STEEPNESS OF SLOPE 1 77 



the lower portions and fill up the channels. The water may 

 overflow for a time and then take a new course. The prevention 

 of such erosion lies chiefly in the proper reestablishment and 

 preservation of the plant cover on watersheds where the flow 

 originates. 



FACTORS INFLUENCING EROSION 



Several factors contribute to the action of erosion, the chief 

 of which are (i) steepness of slope (topography), (2) type of 

 soil, (3) rainfall, (4) melting snow, (5) winds, and (6) vegetative 

 cover. 



That he might ascertain the effect of the more important 

 of these factors and be able to suggest rational means of pre- 

 venting and controlhng erosion, the author initiated in 191 2 

 a special erosion study at the Great Basin Grazing Experiment 

 Station, in the Wasatch Mountains of central Utah.^ Two 

 areas as nearly similar as possible in topography, soil, cHmatic 

 conditions, and vegetation were selected. The areas chosen 

 were located at an elevation of 10,000 feet and were on the 

 same slope. The soil was of Hmestone origin and varied in 

 depth from a few inches to several feet. The area known as A , 

 however, had a somewhat steeper slope than the area designated 

 as B, and the vegetative cover was less dense than on the 

 latter. 



Steepness of Slope. — The steepness of the slope of the lands 

 is one of the most important factors affecting the occurrence of 

 erosion. Under the influence of a given rainstorm lands having 

 a steep slope and a particular kind of plant cover will undergo 

 much more erosion than lands of the same soil type and plant 

 cover that have less slope. Thus, if the estabhshed formula 

 is appHed, namely, that the transporting power of water varies 

 directly as the sixth 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. Then, too, the larger the flow the 

 greater is the velocity of that flow. 



1 Sampson, Arthur W , and Weyl, Leon H., "Range Preservation and its Re- 

 lation to Erosion Control on Western Grazing Lands." U. S. Dept. of Agr. Bui. 

 675, 1918. 



