Methodology for estimating the topographic factor LS of RUSLE3D and USPED using GIS

In the RUSLE3D (Revised Universal Soil Loss Equation–3D) and USPED (Unit Stream Power-based Erosion Deposition) models, the effects of topography on soil loss are represented by the combined factor LS, where L is the slope length factor and S the slope gradient factor. The problems with measuring slope gradient and length over large areas are i) they are not always estimated correctly, and ii) different ways are used for their calculation. GIS (Geographical Information Systems) software has several algorithms for estimating topographic parameters included in the equations of LS. The objective of this research was developing a methodology for LS calculation using GIS, in order to define the most accurate algorithm for each parameter. For the estimation of S and upslope contribution area (~ L), the Zevenbergen and Thorne algorithm and the Deterministic Infinity algorithm, respectively, were selected.