BROAD CBESTED WEIRS 



ir>r> 



Types H to L. 



COMPOUND WEIBS (M to P). FIG. 89c. 



From a consideration of these various tables it appears that with dams 

 having an ogee cross section, or having an up-stream slope, the discharge 

 usually increases according to some higher power of the head than the 

 l/5th. Eecent gaugings of the flow over large dams of these types 2 

 indicate that this power may attain a value as high as 1/75, though it 

 usually lies between 1*50 and T65. 



Effect of Condition of Nappe, on Discharge over wide, flat-crested Weirs. 



Just as with a thin weir the nappe from a wide-crested weir may either 

 spring clear of the down-stream face, be depressed, or be drowned. A 

 simple depression of the nappe has, however, little effect on the discharge, 

 slightly increasing it for low heads and diminishing it for high heads. 

 If the nappe is drowned the effect is very slight so long as the stream 



1 Type N is identical with M, but with the addition of a 12 inch x 12 inch timber baulk on 

 its ens'. 



2 Engineering News, New York, September 29, 1910. p. 321. 



