N Co  U :1 r4 4-)  c  0 C)  f: 0  H H H  i  Cl)  Q  z  •  -  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.  =  =  =  =  =  feet 5.2 seconds 26.6 ft/sec 138.4 feet 23.1 fathoms  5.6  =  =  =  =  =  18.22 sm 15.83 rim 34.5 mph 30 knots 2.8 hours  50,000 0.00815 S/To 2 15 wavelengths 0.00815 S/To 78 seconds  — 08  +  M  \  Natural Scale  N  \  \  •.  a,  \  \  1:50,000 1 cm = 0.31 statute miles = 0,27 nautical miles  /‘  ‘‘  / 1  f  \f  48  \  s\c //  \  2  - - - - - -  \  jr\  BANK  WRECK BEACH STUDY AREA  34I\  :\...  Bn\4  ../ _\.i  \27  .. ..  \  28  26 D A B URRR  ----  I  9z L.  Th  :•:  4:  I2S\  0 Point  I_____  j8iI  :  --  -  I J’ lo cJ’\ 1  I \\  Z 8  S  \  .FIR  \\  ,7 --  \  ....  48)  is \54Jr:\  Jr  X  \  4 / 1 ç >\\  \  ••..•_\  70  \\:843  \  \  Jr  /  \\\).\  4  Canadian Hydrographic Charti #3480, 1971  =  =  =  = =  --  - -  ---------  84  N  \\  NW  FIGURE 8. NW wind direction wave refraction diagram.  t  S n  Wave Scale  tm  U  Fe  Wind Regime  Ho To Co Lo  Wave Regime  NW WIND DIRECTION WAVE REFRACTION DIAGRA!1  I  H  = 6.4 feet seconds == 5.5 28.2 ft/sec feet. == 154.0 25.8 fathoms  26.81 s 23.30 rim 34.5 mph 30 knots 3•7 hours  •  84  i  I’’4__I  1  I  —  1.. I  :1  •L  I  1i50,000 0.31 statute. miles 1 cm = 0.27 nautical miles  /  —i  £3  i  I  I) I \ l./  75  I  I6  -•—.————.  GpF  I-•  \I  (  i  4  i  ‘  I  I’”  /  •‘._I  4  I  42  Hf  jYJ •:i...iIW(Pt  / ’ ...1sJ 5 3.V 7  rey  27  -  %sç  I_•r I  36  5AN  28  ‘___•po  N :  )(  511 COLUMBIA  n:  R  wEAcH STUDY AREA  8e1,7.  /:  u/z//÷y  II  /  .  1>’t’..ig  7’74/s  I  \\39 /çT  /‘_•  l68l\  I  1’  I  ,  •--I  I—45  ———  4I/.%/../  I-m•  I  21  J.,j  I /  -.----..-  I  •::hI ,t I  t— I  J  co/-JJ I •-—I •‘—I Cd,!  .‘.‘•—•‘•‘  r iir  I  /•[  ,..  Ir.’-  • 1.•.,•,•—,—..-•I  FIGURE 9. WNW wind direction wave refraction diagram.  Natural Scale  I  , L-— I —I _._I_.ou  __I-,-’-._.._I  I I  I  75  i—i I / LJ4r -i’ A wLj  •  Canadian Hydrographio Chart #3480, 1971  S n  == 50,000 2 0.00815 S/To 1+ wavelengths = t = 0.00815 S/To = 74 seconds  Wave Scale  Fe  == U = = tm =  Wind Regime  Ho To Co Lo  Wave Regime  W!M WIND DIRECTION WAVE REFRACTION DIAGRAM  w  =  =  = =  =  28..? ft/sec 160.6 feet 26.8 fathoms  seconds  6.6 feet  5.6  -.•  •  .  50,000 0.00815 S/To 2 13 wavelengths 0.00815 S/T 0 73 seconds  : --  68  -z  1:50,000 1 cm = 0.31 statute miles = 0.27 nautical miles  /  9  75  ,•  /  j  I  39  /  9  )\  (  (9i  ‘ :  /  /  41 i  ,‘c:  \  S  —-r-•  \  /  34  /  ——— 4•—  I I  1 j8  /  pF 3)12  /  8  FIGURE 10. West wind direction wave refractiQn diagram.  Natural Scale  Canadian Hydrographic Chart #3480, 1971  = =  =  =  =  -  9  28  — —  /37  /  108  WESrW >))>> N  .  S  29.69 sm 25.30 nm 34.5 mph 30 knots 4.1 hours  4  —zr  =  =  =  =  75  /  Wave Scale  t  U  Fe  Wind. Regime  Co Lo  To  -HO  Wave Regime  WEST WIND D1RECTIO!bT WAVE REFRACTION DIAGRAM  -,  :  2  A  /  ..  —:; I>’%,  ——  26  •Il)  Iz  ‘:.,  ;•—  ?:  I?  2/  ‘  \...  I1  •..:•::  2_ 4  •.  :i9  :7IHI:  —  .‘  g  .1.-  7T” Os 3  4  ——-i  •1  —-,—  2  IC  I>  II  UNIVE  •  SP  ‘••--.  .  .  ISH  Point  R:ulA  •  ‘‘%_.  ••%.  27  17  .  ..  :•  •  SANK  •-..