50 IRRIGATION FARMING. 



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 con- 

 fined 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 embank- 

 ments are built on both sides, the side slopes may be as 

 flat as three to one from the bottom of the cut to the 

 top of the bank without any berme. Many fair-sized 

 canals even up to twelve or sixteen feet wide, and carry- 

 ing 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 con- 

 tact with in flowing in a ditch, the greater the friction 

 will be and the less the velocity and quantity of water. 

 Therefore to obtain the greatest velocity and quantity of 

 water the ditch should be as straight as possible. If 

 ix-nds are necessary they should not be abrupt, but as 

 -r.i'lual as possible. A very good example of an easy 

 curve is shown in Figure 9. 



For a steady flow the grade should be the same the 

 L-utirc length of the ditch, or as nearly so as circumstan- 



