NOTCHES AND WEIRS' 



149 



cent, with a crest height of 6*65 feet, and of 8'8 per cent, with a crest 

 height of 11 '25 feet. The heads in these experiments ranged from 

 5 to 4 feet. 



Effect of a Sloping Apron on the Down-stream Side of a Sharp- 



f crested Weir. 



If such a weir, having a vertical up-stream face and a sharp crost is 

 fitted with a sloping apron on the down-stream side, the discharge is 

 increased to an extent which depends on the slope of the apron. Bizin, 

 experimenting on such weirs having heights of T64 and 2*64 feet and 

 with heads ranging from '3 to 1*5 feet, deduced the approximate formula 



K = 



3'85 



for values of the slope S between 1 and 12. 



Effect of Rounding the Up-stream Edge. 

 A slight rounding of the up-stream edge, by diminishing the contraction 



FIG. 79. 



of section as indicated in Fig. 79 a, always causes an increased discharge. 

 Messrs. Fteley and Stearns, from experiments with crest radii up to 

 1 inch, found that, so long as the nappe was fully aerated, the effect of 

 the rounding was to increase the effective head by h', where h r = '1 r 

 (Fig. 796). 



Effect of Clinging Nappe. 



The experiments of Bazin showed very clearly the importance of taking 

 into consideration the particular form assumed by the nappe. 



If discharging freely, with free admission of air underneath, such a 