__  11  /•  ,,  / M  /  \  i 9  :  4I4  18  /  =  =  =  7.0 feet 5.8 seconds 29.7 ft/sec 172.2 feet 28.7 fathoms  =  t  33.08 sin 28.75 nm 34.5 mph 30 knots 4.5 hours  73  M  .  A  V  —————  —  \  \  ////  ..  . .  37  ———  /  1:50,000 1 cm = 0.31 statute miles 0.27 nautical miles  /  /  ,,  69  75  “  /  I  (w  1 i’4  1i  ‘  \—--1  39  34\  V) ____\  ‘  I  .—  — -  G  •....  •.  f’  4  -•-‘ j  \  LL.  ..  . ..  1  ,-.,.  .  P  ?  .  j  i  ‘9  ‘  i.:— — 4 -t  -‘  .-....--  ‘‘47  l3  I  IS H .  BA N K  -..•‘“.,_L.r  4 S% I 1  7  —...-..—..--“-/  (___•  u  I I  ——I  nJ  r::uMeIA  \‘-.-1’  ‘Ij.• L  . ‘Ii,:  ..  .  •‘jWRECK BEA%s.\ STUDYAREA  I!  -  —  -  +((f \  .-  I  I IIx  )/) o j 5  ,,r  .  3 •.  •..—  -1  ..—FIIT  /  ..  ..—  27  —.le  —a-.  4  -  .—.  ;‘:  .  /  — —  —  ..—....  —  718  41  ...—..  :_7.____________ 89  /  /  ..  /  ...  FIGURE 11. WSW wind direction wave refraction diagram.  Natural Scale  çi  -  —  69  ——— ——--  øj  j,—.—  -..—,  ...-  Canadian Hydrographic Chart #3480, 1971  =  8= 50,000 2 0.00815 S/To 12 wavelengths 0.00815 S/To 70 seconds  Wave Scale  =  =  =  U  Fe  Wind Regime  Ho To Co Lo  Wave Regime  WSW WIND DIRECTION WAVE REFRACTION DIAGRAM  -  C  = =  = =  =  27.1 ft/sec 143.8 feet 24.0 fathoms  5.3 seconds  6.0 feet  =  =  =  =  21.75 sm 18.90 tim 34.5 mph 30 knots 3.3 hours  =  0.00815 S/To 77 seconds  50,000 2 0.00815 S/To 15 wavelengths  •.. 126  ,“  ‘4  FIGURE 12.  1*50,000 0.31 statute miles 1 cm = 0.27 nautical miles  :“‘  SW wind direction wave refraction diagram.  Natural Scale  Canadian Hydrographic.Chart #3480, 1971’  t  =  n  =  =  S  Wave Scale’  t  U  Fe  Wind Regime  Ho To Co Lo  Wave Regime  SW WIND DIRECTION WAVE REFRACTION DIAGRAN  6/  /  ‘K .‘•c: I, ,  —— -  ‘  .‘-  :.J/7,)  vz  :ts1:.  \i.X&;: I:+:.  I••/••  (\,>( ‘s;:  30I;  -,  ‘  24Y\k  1  f/i  ;/  nt  Rc:LuMBIA  BEACH STUDY AREA  iS  7  L_  27  42  WAVES FROM THE SW SECTOR  4.3  Waves from the SW sector in general diverge around the headlands. energy.  The South Arm jetty absorbs most of the direct  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. be minimal.  The wave attack angle from the NW tends to  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. waves tend to strike the west beach straight on.  Converging  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  -  S  45  West Beach  u4  & March 25, 1975 — -.  Photograph location 18  4,  4-  :  ‘4,  r  WNW  Towers Beach arch photograph cations 22 -  March 25, 1975 Photograph location 19  FIGURE 13. Photograph sequence showing NE longshore transport waves breaking at an angle to Wreck Beach.  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. 25,  1975.  Such a period of wind conditions occurred on March 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, effect, K,  , 0 H  is modified by the shoaling  and by the refraction effect, KR;  that is H=HOKSKR.  The H 0 is related to wind velocity and fetch as listed in Table III.  The shoaling coefficient, K , represents the effect of a 5 change in water depth on a wave height and results from a wave moving into progressively shallower water.  5 value depends The K  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. Engineers, Volume III.  