NOTCHES AND WEIRS 



145 



6*56 feet long, and with heads ranging from "17 to 1'97 feet, and also 

 from an examination of the results of Fteley and Stearns, deduced the 

 formula 



Q = 



I V 



f^c.f.s. 



for a weir with no velocity of approach. For a weir with velocity of 

 approach, the effective head H + T69 h, and on substituting for h in 

 terms of the depth of approach channel Bazin finally gets 



Q = 1 1 + -55 ( VI | -405 + 5^*U VTJ * ,f,. 



H 



Approximately, for heads from 4 inches to 1 foot we have 



b V 2 g PI 2 cub. ft. per sec. 



correct within about 2J per cent. In these formulae P = height of the 

 weir crest above the bed of the approach channel. All dimensions are in 



a. 

 feet. Expressing the formula in the form Q = K b H 2 , the following 



values of K are deduced from Bazin's experimental results : 



The following table shows the ratio of the velocity-of-approach correction 

 applied by various experimenters for a suppressed weir. 



This large difference is, however, more apparent than real, as the larger 

 velocity corrections are compensated by smaller weir coefficients. Actually 



H.A. 



