roberts bank container expansion coastal geomorphology ... · this report is included as appendix a...

ROBERTS BANK CONTAINER EXPANSION COASTAL GEOMORPHOLOGY STUDY

Appendix A

Prepared for: Vancouver Port Authority

Prepared by: northwest hydraulic consultants

30 Gostick Place North Vancouver, B. C.

V7M 3G2

In association with: Triton Consultants Ltd.

3530 West 43rd St. Vancouver, B. C.

V6N 3J9

November 2004 33863

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Wind and Wave Climate – Appendix A - i - November 2004

EXECUTIVE SUMMARY

This appendix describes the wind and wave climate at Roberts Bank, BC. It is intended to

provide background information to support the draft report of the Coastal Geomorphology Study

concerning the Deltaport Third Berth Project. The information and analysis in this report

characterize the wind and wave climate of the southern Strait of Georgia in general, and the

Roberts Bank portion of the Fraser River delta in particular. This appendix incorporates a review

of existing information, as well as analysis of available data. Triton’s Coastal Engineering

Analysis Package (CEAPack) was used to fill data gaps in the available datasets and to generate

wave data for the Roberts Bank site.

The winds across the Vancouver region consist of westerly winds from the Strait of Georgia,

outflow and easterly winds from Howe Sound and the Fraser Valley, and southerly winds from

the Juan de Fuca Strait and Puget Sound. The easterly winds occur most frequently, but some of

the strongest and most dangerous winds are from the west. Easterly winds are generally backed

into the east and northeast near the North Shore Mountains, but are more frequently from the

southeast over the southern sections of the region. The frequency of westerly winds in Burrard

Inlet is much less than over more southern areas.

Although there are no continuous long-term wind measurements recorded at the Roberts Bank

port site, it is fortunate that there exists a database of measured overwater or near-coast wind

data in the Strait sufficient to preclude the need for detailed mesoscale atmospheric modelling.

Given this, a reliable estimate of site wind conditions was developed using measured MSC data

in the southern Strait of Georgia.

The wave model, which was developed using Triton’s WaveHind software, was calibrated and

verified against the measured offshore data for a range of driving wind conditions. Once

calibrated, the model was used to generate a time series of incident offshore Strait of Georgia

wave conditions coincident with the wind database

The propagation of offshore Strait of Georgia waves inshore to the site was computed using

Triton’s implementation of the numerical model SWAN (Simulating WAves Nearshore). This

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Wind and Wave Climate – Appendix A - ii - November 2004

model is based on the wave-action balance equation in the presence of currents, or energy

balance in their absence (present application) with the inclusion of all significant wave energy

source and sink terms using first-, second- and third-generation wave physics.

Thus a detailed computation of the expected wave climate in the project area has been generated

using numerical models verified against a reliable dataset.

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Wind and Wave Climate – Appendix A - iii - November 2004

TABLE OF CONTENTS

1.0 INTRODUCTION............................................................................................................. 1

1.1 SCOPE OF WORK ...................................................................................................... 1

1.2 METHODOLOGY ....................................................................................................... 1

2.0 LOCAL WIND PATTERNS............................................................................................ 2

2.1 GENERAL ................................................................................................................. 2

2.2 LOCAL WINDS ..................................................................................................... 3

2.2.1 Outflow Winds – Northeasterly pressure-slope...........................................3

2.2.2 East to Southeast Winds – Easterly and Southeasterly pressure-slope........5

2.2.3 Southerly to Southwesterly Winds – Southerly and Southwesterly

pressure-slope ..............................................................................................8

2.2.4 Westerly Winds – Southwesterly and westerly pressure-slope ...................8

3.0 WAVE CLIMATE.......................................................................................................... 13

3.1 WIND ..................................................................................................................... 13

3.2 WAVES .................................................................................................................. 16

3.2.1 Offshore Waves .........................................................................................16

3.2.1.1 Measured Offshore Waves ............................................................ 16

3.2.1.2 Numerically-Predicted Offshore Waves ....................................... 20

3.2.2 Nearshore Wave Transformation...............................................................25

4.0 CONCLUSION ............................................................................................................... 34

5.0 REFERENCES................................................................................................................ 35

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Wind and Wave Climate – Appendix A - iv - November 2004

List of Tables

Table A2-1: General Trends in Wind Direction ............................................................................. 2

Table A3-1: MSC Wind Stations.................................................................................................. 13

Table A3-2: Wind Speed versus Wind Direction ......................................................................... 15

Table A3-3: Wind Speed versus Calendar Month ........................................................................ 15

Table A3-4: MEDS Wave Station Listing .................................................................................... 17

Table A3-5: MEDS Measured Wave Height versus Period - Roberts Bank .............................. 18

Table A3-6: MEDS Measured Wave Height versus Period – Halibut Bank................................ 19

Table A3-7: MEDS Measured Wave Height versus Direction – Halibut Bank ........................... 19

Table A3-8: MEDS Measured Wave Height versus Month – Halibut Bank................................ 20

Table A3-9: Overwater Fetches – Operational Model.................................................................. 23

Table A3-10: Offshore Wave Height versus Period for All Directions - Hindcast ...................... 24

Table A3-11: Offshore Wave Height versus Direction - Hindcast............................................... 24

Table A3-12: Offshore Wave Height versus Calendar Month - Hindcast.................................... 25

Table A3-13: Modelled Wind and Wave Conditions ................................................................... 28

List of Figures

Figure A2-1: Outflow Winds – Northeasterly pressure-slope ........................................................ 3

Figure A2-2: Outflow Winds – Northeasterly pressure-slope (2) .................................................. 4

Figure A2-3: East to Southeast Winds – Easterly and Southeasterly pressure-slope ..................... 6

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Wind and Wave Climate – Appendix A - v - November 2004

Figure A2-4: East to Southeast Winds – Easterly and Southeasterly pressure-slope (2) ............... 7

Figure A2-5: East to Southeast Winds – Easterly and Southeasterly pressure-slope (3) ............... 7

Figure A2-6: Westerly Winds – Southwesterly and westerly pressure-slope................................. 9

Figure A2-7: Westerly Winds – Southwesterly and westerly pressure-slope (2) ......................... 10

Figure A2-8: Westerly Winds – Southwesterly and westerly pressure-slope (3) ......................... 11

Figure A3-1: Roberts Bank Wind Rose, All Months.................................................................... 14

Figure A3-2: MEDS Wave Station Plot........................................................................................ 16

Figure A3-3: Example of Wave Hindcast Calibration/Verification ............................................. 22

Figure A3-4: Offshore Wave Rose – Hindcast Data .................................................................... 23

Figure A3-5: SWAN Existing Conditions Bathymetry – Outer and Nested Grid........................ 26

Figure A3-6: Typical Wave Conditions – 10 knot SE wind, mean water level............................ 30



