SIZE OF DRAINS 179 



The number of acres drained is found by dividing the 

 discharge by a constant representing the number of cubic 

 feet per second necessary to relieve one acre of a given 

 depth of water in 24 hours. The constants most used 

 are: 



0.0052 cu. ft. per second = | in. per acre in 24 hours 

 0.0105 " " " " = I " " " " 24 " 

 0.0140 " " " " - 1 " " " " 24 " 



0.0210 '" " " " = I " " " " 2 4 " 



0.0315 " " " " = I " " " " 24 " 

 0.0420 " " " " = I " " " " 24 " 



In using the formula, the number of acres in the water- 

 shed multiplied by the assumed constant may be sub- 

 stituted for Q and the formula solved for the diameter of 

 the tile. Other methods of computing sizes, such as the 

 Chezy-Kutter formula given by Parsons (10), are used. 



Hart (5) has the following to say about the size of drains 

 for irrigated lands and construction methods: 



"The spacing of drains in the irrigated section usually 

 is much greater than in humid sections and frequently 

 a single line of drain may effect the reclamation of a con- 

 siderable acreage. From this it will be concluded that 

 larger drains will be required in the drainage of irrigated 

 lands. It has been found that they need not be propor- 

 tionately large, however, since the amount of water which 

 it is necessary to take care of is smaller for a given acreage. 

 In the arid section, there is likely to be a continuous 

 discharge of drainage water throughout the year, and 

 frequently the discharge is very uniform at all times. 

 However, there are certain maximum flows, usually during 

 the period of greatest irrigation application, and it is neces- 

 sary to provide a drainage capacity that will take care of 

 such flows. 



