HYDROLOGY OF NEW YORK 



313 



Temporarily, much greater fluctuations than indicated in the 

 foregoing table have been experienced, due largely to wind action, 

 to which Lake Erie, on account of its shallowness, and the fact 

 that its general direction is favorable for the sweep of the pre- 

 vailing winds, is peculiarly subject. Tn regard to the measure- 

 ments of the Lake Survey, it may be remarked that they indicate 

 large variations in discharge from all of the lakes, from the effects 

 of winds and other disturbing causes, but give little clew to the 

 quantities at either of the extremes of high or low water. Ac- 

 cording to Lyman E. Cooley the extreme low-water discharge is 

 probably 20 to 30 per cent less than the Lake Survey figures, and 

 extreme high water 20 to 30 per cent more. 



Measurements of the amount of water flowing in Niagara river 

 were begun in December, 1891, at a time when the water in Lake 

 Erie was very low and the conditions were considered specially 

 favorable for minimum discharge. The results are given in the 

 Annual Keport of the Chief of Engineers for 1893, part VI, pp. 

 4364-1371. The point selected was about 1000 feet below the Inter- 

 national bridge at Black Rock, near the foot of Squaw island, at 

 which point the river is free from eddies. Niagara river, on leav- 

 ing Lake Erie, has a nearly straight channel about 2000 feet wide 

 for the first 2 miles. The fall in this section is from 4 to 5 feeT, 

 and the velocity ranges from 7 miles per hour at the upper end to 

 about 5 miles at the lower end. The point was chosen, after care- 

 ful ronsideration. as the point in that vicinity least subject to 

 disturbance. In taking the cross sections, the width, which varies 

 slightly with different stages of the river, was accurately deter- 

 mined for gage readings 1 foot apart, and for extreme points the 

 width was determined by interpolating values derived from the 

 known slope of the river banks. A local gage was established at 

 the draw pier of the International bridge, by setting gage boards on 

 each side of the pier, with the zeros of the gages on the same level. 

 The local gage was read at the beginning and close of all velocity 

 observations, and the gage at Buffalo was read at 7 a. in. and 1 

 and 7 p. m. The zero of this latter gage is at the mean level of 

 Lake Erie, or 572.23 feet above mean tide at New York in the 

 Erie canal levels, or as used by the government engineers, 572.96 

 feet. During the velocity observations in December, 1891, Lake 

 Erie was about 1.5 feet below its mean level, and is stated not 



