A NATIONAL PLAN FOR AMERICAN FORESTRY 



445 



ufacturing, canning, dairying, and poultry raising, and plays a very 

 important part in the sheep, beef-cattle, and meat-packing industries. 

 The great demand for water is well illustrated by conditions on the 

 Sevier River. All the water in the channel is diverted several times for 

 irrigation, 7 or 8 dams being used for this purpose and in part to form 

 storage reservoirs. The return seepage from the agricultural lands 

 below each dam supplies water for the next reservoir. In years of 



RELATIVE INFLUENCE OF FORESTS 

 ON WATERSHEDS 



" HHi^l MAJOR INFLUENCE 



H MODERATE INFLUENCE 

 F/;;//iM SLIGHT INFLUENCE 



FIGURE 13. Great Basin. 



normal or greater precipitation all the reservoirs fill at least above the 

 point of dangerous water shortage. In years of sparse precipitation, 

 however, 2 or 3 of which usually occur in every decade, the lower reser- 

 voirs and some of the upper ones fail to receive enough water for more 

 than 1 or 2 irrigations and occasionally the lowest reservoir receives 

 none. 



Nearly all the water for irrigation comes as run-off from forest 

 areas. These total some 20 million acres, only 14 percent of the whole 

 basin area. They occur mainly above 5,000 feet elevation, on moun- 

 tains and plateaus. Valleys or desert basins alternate with the 