Figure A3-9: Typical Wave Conditions – 20 knot SE wind, low water level .............................. 31

Figure A3-10: Typical Wave Conditions – 20 knot SE wind, mean water level.......................... 31

Figure A3-11: Typical Wave Conditions – 20 knot SE wind, high water level ........................... 31

Figure A3-12: Typical Wave Conditions – 20 knot NW wind, mean water level........................ 32

Figure A3-13: Typical Wave Conditions – 20 knot west wind, mean water level ....................... 32

Figure A3-14: Typical Wave Conditions – 20 knot SW wind, mean water level ........................ 33

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Wind and Wave Climate – Appendix A - vi - November 2004

Figure A3-15: Typical Wave Conditions – 20 knot south wind, mean water level...................... 33

Figure A3-16: Typical Wave Conditions – 20 knot SE wind, mean water level.......................... 33

Vancouver Port Authority Northwest Hydraulic Consultants Ltd/Triton Consultants Ltd. Roberts Bank Container Expansion File: 33863 Wind and Wave Climate – Appendix A - 1 - November 2004

1.0 INTRODUCTION

1.1 SCOPE OF WORK

This report is included as Appendix A of the DRAFT Coastal Geomorphology Study (Northwest

Hydraulic Consultants and Triton Consultants Ltd., 2004). The appendix is intended to provide

background information to support the draft report of the Coastal Geomorphology Study

concerning the Deltaport Third Berth Project. The information and analysis in this report

characterize the wind and wave climate of the southern Strait of Georgia in general, and the

Roberts Bank portion of the Fraser River delta in particular. The information that has been

compiled provides a good basis for understanding and predicting potential impacts from the

planned Third Berth Project.

1.2 METHODOLOGY

This appendix incorporates a review of existing information, as well as analysis of available data.

Existing information about the local winds was extracted from the CD ROM Coastal Weather

for British Columbia Mariners prepared by the Meteorological Service of Canada (MSC, 2000).


port site, a reliable estimate of site wind conditions was developed using measured MSC data in

the southern Strait of Georgia. Triton’s Coastal Engineering Analysis Package (CEAPack) was

used to fill data gaps in the MSC datasets and generate wave data for the Roberts Bank site.


2.0 LOCAL WIND PATTERNS

The information in this section was extracted from the CD ROM Coastal Weather for British

Columbia Mariners prepared by the Meteorological Service of Canada (MSC, 2000).

2.1 GENERAL

The winds across the Vancouver region consist of westerly winds from the Strait of Georgia,

outflow and easterly winds from Howe Sound and the Fraser Valley, and southerly winds from

the Juan de Fuca Strait and Puget Sound. The easterly winds occur most frequently, but some of

the strongest and most dangerous winds are from the west. Easterly winds are generally backed

into the east and northeast near the North Shore Mountains, but are more frequently from the

southeast over the southern sections of the region. The frequency of westerly winds in Burrard

Inlet is much less than over more southern areas. Table A2-1 summarises the general trends in

wind direction.

Table A2-1: General Trends in Wind Direction

The region covered in this section is the southern section of the official Strait of Georgia, as it is

used in the marine forecast. It is separated from the rest of the Strait of Georgia for the wind

patterns are somewhat different from the rest of the strait.

Jan Apr Jul OctNortheast N, NE 1, 2 14 11 5 11Easterly E, SE 2, 3, 4, 5, 6 54 39 44 45Southerly S, SW 4, 5, 6 11 17 14 10Westerly W, NW 1, 6, 7, 8 15 28 30 27Calm 6 5 7 7*Based on: Sand Heads, Vancouver Airport and First Narrows

Basic Winds

Wind Directions

Regional Patterns

Seasonal Frequencies


2.2 LOCAL WINDS

2.2.1 Outflow Winds – Northeasterly pressure-slope

When a ridge of high pressure develops over the British Columbia Interior, outflow conditions

spread through Howe Sound, the Fraser Canyon and Harrison Lake. The pressure-slope direction

is northeasterly. The Vancouver region is affected by flow that moves across the Fraser Valley.

The plume of strong winds extends from the narrow confines of the upper part of the valley,

across Sumas Prairie, south of the river near Matsqui and then is steered by the mountains to the

south, to move out across Birch Bay and into the strait. The more northerly parts of greater

Vancouver will only have light easterly winds. When outflow winds rise to gale force 35 to 45

knots in Howe Sound and in the upper reaches of the valley, the easterly winds that move into

Vancouver Harbour are usually only 5 to 10 knots, or at most 15 knots. However, from southern

Vancouver to Bellingham the winds may be easterly, near 20 to 25 knots, and with a very strong

outflow, can reach gale force. The same pattern of winds can happen, though with much reduced

speeds, at any time of the year, as a result of night-time drainage from the mountains.

Figure A2-1: Outflow Winds – Northeasterly pressure-slope

The winds from Howe Sound usually end within one or two kilometres south of its entrance, off

Point Atkinson. Squamish outflow winds can, in a very specific pattern, extend out to Point


Grey, and can even move south of Tsawwassen Beach to the Gulf Islands. This occurs when the

ridge of high pressure rotates more toward the north. In this case, northwest winds move all the

way down the Strait of Georgia, to just west of Vancouver where they converge with the easterly

winds coming out of the Fraser Valley. The northerly winds in Howe Sound are drawn into this

convergence zone and move southward out of the sound. Wind speeds of 40 knots can be

reached. Only the westernmost anchorages of English Bay will receive any of this northerly

wind. Northerly swells, which bend into the bay, may be more important. The tides can help to

hold off, or carry in, the swell.

Figure A2-2: Outflow Winds – Northeasterly pressure-slope (2)

Indian Arm also experiences outflow winds, but they do not occur with every Squamish outflow,

and even when they do, they are usually not as strong as the peak wind in Howe Sound. In order

for strong northerly winds to pour into Indian Arm the cold air must be sufficiently deep, so that

when it reaches Squamish it will be able to flow southeastward through the Stawamus and Indian

River valleys. Since the ability of the air to flow down into Indian Arm is linked to the air

temperature, the winds may show more of a diurnal afternoon decrease when the air temperature

of Squamish increases. The winds in Howe Sound, which are not as restricted by temperature

variations, will not show such a marked afternoon decrease. Perhaps the winds passing Squamish

must also be more northerly, in order for them to flow down the river valleys. The path of winds


into Indian Arm is not as direct as it is in Howe Sound, therefore the winds are generally less. If

the winds at Pam Rock are near gale force 35 knots, the maximum winds in Indian Arm will be

about 25 knots. The strongest winds occur near the narrowest parts of the channel and near the

major bends in Indian Arm. Generally there are more places to shelter in along the west side of

Indian Arm, but this will change as the flow meanders past the turns of the inlet. The winds that

move into Deep Cover are lifted up by the hill behind the cover, so that the winds on the water

become lower the closer you go towards the shore. The winds become light close to the opening

of Burrard Inlet.

