TP 10820 E

WIND AND WAVE CLIMATE ATLAS

VOLUME IV - THE WEST COAST OF CANADA

Prepared by

MacLaren Plansearch (1991) Limited
Suite 200, Park Lane Terraces
5657 Spring Garden Road
Halifax, Nova Scotia
B3J 3R4

Prepared for

Transportation Development Centre
Policy and Coordination Group
Transport Canada

August 1993

DISCLAIMER

"The contents of this report reflect the views of the authors and not necessarily the official views or opinions of the Transportation Development Centre, Policy and Coordination Group, of Transport Canada."

ACKNOWLEDGEMENT

The sponsorship and technical support given in the preparation of this work is acknowledged as follows:

• Transport Canada - Transportation Development Centre
• Transport Canada - Canadian Coast Guard-Ship Safety
• Energy, Mines and Resources Canada - Program for Energy R & D
• Environment Canada - Canadian Climate Centre
• Fisheries and Ocean - Marine Environment Data Service

Publication Data Form

INTRODUCTION

Offshore exploration and shipping activities are affected by the climate conditions in the area. With an accurate description of the operating environment, ships and other marine structures can operate safely in these areas. This study was initiated by the Transportation Development Centre (TDC) on behalf of the Canadian Coast Guard, Transport Canada to develop a wind and wave climate atlas for the Canadian waters (e.g. the East Coast, Gulf of St. Lawrence, the Great Lakes, and the West Coast). The objective of this project is to collect, consolidate, and present the existing environmental data in a format which could be used to assess the strength and operational requirements of vessels and other marine structures for operation in these regions.

The atlas is divided into four volumes describing the following regions:

Volume I - The East Coast of Canada;

Volume II - The Gulf of St. Lawrence

Volume III - The Great Lakes.

Volume IV - The West Coast of Canada.

Each region was divided into a number of subareas (or sites) to represent the various conditions within the region. The division of the subareas was based on the availability of data within the region, shipping lanes and fishing grounds, and the meteorological conditions within each subarea.

This volume presents the West Coast of Canada. The study area covers the Canadian waters to 200 miles offshore. The area was divided into seven (7) subareas as shown in Figure I. These subareas followed closely Environment Canada's marine forecasting areas. The atlas covers those waters beyond the depth contour of approximately 50-100 m following the shorelines of Vancouver Island, the Charlottes and the islands bordering Hecate Strait (i.e. deep waters). The waters between the mainland and Vancouver Island (i.e. Strait of Georgia and Juan de Fuca Strait) are not covered in this atlas.

DATA SETS

An extensive database was compiled from all relevant data sources, which included both measured/observed data and hindcast studies. An extensive review and evaluation of these data sources, user requirements, analysis techniques, etc. is provided in a separate report (Phase I Report, MacLaren Plansearch Limited, 1989, Transport Canada publication # TP 10867E) and in Phase I - Interim Report for the West Coast of Canada (MacLaren Plansearch Limited, 1993).

The data sets used to produce the climatological statistics presented herein were:

For the West Coast, a special version of -the ODGP which includes Capes and Islands (CAIPS) was used to resolve the large islands effect (Canadian Climate Centre, 1992).

For each sub-area, the maximum wind and wave values during three-hour time intervals were selected from each data set. The buoy wind data were used for providing the wind statistics, and the waverider / NOAA / AES buoy wave data were used for providing the wave statistics. The three-year ODGP hindcast data were used when data from the other data sets were insufficient. Also, for duration statistics (e.g. persistence analysis), a continuous time series of the parameters considered is needed. The ODGP data set was used (in conjunction with measured data) for this purpose, and also for providing wave direction statistics.

Note: It should be emphasized that the ODGP model hindcasts used in this atlas represent deep water wave conditions, and therefore must be treated as such. Shallow water effects should be considered locally

WINDS

The three-hourly marine wind data were used in the analysis presented in this atlas. It presents one-hour mean winds. Following conversion factors (U.K. Department of Energy, 1977) may be used to convert wind speed to other averaging periods.

