Oceanography of the British Columbia Coast
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CANADIAN SPECIAL PUBLICATION OF FISHERIES AND AQUATIC SCIENCES 56 DFO - L bra y / MPO B bliothèque Oceanography RI II I 111 II I I II 12038889 of the British Columbia Coast Cover photograph West Coast Moresby Island by Dr. Pat McLaren, Pacific Geoscience Centre, Sidney, B.C. CANADIAN SPECIAL PUBLICATION OF FISHERIES AND AQUATIC SCIENCES 56 Oceanography of the British Columbia Coast RICHARD E. THOMSON Department of Fisheries and Oceans Ocean Physics Division Institute of Ocean Sciences Sidney, British Columbia DEPARTMENT OF FISHERIES AND OCEANS Ottawa 1981 ©Minister of Supply and Services Canada 1981 Available from authorized bookstore agents and other bookstores, or you may send your prepaid order to the Canadian Government Publishing Centre Supply and Service Canada, Hull, Que. K1A 0S9 Make cheques or money orders payable in Canadian funds to the Receiver General for Canada A deposit copy of this publication is also available for reference in public librairies across Canada Canada: $19.95 Catalog No. FS41-31/56E ISBN 0-660-10978-6 Other countries:$23.95 ISSN 0706-6481 Prices subject to change without notice Printed in Canada Thorn Press Ltd. Correct citation for this publication: THOMSON, R. E. 1981. Oceanography of the British Columbia coast. Can. Spec. Publ. Fish. Aquat. Sci. 56: 291 p. for Justine and Karen Contents FOREWORD BACKGROUND INFORMATION Introduction Acknowledgments xi Abstract/Résumé xii PART I HISTORY AND NATURE OF THE COAST Chapter 5. Upwelling: Bringing Cold Water to the Surface Chapter 1. Historical Setting Causes of Upwelling 79 Origin of the Oceans 1 Localized Effects 82 Drifting Continents 2 Climate 83 Evolution of the Coast 6 Fishing Grounds 83 Early Exploration 9 El Nifio 83 Chapter 2. The Coast Today Coastal Currents 84 Seafloor Topography 13 Seamounts 14 PART III OCEAN WAVES Inlets, Estuaries, and Sills 16 Temperature Distribution 19 Chapter 6. Nature of Ocean Waves Salinity Distribution 20 Terminology 87 Wind Patterns 23 Water Motion 88 Shores and Beaches 25 Wave Growth 91 Minor Beach Features 28 Sea and Swell 92 Spits and Cusps 32 Group Speed 92 Sea Cliffs to Tidal Flats 34 Freak Waves 93 Man-Made Structures 39 Rips 94 Whitecaps 95 PART II GENERAL. PHYSICAL OCEANOGRAPHY Wave Dissipatiôn 95 Internal Gravity Waves 96 Chapter 3. Tides and Tidal Streams Ship Waves 102 Early Knowledge 45 Chapter 7. Generation of Wind Waves Datum 45 A Difficult Problem 105 Measurement of Tides 46 Wave Generation Mechanisms 105 Nature of Tides 47 Growth of Wind Waves 107 Equilibrium Theory of Tides 51 Wave Statistics 108 Types of Tides 53 Wave Spectra 112 Long-Period Tides 55 The Beaufort Scale 114 Tidal Constituents 56 Wave Attenuation 115 Coastal Tides 57 Winds and Waves in a Moving Fetch 116 Nonastronomical Tides 59 Tidal Friction 60 Chapter 8. Shallow-Water Waves Tidal Streams 61 Refraction 119 Factors that Influence Tidal Streams 63 Diffraction 120 Current Ellipses 66 Reflection 121 Tidelincs 67 Steepening 122 Red Tide 68 Breaking 122 Longshore Currents 123 Chapter 4. Secondary Currents Rip Currents 123 Wind Drift 71 Relaxation Currents 72 Chapter 9. Tsunamis (Tidal Waves) Slippery Water 72 Generation 130 Ekman Spiral 73 Wave Travel 132 Density Currents 74 Height at Sea 132 Sea-Slope Currents 76 Height Near Shore 132 Jets and Eddies 76 Tsunami Warning System 134 Contents (concluded) PART IV OCEANOGRAPHY OF INSHORE WATERS Chapter 10. Strait of Georgia Chapter 14. Northern Shelf Region Physiography 139 A Brief History 235 Temperature and Salinity Distributions 140 Shoreline Features 235 Wind Patterns 143 B athymetry 237 Waves 144 Glaciation 238 Tides 147 Temperature and Salinity 238 Tidal Streams 149 Winds 239 Measured Currents 155 Fog 239 Water Renewal 163 Waves 239 Fraser River Estuary 165 Tides 240 Burrard Inlet —Indian Arm 169 Circulation 241 Howe Sound 179 GLOSSARY .. 247 Chapter 11. Juan de Fuca Strait REFERENCES 255 Physiography 187 APPENDICES Temperature and Salinity Distributions 187 Appendix A Metric — English Units Wind Patterns 189 and Equivalents 261 Waves 191 Appendix B Marine Research Tides 192 Institutions of the Tidal Currents 194 Northwest Pacific Coast 261 Observed Currents 196 Appendix C Immersion Hypothermia 263 Sooke Inlet 199 Appendix D Lunar Versus Solar Chapter 12. Johnstone Strait Region Tide-Generating Forces 263 COLOR PLATES 265 Background 201 INDEX 281 Bathymetry and Water Properties 202 Winds 205 Waves 205 Tides 207 Currents 208 PART V OCEANOGRAPHY OF OFFSHORE WATERS Chapter 13. Deep-Sea Region Plate Tectonics 217 Physiography 217 Water Properties 219 Seasonal Heating and Cooling 220 Climatology 221 Waves 224 Tides 227 Currents 228 vi FOREWORD Oceanographers are a cult unto themselves. To outsiders they appear as people who, for reasons apparently known only to themselves, have a passion for analyzing water. Their god is the sea, their creed to understand, to interpret, and ultimately to respect its seemingly endless mysteries. The language they use in their chapels is mathematics