2.2.2 East to Southeast Winds – Easterly and Southeasterly pressure-slope

Easterly winds, ranging from just north of east to southeast, are the most common winds in the

Vancouver area. With the approach of a front, the pressure-slope direction will back into the east.

The winds across the region will vary considerably, depending on the direction from which the

front approaches.

When a front approaches from the west or northwest, and the pressure-slope direction is south of

east, then the southeast winds first appear in the northern part of the Strait of Georgia and

gradually spread south toward the Vancouver area as the front draws closer. The strongest

southeast winds cut a swath across the city, from the southwestern areas near White Rock and

Tsawwassen over to near Point Atkinson. However, the winds will usually be much lighter in the

Vancouver area than the peak winds in the Strait of Georgia. To the northeast of this swath,

particularly closer to the Coast Mountains, with wind tends to back more into the east, and even

northeast, and are much lighter.


Figure A2-3: East to Southeast Winds – Easterly and Southeasterly pressure-slope

When a front approaches from the southwest, the pressure-slope direction will back to north of

east. This rotation of the pressure-slope moves the plume of strong southeast winds farther away

from Vancouver, and closer to Vancouver Island. Places like East Point on Saturna Island, will

wobble from east to southeast. Most parts of the region northeast of Sand Heads will have east or

northeast winds, and generally less than 15 knots. In this situation the flow patter is more like an

outflow condition. The strongest winds do not begin in the northern part of the Strait of Georgia,

but will arise, more or less equally, in the southwest area close to Vancouver Island. Once

established, the plume of strong southeast winds extends from the mouth of Puget Sound

northward, hugging close to the Vancouver Island shore. The winds spread out across the Strait

of Georgia farther to the north. As the pressure-slope direction veers more toward the southeast

the strong plume of southeast winds will move northward across most of greater Vancouver. The

winds at Point Atkinson will be strengthened and backed into the east by channeling along the

North Shore Mountains. Their speed can be 5 knots stronger than at Sand Heads. When the

pressure-slope direction veers more toward the south, the winds at Point Atkinson will ease

considerable and will become much lighter than at Sand Heads. The winds in Indian Arm will

remain from the north, though not normally very strong, throughout these different frontal

scenarios.


Figure A2-4: East to Southeast Winds – Easterly and Southeasterly pressure-slope (2)

When a ridge of high pressure develops to the south or southeast of the region, the winds will be

from the east or southeast, even without a front approaching. This would be a ‘pushed’ southeast

wind. Such a wind can develop at any time of the year, but is quite common during the summer

when a ridge of high pressure lies west of Vancouver Island. The ridge only needs to rotate

slightly, so that the pressure-slope direction turns toward the south, for Juan de Fuca return flow

winds to move north across western Vancouver.

Figure A2-5: East to Southeast Winds – Easterly and Southeasterly pressure-slope (3)


2.2.3 Southerly to Southwesterly Winds – Southerly and Southwesterly pressure-slope

South or southwest winds are not common winds, but result during a transition from southeast to

westerly winds. The strongest southwest winds usually accompany the passage of a front over

the region. These winds will be strongest closer to Vancouver Island but tend to weaken and

back into the southeast near Vancouver. Along the North Shore mountains the winds remain

from the east or southeast until they turn fully into the west. Southwest winds can also occur in

different parts of the area with sea breeze winds during the summer. Indian Arm experiences

southerly winds during sunny summer afternoons when upslope winds develop through the inlet.

The strongest southerly winds will develop when a deep low passes directly over the south coast

and into the Interior to the north of the region.

2.2.4 Westerly Winds – Southwesterly and westerly pressure-slope

On a typical summer day, northwest winds will spread down the Strait of Georgia during the

night to reach Entrance Island near dawn. These winds generally ease a short distance southeast

of Entrance Island without making it all the way to Vancouver. This occurs due to the opening

out of the strait in that area, causing the channelling effect to be reduced. But perhaps more

importantly, the northwest winds stop when they encounter the east to southeast winds which are

over the Vancouver area. The southeast winds are the result of the westerly winds in Juan de

Fuca Strait turning northward overnight and backing into the southeast due to topographical

channelling. The convergence line between the northwest winds from the Strait of Georgia and

the westerlies from Jan de Fuca Strait frequently lies in this area between Vancouver and

Entrance Island. When the line of convergence is close to Vancouver, a mariner might find light

southeast winds near the coast but just a little farther offshore the winds will be from the

northwest.

The northwest winds will spread all the way to Vancouver when the pressure slope rotates to

west of about 240o. The black line, marking the edge of the northwesterlies, will be seen

gradually approaching Burrard Inlet.


Figure A2-6: Westerly Winds – Southwesterly and westerly pressure-slope

If the northwest winds do not spread all the way down to Sand Head and Vancouver in the early

morning, light southeast winds will be present over the region and the conditions are ripe for the

development of a sea breeze. Sea breeze winds require very light wind conditions plus strong

heating from the sun. During the shortest days of winter, sea breeze winds are barely possible.

The strongest sea breeze winds occur in the late spring and early summer when the contrast in

temperature between land and water is greatest. The coastal sea breeze winds can be increased by

being drawn into the upslope valley winds of the upper parts of the Fraser Valley. The most

common time for the onset of a sea breeze in English Bay is near 1000 hours, although it will

occasionally begin as early as three hours after sunrise. The strength of the sea breeze increases

rapidly through the late morning, continues through the day, then decreases almost as rapidly in

the late afternoon. Usually the westerly winds in the early morning are near 10 to 15 knots, the

sea breeze winds will be delayed until late in the afternoon. If it is cloudy, they will not develop

at all.

The winds in Indian Arm during the time of light summer winds will normally be northerly

overnight and in the early morning, due to night time drainage, and southerly during the

afternoon, from air being sucked up the valley slopes. The strongest southerly winds will be near

the northern end of Indian Arm.


Southeast winds are usually stronger in the early morning if the winds through Juan de Fuca

Strait were particularly strong westerlies during the previous afternoon, and the pressure-slope

direction has backed far enough toward the south to propel the winds northward toward

Vancouver. This pattern will develop when the ridge of high pressure west of Vancouver Island

rotates enough counter-clockwise for the lee trough, which lies off the Barkley Sound area, to

collapse. This will allow strong northwest winds to pour into Juan de Fuca Strait, thereby

increasing the westerly winds at Race Rocks to near gale force 35 knots by early evening. If the

ridge rotates a little farther back, so that the pressure-slope direction becomes southerly, these

winds will spread over the Gulf and San Juan Islands during the late evening and will reach the

Vancouver area overnight. The southeast winds that develop from this Juan de Fuca return flow

will reach the Coast Mountains and the Sunshine Coast in the early morning and will spread back

across the strait toward Entrance Island an hour or two later. These winds usually ease during the

afternoon, but normally not soon enough for a sea breeze to develop.

