Drainage by Gravitation, 33 



eddies. The constant to be used in the formula for calculating 

 the discharge, varies from -96 in the best form, and large 

 sluices to '60 in small structures with hanging doors. In 

 calculating the velocity, allowance has to be made for the 

 head due to the velocity with which the water approaches the 

 sluice. If the sluice is of sufficient capacity, this will over- 

 come the friction, and carry the water through without any 

 heading up. 



For example, take the case of a sluice with three openings 

 of 16 feet each, and a depth of 9 feet, the drain running with 

 a velocity of 1*50 feet per second, and discharging 1200 

 cubic feet per second. The quantity passing through each 

 opening would be 400 feet, and the velocity required with 

 the area of the sluice would be 2*778 feet per second. The 

 head required for this velocity, allowing 4 per cent, for friction, 

 that is multiplying by the factor -96, would be '1308 feet. 

 Deducting the head due to the velocity of approach of 

 1-50 feet or '0381, leaves the head required at the sluice 

 •0927 feet, or a little over one inch. 



Area of waterway =i6*0X9*0X3 = 432*0 feet 



Total quantity coming down drain divided by area of 



1200 

 sluice = = 2*778 velocity required. 



Feet 

 ~ ^— j == "1308 



Lessheadofapproach=(3l^)=-O38i 



Head required at sluice '0927 



The proportion of depth to total width of the water passing 

 through sluices, varies in practice from one-fourth in the 

 smaller sluices to one-fifth and one-sixth in those of larger 

 capacity. 



D 



