68 



THE IRRIGATION AGE. 



ditch banks. Therefore the range of the grades which may be given 

 to a ditch is limited. In ordinary soils a grade of 2 inches in 100 feet 

 may be given to small ditches, and in clay soils as much as 3 to 5 

 inches in 100 feet may be given. 



Should the line run in this way be too long, the stream below the 

 point where the line strikes it should be examined to see if there is any 

 place where the water can be raised by a dam high enough to flow into 

 the proposed ditch. In case no such place is found, a water supply 



PIG. 4. Diversion of a small stream into a reservoir. 



from that source must be abandoned. If this preliminary line shows 

 that the water can be brought to the land by a reasonable expenditure 

 of labor and money, the ditch line should be carefully located as before 

 described (p 18, vol. 1). 



It may be that the place where the line strikes the stream is not a 

 convenient place for diverting water. In such a case the head of the 

 ditch may be moved upstream, and a drop put in to avoid too heavy 

 grades, or the head may be moved downstream and the water raised to 

 the ditch by a dam. 



BUILDING THE DITCH. 



Having decided upon the point of diversion and located the ditch 

 line, the farmer is ready to build the ditch. Experience in making 

 drain ditches will help in this. But there is this difference: Drain 

 ditches must be kept in the ground as deep as practicable, while irri- 

 gation ditches must be kept as near the surface as may be, in order that 

 the water can be easily taken out. The line of the ditch should first 

 be marked by a furrow. To do this, let one man guide the team } 

 walking between the heads of the horses, holding a bit in each hand, 

 while another holds the plow. If the surface of the ground is such as 

 to permit a wagon to pass along the line, the plow may be attached to 

 the rear axle, the driver directing the team from the seat of the wagon. 

 The furrow should be turned to the lower side of the ditch. If the 

 surface of the ground is comparitively level across the line of the 