Corps of Army  These values and corresponding water depths  are listed on Figure 14 in the Refraction Diagram Information Block. The K 5 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, L . 0 length, L,  The values of the shallow water wave  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:  5 K  -  shoaling coefficient mation Block,  KR  -  (Listed in Refraction Diagram Infor  shown on the refraction diagram)  refraction coefficient  (Shown on the refraction diagram  between orthogonals) 0 T  -  wave period in deep water  (significant wave period  Table III) 0 L L  -  —  wave length in deep water  (Table III)  wave length in nearshore region Diagram Information Block,  (Listed in Refraction  and shown on the refraction  diagram) 0 H  -  wave height in deep water  (significant wave height  Table III) H  -  wave height in nearshore region the refraction diagram)  (H  =  HOKSKR and shown on  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,  where foam first appears on the wave crest.  is the point  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,  ing is initiated.  the crest to trough dimension when break  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. heights and depths are compiled from Table III.  Breaker  53  LIMITS OF THE WRECK BEACH LITTORAL ZONES Breaker Height  Wind Velocity U  Breaker Depth db  b TM Feet  A Peak Extreme Winds B General High Winds C Other Winds  Elevation Range of Breaker Zone  Feet  Width of Breaker Zone  West Beach  Feet  Feet  Tower’s Beach Feet  Volume Transported  East End  1973—74  1974—75  Feet  c.y/year  c.y/year  5.1  6.5  —  8.0  12  2300  2200  2500  6,150  10,581  3.8  4.8  —  6.0  10  2000  2000  2300  12,023  17,507  1.6  2.0  —  2.5  6  1000  1300  2000  17,759  16,717  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 HHW 14.4’  Mean Water Level  LLW 4.1’  10.1’  Large Tides HHW 16.2’  LLW 0.3’  Contour datum on Chart 43481: 16.0’— .l6.2’-Lge.HBW--  -  4.1’ Av .LLW  0.0’—  0 fathom (0’)  contour  3 8  :‘  ..  ge.LLW  .  0.63 fathom (3.8’) contour  —2.0’— 1 fathom (6’) contour Therefore, Datum for determining deep end depth of Elevation Range 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. for each covered ranges of about 3 to 14 feet.  Tidal cycles 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, 1974 covers the east end beach.  The June,  1973 through May, 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  November 18,  I —  4  July 19, 1973  January  A  13, 1974  ¶1  March 2, 1974  location 1, FIGURE 1. Photograph sequence at photograph East End, prior to construction activities.  57  30, 1974  August 28, 1974  September 26, 1974  November  26, 1974  FIGURE l6. Photograph sequence at photograph locations 1 & 2, East End, following construction activities.  58  January (0, (975  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.  61  August 19.  (97A  -  I  j February  1975  4, 1975  .  --  —9 •  F  2  ‘  .,.  ‘—.-—  :  FIGURE 19. Photograph sequence at photograph location 10, West Beach groin, following construction activities.  62  Auqust 15. 1974  February 4,  1975  -  Auqust 28, 1974  September  November  February  16, 1975  26, 1974  26. 1974  FIGtJR 20.  