Figure A2-7: Westerly Winds – Southwesterly and westerly pressure-slope (2)

Only with particularly strong diurnal northwest winds, and when the ridge of high pressure lies

to the north of the region, will the winds continue past Entrance Island and spread directly across

Vancouver and farther south toward Bellingham. If the northwest winds that reach Vancouver

are part of the normal diurnal cycle they will ease in the early afternoon. Locations close to the


coast may develop westerly sea breeze winds during the late afternoon. If the northwest winds

have developed due to a northerly pressure-slope, the winds will not die down during the

afternoon, but will in fact increase a little with the addition of a sea breeze wind. The strength of

the afternoon winds will be 20 to 25 knot and will ease slightly to 15 to 20 knots overnight.

These winds will continue into the next day, and can persist for several days if the pressure-slope

direction remains from the north. In this situation the winds will be particularly strong at Sand

heads, where the seas can build sharply, especially when against a strong river outflow. In this

situation a small boat may have difficulty moving out of the river and getting past the green light

at the mouth of the jetty. The westerly winds that move into English Bay and Burrard Inlet are

strongest on the southern side of the bay. This can make the wave conditions rather

uncomfortable, if not dangerous, with an ebb tide near First Narrow. During these windy days in

the Vancouver area the winds tend to be light farther up the strait, north of Ballenas Island.

Figure A2-8: Westerly Winds – Southwesterly and westerly pressure-slope (3)

Northwest winds which develop after the passage of a front can produce the strongest of all the

winds in the Vancouver region. They do not usually last as long as the east or southeast winds,

but often have a much greater impact. March is often a time of strong northwest winds. The

strongest northwest winds occur behind a front that has approached from the northwest, or

behind a deep low which has passed eastward over southern Vancouver Island. The latter of


these two scenarios is usually the worst. In both cases the winds can shift from east or southeast

ahead of the front or low, and rise to strong northwest winds very quickly. IN extreme events,

shifts can occur in minutes, from southeast 30 to 35 knots to northwest 45 to 50 knots.

Fortunately, this does not occur often, but shifts like this, although with much less wind speed,

usually happen every winter. Even if northwest winds only rise to 25 or 30 knots behind a front,

they can still be quite powerful, for the air is cold and therefore carries more of a punch than

warmer air. Northwest winds that develop behind a front spread quit uniformly across the entire

region.


3.0 WAVE CLIMATE

3.1 WIND


port site, it is fortunate that there exists a database of measured overwater or near-coast wind

data in the Strait sufficient to preclude the need for detailed mesoscale atmospheric modelling.

Given this, a reliable estimate of site wind conditions was developed using measured MSC data

in the southern Strait of Georgia.

Table A3-1 summarizes MSC hourly data sets that are most relevant to the project and that were

obtained for this study.

Table A3-1: MSC Wind Stations

The three stations shown in bold text were analyzed in detail using Triton’s Coastal Engineering

Analysis Package (CEAPack). The CEAPack software suite contains analysis routines that were

used to fill data gaps in the MSC datasets and generate a single-element triangular irregular

network (TIN) linking the three sites. The TIN was used to linearly interpolate the wind speed

and direction vectors spatially and temporally near the southwest corner of the existing Robert

Bank Superport; differences between conditions there, the proposed Deltaport Expansion (DPE)

berth, and offshore cannot be resolved so have been neglected throughout this study. The final

Lat Long(N) (W)

1108290 Tsawwassen Ferry

Feb 1976 to Jul 1997 49o00’ 123 o 08’ 3

1107010 Sand Heads May 1967 to present 49 o 06’ 123 o 18’ 01106200 Point Atkinson Jan 1969 to present 49 o 20’ 123 o 16’ 9102BFHH Entrance Island Dec 1969 to May 1997 49 o 12’ 123 o 49’ 8

1027403 Sisters Island Jan 1995 to present 49 o 29’ 124 o 26’ 51108447 Vancouver

Airport Jan 1953 to present 49 o 18’ 123 o 07’ 0

1017101 Saturna Island Mar 1968 to present 48 o 47’ 123 o 03’ 38

ID Station Name Period of Record Elev. (m)


product of this analysis was a time series of hourly wind speed and direction data at 10 m

elevation spanning the interval January, 1963 to present.

Figure A3-1 and Table A3-2 summarize the wind climate at the site derived from this dataset in

wind rose and bivariate histogram format respectively.

Figure A3-1: Roberts Bank Wind Rose, All Months

The numbers tabulated in Table A3-2 indicate the number of hours in the period of record that

sustained wind speeds were within the speed and direction ranges shown. For example, the data

indicate that wind speeds were between 1 and 5 knots from the north during 10066 of the 347985

hours for which there are valid data (i.e., 2.9% of the time).


Table A3-2: Wind Speed versus Wind Direction

Note that hourly wind speeds in excess of 30 knots are rare, occurring 1372 hours in the period

of record (1027+277+60+7+1) or 0.4% of the time on average. Table A3-3 shows the variation

of wind speed by month.

Table A3-3: Wind Speed versus Calendar Month

Note that the highest frequency of winds greater than 30 knots occurs during December followed

by March.

N NE E SE S SW W NW0 - 1 72531 - 5 102830 10066 9218 13550 16604 15314 9587 11790 167015 - 10 124668 5147 5960 21735 30468 16580 8829 9798 2615110 - 15 68620 905 2637 13664 18039 9442 4884 5028 1412115 - 20 29760 132 1077 5077 8280 5797 2019 1943 543520 - 25 10152 28 290 1269 3758 2127 355 653 167225 - 30 3330 8 41 248 1653 707 52 171 45030 - 35 1027 0 0 25 660 171 11 32 12835 - 40 277 0 0 2 202 44 3 2 2440 - 45 60 0 0 3 41 10 0 0 645 - 50 7 0 0 0 4 1 0 0 250 - 55 1 0 0 0 0 0 0 0 1Total 347985 16286 19223 55573 79709 50193 25740 29417 64591

Direction (from)Speed (knots) Total

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

0 - 1 72531 - 5 102830 6796 7118 7717 8287 9852 9048 10385 11191 10697 9278 6385 60765 - 10 124668 9578 8925 9635 10616 11996 12582 12069 11654 10599 9501 8662 8851

10 - 15 68620 6867 6040 6428 6236 5341 5571 5247 4687 4321 5048 6215 661915 - 20 29760 3835 3134 3286 2572 1604 1369 1416 1084 1282 2373 3652 415320 - 25 10152 1445 1251 1213 710 435 283 197 147 236 790 1603 184225 - 30 3330 514 446 477 170 122 47 14 12 53 257 516 70230 - 35 1027 134 141 181 46 24 0 0 0 11 75 148 26735 - 40 277 40 38 44 2 3 0 0 0 0 13 52 8540 - 45 60 7 12 10 0 0 0 0 0 0 5 14 1245 - 50 7 1 2 1 0 0 0 0 0 0 1 2 050 - 55 1 0 0 1 0 0 0 0 0 0 0 0 0Total 347985 29217 27107 28993 28639 29377 28900 29328 28775 27199 27341 27249 28607

Calendar MonthSustained Speed (knots)

Total(observations)


3.2 WAVES

3.2.1 Offshore Waves

3.2.1.1 Measured Offshore Waves

The entire Marine Environmental Data Service (MEDS) database of measured wave data in

Southern BC was obtained for this study. Figure A3-2 shows wave data buoy locations and Table

A3-4 shows the period of record coverage of these deployments.

