i CAUSES OP THE CURRENT IN LITTLE CURRENT CHANNEL OP LAKE HURON by WARREN DAVID FORRESTER B.A. The University of Toronto, 191+7 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT S POR THE DEGREE OF MASTER OF SCIENCE in the Department of Physics We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLOMBIA April," 1961 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 permission. (W.D. Forrester) Department of Physics The University of British Columbia, Vancouver 3, Canada. Date April, 1961. ABb2ftACT A current is observed to flow most of the time through Little Current Channel, between North Channel of Lake Huron and Georgian Bay. The current varies considerably in its speed, and frequently reverses its direction. Inconvenience is experienc• ed by ships wishing to pass through the narrow and shallow chann el at Little Current, as they must await an opportunity to do so at slack water or on an opposing current. A field survey was carried out during the summer of 1959 in the vicinity of Little Current, Ontario, to determine the cau ses of this current and to ascertain whether or not predictions for the state of the current might be made sufficiently in ad• vance to be of assistance to shipping in the area. The field survey is described herein, and the analysis of the data is dis• cussed in detail. The current in Little Current Channel is shown to be ess• entially a hydraulic flow, driven by differences in water level at the two ends of the channel. The differences in water level are attributed to the action of wind, atmospheric pressure, seiches, and lunar tides, in North Channel and Georgian Bay. The actions in North Channel are considered to be greater than those in Georgian Bay, and are most fully treated. It is concluded that the only contribution to the current at Little Current that could be predicted more than a day in ad• vance is that due to the lunar tide, and that to predict this would be of little value, since on many occasions the other in• fluences would distort and even conceal completely the tidal contribution. It i3 recommended, however, that a discussion of the causes of the current be incorporated into the Canadian Hydrographic Service's publication, Great Lakes Pilot, as a matter of local interest, and as an aid to mariners wishing to make their own short-term forecast of the current. iv TABLE OP CONTENTS Page ABSTRACT ii LIST OF TABLES . iv LIST OP ILLUSTRATIONS v ACKNOWLEDGEMENTS vi INTRODUCTION 1 METHOD 3 INSTRUMENTATION 8 RESULTS 13 DISCUSSION General: 17 Effect of Tidesj Seiches, Wind and Atmospheric Pressure: 21 (1) Tides: 21 (2) Seiches: 26 (3) Wind and Atmospheric Pressure:.. 32 CONCLUSIONS 38 LITERATURE CITED 1+1 LIST OP TABLES Page Table I: Preliminary Estimates of g and H of M2 23 Table II: Estimates of g and H of Tidal Constituents from Harmonic Analyses 2£ LIST OP ILLUSTRATIONS Page Pig. 1: Amplitude and Phase-lag of M£ at Gauging stations.. 1+2 Pig. 2: Observation stations on and around North Channel and northern Lake Huron 1+3 Pig. 3: Observation stations on and near Little Current Channel 1+1+ Pig. k: Water Level Gauge, 1/12 Scale 1+5 Pig. 5: Gurley Current Meter, 1/1+ Scale 1+5 Pig. 6: Pendulum-type Current Direction Detector 1+6 Pig. 7: Wiring Diagram for Current Speed and Direction Recorder 1+6 Pig. 8: Currents in Little Current Channel (f t./sec.)...... 1+7 (a) for Current at Bridge flowing East at 2.0 ft./sec. (b) for Current at Bridge flowing West at 2.0 ft./sec. Pig. 9: Water Temperature Lowering at Little Current, associated with West-flowing Current 1+8 Pig. 10: Short-period Seiche action at Gore Bay 1+8 Pig. 11: Comparison of Current Speed with Water Level Difference along Little Current Channel 1+9 Pig. 12: Water Level Difference versus Square of Current Speed in Little Current Channel.. $0 Pig. 13: Priliminary Estimate of Lunar Tidal Effect in North Channel 51 Pig. li+: Autocovariance Function 52 Fig. 15: Power Spectrum 52 Fig. 16: Smoothed Plots of Water Level, showing 5-hour Seich(from e hourlActioy n readingin Norts h ofChannel continuou. s records).. 