174 



FARMERS' INSTITUTES. 



The capacity in this case is nearly four times as great, while the area is 

 only about 3f times as great. 



The following table for capacity of open drains was computed from the 

 formula mentioned by B. F. Wells, C. E., of Marshall, Mich. 



The following is a selection of only a few quantities given in an extensive 

 table. (Table is published in full in " Bellow's Surveying.") 



Table — Acres from which one-half inch of ivater ivill be removed by open drain within 



24 hours — side slope, 45". Drain full. 



The fall that can be secured where open drains are laid, very seldom 

 exceeds eight feet per mile and usually is not in excess of four feet per mile. 



TABLE FOE SIZE OF TILE. 



Note— One acre covered with one-half inch of water is equivalent to 1,815 cubic feet. Capacity of 

 drain is expressed in cubic feet per day by multiplying each number by 1,815. If tiles are laid to- 

 grades where numbers are not given, extraordinary caution must be used. 



Apj)roximate formula: 



f A ^ acres drained. 

 /fVJT, J -'-^ = diameter of tile in inches. 

 A = 3.8v/-L>- ) h = rise. 



[ 1 = length. 



