EANGE PRESERVATION AND KKOSIOX CONTROL. 9 



thrown together into a single channel, as on arest A, where the force 

 of the water is accumulative. Thus the sum of conditions favor a 

 larger run-off from area A than from area B. There is no permanent 

 stream on either area, and run-off occurs only after rainstorms or 

 from melting snow. 



MELTING SNOW. 1 



The accumulation of the winter snows of 1915-16 showed a water 

 equivalent of 9.1 inches on area A and 9.2 inches on area B. This 

 represents approximately 326,800 cubic feet of potential water on 

 each of the 10-acre areas awaiting the spring thaw. What becomes of 

 the water from the melting of this snow ? The water registers show 

 that 292,998 cubic feet ran off area A, while only 42,216.8 cubic feet 

 ran off area B. This difference in run-off is due to the fact that 

 the soil on area B contains more organic matter and has a better 

 ground cover than area A. A small part of the snow water, of 

 course, evaporates into the air, but the greater portion of that not 

 accounted for in surface run-off is absorbed by the soil. Part of the 

 water that percolates into the soil finds its way to the main drainage 

 channels and serves as irrigation water in the valley below; the 

 remainder becomes an important factor in the promotion of growth 

 of range forage. The run-off occasioned by the melting of the 

 snow accumulated in 1915-16 caused the removal of 172 cubic feet 

 of soil from area A as against 82 cubic feet from area B. 



As might be expected, there is less sediment per cubic foot of run- 

 off from melting snow than from summer rainstorms. Further, the 

 total amount of sediment brought down is less than that deposited 

 by the single rainstorm of July 21, 1915, although the stream flow 

 from the melting snow was approximately seven times greater. 



1 In order that the water, both from melting snow and from rainstorms, which flows 

 from the areas may not escape through lateral rills and the record of stream flow be thus 

 impaired, the gullies along the sides of the areas have been dammed. In order to measure 

 accurately the run-off and sediment, a settling tank of adequate size, provided with. weir 

 and water register, has been installed at the lowest drainage point on each area. The 

 amount of sediment deposited from each individual rainstorm and from the melting of the 

 season's accumulation of snow is determined on the basis of the dry weight. 



Owing to the intimate relation existing between run-off and erosion and certain climatic 

 factors, the more important features are recorded throughout the year. Two standard 

 rain gauges have been placed on each area. In addition, a tipping bucket rain gauge, 

 located midway between the two erosion areas, records the amount and duration of each 

 storm, as well as the rapidity of the rainfall. Snowfall measurements are taken at regu- 

 lar intervals of from 7 to 10 days throughout the winter season. In the spring before 

 thawing occurs a detailed snow survey is again made. In this way the annual and the 

 monthly precipitation on each area are known and the intensity and duration of the indi- 

 viduar rainstorms accurately recorded. 



The temperature and wind velocity are recorded by means of the thermograph and the 

 anemometer, respectively, in the usual way. Temperature, like precipitation, is taken 

 throughout the year, while the wind velocity is recorded only during the main growing 

 season. 



46360°— 18— Bull. 675 2 



