86 CONSERVATION OF GROUND WATER 



crease the hazard of floods by reducing channel capacities 

 and increase the concentration of mineral salts in the soil, 

 at least temporarily. There is no question that this waste 

 should be stopped, either by clearing the vegetation or 

 by getting the water out of reach, but practical and ef- 

 ficient methods have not yet been worked out. The salt 

 cedar in particular is prolific and is not easily eradicated. In 

 some areas it is possible to eradicate water-loving vegetation 

 by pumping until the water table is lowered beyond the 

 reach of the roots. In Safford Valley such pumping would 

 deplete the flow of the river, and if the water table could 

 be depressed sufficiently to reduce evapotranspiration in the 

 bottom lands, much of the water for Coolidge Reservoir 

 might eventually have to come from wells rather than from 

 stream flow. 



Another evidence of surplus ground water in many arid 

 valleys is the waterlogging of lands once suitable for cultiva- 

 tion. This problem of rising water table has been solved in 

 many areas, especially in California and Arizona, by pumping, 

 and more generally by drainage canals. But there are thou- 

 sands of acres of waterlogged land in Helena Valley and other 

 valleys in Montana, in San Luis Valley in Colorado, and in 

 other irrigated valleys. Generally the high water table has 

 developed as a result of irrigation and thus is a problem re- 

 lated to man's use of land and surface water, discussed in the 

 following chapter. 



Helena Valley, Montr* The agricultural lands of Helena 

 Valley are largely dependent upon gravity diversions from 

 streams for irrigation, as in many other high mountain val- 

 leys of Montana. Lands in the lowest part of the valley were 

 the first to be irrigated. As lands higher on the slopes were 



29 Reference: Lorenz, H. W., F. A. Swenson, and H. A. Swenson, Geology and 

 Ground-water Resources of the Helena Valley, Montana, 

 US. Geol. Survey Circ. 83, in press. 



