HYDROLOGY OF NEW YORK 



331 



each experimental weir below the standard weir, and observing 

 the heads synchronously on each. In these experiments a steady 

 current was established in the channel, and observations of the 

 known value passing over the standard weir were made, which 

 volume also passed over the weir under investigation, lower down. 



If we let E and h denote, respectively, the head upon the 

 standard weir and upon the lower weir, L and I, their correspond- 

 ing lengths, and M and m, the coefficients of discharge, and then, 

 adopting provisionally Formula (1) for the standard weir — 



Q = MZJBT s f^H; (32) 



and similarly for the lower weir 



Q = mlh x /^J h (33) 



Equating these two values of Q, we have 



MLII^Jj ^ 2 y= mlh 2g, or 



MLH 1 = m I h l 

 from which we deduce the value of m: 



•-*{$)*(?$ 



or, conversely : M — m (^f~^ x (^JT^) 



(34) 

 (35) 



As already stated, Bazin's preliminary gaging operations gave, 

 once for all, the coefficient M for the standard weir for each 



value of H. The ratio -y which is very nearly unity, remained 

 constant for all experiments of any one series, and, therefore, we 

 have only to measure the heads H and h in order to obtain the 

 coefficient m. 1 



A description of the method of gaging pursued on the several 

 streams is not given at length here because it may be found in 

 full detail in the places cited, namely, in the Report to the Board 

 of Engineers on Deep Waterways and in the paper On the Flow 

 of Water Over Dams, to either of which reference may be made. 



Discharge measurements of Genesee river. The runoff data of 

 Genesee river for the water years 1890-1898, inclusive, in inches 

 on the catchment area, have been given in table No. 43. The 



J On the Flow of Water Over Dams, Trans. Am. Soc. C. E., Vol. XLIV, pp. 

 220-398. 