Photograph sequence at photograph location 13, West Beach, following construction activities.  63  August 28. 1974  September 26  1974 -.-  March  (8, (975  March  31. 1975  —(-  -:1 .-  October  —--—-  (0, 1974  -  May 12, 1975  FIGURE 21  n 18, Photöraph sequence at photógrap? locatio . West Beach, following construction activities  64  August 15. 1974  September  February 10.  1975  26, 1974  October 10, 1974  ‘vember 26, 1974  FIGURE 22. Photbgraph sequence at photograph location 19, Towers Beach, following construction activities.  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.  FIGURE 23.  Chart of photograph sequences prior to construction activities.  -J  I  .  I I  —  .  Facet  Face  •  +‘H1n  .  -  -  .  •  •  .  :1.  e  ————  ,.  . .  _._!  ..  1  H  .  I.  .7  .  1  I  —  ——  —  I  I:fl  —-  :  I  I  .  I—  .:  :  •,.i  I  ii I  Iii  —  I  -  —U—— . .  —. .-.  .  —  -H’- — .;;  .11  :  ::fL tT ..  ,.....,.  —  _..I*•  ...  .,  1!  •±.I...  .rz:  I  I  :‘—1I  •-  —  ----r-  r*r  I  -  .  —+—---  .  EJ’,  4— 1  :.:::.::  E-t  i  -I  H  ,i  -—__T•_-.  .•. —  -  F  IC...  —  -  -  —  .  .  : i  Li’  i  —  —.-.,.•  .  —  I  :4iJ .  41  LM—f  -i_ Lttt L±r+J+j1  r  I  I-  I.  ii.!  Ii  I  .  ;.:  II  I  1  .  Ii i I .  1  J}i  H-’-i 44  .  i.!.:;.lr • •  ..4..i.  —i  Il_!II  +h1!  •L,.UiJ J..L!ii.Ji  -  I  -—  .fTrlTr  r-rr’—r,  •i..I  I;•  Ijl  •  F-F  —  —  -+H—H  i;  .  —  .•_.,.  Hill  I  -  I  I Li-  IjIf:[I  —  4’; :  —  .*-• :1 ‘ii  zt-r  Ii [Il1I •-zrt-Tp—I  -  !iII.I_lIIfl..t..lI.j.I.fl  --,;: —  il_f..  —  -  -  —  —  =r p ..-d—.  ,.  I  ...  Ti H14--H  t  1i*f  zr..i!L7  •j.  Lift  —r  4  —  V  [j’:?1 1h1i :1 JJ 4hnt’ 4’ .:  r—1———————r—j——  -rI i[]Ti.  -I I  .  :: 1 jtr  1 ...E  Lj. 1  I  Iii  I  WH  —  —  1 H1’Hh:  .  j  1 t  1,1  .  .  .  fl: 44r4  rVFt.H T1lThfftf  1 < Q,0•  FIGURE 24. Chart of photograph sequences following construction activities.  e  -  _-  .  .  WesiBeac 1 LowerBeachFace.  .  West Beoc Lower Be ch Face  .  West Beach . Upper Groi End:  :  ::rTT  r  West Towe fjr Upper Sea h Faet.  I Towers Bee Ide OuttaI Downdrift  —-:r-r-;  TowersBea.h Updnft Side Outf.a.II.:.  ost Tower  rT  Upper Groin End  —.-————.————.——..—..————.—.  -  .  -  _j.  aceUj  I  EastTower.H[  East Tower Lower Groin  EastEnd Upper Groi  .  !a  8 —..—..—..  7.  6  :  4  2  1—1—1  .  ’ 9 3 c  EasFEnd Upper Beoc  %c  PHOTOGRAPH LOCATION  DATE  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.  22-Nov.26  S 0  -  +  —  accumulation of material erosion of material no change no :infomation  —  —  +  —  + +  S  +  -  0  0 0  —  —  -  —  -  — —  -  -  -  -  -  -  -  -  —  —  -.  —  -  -  S  +  S  +  S  +  —  S  +  1974—75  S  1973—74  S  1974—75  East Tower Looking East  -  -  —  —  —  —  -  -  -  +  +  + + +  1973—74  East Tower Looking West  -  -  +  -  -  —  +  -  —  —  -  +  +  -  -  -  -  -  -  —  —  —  —  —  -  -  —  1974—75  -  1974—75  -  1974—75  West Beach  West Tower Looking East  -  West Tower Looking West  0  + +  + +  + +  +  +  +  —  -  -  1973—74  S S  -  —  +  +  -  -  -  s  s  S S  1974—75  East End  FIGURE 25. Chart correlating photograph information with cross-sectioning data on upper beach faces.  