Journal of Watershed Management Research

Topographic factor is an important factor of computer models of USLE family due to the high sensitivity of model results to its variation and complicated effects of topography on soil erosion. Moore and Wilson (1992) have introduced a well-known method to compute LS factor of RUSLE model using digital elevation model (DEM).The objective of this study was to determine the proper cell size of DEM for computing LS factor in a 7116 ha area, in Rashakan region at the southern part of Urmia. DEM models with cell sizes of 30, 50, 75,100, 200 and 400 m were prepared in ArcGIS 10 environment and the raster based maps of LS were derived from each DEM model based on Moore and Wilson method. Spatial dependence of the LS factor was analyzed and the proper cell size of DEM model was selected based on the degree of spatial dependence. Results showed that the spherical model explain the spatial pattern of  LS factor and the DEM model with 75 m cell size has the strongest spatial dependence (0.523) and the highest coefficient of variation (0.983). As a result, in this region DEM with 75 m cell size is suggested as a proper cell size to compute LS factor based on Moore and Wilson method.