88 



DRY-FARMING CONGRESS, WICHITA, 1914 



3,387, 60 acre-feet. In other words, is it not apparent that the higher, 

 heavily-forested mountains are the principal sources of water supply, when 

 we find that one square mile above 8,930 feet in elevation furnishes enough 

 water to irrigate 219 acres, while the average square mile, for the entire 

 drainage, which is at least one-half prairie and foothills, furnishes only 

 enough water to irrigate 23 acres ? If the high mountains are the source 

 of most of the water, as these figures seem to indicate, then is it not of 

 the utmost importance that these mountain areas be protected in such a 

 was as to furnish a perpetual supply ? 



Now let us explain the records to see what proof we may find of the 

 effect of the forest cover on this water supply from the mountain regions. 

 We are all aware, of course, that the precipitation, especially in the form 

 of snow, is much greater at high elevations than in the low mountains or 

 on the plains. We are also aware that forests grow on the higher moun- 

 tains because of the abundant precipitation, and that there are certain 

 areas, very high mountain peaks, which bear no timber, yet undoubtedly 

 furnish much of the late water for irrigation. In looking at this question, 

 therefore, we are concerned only with those moderately high mountain 

 areas where forests reach their best development, where the precipitation 

 is from 20 to 30 inches per annum, and where the atmosphere warms up 

 sufficiently early in the spring to cause rapid melting, freshets, and a loss 

 of water for later irrigation purposes. 



If we are willing to take the results of the Geological Survey experi- 

 ment in the White Mountains, as applying approximately to similar forest 

 areas in the Rockies, we find the following facts: Two areas of approxi- 

 mately 5 square miles each were studied. These areas was very similar 

 in every respect except that one had been burned over from one to three 

 times, while the other was covered, to the extent of 80 percent of its 

 area,, with virgin forest. During 1912 the streams flowing from these two 

 areas were carefully studied, as was also the amount of snow and rain 

 which fell upon them, and other factors. During the period of rapid melt- 

 ing in the spring, April 2-29, 1912, it was found that snow and rain equal 

 to a water depth of 10.5 inches disappeared on the burned area, while 

 "during the same period only 6.8 inches, or 65 percent as much, disappeared 

 on the forested area. During this same period the streamflow from the 

 burned area amounted to 12.874 inches, while that from the forested area 

 amounted to 6.482 inches, or almost exactly one half the run-off of the 

 burned area. It is seen from the above that while the snow was melting, 

 the burned area made a drain upon its stored ground water of about 2.3 

 inches, while the forested area stored some of its snow water in the ground. 

 This difference, in the mind of the Geological Survey expert, was due to 

 the presence on the forested area of a deep mat of vegetal soil, while 

 the burned area had only a mineral soil, incapable of absorbing and hold- 

 ing any excess of water. Isn't the difference also due to the slower melt- 

 ing of the snow under the forest cover? 



The thing of prime interest to us about this experiment is the fact 



