3 THE IMPROVEMENT OF RIVERS. 



The coefficient c has been deduced by experiment and may be found from the fol- 

 lowing table of values, as given by Trautwine.* In it H represents the still-water 

 height of the upper pool above the crest of the weir, and h is as given above. This 

 formula takes no account of the velocity of approach. 



Velocity of Approach. Free Discharge. In cases where the velocity of the approach- 

 ing water is such that it must be taken into consideration, as is usually the case with 

 weirs except when the discharge is low, the foregoing formulas must be corrected 

 accordingly. The following general formula has been supplied, based on the result 

 of the researches of Francis, Fteley and Stearns, Bazin, and others, and applicable 

 to weirs discharging into free air, with or without end contractions : f 



(3) 



where Q = discharge in cubic feet per second ; 

 C' a constant for a given value of H ; 

 K = a coefficient from Bazin's experiments; 



/ = length of weir in feet; 



H = height of water above crest of weir at the place of actual measurement ; 

 n= number of end contractions. 



The following table gives the value of the coefficients, in which 

 a -(/-o. inH)H; 

 A area of water-section in channel of approach ; 



= ratio of area of weir-section to area of section of channel of approach; 

 A 



a 

 K = constant for given value of -r ; 



C'- 



ii it 



(i it 



H. 



* Engineer's Pocket-book, p. 2677. 



t Proceedings of the American Society of Civil Engineers, August, 1900. Discussion by Mr. Walter C. 

 Parmlcv. 





