Soil erodibility is a measure of the susceptibility of a given soil to erosion by rainfall and runoff. The soil types on a particular site can be identified using the maps included in published soil surveys. Soil surveys are available from the Natural Resources Conservation Service. The topographic factors L and S are used to adjust the erosion rated based upon the length and steepness of the slope. The erosivity of runoff increases with the velocity of the runoff water.
Steep slopes produce high runoff velocities.
Soil loss increases with increasing slope due to the greater volume of runoff accumulating on the longer slope lengths. The slope length is the distance from the point of origin of the runoff to the point where the slope steepness decreases sufficiently to cause deposition or to the point where runoff enters a well-defined channel. The cover and management factor, C, is the ratio of soil loss from land use under specified conditions to that from continuously fallow and tilled land. The USLE was developed for use on agricultural fields. It is adapted to use in nonagricultural conditions by appropriate selection of the C factor.