HYDROLOGY OF NEW YORK 



373 



in which — 



B = the width of the crest in linear feet; 



C = the coefficient for a thin-edged weir, corresponding to a 



depth d. as per equation (39), and 

 C = the adjusted coefficient corresponding to a given breadth 

 B and a depth d. 1 



In the case of the Mechanicville dam we have a stone crest 7 

 feet in width and slightly inclined upstream. The width of the 

 river a short distance above the dam is considerably over 800 feet ; 

 the depth for some distance back is from 16 to 20 feet. In order 

 to avoid a correction for velocity of approach, a crest was assumed 

 5 feet wide and values of C were computed on that basis. 



Having obtained values of C for = 0.25, 0.50, 0.75, 1.00, 1.25. 

 1.50, 1.75 feet, and so on up to 8 feet, corresponding values of Q 

 were computed and plotted at a large scale as a curve with values 

 of (7 as abscissas and the corresponding flows as ordinates. From 

 this curve intermediate values of Q have been read off. 



The water wheels at Mechanicville have a capacity when they 

 are all running of about 2100 cubic feet per second. The working 

 head varies from 15 to 17 feet, depending upon the condition of 

 the flashboards. A test of a 39-inch Hercules wheel, which has 

 been in use about eight years, shows the actual discharge to be 

 substantially as given in the manufacturers' tables when running 

 at the speed of greatest efficiency. 



The crest gage is read twice a day and a mean taken for the 

 hight. A continuous record is also kept of the run of the water 

 wheels at the mill. 



Discharge measurements of Hudson river at Fort Edward. 

 This station is located at the dam of the International Paper 

 Company, which was established by the winter in 1895 in connec- 

 tion with the upper Hudson storage surveys. The dam is of 

 timber on rock foundation and with very little leakage. The 

 crest is nearly level, 587.6 feet in length. Flashboards are main- 

 tained on the dam 15 to 18 inches in hight. 



There are sixty-two water wheels in the adjoining mill. A 

 record is kept of the daily run of each in hours, as well as the 

 workiug head, which is about 19 feet. The capacity of the wheels 



'The method of deducing equations (30) and (40) may be found in 

 Mullin's Irrigation Manual. 1S90. pp. 11. 12, 138, 139, 171, 172. 



