74 



Bulletin 86 



losses in the Salt River Valley were reported in 1915 by the Recla- 

 mation Service as 45 percent, and in 1917 as 32 percent. For small 

 canals these losses are often over 5 percent per mile in adobe soil 

 and 15 to 20 percent per mile in porous soil. An extreme case is 

 shown in Fig. 3. Here the entire flow is lost. The ditch has a 

 valuable water supply at its head and the vain effort is made to 

 hurry the water over the sand on a steep grade. When the photo- 

 graph was taken, the last drop of water was sinking away near the 

 willow tree shown by the arrow, while three miles away alfalfa and 

 other crops dependent on this stream were drying up and dying. 

 In southern California there are extensive distribution systems 



Fig. 3. — Small irrigation ditch near Tucson, showins- less of entire How by seepage. 



(From Bulletin 55.) 



that are piped throughout so that the loss of water in distrilnition is 

 practically nothing. As a result of this and other economies the 

 duty of the water is nearly nine acres per (Arizona) miner's inch of 

 flow. The average duty of water in southern Arizona can be in- 

 creased greatly by the use of cement pipe for small ditches and con- 

 crete linings for larger ditches and canals. 



There are additional reasons for the use of cement pipe for 

 irrigation ditches. The maintenance of open ditches is difficult. 

 Under the subtropical skies of Arizona, weeds and algae grow 

 rankly and occupy the whole cross-section of the ditch. Bermuda 

 and Johnson grass thrive along the banks. Unless this vegetation is 