Mar..18-Mar.25 Mar.25-Mar.31 Mar.31-May 12  Feb.4-Feb.16 Feb.16-Mar.18  Jan.6-Jan.1O Jan.1D-Feb..4  Nov.26-Jan.6  Oct.  Sept.26—Oct.22  Aug.1-Aug.15 Aug.15-Aug.28 Aug.28-Sept.26  DATE  LOCATION  UPPER BEACH FACE  cD  -1  FIGURE 26.  -  S 0  —  +  —  -  —  -  —  +  -  -  —  —  +  +  +  0 S  East Tower Upper  -  + +  —  0  -  +  0  ÷  +  -  —  -  +  — -  -  —  —  —  +  +  + + +  +  -  -  +  +  +  +  0 + +  0  1974—75  East End  + +  —  -  -  -  0 S S  1974—75  East Tower Lower  —  —  +  —  -  0 +  1974—75 1974—75  Outfall Down— drift  accumulation of material erosion of material no change no information  -  +  -  -  +  -  -  -  —  -  —  —  -  —  +  0 S  1974—75  Outfall Updrift  Chart correlating photograph information with cross-sectioning data at groins.  Mar.l8-Mar.25 Mar. 25—Mar.31 Mar.31-May 12  Feb.4-Feb.l6 Feb.16-Mar.18  Jari.6—Jan.lO Jan.l0—Feb.4  Nov.26—Jan..6  +  +  0 -  Sept.26-Oct.22  Oct.22-Nov.26  West Beach Lower  1974—75 1974—75  +  •  West Beach Upper  Aug.l—Aug.15 Aug.15-Aug.28 Aug.28-Sept.26  DATE  LOCATION  GROINS  o  S  —  +  ‘  +  +  +  + +  + +  + + +  +  S  +  —  —  —  -  —  -  — -  —  —  -  —  -  -  -  -  + + +  —  —  + + +  —  —  —  —  + + + +  -  +  -  —  -  +  +  sandbar moving in or up beach face sandbar moving out or down beach face no change no information  +  —  —  -  -  -  -  +  +  +  -  -  -  +  ‘1974—75  +  -  -  ‘1973—74  + + +  1974—75  East End  + + +  + +  1973—74  East Tower Looking East  data FIGURE 27. Chart correlating photograph information with cross-sectioning on sandbars.  .  Mar.18-Mar.25 Mar.25—Mar.31 Mar.3l—May 12  Feb.4—Feb.16 Feb.16—Mar.18  Jan.6-Jn.1O Jan.1O-Feb.4  -  +  Oct. 22-Nov. 26  Nov.26-Jan.6  +  Sept.26-Oct.22  -  +  + +  + + +  Aug.l-Aug.15 Aug.15-Aug.28 Aug.28-Sept.26 -  + + -  1973—74  1974—75 1974—75  West Beach  East Tower Looking West  West Tower Looking East  July 7-July 19 July 19-Aug.1  DATE  LOCATION  SANDBARS  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, Selection  26,  27.  criteria for peak extreme wind periods is outlined in  Section 3.2 of Chapter III.  0  -  —  .4.  :,  .  .  j::  .4 ‘6  P’  ‘1  CD  -Ei.  P  C  -  L4-  C,  0  nd S nd bar  0.  (.  -  :..  IE 1  4  -.  :  .:  I  • ..,4  -  .  -  •  4—i  3tSM  4’. -  •--  ER  4±.  H.  -I  :th  .  ‘&  ::.  -  .  ..  / T/1 $  .V LO ITl S  L014  .:.  V L. C  4 i_I  l4..L!.  H  __!__[  H- Li  -—4--—  -  -  4-  tl-t  ±ii:.  r  .  ..  IES  -  I  ’x 6  : -  V  I  1  .1..  i4LL.  ±.H-t  .  L:  1  I,  I  -  LL  1  NSI  ----+±.  p  C  0  -  0-.  .  Hit  -t -t. 4  -4--i---  c..  ‘.0 -4  H LL  I 7  j  :1 4:  t  SH RTb  :t±tr i:t. it  fir-  :1i  4jJ  LC WEd’ L.O iri rs  L.  -T  I-[1  t  LI  L Lt  .it +L  II  •• tFl .SL  zt44.  LU  r  CD  “  L C I TI ES  V L.’  4-;  :c  o  IE  -—I_I.’.  jEtL  -0  Z 0  ---rr — —  -  CD C,  -.  -3  w  L. Ci GE4 JR TI-C  R—  L.i_L  4.LLL  1- IGH R  : : IEL )CI  .  .:::  ::  ça /EL ) C / 4  jL  4.L4 .4..1.4-..  4.4 -i--4-4-4- -H-4--  z  0  HEE +4-  -r  1- -1-  ‘1 F CD  4f-J-’.14-J-H!H  ---  4:1:1 T t4zrJ  9/-1c RT DL RA •, CI slj.  it.  .4.  .z:.,  H  :;: :4  -F  : i:;:  ,..  -  flT  .oc.  Upp r Bec  ><—  West Beoc  F--f-1  Son bar  West  • .  -i 444.  --H-  Ii t.t  E.  3’  4O YI’ O• A TIVI IES  ,  Uppe r Bea h.! I.  