Figure A3-2: MEDS Wave Station Plot


Table A3-4: MEDS Wave Station Listing

The stations shown in bold are of primary interest to this study and were reviewed in detail.

Table A3-5 is a summary of measured wave conditions at Roberts Bank (MEDS 108) expressed

in terms of significant wave height (Hs)1 and peak spectral period (Tp)2. Note that the

observations showing wave periods in excess of 10 seconds are thought to be erroneous since

these low frequency waves cannot be generated within a relatively small body of water such as

1 Average trough-to-crest height of the highest 1/3rd of all waves. 2 The wave period corresponding to the peak of the wave energy spectrum.

LAT LONG°N °W

C46206 11/22/1988 8/24/2003 48.83 126 73 4530 La Perouse BankMEDS303 9/17/1998 5/7/1999 49.03 125.8 40 199 Tofino DWRMEDS103 6/26/1970 6/17/1998 48.99 125.74 40 8958 TofinoMEDS336 10/1/1997 12/19/1997 50 125.19 999 77 Cape Mudge

C46131 10/20/1992 8/24/2003 49.91 124.99 18 3359 Sentry ShoalMEDS117 10/12/1977 3/25/1978 49.98 124.77 37 150 LundMEDS111 12/10/1976 3/14/1977 49.84 124.53 6 95 Powell River (Inner)MEDS112 12/10/1976 3/14/1977 49.84 124.53 9 90 Powell River (Outer)MEDS114 11/24/1976 2/24/1977 49.35 124.35 4 83 French Creek (Inner)MEDS115 11/24/1976 3/15/1977 49.35 124.35 7 92 French Creek (Outer)MEDS273 7/19/1989 7/19/1989 49.26 124.05 52 0 NanaimoMEDS097 1/11/1974 5/16/1974 49.34 123.74 53 115 Halibut Bank

C46146 3/13/1992 8/24/2003 49.34 123.73 40 3515 Halibut BankMEDS123 4/5/1979 3/27/1980 49.35 123.7 50 350 Fishermans CoveMEDS285 11/27/1990 4/30/1991 48.33 123.55 14 98 Pedder BayMEDS121 3/30/1978 4/3/1979 49.4 123.5 37 358 Gibsons LandingMEDS259 4/10/1987 6/18/1987 49.66 123.48 54 50 Patricia BayMEDS317 10/29/1992 1/5/1994 48.43 123.45 11 421 Esquimalt Harbour

C46134 2/19/2001 7/9/2003 48.66 123.45 68 661 Pat Bay Test BuoyMEDS004 3/10/1976 3/24/1977 48.42 123.39 5 356 Victoria HarbourMEDS095 12/3/1975 7/28/1976 48.43 123.39 4 140 Victoria (K)MEDS108 6/25/1981 6/29/1981 49.07 123.38 250 5 Roberts BankMEDS102 2/7/1974 4/3/1976 49.17 123.31 110 643 Sturgeon Bank

C46182 9/8/1989 11/21/1991 49.48 123.29 88 462 Pam RocksMEDS108 2/7/1974 4/3/1976 49.02 123.27 139 531 Roberts BankMEDS122 7/5/1978 7/30/1979 49.28 123.27 11 357 Point GreyMEDS124 4/6/1979 3/29/1980 49.35 123.27 6 314 Fishermans CoveMEDS106 12/19/1972 5/18/1974 49.35 123.23 40 487 West VancouverMEDS107 10/22/1973 3/24/1974 49.33 122.93 7 147 Deep CoveMEDS116 10/14/1977 3/3/1978 49.01 122.83 13 103 White Rock

GOOD DAYS

STATION NAMEID START DATE

END DATE

Depth (m)


the Strait of Georgia, nor can they effectively propagate into the Strait from the deep ocean. Note

also that the instrument used to acquire these observations was a Datawell Waverider buoy

which does not measure wave direction.

Table A3-5: MEDS Measured Wave Height versus Period - Roberts Bank

Table A3-5 demonstrates that large waves are rare within this sample; offshore significant wave

heights are greater than 1.5 m only about 0.5% of the time.

A similar analysis was made using the more reliable, although distant from the site, dataset from

Halibut Bank. Table A3-6 through Table A3-7 show the relationship between significant wave

height and peak period, dominant direction, and calendar month respectively. The Halibut Bank

data indicate that the most frequent and largest measured waves at that location are from the

southeast, with significant wave heights exceeding 1.5 m just over 0.5% of the time. The most-

probable peak wave period associated with the larger waves is 6 to 8 seconds.

2 - 4 4 - 6 6 - 8 8 - 10 10 - 20

0.0 - 0.10 3770.10 - 0.25 1730 1374 282 62 2 100.25 - 0.50 1142 959 142 29 2 100.50 - 0.75 480 281 186 10 0 30.75 - 1.00 233 44 178 4 1 61.00 - 1.25 96 3 91 0 1 11.25 - 1.50 48 1 44 1 1 11.50 - 1.75 12 0 10 2 0 01.75 - 2.00 4 0 2 1 0 12.00 - 2.25 1 0 1 0 0 02.25 - 2.50 0 0 0 0 0 02.50 - 2.75 2 0 0 2 0 02.75 - 3.00 1 0 0 1 0 03.00 - 3.25 1 0 0 1 0 0

Total 4127 2662 936 113 7 32

Significant Height (m) Total

Peak Spectral Period (s)

(observations)


Table A3-6: MEDS Measured Wave Height versus Period – Halibut Bank

Table A3-7: MEDS Measured Wave Height versus Direction – Halibut Bank

2 - 4 4 - 6 6 - 8 8 - 10

0.0 - 0.10 397350.10 - 0.25 10172 3141 3455 3403 1730.25 - 0.50 4158 3714 238 161 450.50 - 0.75 4082 3473 602 7 00.75 - 1.00 1565 645 916 3 11.00 - 1.25 1073 93 976 4 01.25 - 1.50 296 0 294 2 01.50 - 1.75 194 0 177 17 01.75 - 2.00 66 0 50 16 02.00 - 2.25 42 0 31 11 02.25 - 2.50 12 0 8 4 02.50 - 2.75 12 0 3 9 02.75 - 3.00 1 0 0 1 03.00 - 3.25 0 0 0 0 03.25 - 3.50 0 0 0 0 0

