RANGE PRESERVATION AND EROSION CONTROL. 11 



In correlating the meteorological data with stream flow from melt- 

 ing snow it was found that the stream flow follows very closely the 

 fluctuations in temperature. The relative behavior of these factors 

 is shown in figure 2. The flow increases with the rising temperature 

 of the day and reaches the maximum at practically the same time, 

 that the mercury is at the highest point. The flow practically ceases 

 between 8 p. m. and 10 p. m. and remains practically at zero during 

 the cooler hours of the night, only to rise again with the increased 

 temperature of the following day. High winds are found greatly to 

 increase the rate of evaporation of the snow cover, but they affect the 

 run-off relatively little. 



Any medium, such as an effective vegetative cover, which serves 

 to insulate the heat from the snow cover, breaks the effect of high, 

 dry winds, and at the same time intercepts the run-off more or less, 

 will tend to conserve the snow, regulate run-off, and make possible 

 the absorption of a larger amount of water. This fact has been 

 demonstrated on the wooded portion of the selected areas as well as 

 on the extensively denuded, sparsely vegetated, and timbered lands 

 on the forest generally. 



To sum up the facts concerning the action of melting snow : Ero- 

 sion from melting snow is a more serious factor than generally sup- 

 posed when the vegetative cover is sparse and the slope steep. Both 

 run-off and erosion from melting snow vary in intensity more or less 

 directly with the character of certain climatic factors, especially tem- 

 perature. In general, the soil is not frozen under a cover of a few 

 inches of snow if the latter falls before cold weather early in the 

 winter; so whenever melting takes place erosion may occur unless the" 

 soil is held firmly in place. The most rapid melting of snow and 

 the most serious erosion occur where there is a lack of vegetation. 

 In general, snow lies the longest on timbered lands. 



RAIN. 



An examination of the accompanying tables showing rainfall and 

 the resulting run-off, or lack of it, disclosed several interesting facts. 

 In the first place, out of the 26 rainstorms for the year 1915 (Tables 

 1, 2, 3), distributed over the four months from June to September, 

 inclusive, only one storm — that of July 21 — produced run-off. At 

 this time, according to the record of the four rain gauges, 0.70 and 

 0.71 of an inch of rain fell on area A and 1.48 and 1.38 on area B, 

 within a period of 65 minutes. From area B the run-off was 335 

 cubic feet and it carried 94 cubic feet of air-dry sediment, as com- 

 pared to 3,019 cubic feet of run-off on area A and 717 feet of air- 

 dry sediment (fig. 3). It should be kept in -mind that the run-off 

 from area A was enormously greater than on area B in spite of the 