53 Fig. 17: Plots of 5-h.our Running Means, showing 10-hour Seiche in North Channel 51+ Pig. 18: Plots of 10-hour Running Means, showing Wind and Pressure Effect in North Channel 51+ Pig. 19: Water Level Difference versus Square of Wind Speed in North Channel; 10-hour Means 55 vi ACKNOWLEDGEMENT S The author wishes to acknowledge the valuable advice and guidance received during this study from Drs. G.L. Pickard and R.W. Burling of the Institute of Oceanography of the University of British Columbia; the aid of the Canadian Hydrographic Ser• vice of the Department of Mines and Technical Surveys in provid• ing personnel and facilities to help carry out the field work and certain of the calculations; the assistance of the Research Branch of the Ontario Department of Lands and Forests in under• taking parts of the field operation; the cooperation of the Met• eorological Branch of the Canadian Department of Transport and the Weather Bureau of the United States Department of Commerce in providing meteorological data; and the assistance of the Com• puting Centre of the University of British Columbia in carrying out some of the lengthy digital computations. 1 INTRODUCTION The masters of ships on the Great Lakes have reported be• ing inconvenienced by an apparently unpredictable current in the narrow channel at Little Current, Ontario, connecting Georgian Bay with the North Channel of Lake Huron. A general chart of Georgian Bay, Lake Huron, and North Channel is given in Fig. 1; a more detailed chart of North Channel is given in Fig. 2; and a further enlargement of the narrow channel at Little Current is given in Fig. 3, Although this narrow channel bears no name on charts of the Canadian Hydrographic Service, it is locally known as Little Current Channel, and will be so referred to herein. Through Little Current Channel a current flows, sometimes from west to east and sometimes from east to west, sometimes in the direction of the local wind and sometimes in the opposite dir• ection. Ships passing through the narrow and shallow passage be• tween the north side of the Little Current swing bridge and the south shore of Goat Island must proceed slowly, but they must also maintain a speed of four or five knots through the water in order to retain steerage control. To attempt this passage with a following current greater than about one knot would apparently dangerously reduce control over the ship, since if sufficient speed for steerage were maintained, the speed relative to the bottom, the shore, and the bridge would allow insufficient man• oeuvring time. Consequently, it is customary for ships to an• chor outside Little Current Channel until they may make the pass• age in slack water, or, preferably in an opposing current. It had not been possible to foretell how long a ship might have to wait for a favourable current since on some occasions the water 2 flows fairly steadily in one direction for a full day or more, while on others it reverses direction again after less than an hour. In 1959, the Canadian Hydrographic Service, the federal agency responsible for chart, water level, tidal, and current information in Canadian navigable waters, decided that an in• vestigation of this problem at Little Current should be under• taken. The object of the investigation was to obtain an under• standing of the origin of the flow, and, if possible, to develop a procedure by which it might be predicted. The author was priv ileged to carry out the necessary field work and the analysis of the results. METHOD The factors that might contribute in varying degree to the phenomenon of the reversing flow at Little Current were consider• ed to be the following: (a) Wind stress on the water surface in Little Current Channel producing a direct wind current. (b) Wind stress on the water surface of North Channel, Georg• ian Bay, and Lake Huron, causing a tilt on the surface of one or all of these basins and so producing a hydraulic head at Little Current. (c) Atmospheric pressure differences, tilting one or all of the surfaces of the three basins referred to in (b), and similarly producing a hydraulic head at Little Current. (d) Seiches, initiated by wind or atmospheric pressure changes but continuing to oscillate at the natural periods of the different water basins until finally damped out. (e) Tides in Lake Huron and Georgian Bay, the presence of which had already been detected although the amplitude is very small. (f) Fluctuation in the discharge of the Saint Marys River, causing a corresponding fluctuation in the water level of North Channel. It was impossible in the two months available for the field op• eration to install and operate sufficient meteorological and hydrological monitoring equipment to permit an exhaustive study of all the factors mentioned above.