Preservation of the Falls 



of lake Erie is about 76 clays, and for a decreasing supply it is 1911 

 about 1 32 days. White 



The extreme variation of level of lake Erie during the period 

 1860-1907 is 3.89 feet, with a maximum range in one year 

 (1892) of 2.28 feet, a minimum range in one year (1895) of 

 .87 feet, and an annual average of 1 .56 feet. The amount of 

 water which lake Erie discharges through the Niagara river is a 

 variable quantity and depends upon the elevation of the water 

 surface, or, as it is termed, the stage, of the lake. For the Great 

 Lakes system it is customary to give the stages of the respective 

 bodies of water above a fixed datum. Mean tide water at New 

 York is the datum usually selected. 



Consider an illustration. A variation in the stage of lake Erie 

 of a single foot, at Buffalo Lighthouse, Buffalo, corresponds to a 

 difference in the rate of discharge from the lake of from twenty 

 to twenty-five thousand cubic feet of water per second. The 

 increments of discharge per foot change in stage vary for different 

 sections of the river. They are expressed in cubic feet per second, 

 at Buffalo Lighthouse, as follows: 



Stage Increment in C. F. S. 



572.67 (mean) 23,400 



570-571 19,600 



571-572 21,400 



572-573 23,200 



573-574 25,100 



The knowledge such data conveys is, that if the water level of 

 lake Erie, at Buffalo Lighthouse, for example, is 570 feet above 

 mean tide level at New York, and the level rises to 571 feet, then, 

 the Niagara river will discharge at the rate of 1 9,600 cubic feet 

 of water per second more than it was discharging at the 570 foot 

 stage. If, next, the stage rises from 571 to 572 feet, then the 

 discharge rate becomes 2 1 ,400 cubic feet per second greater than 

 it was at the 571 foot stage. 



1159 