West Tow e  West Tower  U, -i  nd Ii per B a.c.h.  0 C  East Tower Sond  HI H ‘ ‘EL 7C/ IES  ..  :.  EL. ) CI  p  CD  East Tower Qpper Beac  East  Eo t  4  .EL 7NG ER: DUF AT/  ;NTE  --- r:r  ::  :4-  .  •0.  4..  •  :‘  a  w  Zh zz ‘Z_*  .  -  :::  ,-  ::  .4  + ‘-+4  ÷  i-z:  a  CD  CD II  ri  CD  (n  C) J.  pJ  t:L1 CD  U  CD  I-1  pJ  GD  tn  0  I•rJ H  -  3  (D  oc  30  OQ  z  0  3’ -4  C  -4 -<  3’ C-) -4  =  3’ C-)  m  rn  3’ -4  -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. March 30,  On  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 Beach configuration). makes a sharp turn,  (Refer to Figure 1 for Wreck  Here the upper shoreline and cliff  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  CD çj  U) U) CD  •  o  P.) I-’ U)  P.) II CD P.)  U)  H  J•’  ct  P.) 51  i—’  i-i.  P.)  CD  ft  01  -.1  ‘..D  F-’  .  P.) 51  CD P.) 51  CD  51  P.)  I-5  k)  CD Fl  CD  0  Fl  CD  0  CD  çt  ft  CD P.) U) rt  CD P.) U) rt P.) ).<  0  CD  CD  F-’  rt r1  :  CD P.) II  51  Fl Fl H < CD  P)  P.)  CD  CD  rt  cJ  Pi i  P.) U) U) CD 51  I5  P.) I-’ U) 0  j  p.)  F-’  H  rt  CD  rt  I-.’ .ø —J  l<  .  .)J  I-5 CD  p.)  CD i  rt-  U)  P.)  CD  CD  r1  i  0  ‘<  r1 0  CD  I-’.  0 <  .)  1974-75  1973-74—  1974-75—  WEST TOWER SANDBAR  EAST TOWER SANDBAR  EAST TOWER SANDBAR  —  974-75--  74  -;-  n°— .1  I.  .‘  FIGURE 29. Annual sandbar movement.  EAST END UPPER BEACH 1973-74  EAST END SANDBAR  EAST END SANDBAR  EAST TOWER 1974- 75— UPPER BEACH  EAST TOWER UPPER BEACH 1973-74  1974-75—  WEST BEACH SANDBAR  -r  %C  u -ri-i-  rI  iTT i-r  \  ‘  wT iu.  I I iLOI  11  I I  1LT T fl-  fr e0  I  1  i I  -‘  I’  1’  I  _L I  (.  Il r TjFL i T r  <e  -I-  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,  sediment characteristics and beach slope.  angle of approach,  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,  L 2 0 7GT/wH where w  = =  S  = =  =  Ersino(bcoso(o  specific weight of sea water 64 pounds per cubic foot 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, as the Hourly Transport Volume.  and is listed in the Tables  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 FREQ  -  1973—74 hr %  —  —  —  5.0  438  5.0  438  5.0  438  —  —  —  1.0  88  1.0  88  1.0  88  —  —  —  —  —  —  1.0  88  1.0  88  1.0  88  —  —  —  —  —  1.0  88  1.0  88  1.0  88  —  0.5  47  —  —  4.0  350  3.5  303  350  —  4.0  —  81  2.2  192  0.5  44  1.0  89  4.6  401  2.8  244  6.0  526  57  0.7  64  0.4  33  0.2  13  8.0  698  8.1  711  9.0  788  1973—74 hr %  NE  —  —  —  —  —  NNE  —  —  —  —  N  —  —  —  NNW  —  —  NW  —  —  WNW  0.9  N  0.7  SW  1974—75 hr %  1974—75 hr %  1973—74 hr %  1974—75 hr %  WIND\ DIRECT\..  wsw  D Annual Average Yearly hr  C Annual  B Annual  A Annual  —  —  —  —  —  4.0  350  4.0  350  350  —  —  4.0  —  —  —  —  —  —  3.5  307  3.5  307  3.5  —  —  307  —  DIRECTIONAL HOURLY WIND FREQUENCIES  WIND DIRECTION, NE  1974  1973  1974  1973  1974  1973  C Freshet  B Freshet  A Freshet  WIND FREQUENCY  %  hr  %  hr  %  hr  %  hr  %  hr  %  hr  -  -  -  -  -  -  -  -  -  -  -  -:  -  -  -  -  -  -  -  -  -  -  -  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.  