Total 61408 11066 6750 3638 219


Peak Spectral Period (s)

(observations)

N NE E SE S SW W NW

0.0 - 0.10 397350.10 - 0.25 10172 962 604 1640 2247 789 558 1645 17270.25 - 0.50 4158 191 77 686 977 190 122 1079 8360.50 - 0.75 4082 66 47 1118 824 140 62 1161 6640.75 - 1.00 1565 4 7 486 370 41 6 379 2721.00 - 1.25 1073 1 2 461 271 36 7 152 1431.25 - 1.50 296 0 0 134 106 5 1 14 361.50 - 1.75 194 0 0 87 75 3 0 6 231.75 - 2.00 66 0 0 32 30 1 1 0 22.00 - 2.25 42 0 0 18 18 0 0 0 62.25 - 2.50 12 0 0 7 5 0 0 0 02.50 - 2.75 12 0 0 8 4 0 0 0 02.75 - 3.00 1 0 0 0 1 0 0 0 03.00 - 3.25 0 0 0 0 0 0 0 0 03.25 - 3.50 0 0 0 0 0 0 0 0 0

Total 61408 1224 737 4677 4928 1205 757 4436 3709

Direction (from)Significant Height (m) Total

(observations)


Table A3-8: MEDS Measured Wave Height versus Month – Halibut Bank

At the time of writing, VPA have installed a directional wave and current sensor offshore of the

site which is intended to remain in place for the foreseeable future. Measured data from this

sensor were not available for inclusion in this analysis.

3.2.1.2 Numerically-Predicted Offshore Waves

In order to develop a statistically meaningful long-term record of wave conditions at the DPE

site and in the local area of interest, a numerical model of offshore wave conditions was

developed for this study. The wave model, which was developed using Triton’s WaveHind

software, was calibrated and verified against the measured offshore data described previously for

a range of driving wind conditions. Once calibrated, the model was used to generate a time series

of incident offshore Strait of Georgia wave conditions coincident with the wind database.

WaveHind is a variable-fetch single-station parametric wave model that is a well-tested, practical

engineering tool based on the wave prediction equations described in the Shore Protection

Manual (US Army, 1977). It is based on the assumption that winds are relatively uniform over

the water body of interest, and that wave conditions may be described by only three parameters;


0.0 - 0.10 39735 3032 3309 3926 4591 3985 2965 2606 2415 2598 3566 3289 34530.10 - 0.25 10172 337 561 725 663 938 1139 1146 1411 1441 880 473 4580.25 - 0.50 4158 250 148 227 165 270 373 429 804 584 379 276 2530.50 - 0.75 4082 311 208 258 179 239 340 406 575 442 376 399 3490.75 - 1.00 1565 152 67 119 55 122 124 167 111 101 167 185 1951.00 - 1.25 1073 96 72 129 27 58 49 24 33 57 126 193 2091.25 - 1.50 296 19 47 30 12 5 11 4 0 11 24 74 591.50 - 1.75 194 9 28 41 1 1 2 0 0 1 21 38 521.75 - 2.00 66 5 12 15 0 0 0 0 0 0 6 13 152.00 - 2.25 42 2 2 11 0 0 0 0 0 1 6 5 152.25 - 2.50 12 0 1 1 0 0 0 0 0 0 5 0 52.50 - 2.75 12 0 1 4 0 0 0 0 0 0 2 4 12.75 - 3.00 1 0 0 0 0 0 0 0 0 0 0 1 03.00 - 3.25 0 0 0 0 0 0 0 0 0 0 0 0 03.25 - 3.50 0 0 0 0 0 0 0 0 0 0 0 0 0

Total 61408 4213 4456 5486 5693 5618 5003 4782 5349 5236 5558 4950 5064


Calendar Month

(observations)


significant wave height, spectral peak period and dominant direction. The model uses the best

available estimate of overwater winds in the form of hourly wind speed and direction data in

conjunction with overwater fetch distances in each of the eight compass point directions. It

computes wave conditions by stepping hour-by-hour through the wind time series. At each hour,

the model looks backwards in time to find the number of hours that the wind direction was

unchanged (i.e., within a constant compass-point sector) and was non-calm. The model then

determines which combination of average wind speed and duration yields the largest wave height

(e.g., the largest of 40 knots for one hour, 38 knots for two hours, 35 knots for three hours, etc.);

this largest height is then considered to be the best estimate of the actively-generated sea wave

component.

When the wind direction changes, the previously computed sea conditions are allowed to decay

based on the rate of wave energy flux out of the previous sea (now the swell) sector and the

number of hours since the wind direction last changed. Wave conditions in the new sea sector are

computed as described above, and the total wave condition is found by combining sea and swell

wave parameters. The combined condition is computed by summing sea and swell wave

energies, and assigning the total peak period and direction to that of the larger of the sea and

swell components. The final output of the model is an hourly time series of total offshore wave

parameters that can be analysed to yield operational and extreme wave statistics, and transformed

by applying transformation coefficients that modify the dataset to reflect conditions elsewhere

(e.g., at locations of interest inshore).

The model was verified by hindcasting wave conditions at the Halibut Bank wave sensor

(49.34oN, 123.73oW) in approximately 40 m of water. Figure A3-3 shows a comparison of

measured and predicted wave conditions for several representative time periods; the comparison

is considered good.


Figure A3-3: Example of Wave Hindcast Calibration/Verification

Following verification of the model, a hindcast location nearer to and offshore of the site was

chosen for the production model runs. The site was located directly offshore of the existing

Roberts Bank Terminal in 85 m CD of water at 49.0oN, 123.18oW. This point lies at the

intersection of the International Boundary and the approximate bearing of the existing causeway

alignment.

Table A3-9 lists the overwater fetch distances were used in the production model.


Table A3-9: Overwater Fetches – Operational Model

The resulting wave timeseries produced by the model was analysed and summarised. Figure A3-

4 shows the dataset in wave rose format. Table A3-10 through Table A3-12 show the same

information in bivariate histogram format; observations represent the number of hours in the

period of record.

