RANGE PKK.SERVATTON AND EROSION CONTROL. 



15 



A significant feature to be noted from the 1916 precipitation and 

 run-off records is the fact that run-off occurred on area A as a result 

 of storms that produced no flow from area B, in spite of the fact that 

 area B received just as much or generally more rain than area A. 

 Surface conditions again account for this fact. 



Table 4 summarizes the rainfall for the two years 1915 and 1916 

 and the resulting erosion and run-off. It shows the comparative 

 effects of gentle storms and storms of unusual violence, such as not 

 infrequent^ occur in the higher mountain region of the Manti 

 Forest. From Table 4 it is apparent that of the summer rains of 

 1916, totaling 7.70 inches on area A and 8.13 inches on area B, 14 

 storms on area A and 8 on area B were effective in producing run-off. 

 In 1915 there was but one such storm, yet the erosion from this sin- 

 gle storm was very much greater than from the several storms of 

 1916. The most significant fact shown is that the per cent of sedi- 

 ment carried in the run-off is proportionately higher as the velocity 

 of the flow increases. Thus if we apply the established formula, 

 namely, that the transporting power varies directly as the six*h 

 power of its velocity, it is evident that if the velocity of a flow is 

 increased two times its transporting power is increased 64 times. It 

 is understood too, of course, that the larger the flow the greater is 

 the velocity of that flow. 



To sum up, the extent of erosion and run-off depends upon (1) 

 the rate at which the rain falls, (2) the steepness of the slope, (3) 

 the presence of well-established gullies, (4) the character of the soil, 

 and (5) the density and character of the vegetation. 



Table 4. — Run-off and erosion from rainstorms. 



Year. 



Area. 



Total 

 number 

 of storm 



days. 



Total 

 rainfall. 



Effec- 

 tive 1 

 Storm 

 days. 



Effec- 

 tive ! 

 rainfall. 



Run-off. 



Sedi- 

 ment. 



Sedi- 

 ment. 



1915 



A 



B 



A 



B 



26 

 26 

 36 

 36 



5.79 



- 6.48 



7.70 



8.13 



1 



1 

 14 



8 



Inches. 

 0.70 

 1.43 

 4.05 

 3.23 



Cubic feet. 

 3, 018. 96 



335. 15 

 2, 266. 68 



835.55 



Cubic feet. 

 716. 92 



9429 

 197. 49 



59.81 



Per cent. 

 23.70 



1915 



28.13 



1916 



8.70 



1916 



7.20 







1 Effective here refers to storms that produced run-off. 

 WIND. 



In addition to the conspicuous action of the gully or shoe-string 

 type of erosion described above, erosion caused by the action of the 

 wind more or less unif ormly over the soil surface is a factor of high 

 importance in determining the fertility of the soil under certain 

 conditions. 



Following the destruction of the vegetative cover, either entirely 

 or in part, the wind movement becomes particularly active in the 



