The volume of Western Lake Erie exclusive of oandusky Bay is 6.l5 

 cubic miles (25.58 cubic kilometers). This figure was obtained by the use 

 of Penck's formula (Juday, I91U, p. 122). The volume of the entire lake is 

 120 cubic miles (h99 cubic kilometers), or about 20 times the volume of 

 Western Lake Erie. 



Fluctuations of Lake Level 

 Fluctuations ovdng to changes in volume 



The volume of water in Lake Erie is changing constantly, and these 

 changes are reflected in fluctuations of the mean lake level. There are 

 five factors whose interrelationships determine changes in volume:- (1) in- 

 flow from the upper lakes: (2) run-off from the drainage basin; (3) rainfall 

 on the lake: (h) evaporation; and (5) outflow through Niagara River and arti- 

 ficial diversion channels. The problem of evaluating these factors and 

 determining their interrelationships is one of extreme complexity; and by 

 reason of the diversions at Chica^p since I9OO the whole question of lake 

 levels has become highly controversial. It is neither possible nor desirable 

 to enter into a discussion of the problem here. Of the many reports on the 

 subject, the volume by Horton and Grunsky (1927) will be found valuable be- 

 cause of its completeness and the inclusion of a bibliography. Disregarding, 

 then, the factors which determine volume, and hence mean lake level, some of 

 the data on observed fluctuations will be considered briefly. 



Seasonal fluctuations 



Hayford (1922, p. 112) stated that "the actual variation of the mean 

 elevation of the whole surface of any one of the Great Lakes is, as a rule, 

 as much as 0.01 foot in two days, that it is frequently more than 0.02 foot 

 in 2U hours, and that on rare occasions it may exceed O.08 in that period." 

 Such small variations are not evident to the eye of an observer because they 

 are masked by transient disturbances of the level, but since the variations 

 are principally in one direction for many days, the change in level, by accu- 

 mulation, finally becomes evident without the use of special instruments. 



For many years the United States Lake Survey has been keeping an accurate 

 record of levels in the Great Lakes by means of gauges placed at strategic 

 points along the shores. In Table 2 and Fig. 5 are shown the averages of the 

 monthly mean levels at Cleveland, Ohio, for the period 1860-1930. It may be 

 seen that, on the average, the level has been low in winter and high in summer;jj 

 the lowest month has been February and the highest June. It should not be 

 assumed that the low point always occurs in February or the high point in June 

 During the 71-year period the low point has occurred also in January, March, 



32 