Figure A3-4: Offshore Wave Rose – Hindcast Data

Direction Fetch (Nm) DescriptionNorth 4.9 to Westham IslandNortheast 3.8 between two causewaysEast 3.4 Passing just south of Tsawwassen FerrySoutheast 33 just beyond Lummi IslandSouth 12 to Saturna IslandSouthwest 9 to southern Galiano IslandWest 15 to northern Galiano IslandNorthwest 62 to Hornby Island


Table A3-10: Offshore Wave Height versus Period for All Directions - Hindcast

Table A3-11: Offshore Wave Height versus Direction - Hindcast

0.0-1.0 1.0-2.0 2.0-3.0 3.0-4.0 4.0-5.0 5.0-6.0 6.0-7.0 7.0-8.0 8.0-9.0 9.0-10.0

0.0 - 0.10 99389 99389 0 0 0 0 0 0 0 0 00.10 - 0.50 171328 0 37758 92715 36581 3621 537 108 8 0 00.50 - 1.00 58355 0 0 973 29391 25777 1795 368 46 5 01.00 - 1.50 13456 0 0 0 128 3467 9190 611 51 9 01.50 - 2.00 3973 0 0 0 3 6 717 3096 137 14 02.00 - 2.50 1107 0 0 0 0 0 1 401 689 16 02.50 - 3.00 300 0 0 0 0 0 0 0 244 56 03.00 - 3.50 62 0 0 0 0 0 0 0 0 62 03.50 - 4.00 13 0 0 0 0 0 0 0 0 4 94.00 - 4.50 2 0 0 0 0 0 0 0 0 0 2

Total 347985 99389 37758 93688 66103 32871 12240 4584 1175 166 11

Tp (s)

Total Observations (count)Hs (m) Total

N NE E SE S SW W NW

0.0 - 0.10 993890.10 - 0.50 171328 3429 6662 34046 44134 21619 10975 11919 385440.50 - 1.00 58355 96 1001 3917 18427 8675 3070 3500 196691.00 - 1.50 13456 2 21 122 5488 1693 73 575 54821.50 - 2.00 3973 1 1 6 2161 149 4 43 16082.00 - 2.50 1107 0 0 1 651 16 0 0 4392.50 - 3.00 300 0 0 0 207 0 0 0 933.00 - 3.50 62 0 0 0 26 0 0 0 363.50 - 4.00 13 0 0 0 1 0 0 0 124.00 - 4.50 2 0 0 0 0 0 0 0 2

Total 347985 3528 7685 38092 71095 32152 14122 16037 65885


Dominant Direction (from)

(observations)


Table A3-12: Offshore Wave Height versus Calendar Month - Hindcast

3.2.2 Nearshore Wave Transformation

The propagation of offshore Strait of Georgia waves inshore to the site was computed using

Triton’s implementation of the numerical model SWAN (Delft University, 2003). SWAN

(Simulating WAves Nearshore) is used to obtain realistic estimates of wave parameters in coastal

areas, lakes and estuaries given wind, bottom and current conditions. The model is based on the

wave-action balance equation in the presence of currents, or energy balance in their absence

(present application) with the inclusion of all significant wave energy source and sink terms

using first-, second- and third-generation wave physics.

The following wave propagation processes are represented:

• rectilinear propagation through geographic space;

• refraction and shoaling due to spatial variations in water depth;

• refraction and shoaling due to spatial variations in current speed and direction (not used in present application);

• blocking and reflections by opposing currents (not used in present application); and,

• transmission, blockage, or reflection from sub-grid obstacles.

The following wave generation and dissipation processes are represented in SWAN:


0.0 - 0.10 99389 7479 7225 7800 8115 9304 8321 9006 10209 9354 9035 6739 68020.10 - 0.50 171328 14769 13275 13929 14553 15463 15782 15283 14394 13868 13145 13003 138640.50 - 1.00 58355 5331 5365 5535 4972 4094 4338 4529 4243 3963 4620 5688 56771.00 - 1.50 13456 1469 1195 1644 1166 774 660 869 576 709 1085 1618 16911.50 - 2.00 3973 465 443 523 303 198 244 207 76 118 304 467 6252.00 - 2.50 1107 139 105 139 86 79 58 10 2 43 63 147 2362.50 - 3.00 300 45 42 47 0 13 0 0 0 0 14 36 1033.00 - 3.50 62 7 6 30 0 0 0 0 0 0 2 7 103.50 - 4.00 13 1 5 0 0 0 0 0 0 0 0 5 24.00 - 4.50 2 0 2 0 0 0 0 0 0 0 0 0 0

Total 347985 29705 27663 29647 29195 29925 29403 29904 29500 28055 28268 27710 29010


Calendar Month

(observations)


• generation by wind;

• dissipation by whitecapping;

• dissipation by depth-induced wave breaking;

• dissipation by bottom friction;

• wave-wave interactions (quadruplets and triads);

• interaction with obstacles; and,

• wave-induced set-up of the mean sea surface.

Diffraction is not explicitly accounted for in the equations upon which SWAN is based.

However, in irregular short-crested wave fields, the effect of diffraction is small except in a

region less than one or two wavelengths away from the diffracting point (Booij et al., 1993) and

has therefore been neglected in the present analysis.

SWAN version 40.30 was implemented for this project based initially on the Existing Conditions

seabed geometry; an additional model was developed for DPE. To achieve a reasonable balance

of computational efficiency and spatial resolution, the models were constructed as nested grids

with a 100 m resolution in the outer domain and a 25 m resolution in the immediate vicinity of

the terminal. Figure A3-5 provides a visual impression of the resolution of the outer and nested

domains of the Existing Conditions model. The resolution of the DPE model geometry is similar.

Figure A3-5: SWAN Existing Conditions Bathymetry – Outer and Nested Grid


Ideally, both the Existing Conditions and DPE models described above would be run in dynamic

mode, time-stepping hour-by-hour through the 40 years of wind, wave, and water level

conditions in the offshore metocean database. This would yield 40 years of highly accurate wave

conditions at each gridpoint in the model. Unfortunately, wave generation and propagation

models are slow running and several months of computer CPU time would be required for such

an analysis. For this reason, a compromise was struck between rigor and practical computational

effort which consisted of an approach that assumes a single wave condition is associated with

each individual wind speed and wind direction range considered. This means that a manageable

number of steady-state SWAN runs with prescribed incident wind and wave parameters can be

used to reasonably describe a continuous transfer function relating conditions offshore to those at

inshore locations of interest. The derived transfer function can then be applied to the 40 years of

offshore wave data to yield a continuous hindcast of wave conditions at any inshore location of

interest.

Steady-state wave conditions were computed at low, mean and high water level for both Existing

Conditions and the DPE geometry for each of the incident wind and wave conditions indicated in

Table A3-13.


Table A3-13: Modelled Wind and Wave Conditions

The tabulated parameters represent hourly sustained wind speeds, significant wave heights and

peak spectral periods.