and their priests are computers. No wonder then that the members of the cult find themselves locked away in remote institutions, removed from view by the public. This book represents an attempt by one of them to explain the workings of the cult and to describe the nature of their religion in language that all can understand. This work is not so much a text book as it is a biography, a biography of the sea. In an easy conversational style and with numerous illustrations the author describes the origin, physical characteristics, and nature of the forces that act within and upon the eastern Pacific Ocean. He describes the origin, shape, and structure of the sea floor as well as the development of coastlines and beaches. Without being turgid or condescending, the author carefully explains the complex movements of water masses, first in general terms and then specifically with regard to the various coastal regions of British Columbia. He describes the seasonal variations in salinity and temperature and, in a remarkably lucid manner, the complex interaction of planetary body forces which result in the variability of tides. Many of his own experiences as well as those of his colleagues are used to illustrate some of the more spectacular effects of water mass motions, such as the tidal rips in the northern Strait of Georgia, internal gravity waves in Knight Inlet, and the unique tidal whirlpools in Gilford Passage. These and many other aspects of coastal oceanography are presented in such a way that the excitement of the author for the nature of his work is transferred to the reader. This book should have wide appeal. Not only is it suitable for scientists and their students, but should become a standard reference to be found in the libraries of commercial vessels as well as in the collections of yachtsmen. Although the author has no pretensions as to its evangelical significance, he has, with this book, made an outstanding contribution to the enjoyment of the coastal waters of British Columbia. C. J. YORATH Geological Survey of Canada Sidney, B.C. vii BACKGROUND INFORMATION Introduction The origins of this book date back more than six years when I first began a series of oceanographic articles for an innovative Vancouver-based yachting magazine. Then, as now, numerous books had been written about the sea but only rarely did one of them refer to the fascinating oceanic processes that characterize the coastal waters of British Columbia and Washington State. This work has evolved from the same information void that inspired the original yachting articles. As in any metamorphosis, however, its contents mark a substantial advance in quantity, diversity, and sophistication. In writing the book, I have endeavored to present a text that would be readily comprehensible to the intelligent layman without compromising the scientific content. To attain this sometimes elusive goal, the book has been divided into three major sections: the first (Part I) covers the origin and present physiographic makeup of the oceans; the second (Parts II and III) deals with many principal features and concepts of physical oceanography and provides the necessary fundamentals to an understanding of oceanic phenomena discussed in later chapters; the third (Parts IV and V) describes in detail the physiography, meteorolog-y, and oceanography of the coastal and deep-sea regions of the Northeast Pacific Ocean. All material, including the appendices and more than two hundred and seventy diagrarns, has been subjected to careful scrutiny by experts in the various fields of marine science to ensure its relevance and authenticity. It is hoped that the end product will provide the reader with an enjoyable, as well as practical, guide to the nature of the world oceans and instill a new degree of respect for the physical beauty of the Pacific west coast. Acknowledgments I gratefully thank the many colleagues and friends who have contributed to the contents of this book. I am especially indebted to Professor George Pickard, recently retired Director of the Department of Oceanography at the University of British Columbia, and to Dr Christopher Yorath, Head of the Marine Geology Section of the Pacific Geoscience Centre, who not only provided valuable advice and criticism of the manuscript but also were a source of personal encouragement and inspiration. Considerable thanks are due Ms Sharon Thomson and Mr Robert Sandilands for carefully reviewing an early draft of the text and Dr Rob Macdonald for expertly reviewing the penultimate version. My sea-going colleagues Mr Stan Huggett, Dr Patrick Crean and Mr James Holbrook are acknowledged for so generously pro- viding me with technical information while Mr Allan Douglas is acknowledged for his excellent work on the many computer graphics in the figures. My appreciation also to Ms Doris van Aanhout, who skillfully transformed my handwriting into the first draft of the manuscript; to Ms Susan McKenzie, who assisted with the many subsequent revisions; and to Ms Billie Mathias, who helped complete the manu- script.