IRRIGABLE LANDS OF THE VALLEY OF THE SEVIER. 141 
Feet 
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This estimate is also liable to reduction, being undoubtedly a little in 
excess of the amount available at the critical period. This reduction may 
be as great as 15 per cent., which would leave very closely 200 cubic feet 
as the water supply of the San Pete Valley, which, added to the total of 
the Sevier above Gunnison, gives for the whole drainage system of the 
Sevier River a water supply of 860 feet per second at the time when the 
greatest amount is required. 
The next factor to be inquired into is the amount of land which a cubic 
foot per second of water can irrigate. This is, of course, highly variable, 
depending upon the nature of the soil, and the economy with which the 
water is applied, and the frequency of the irrigations. New lands freshly 
broken require much more water than the older ones which have been 
planted and watered for several years; and in fact the quantity diminishes 
with each season for a long term of years. In the San Pete Valley, which 
has been longest cultivated, the decrease in the amount of water applied to 
the oldest lands has not yet ceased, though some fields have been cultivated 
with regularity since 1857. The fresh soils are highly porous and absorp- 
tive, requiring a large quantity of water for their irrigation, and not retain- 
ing this moisture well under the great evaporative power of a dry and hot 
atmosphere. With successive irrigations, the pores of the soil are gradually 
closed and the earth is slowly compacted by the infiltration of impalpable 
silt brought by the irrigating waters. It absorbs water much more slowly, 
and retains it a much longer time. There is, however, a check to this 
increased irrigating power, arising from a wasteful mode of agriculture. — It 
has not been the practice to employ fertilizers, nor any other conservative 
means of keeping up the fertility of the soil, and the yield of the crops 
growing smaller, the old lands are frequently abandoned, and fresh adjoin- 
ing lands are broken, planted, and watered. It has been the practice to 