Calm 1 1.979 0.1 1.1

N 1 4.69 0.25 2.3 S 1 14.43 0.25 2.3N 5 1.876 0.75 4.7 S 5 10.2 0.75 4.7N 10 0.352 1 5.2 S 10 5.511 1 5.2N 15 0.058 1.25 5.7 S 15 2.767 1 5.2N 20 0.014 1.5 6 S 20 1.028 1.25 5.7N 25 0.003 1.75 6.4 S 25 0.327 1.25 5.7N 30 0 2 6.8 S 30 0.081 1.5 6

S 35 0.024 1.75 6.4S 40 0.006 2 6.8S 45 0.001 2.25 7.2

NE 1 5.538 0.25 2.3 SW 1 7.418 0.25 2.3NE 5 2.948 0.75 4.7 SW 5 4.727 0.5 3.8NE 10 1.245 1 5.2 SW 10 2.252 0.75 4.7NE 15 0.441 1.25 5.7 SW 15 0.799 1 5.2NE 20 0.122 1.25 5.7 SW 20 0.154 1.15 5.2NE 25 0.021 1.5 6 SW 25 0.024 1.4 5.6NE 30 0.001 1.5 6 SW 30 0.005 1.5 5.8

SW 35 0.001 1.6 6

E 1 15.97 0.25 2.3 W 1 8.464 0.25 2.3E 5 12.25 0.75 4.7 W 5 5.182 0.75 4.7E 10 6.268 1 5.2 W 10 2.397 1 5.2E 15 2.15 1.25 5.7 W 15 0.889 1.15 5.4E 20 0.552 1.25 5.7 W 20 0.293 1.3 5.7E 25 0.11 1.25 5.7 W 25 0.075 1.4 5.8E 30 0.013 1.25 5.7 W 30 0.014 1.55 6E 35 0.002 1.25 5.7 W 35 0.001 1.8 6.4E 40 0.001 1.25 5.7

SE 1 22.92 0.25 2.3 NW 1 18.58 0.25 2.3SE 5 18.36 0.8 4.5 NW 5 13.96 0.5 3.8SE 10 9.976 1.35 5.8 NW 10 6.733 0.75 4.7SE 15 4.548 1.6 6.1 NW 15 2.484 1 5.2SE 20 2.027 1.85 6.5 NW 20 0.773 1.25 5.7SE 25 0.855 2.1 7 NW 25 0.225 1.5 6SE 30 0.312 2.35 7.3 NW 30 0.056 2 6.8SE 35 0.097 2.6 7.6 NW 35 0.014 2.5 7.5SE 40 0.023 2.8 8 NW 40 0.003 2.75 7.9SE 45 0.003 3 8.3 NW 45 0.001 3.25 8.5

Wave Period

(s)

*Frequency of exceedance for specified direction in all cases except for calms in which case the value represents the frequency of occurrence.

Dir (from)

Wind Speed (kts)

Freq.* (%)

Wave Period

(s)

Wave Height

(m)

Wind Speed (kts)

Wave Height

(m)

Dir (from)

Freq. (%)


The pairing of wind and wave parameters was derived from a simple joint probability assessment

using the hindcast wind and wave database. Each pairing was determined by first plotting a

bivariate histogram of hourly wind speed (5 knot bins) versus significant wave height (0.5 m

bins) for each wind direction (45 degree bins). The histograms were then used to determine the

most commonly occurring joint condition for each wind speed bin interval. It is noted that, for

some wind conditions, there was considerable variability in offshore wave height which is a

reflection of the fact that sea conditions in the Strait are not always fetch limited. The significant

wave height associated with the next highest wave height bin (to introduce a degree of

conservatism into the analysis) was then assigned to that wind condition. The wave direction was

assumed to be the same as that of the wind which is a reasonably accurate approximation for

locally-generated seas such as those in the Strait. The associated wave period was assigned using

the chosen wave height and an empirical best-fit wave height/wave period relationship developed

from the wave database.

Note that the traditional coastal engineering approach to this type of analysis is to compute wave

transformations for a range of offshore wave periods and directions, and to assume that the

computed inshore conditions are scale linearly with wave height and are completely independent

of wind speed. Such an approach could not be used for the present study because it would have

required that wave growth within the local study area be ignored. Wave growth effects are

considered to be an essential element of this study, particularly across the shallow regions of

Roberts Bank.

The results of the model are not well suited for presentation in report format due to the large

number of runs (hundreds) and detail of the information available for each run. For this reason,

the complete set of results is provided on compact disk that is available upon request.

A few representative plots are included below to demonstrate the type of information that is

available. Figure A3-6 through Figure A3-8 show the spatial variation of waves during typical

10, 20 and 30-knot southeast wind conditions for existing and post-project conditions at mean

water. The colour contours indicate significant wave height and the vectors indicate the direction

towards which waves are propagating. Note that the differences in pre- and post-project wave

conditions are insignificant except in the immediate vicinity of the proposed DPE berth.


Figure A3-6: Typical Wave Conditions – 10 knot SE wind, mean water level




A similar conclusion can be drawn at other water levels; Figure A3-9 through Figure A3-11

show that the pre- and post-project differences are minor at low, mean and high water level.

Figure A3-9: Typical Wave Conditions – 20 knot SE wind, low water level


Figure A3-11: Typical Wave Conditions – 20 knot SE wind, high water level


The effect of wind direction on wave conditions can be seen in Figure A3-12 through Figure A3-

16. These mean water plots demonstrate 20-knot winds from NW, W, SW, S and SE.

Figure A3-12: Typical Wave Conditions – 20 knot NW wind, mean water level

Figure A3-13: Typical Wave Conditions – 20 knot west wind, mean water level


Figure A3-14: Typical Wave Conditions – 20 knot SW wind, mean water level

Figure A3-15: Typical Wave Conditions – 20 knot south wind, mean water level


Again, the differences between pre- and post-project are seen to be minor.


4.0 CONCLUSION

This appendix provides a review of available wind and wave data for the southern portion of the

Strait of Georgia. The existing wind data is used to generate the general wave climate at Roberts

Bank, which is verified against existing wave data. The formation of offshore waves is

calculated using Triton’s WaveHind software. Propagation of these offshore waves into the

nearshore area in the vicinity of Roberts Bank was computed using Triton’s implementation of

the numerical model SWAN (Delft University, 2003). Thus a detailed computation of the

expected wave climate in the project area has been generated using numerical models verified

against a reliable dataset.


5.0 REFERENCES

Delft University, 2003. SWAN Cycle III version 40.30 Users Manual. Unauthorized Electronic Version. Prepared by Holthuijsen, L.H., Booij, N., Ris, R.C., Haagsma, I.J.G., Kieftenburg, A.T.M.M., Kriezi, E.E., Zijlema, M., van der Westhuysen, A.J. Available from http://fluidmechanics.tudelft.nl/swan/download/info.htm, February 2004.

Lange, O.S., 1998. The wind came all ways: a quest to understand the winds, waves and weather in the Georgia Basin. Environment Canada, Victoria, B.C.

MSC, 2000. CD ROM Coastal Weather for British Columbia Mariners prepared by the Meteorological Service of Canada.

roberts bank container expansion coastal geomorphology ... · this report is included as appendix a...

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