CD  0 cn  Fl  Ii  p)  CD  CD  rt  0  I-J. II  0  I-i.  rt  3  CD  r1  H  CD II  0  0  p)  w 0  I•rJ H  co  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  Group B.  0 H  =  5.1 feet  0 T  =  4.9 seconds  0 L  =  123 feet  0 H  =  3.8 feet  0 T  =  4.3 seconds  =  95 feet  =  25 knots  =  22 mph  =  20 knots  =  11.5 mph  =  10 knots  =  11.5 mph  =  10 knots  Other Wind Periods: Average maximum sustained velocity  Group D.  28 mph  General High Wind Periods: Average maximum sustained velocity  Group C.  =  0 H  =  1.6 feet  0 T  =  2.7 seconds  0 L  =  37 feet  Northern Wind Periods: Average maximum sustained velocity Average fetch  =  0 H  =  1.0 feet  0 T  =  2.2 seconds  0 L  =  25 feet  6.5 miles  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 A winds includes freshet volume of  =  3477cy  (Table VIII)  0 cy  NE movement by Group B winds  =  4907cy  8524cy  NE movement by Group C winds  (Table VI) (Table VIII)  751cy  SW movement by Group D winds  (Table VI) (Table VIII)  includes freshet volume of 1280 cy  includes freshet volume  (Table VI)  =  Ocy  (Table VII)  2031cy 16908cy  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).  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 VIII)  includes freshet volume of 2567cy SW movement by Group A winds  0 cy  =  2567cy  (Table VI)  (Table VII)  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 19,440 cubic feet toward the NE.  per hour.  (720 cubic yards)  During a 10 hour period of sand could be transported  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. almost an entire tidal cycle.  A 10 hour period covers  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).  SUBTOTALS AVERAGE RATES  29 234 317 320 97  SUBTOTALS AVERAGE RATES  252 1944 2880 2808 828  SUBTOTALS AVERAGE RATES  504 3996 5868 5724 1728  c.f./hr. -  -  17759  -  12023  6150  35932 cy.  8 cy/hr.  389 3701 8418 4148 1103  71 cy/hr.  —  —  327 5616 6080  -  —  —  3108 3042  -  c.y.  175 cy/hr.  2163  170  35  2368 hours  362 427 717 350 307  —  —  35 78 57  —  —  21 14  -  hours  1973i974 Yearly Wind Volume Frequency  e toward the NqE, TABLE VI. Annual longshore transport volum  TOTALS  C. NW WNW W WSW SW  B. NW WNW W WSW SW  A.NW WNW W WSW SW  Wave Direction  Hourly TranspOrt Volume -  —  —  7104 3477  c.y.  -  16717  17507  10581  44805 c.y.  8 cy/hr.  -  325 2617 8524 4148 1103  79 cy/hr.  —  —  12600 4907  —  165 cy/hr.  1988  221  64  2273 hours  303 302 726 350 307  —  175 46  —  —  —  48 16  -  hours  1974—1975 Yearly Wind Volume Frequency  ANNUAL LONGSHORE TRANSPORT VOLUME TOWARD THE NE.  1052 hours  1552 c.y.  1.5 cy/hr.  438 88 88 88 350  31 104 103 75 10  503 339 336 244 130  c.y.  hours  c.f./hr.  TABLE VII. Annual longshore transport volume toward the S.W.  TOTAL  AVERAGE RATE  D. NE NNE N NNW NW  Wave Direction  Average Yearly Volume  Average Wind Frequency  Hourly Transport Volume  ANNUAL LONGSHORE TRANSPORT VOLUME TOWARD THE S.W.  SUBTOTALS AVERAGE RATES  SUBTOTALS AVERAGE RATES  SUBTOTALS AVERAGE RATES  29 234 317 320 97  252 1944 2880 2808 828  504 3996 5868 5724 1728  c.f./hr.  2567  0  284  102  401 hours  60 105 50 43 26  16 44 26 7 9  2164  7094  11825 c.y.  8 cy/hr.  64 910 587 510 93  70 cy/hr.  149 3168 2773 728 276  171 cy/hr.  — —  —  —  290  27 1170 751 545 72 2565  4269  0  6834 c.y.  9 cy/hr.  347 hours  25 135 64 46 20  — —  75 cy/hr.  — —  57  37 2952 1280 4 41 12  0 cy/hr.  —  — —  —  —  —  —  —  -  -  c.y.  1480 1087  -  hours  -  c.y.  1974—1975 Yearly Wind Volume Frequency  10 5  15  hours  1973—1974 Wind Yearly Frequency Volume  TABLE VIII. Freshet longshore transport volume toward the N.E.  TOTALS  C. NW WNW W WSW SW  B. NW WNW W WSW SW  A.NW WNW W WSW SW  Wave Direction  Hourly Transport Volume  FRESHET LONGSHORE TRANSPORT VOLUME TOWARD THE N.E.  .0  95  The Wreck Beach longshore transport estimates predict that typically volumes of 40,000 cubic yards yards  (see Table VI)  ±  20,000 cubic  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  2500 cubic yards  1.7 to 2.2 ft/sec  4700 cubic yards  2.2 to 2.6 ft/sec  March 25,  1975  1500 cubic yards  1.7 to 2.2 ft/sec  March 30,  1975  3300 cubic yards  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. associated with the March 25, ter IV, Section 4.6.  Other information  1975 storm is presented in Chap  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 of f  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. sandbank  As such the  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.  =  1,330,000 cy.  Average volume entering:  Total  Annual Dredging Quantities:  April to March  North Arm Mouth Volumes Dredged Cubic Yards 33,600 164,000 354,000 416,000 286,000 347,000  1964 1965 1966 1967 1968 1969  1965 1966 1967 1968 1969 1970  1970 1971 1972 1973 1974  1971 1972 1973 1974 1975  142,300 397,100 211,000 196,000 93,300  Average volume dredged: sands and gravels  Total  TABLE IX. Fraser River North Arm dredging records  (incomplete)  =  240,000 cy.  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; to 6 feet.  from Group B, up to 10 feet; and from Group C, up  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  (1 fathom) would be a region where winds of Group C  foot contour  (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. 7,000 to 12,000 cubic yards.  The quantities range from  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.  U)  0  (n  CD Dl  Di  C)  CD Di  C)  CD  Di  I-1  r1  0  z  CD  iu.1  DiP)  H  (DCD0 (DCDO ç+ct  ‘-)‘-‘)O  ooa  \OO  11111_a  om  o QJ.)  —‘Co  ) I•-’  I-  C)  a  %I•  \Q  1_ac4  cDP)  .-1_a.  Li3Pa  C)  C.)  F’)  -  =  U)  f.,_j  -.1  F’)  01  FL)  0)  —  —  \_  =  ac..  /  U)  •  ci)  “Liq  “  U)  Ow  01•••  —  —  ccc ‘ —  0c  ct  -  01  =  ..J  •cL-.cc-..Z3 .-  U)  U)  0  —  —.  I’J F’)  0  = =  F’)  ID  • I-.  --.---  —  •-1  \  U)  -\ Is)  0  0  FL)  C.)  01)  U)  ---.-----  10  0)  ...?  /0)  r)  “3  F’)  0  F)  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  WRECK BEACH CLIFFS AS A SAND SOURCE  6.3  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. this rate 8900 cubic yards annually  At  (1 cubic yard per hour)  sediment is supplied from this area alone.  of  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 hour)  also becomes available annually.  (about 1 cubic yard per 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.  Qt-  ci-fl  •  •  C)  —  d-Fl’  CflCD.  Cl)CD -. CDCD  CDcI-0  C)  Cl)CDP3 C)ct-i H(DO  P). 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