68 IRRIGATION FARMING. 



is a drop box for the fall and is often made a reduction 

 box as well. It is useful in places where the water- 

 supply is lessened by serving customers farther up the 

 line, or when the volume of water becomes less from 

 any other cause. Another plan is the use of the 

 inclined flume. By keeping the water grades up, a 

 broader area is kept within the range of service. 

 Grades of from two to five feet a mile will be ample to 

 secure good delivery from the smaller main ditches, 

 while the laterals will require steeper grades, which in 

 many cases may be confined to the approximate level 

 of the field, except on hillsides or quite abrupt slopes, 

 in which case the grades will be carried around the 

 slope as contours. 



As to side slopes, the usual ratio is one to one in 

 cuts of common material, with sometimes one-half to 

 one in harder material and one-fourth to one in rock. 

 For outside slopes of embankments the usual ratio is 

 one and one-half to one, and for inside slopes of banks 

 usually two to one, except in crossing ravines with the 

 bank, when the inner slope may be two and one-half or 

 three to one, owing to the depth of bank below the 

 grade line. In a flat country where the bottom of the 

 canal is kept as near the natural surface as possible, 

 • and embankments are built on both sides, the side 

 slopes may be as flat as three to one from the bottom 

 of the cut to the bank without any berme. Many fair- 

 sized canals even up to twelve or sixteen feet wide, and 

 carrying three or four feet of water, have been made 

 without any berme and seem to have stood well. 



Curves and Friction. — The more earth surface 

 and the greater number of bends the water comes in 



