Variation In Computing The Length Factor In The Universal Soil Loss Equation

The universal soil loss equation, A = R*K*L*S*C*P, estimates average annual soil loss A based on rainfall (R), soil factor (K), length factor (L), slope (S), effective cover factor C, and a practice factor P. In teaching the use of the relationship, students can find values of R on maps, soil factor in tables based on a soil classification readily available in soil surveys, slope S may be estimated from the topographic map of the site., the cover factor C may be ascertained based on a specified crop rotation and the erosion handbook and the practice factor P may be determined from the erosion handbook for specified conservation practices such as terracing, contouring, etc. One source of variation in estimates is to arrive at meaningful slope length L. The erosion handbook suggests that one look for the length of the steepest segments of slope in the typical field of variable slope but leaves to judgment the actual quantification. The paper will report on the variation in techniques that students and professionals learn and use when asked to implement this procedure. A new approach for making a quantitative estimate of the length factor will be presented and compared with research data.