NOAA Technical Report ERL 399-PMEL 29 Circulation in the Strait of Juan de Fuca Some Recent Oceanographic Observations G. A. Cannon, Editor J. R. Holbrook and R. A. Feely, editorial assistants Contributing Authors Coastal Physics, PMEL G. A. Cannon, R. L. Charnell, N. P. Laird, H. O. Mofjeld, D. J. Pashinski, J. D. Schumacher Chemistry and Biology, PMEL E. T. Baker, D. M. Damkaer, R. A. Feely, J. D. Larrance Deep Sea Physics, PMEL D. Halpern, J. R. Holbrook Numerical Studies, PMEL J. A. Galt, J. Karpen, J. E. Overland, C. H. Pease, R. W. Stewart Oceanographic Division, NOS B. B. Parker Remote Sensing Studies, PMEL C. B. Sawyer Pacific Marine Environmental Laboratory Seattle, Washington June 1978 u.s. DEPARTMENT OF COMMERCE Juanita M. Kreps, Secretary National Oceanic and Atmospheric Administration Richard A. Frank, Administrator Environmental Research Laboratories Boulder, Colorado Wilmot Hess, Director NOTICE Mention of a commercial company or product does not constitute an endorsement by NOAA Environmental Research Laboratories. Use for publicity or advertising purposes of information from this publica­ tion concerning proprietary products or the tests of such products is not authorized. II CONTENTS Executive Summary. ............................................ .. v Abstract 1 1. Introduction ................................................ .. 1 2. Physical setting " 3 2.1 Geography .............................................. .. 3 2.2 Tides and tidal currents. .................................... .. 4 2.3 Winds. .............. .. ........................... ... ... .. 6 General description. ....................................... .. 6 Recent observations. ....................................... .. 9 Model results. ............................................ .. 12 3. Oceanography. .............................................. .. 16 3.1 Surface drifter observations. ................................. .. 16 3.2 Suspended sediments. ...................................... .. 17 3.3 Western Strait currents and water properties. .................... .. 22 Mean flow. .............................................. .. 23 Variations ............................................... .. 2S Winter wind forcing ........................ .. 2S 3.4 Eastern strait-San Juan Island currents 31 3.S Plankton observations. ..................................... .. 34 4. Oil-spill trajectory modeling. ................................... .. 36 4.1 Model description. ........................................ .. 36 4.2 Sample trajectories ........................................ .. 37 S. Other studies. ............................................... .. 42 6. Summary and conclusions. ..................................... .. 44 7. Acknowledgments. ........................................... .. 47 8. References. ................................................. .. 48 iii EXECUTIVE SUMMARY The Strait of Juan de Fuca is a major shipping driven currents, rather than tidal currents, domi­ route for both the United States and Canada. nate the relatively shallow water near Cherry Tanker traffic is likely to increase in these waters Point, one of the major oil terminals in the region. now that the Trans-Alaskan pipeline is complete. Drift cards released south of San Juan Island in the Much new work has taken place since the publica­ middle of the eastern basin of the Strait, an inter­ tio,n of the most recent oceanographic description section of major traffic lanes, were found on all of this estuary over fifteen years ago. The present beaches surrounding the eastern basin. Drift cards report was written at the request of the NOAA that progressed farther seaward tended to ground Administrator to provide an up-to-date, compre­ on Vancouver Island in winter and on the hensive synthesis of results of the most recent Olympic Peninsula in summer. A computerized studies for use in decisions regarding these waters. oil-spill trajectory model, while still incompletely The primary emphasis of the NOAA efforts has developed, also indicated several possibilities of been on transport mechanisms that might affect flow ending on beaches in the eastern basin. the redistribution of spilled oil. Additional field Moored current meter observations in the western studies east of Port Angeles are continuing basin showed that, during intervals of coastal through 1978. storms, the surface currents flowed into rather These studies have shown that a variety of than out of the Strait for a few days. This flow transport processes exist in the Strait of Juan de was accompanied by intrusions of coastal ocean Fuca that could result in considerable redistribu­ water as far as 90 km from the mouth and reten­ tion of spilled oil, or any other contaminant, tion of surface water