1-hr mean	1.0
10-minute mean	1.05
I-minute mean	1.17
3-second gust	1.34

In the marine observations data set, the anemometer height of the measured wind speeds varies with each buoy. Therefore, all wind speeds were adjusted to a standard anemometer height of 19.5 m (65 ft.) above mean sea level (which is the average height of a ship anemometer), using the marine planetary boundary layer approach (Cardone, 1978). The ODGP hindcast winds were determined for 19.5 m height.

All wind speed statistics were compiled using the buoy and model data. The following data sources were utilized:

Sub-Area	Data Source
1	Buoy Data
2	Buoy + ODGP
3	Buoy + ODGP
4	Buoy + ODGP
5	Buoy + ODGP
6	Buoy
7	Buoy

WAVES

Waverider and NOAA / AES buoy data were used for non- directional wave spectral analysis and significant wave height and wave period statistics in areas where a sufficient number of measurements were available. The three-year ODGP hindcast data base was used for the remaining areas, and for directional statistics such as wave roses and percent frequency of occurrence by direction tables.

The following databases were used for the wave statistics:

Sub-Area	Non-directional Statistics	Directional Statistics
1	WR	ODGP
2	WR	ODGP
3	WR	ODGP
4	WR/ODGP	ODGP
5	WR/ODGP	ODGP
6	WR	ODGP
7	WR	ODGP

where WR is measured wave data (i.e. MEDS, NOAA or AES buoys), and ODGP is the ODGP model hindcast data. It should be noted that due to the use of these two different data sources, slightly different wave statistics would be expected for a given sub-area (e.g. number of data points used in analysis using these different data sources).

Notes:

• Wave height used in this atlas represents significant wave height (Hs or HI/3) which is defined as the average of the one-third highest waves in a wave record; it can be estimated from the energy spectrum (or total variance) by:
  

      H_s = 4*SQRT(Total variance)

• The ratio of Hmax/Hs (where Hmax is the maximum individual wave height in a wave record) is of great engineering concern, since Hmax and its associated period are required for engineering design (e.g. fluid loading calculation). This ratio can be estimated using suitable wave height probability distribution (e.g. Longuet-Higgins (1952), Longuet-Higgins (1980), Forristall (1978)). Assuming a Rayleigh distribution, which has been widely used for deep-water waves, the following relation may be used as a first approximation:
  

      Hmax = 1.85 H_s

• This value can vary significantly depending on conditions such as water depth, wave period, etc. and should be used with caution.

EXTREME STATISTICS

Extreme value statistics were calculated by using the method of moments (MOM) to fit a Gumbel distribution to peak storm wind and wave values. The criteria for selecting wind storms were winds surpassing a threshold of 35 knots for a minimum duration of 12 hours and storm peaks at least 24 hours apart. From this, a preliminary list of potential storms was obtained and verified. The peak wind speed for each storm was then identified and used in the extreme analysis.

The significant wave height extreme statistics were based on the hindcast of the top severe wave-generating storms in the study area using the ODGP model, see Canadian Climate Centre (1992), in addition to the measured storm peaks (Hs> 7.0 m).

SPECTRAL FAMILY

Many marine engineering applications require knowledge of the shape of the wave spectra. The analysis used in this atlas is based on the six-parameter model of Ochi and Hubble (1976). To generate the representative spectrum for a given sea-state value, the model function was fitted to the measured or hindcast data. Statistical analysis of the fitted parameters leads to a family of spectra, i.e. most probable spectrum and a set of 95% confidence spectra. Six sea-state classes were considered: Hs=0.5-2 m, 2-3 m, 3-4 m, 4-5 m, 5-6 m, and greater than 6 m.

