184 CONSERVATION OF GROUND WATER 



slopes and intense rainstorms could not be modified, how- 

 ever, and it is perhaps unwise to guarantee immunity from 

 destructive flows even now. 



Some of the research on the Wasatch Range has been 

 devoted to the water cost of various types of vegetative 

 cover. It has been found, for instance, that grass takes a 

 lesser toll than forest cover from the annual water supplies, 

 because of the smaller depletion of soil moisture by its 

 shallow roots. Stream-bank vegetation takes large quantities 

 of water from the small perennial streams in the canyons. 

 Since mud-rock flows are commonly generated in higher 

 areas and would tear out this stream-bank vegetation as they 

 pass, it serves little purpose in preventing erosion. The 

 stream-bank vegetation may well become a casualty in the 

 fight to obtain increased water supplies for man's use. 



Most of the water supplies for valley communities comes 

 from the melting of snow on the Wasatch Range in the 

 spring. The effect of this melting shows up within a few 

 hours in the canyon streams. Yet the melting of snow- 

 banks in the forest does not result in overland flow but in 

 infiltration. The rapid movement of that water to the 

 streams suggests subsurface storms flow through permeable 

 soils. Thus here, as at Coweeta, there is detention storage 

 in the porous soil, but, judging by the small base flow in 

 the canyon streams, relatively little retention in the under- 

 lying impermeable rock materials. Summer precipitation 

 is almost all returned to the atmosphere and provides a 

 negligible proportion of the net water supplies to the valley. 



Sierra Anclia Experimental Forest, Ariz.— This forest is 

 in the water-deficient area of the Salt River drainage basin. 

 Vegetation could use all the annual precipitation if it were 

 available at the right time. Seasonal distribution of precipi- 

 tation, however, is such that about two-thirds falls during the 

 winter dormant season. Nearly all the rest comes in cloud- 



22 Reference: Rich, L. R., "Consumptive Use of Water by Forest and Range 

 Vegetation," Am. Soc. Civil Engrs., April 1950 meeting. 



