AN EQUATION FOR ESTIMATING THE (R) USLE SLOPE STEEPNESS FACTOR, S

Abstract

Currently three equations are used for calculating slope steepness factor for the revised universal soil loss
equation (RUSLE); one for slopes less than nine percent, the second for slopes equal or greater than nine
percent, and the third equation that has been proposed for use in China for slopes equal or greater than 17
%. The three equations have linear relationships between slope steepness factor, S and the sine of the slope
angle, q. The three equations under predict the factor, S when used on slope steepness beyond the data sets
used to develop them. In addressing this problem several alternative forms of equations (linear, power, and
polynomial) were tested using field plot soil loss data gathered by several researchers in different countries
for slopes ranging from three percent to 55 %. A single power function relating the sine of the slope angle, q
to the slope steepness factor, S has been identified to be more suitable and accurate for estimating the RUSLE
slope steepness factor, S.