LIST OF PARAMETERS & ANALYSIS PERFORMED

The following is a list of statistics provided for area xx (and the corresponding page number):

Wind Speed Statistics
Annual Percentage Occurrence	xx-1
Annual Percentage Exceeding	xx-1
Annual Frequency of Occurrence by Direction (Wind Rose)	xx-1
Annual Percentage Exceeding for Given Time Durations (Persistence)	xx-1
Extreme Analysis	xx-1
Monthly Frequency of Occurrence by Direction (Wind Rose)	xx-2,3
Monthly Percentage Occurrence	xx-4,5
Monthly Percentage Exceeding	xx-6,7
Monthly Statistics (mean, maximum, minimum, 95% limits, etc.)	xx-8
Annual Percent Frequency of Occurrence by Direction (Table)	xx-8
Significant Wave Height Statistics
Annual Percentage Occurrence	xx-9
Annual Percentage Exceeding	xx-10
Annual Frequency of Occurrence by Direction (Wave Rose)	xx-9
Annual Percentage Exceeding for Given	xx-10
Time Durations (Persistence)	xx-10
Extreme Analysis	xx-10
Monthly Frequency of Occurrence by Direction (Wave Rose)	xx-11,12
Monthly Percentage Occurrence	xx-13,14
Monthly Percentage Exceeding	xx-15,16
Monthly Statistics (mean, maximum, minimum, 95% limits, etc.)	xx-19
Annual Percent Frequency of Occurence by Direction (Table)	xx-19
Most Probable Spectra	xx-21
Wave Spectral Coefficients (Table)	xx-22
Wave Peak Period Statistics
Annual Percentage Occurrence	xx-9
Annual Percentage Exceeding for Given Time Durations (Persistence)	xx-10
Monthly Percentage Occurrence	xx-17,18
Joint Probability Statistics
Annual Occurrence of Significant Wave Height and Wind Speed	xx-20
Annual Occurrence of Significant Wave Height and Peak Period	xx-20

REFERENCES

Canadian Climate Centre, 1992. Wind / Wave Hindcast Extremes for the West Coast of Canada. Report prepared under DSS contract #KM169-8-7418 / 01-SE, 143 p. plus appendices, by MacLaren Plansearch (1991) Limited and Oceanweather Inc.

Cardone, V.J., 1978. Specifications and Prediction of the Vector Wind on the United States Continental Shelf for Applications to Oil Slick Trajectory Forecast Program. Final Report, Contract T-35430, NOAA, U.S. Department of Commerce, Silver Spring, Maryland.

Eid, B.M., C.M. Morton, V.J. Cardone and J.A. Greenwood, 1989. Development and Evaluation of a Wave Climate Database. Proceedings of the 2nd International Workshop on Wave Hindcasting and Forecasting, Vancouver, B.C., April 25-28, 1989.

Forristall, G.Z., 1978. On the Statistical Distribution of Wave Heights in a Storm. J. Geophysical Res. 83: No. C5, 2353-2358.

Longuet-Higgins, M.S., 1952. On Statistical Distribution of the Heights of Sea Waves. J. Mar. Res. 11: pp. 245-266.

Longuet-Higgins, M.S., 1980. On the Distribution of the Heights of Sea Waves; Some Effects of Nonlinearity and Finite Band Width. J. Geophysical Res. 85: No. C8, pp. 1519-1528.

MacLaren Plansearch Limited, 1989, Preparation of a Wind and Wave Climate Atlas, Phase I Interim Report - Initialization, Planning, Data Compilation, and Methodology, Report submitted To Transportation Development Centre, Transport Canada, Montreal, Quebec, March 89, TP 10867E.

MacLaren Plansearch (1991) Limited, 1993. Wind and Wave Climate Atlas for the West Coast of Canada. Phase I - Interim Report: Data Compilation and Methodology. Submitted to Transportation Development Centre, Montréal, Québec, March, 1993.

Orchi, M.K. and E.N. Hubble, 1976. Six Parameter Wave Spectra. Proceedings of the 15th Coastal Engineering Conference. Honolulu, pp. 301-328.

Swail V.R., V.J. Cardone and B.M. Eid, 1992. An Extremes Wind and Wave Hindcast off the West Coast of Canada. Proceedings of the 3rd International Workshop on Wave Hindcasting and Forecasting, Montréal, Quebec, May 19-22, 1992.