with little day-to-day variation, enabled 

 him to work out this relationship. He was 

 quick to point out, however, that this 

 relationship was not necessarily applicable 

 to waters other thantthose he studied. He 

 inferred that it would be foolish to seek 

 any equation other than a simple one because 

 of the many variables involved. 



Welch (1952) wrote that in large lakes 

 such as the Great Lakes surface velocity is 

 claimed to be about 5 percent of that of 

 the wind causing it but that the percentage 

 was less than 5 in smaller lakes. This 

 statement is in agreement generally with 

 Stromsten (1929) who found that a wind of 

 800 feet per minute produced a surface cur- 

 rent of 25 feet per minute on Lake Okoboji, 

 Iowa. Expressed in percentages, the surface 

 current there was about 3 percent of the 

 wind velocity. According to Whipple (1927), 

 Ackermann found the surface current to be 

 3 percent of a wind velocity of 5 miles per 

 hour and 1 percent of a wind velocity of 

 30 miles per hour on Owasco Lake, New York. 

 Velocity at a depth of 10 feet was about 

 60 percent of the surface velocity and at 

 20 feet it was 25 percent. 



In this study no attempt has been made 

 to correlate quantitatively wind velocity 

 and surface drift. To do so accurately 

 would require knowledge of the characteris- 

 tics of reasonable steady winds from any 

 one direction, knowledge of the exact time 

 of bottle travel, and an accurate track of 

 the bottle drift. At no time could we be 

 certain of the true course of bottle drift. 

 It was seldom that wind velocity remained 

 fairly stable for several days after the 

 releases and occasions when bottles were 

 actually seen to land were rare. At no 

 time did the two conditions, necessary for 

 accurate computation, exist simultaneously. 

 When steady wind conditions did prevail for 

 several days, no bottles were seen to land 

 that had completed their entire travels 

 under this wind. 



Another major difficulty in determin- 

 ing the relationship between water current 

 and wind velocity in regions of variable 

 winds is the lack of information on the 

 exact rate at which surface currents adjust 

 to a changing wind. Once this problem is 

 solved, we shall be in a better position 

 to compute the relationship quantitatively. 



FACTORS INFLUENCING 

 DRIFT-BOTTLE MOVEMENTS 



Surface currents in Saginaw Bay and 

 Lake Huron are extremely variable and are 

 dependent largely upon wind conditions. 

 However, the effects of winds on the two 

 bodies of water differ to a large extent 

 because of dissimilar morphometry of the 

 basins. Saginaw Bay is shallow, long, and 

 narrow, whereas Lake Huron is much deeper 

 and larger. 



Saginaw Bay 



In Saginaw Bay changes in the local 

 winds will alter surface currents in a very 

 short time as the energy accumulation in 

 currents in Saginaw Bay is far below that 

 of currents in Lake Huron. Because the 

 surface currents in the bay are so depend- 

 ent upon local winds, any pattern described 

 should be related to the winds producing 

 it if results are to be meaningful. 



Forces other than winds which modify 

 the surface currents in the bay result from 

 inflows of streams and rivers and possibly 

 ground water. Lake Huron water also alters 

 current patterns as it enters or leaves the 

 bay. Lake Huron water enters principally 

 along the western area of the bay. 



The shoreline in the lower reaches of 

 the bay, especially the eastern, is ill- 

 defined. Extensive areas in this region 

 are covered with emergent aquatic vegeta- 

 tion. It is apparent that currents in this 

 portion of the bay are relatively moderate. 

 However, it was here that direction of wind 

 and direction of bottle travel were most 

 closely correlated. 



Shore areas in the outer half of the 

 bay indicate much stronger eroding action 

 from currents. Although surface currents 

 flowed outward at some time at different 

 points at the mouth of the bay, the princi- 

 pal outflow was along the eastern shore and 

 thence around the tip of the Michigan Thumb 

 area. The correlation between wind direc- 

 tion and direction of bottle drift in the 

 outer half of the bay broke down at times, 

 most likely because of the influence of the 

 currents entering from Lake Huron. A 

 general counterclockwise circulation with 



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