NATIONAL FOEESTS AND THE INTERMOUNTAIN REGION 5 



masses of debris ; for, though the construction may be strong enough 

 to withstand the rush of flood waters, the capacity of the reservoir 

 is reduced with every freshet, and presently the reservoir is full of 

 useless earth and rock instead of valuable water. Many small reser- 

 voirs throughout the intermountain region, now useless, bear silent 

 witness to this fact. 



There is also the item of time which might be put to productive 

 use but is wasted each year in ridding the canals of their great 

 accumulation of silt and sand. In some places the disposal of 

 these accumulations has become a serious problem. On the irriga- 

 tion project served by the Elephant Butte storage dam in New 

 Mexico, enormous quantities of sand washed into the river from 

 arroyos cause difficulty and great expense in keeping the canals 

 free of sand accumulations. 



SEASONAL VARIATION IN THE VALUE OF WATER TO CROPS 



Less spectacular, but nevertheless real and very great is the loss 

 in effectiveness of the water when it comes down all at once early 

 in the season and then rapidly dwindles away through the summer. 

 Studies made at the Utah Agricultural Experiment Station in regard 

 to the duty of water, which are showing how to make the available 

 irrigation water go farthest in the production of crops, have indicated 

 that nearly every crop needs later water — that is, water through 

 midsummer. Midsummer water is of much more value than a super- 

 abundance at the time of the spring freshets. Irrigation with 

 early water alone frequently results in yields scarcely greater than 

 those produced in the same neighborhood by dry farming. 



Through the destruction of watershed cover, early melting of the 

 snow is encouraged ; the snowdrifts, instead of lying in the shade of 

 the trees to melt slowly as late as Jul}^, are exposed to the full heat 

 of the sun and rapidly disintegrate during the spring. Also, along 

 with the processes that destroy trees and vegetation on the mountain 

 comes the compacting of soil, which lessens its ability to absorb 

 water. Hence surface run-off increases, spring freshets are intensi- 

 fied, and the flow of springs, which furnishes the late water in many 

 of the streams, is decreased. Thus, although the total run-off is 

 actually increased, it is far less useful and may prove dangerously 

 destructive. 



EFFECT OF WATER SUPPLY ON LAND VALUES 



In the intermountain region the total value of farm land amounts 

 to approximately $785,000,000. By far the greater part of this value 

 lies in the irrigated lands rather than in dry-farm areas and pastures. 

 The water for irrigation comes almost entirely from mountains in- 

 cluded in the national forests, which cover approximately 30,000,000 

 acres of the intermountain region. Were the water taken from the 

 irrigated lands, their value would decrease tremendously, for in 

 some cases they would then be valuable only for grazing. Most of the 

 land now irrigated would be unprofitable as dry-farm land. It 

 would be difficult to estimate accurately the actual money value added 

 to the farm lands of the region as the result of irrigation, but it 

 is probable that the amount would reach more than 80 per cent of 



