216 PuLivETiN 88 



average depth of water applied in 1914 was 108.2 inches. Unques- 

 tionably, 50 percent of the water thus applied sank to the water 

 table and was wasted. Many similar cases have been observed in 

 alfalfa irrigation and in furrow orchard irrigation, where the quan- 

 tity of water absorbed at the head ends of the furrows was found 

 to be excessive and wasteful. When these conditions exist, the 

 remedy is less water more rapidly applied, by means of a larger 

 head, or shorter runs, or steeper slopes. 



As a result of the downward percolation of irrigation water from 

 canals and from fields, nearly all irrigation projects are encount^ir- 

 ing difficulties due to waterlogged or seeped lands or to the conse- 

 quent rise of the alkali. The rising water table is disastrous to 

 crops, causing the death of orchards and alfalfa. On several 

 projects of the U. S. Reclamation Service the necessity for drainage 

 works became urgent before the irrigation systems were fully 

 completed. On one of the projects the water table over nearly 

 30,000 acres rose from 90 feet average depth to less than five feet 

 depth in six years, and about 6000 acres of the land became a marsh. 

 Over 15 percent of the total area in the arid region irrigated by 

 individuals and corporations in the past has been abandoned on 

 account of waterlogging. Already there are four important sec- 

 tions of the Salt River Valley which need drainage, and an extensive 

 project for lowering the groundwater table over a large area has 

 been financed by a bond issue and has been begun. An important 

 area in the Upper Gila Valley is being reclaimed by a system of 

 clay tile drains. At a school house near Pima the water table has 

 risen to the surface of the ground and the alkali has crept upward 

 in the brick work to the top of the door. Extensive drainage works 

 are being constructed in the Yuma Valley. 



Although in general the head ends of the fields are given too 

 much water, yet there are exceptions to this rule. Thus, on clay 

 loam and heavy adobe soils, if the lands have considerable fall, the 

 irrigating water runs quickly to the lower ends of the lands without 

 soaking into the ground more than a few inches. A similar effect 

 is produced by very silty water, such as that of the Gila and 

 Colorado rivers ; a silt-blanket is formed at the upper end of the 

 lands and becomes almost impervious. In such cases the remedy 

 is either to divide the head of water over more lands, or to use a 

 flatter gradient, and silt-blankets must be broken up and mulched. 



The frequently discussed problems of what slope to give the 

 lands and what head of water is best are interrelated, and involve 

 also a discussion of the length and width of lands, and the character 