within the system. The speed throughout the region. Winds appear to be the pri­ and duration of the intrusions implied that ocean mary factor causing significant variations in the water on occasion could possibly reach as far east more normal net flow of surface water out to sea. as Whidbey Island. In addition, winds appear to direct the flow There remain a number of unanswered ques­ toward the shores of the Strait. Large flow varia­ tions. The flow patterns that distributed the drift tions occur during every season but summer. The cards around the eastern basin are unknown. evidence presented, while not yet complete, indi­ Also, it is not clear whether the intrusions of cates the strong possibility of significant volumes coastal water enter the eastern basin, or to what of a spilled contaminant reaching beaches within extent storm-related conditions drive the circula­ the estuary instead of being transported out of the tion there. These questions are being addressed estuary. The probability of such a beaching in­ during the present field investigations. Another creases significantly the farther into the estuarine limitation is that the oil-spill trajectory model has system the potential spill occurs. Likewise, the been run only for a typical March and no summer probability of an accident leading to a spill in­ cases have yet been run; additional calculations creases with distance into the system because of are being made this year. Also, time has not narrowing channels near the San Juan Islands and allowed inclusion of data on the winter current re­ intersecting traffic lanes north of Admiralty Inlet, versals in the model. As yet, little is known about the entrance to Puget Sound. processes occurring in the near-shore zone extend­ Tidal currents are the strongest component of ing about a mile or so offshore throughout the the flow in most of this estuarine system, and be­ estuary, in the passages between the San Juan cause of their large magnitude in the more re­ Islands, at the mouth of the Strait, and at the junc­ stricted passages they are navigational hazards. tion with Admiralty Inlet. These areas must await Tidal fronts form north and south of the San Juan future research. Islands in waters that are major traffic lanes, and This report was used for environmental plan­ near-shore eddies and backwaters occur nearly ning even before the final draft was completed. everywhere on the down-current side of head­ The summary and conclusions were presented as lands. Both of these phenomena tend to concen­ "Comments on vessel traffic management in Puget trate floating or suspended material. However, Sound waters and environmental factors entering current-meter and satellite observations of the therein" at U.S. Coast Guard hearings on April Fraser River plume indicate that variable wind- 20-21,1978, in Seattle. v ';:. CANADA ".;:----------49° UNITED STATES Vancouver Island .; Figure 1. Strait of Juan de Fuca, showing nearby features and connect­ ing waterways. Additional place names in and north of the San Juan Islands are shown in Fig. 39. vi CIRCULATION IN THE STRAIT OF JUAN DE FUCA: SOME RECENT OCEANOGRAPHIC OBSERVAnONS G. A. Cannon, ed. ABSTRACT. Oceanographic research in the Strait of Juan de Fuca and some of its adjacent waterways, emphasizing transport mechanisms that might affect the redistribution of spilled oiL has focused on near­ surface circulation and its driving mechanisms. Moored current meters, surface drift cards, satellite images of suspended sediment, and an oil-spill trajectory model were used. The largest flow variations were found during fall-winter-spring. Drift cards tended to ground on Vancouver Island in winter, on the Olympic Peninsula in summer, and on beaches in the eastern basin of the Strait throughout the year. Trajectory model experiments also showed flow ending on beaches in the eastern basin. Numerous tidal fronts were observed north and south of the San Juan Islands, and near-shore eddies occurred everywhere on the down-current sides of headlands. Both of these phenomena tend to concentrate floating or sus­ pended material. Moored current meters showed winter intrusions of oceanic surface water almost to Port Angeles lasting several days to over a week. Outflow often occurred only in the deeper water, with surface water being retained within the system. Winds appeared to be the major cause of all flow varia­ tions. Indications were that significant volumes of any contaminant would probably reach beaches within the estuary. 1. INTRODUCTION The Strait of Juan de Fuca estuary is the prin­ cause of the potential for increased tanker traffic, cipal approach from the Pacific Ocean to the the primary objective of these investigations was major Canadian and United States population to describe