73 



orchardists have replaced the earth ditch by wooden flumes or the more 

 permanent concrete flume or concrete pipe distributing system. 



Where the orchard is small and the slope regular, one head ditch or 

 head flume carrying the water from the point of delivery and placed on the 

 highest part of the land to be irrigated, may be all that is necessary. But 

 for larger orchards and for irregular slopes, it is necessary to have two or 

 more head ditches or flumes to which the water is carried by a supply 

 ditch, pipe, or flume. In laying out stfCh a distribution system the irrigator 

 should study the topography of the land and subdivide his orchard with 

 sufficient head ditches to give furrows which are not too long and too 

 steep. Usually it is desirable to make the furrows not over 600 for ordin- 

 ary sandy loam and 300 feet for more porous sandy soil. 



6 



No. I. 



No.a. 



No.3. 



No.4. 



form of No.4. 



Fig-. 5G. Typical forms of earth ditches. 



1. Earthen Head Ditch. 



The head ditch is placed along the highest boundary of the orchard or if 

 there is a ridge through the center of the orchard, it is placed on this 

 ridge and supplies the furrows running down the slope on both sides. The 

 proper grade depends on the volume of water to be carried and on the 

 character of the soil; the velocity must not be too great or it will erode 

 the soil. On the other hand it is best to have sufficient velocity to prevent 

 the growth of water plants. Velocities of 2 to 2y 2i feet per second are 

 desirable. The diagram (Fig. 56) and accompanying table to which has 

 been added the last column, are taken from Bulletin No. 4: Guide to 

 Irrigation Practice on the Pacific Coast, by S. Fortier, issued by the Pub- 

 licity Committee of the Fifteenth National Irrigation Congress. 



