cause southwest drift of bottles, one of 

 which was recovered 4 days after release. 



The time required for the current to 

 orient to the wind is dependent, of course, 

 upon the strength of the wind and the 

 existing flow pattern. In an area such as 

 Saginaw Bay where a consistent current 

 pattern does not exist, it seems possible 

 that a surface current might change in 

 response to a rapidly changed strong wind 

 in a matter of hours. 



No attempt was made to study subsur- 

 face currents. The Ekman spiral (Sverdrup, 

 Johnson, and Fleming 1942) is frequently 

 mentioned in explanations of surface and 

 subsurface currents. According to this 

 theory, surface currents on the northern 

 hemisphere are directed 45° to the right 

 of the wind, while at greater depths the 

 current turns more to the right and the 

 velocity decreases. Near the bottom of the 

 friction layer the currents are low in velo- 

 city and move opposite to the wind direc- 

 tion. This theory, however, presupposes 

 conditions of equilibrium, a state that is 

 not reached in Saginaw Bay because of the 

 influence of variable winds. Thus it would 

 seem that the theory of the Ekman sprial 

 does not apply. The relative shallowness 

 of the basin also would seem to be an ad- 

 verse factor. Because of the prevalence 

 of shallow water and the consequent transi- 

 tory thermocline development, I suspect 

 that subsurface currents are highly influ- 

 enced by surface currents and may be 

 similar in direction to them. 



Modifying factors exist in the bay to 

 complicate the simple wind-dependent sur- 

 face flow. Outflow of the streams and 

 rivers in the area must have some effect 

 upon surface currents. The largest of 

 these, the Saginaw River, enters the south- 

 ern end of the bay. Some of this river 

 water must diffuse into the bay water but 

 a discrete mass of water has been found to 

 follow the eastern shore of the bay out 

 into Lake Huron proper (Adams 1937). This 

 mass well might be the flow of Saginaw 

 River water. 



A theory proposed by Steele (1957) 

 interprets the hydrography of the northern 

 North Sea in terms of the possible effects 

 of lateral eddy diffusion. This diffusion 

 depends upon the principle "that when a jet 

 issues into a motionless fluid there is 



turbulent mixing along its edges malting 

 the jet gradually spread out. An important 

 feature is that as a result of this mixing, 

 the jet draws in fluid from its surround- 

 ings." If this theory holds true for the 

 North Sea and other bodies of water, it may 

 apply to Saginaw Bay also, especially if 

 all the streams and rivers entering the bay 

 and currents entering from Lake Huron be- 

 have as jets drawing in water laterally. 



Circulation at the mouth of the bay 

 must be affected to a large extent by move- 

 ments of Lake Huron water. Harrington's 

 (1895) work indicated that a strong current 

 flows down the western shore of Lake Huron 

 across the mouth of Saginaw Bay. The pene- 

 tration of Lake Huron water into the bay is 

 still a matter to be resolved through chemi- 

 cal and physical data collected during this 

 study. 



WATER MOVEMENTS OF LAKE HURON 



Previous studies 



The first account of drift-bottle work 

 upon Lake Huron was that by Harrington 

 (1895). He recognized a variability in 

 surface currents of the lake when he stated, 

 "While the winds from the Great Lakes are 

 westerly in their prevailing direction, 

 this is the region of variable weather, and 

 the actual directions of the wind change 

 from day to day. There will, consequently, 

 be considerable variation in the currents 

 from time to time, and this undoubtedly 

 causes a wayward motion of the current 

 bottles." He found that the courses taken 

 by the bottles in Lake Huron exhibited a 

 somewhat more complicated drift than did 

 bottles released in Lake Superior and Lake 

 Michigan. 



Ayers (1956) adapted the oceanogra- 

 phers' dynamic-height method of determining 

 currents to freshwater conditions. Find- 

 ings on Lake Huron in 1954, based on this 

 method, seemed to be in good agreement with 

 results obtained by other methods (Ayers 

 et al . 1956). Analysis of the data from 

 three synoptic runs in 1954 revealed dis- 

 tinct differences in surface circulation 

 at the times (spring, summer, and fall) of 

 the runs. They concluded, further, "The 

 fundamental surface circulation pattern in 

 the upper and central portions of the lake 

 appeared to be counterclockwise. In the 



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