EPM Approach for Erosion Modeling by Using RS and GIS

Lack of information to prepare erosion maps for quantitative and qualitative sediment evaluation is a major need in watershed management in Iran. The goal of this study was to use EPM model and apply GIS to minimize the probable errors in evaluation of soil erosion and sedimentation in Ghareh Aghach watershed in central part of Iran. To achieve this goal, in the first step a topographic map in 1:25000 scale of the study area was digitalized by ILWISE program to provide a contour map. Using the contour map, the slope and aspect maps as well as the digital evaluation model (DEM) of the site were prepared. In the second step the satellite images, aerial photos of 1:40000 scale and data obtained from the field visits were used to provide with geological, geomorphologic, vegetation cover, peddological and land use maps of the study area. By integration of geological, geomorphology facieses and slope maps and classifying them in 5 categories (0–10%, 10–20%, 20–30%, 30–40% and >40%), 21 homogenous uniform sampling units were identified to apply EPM model. Model information layers comprised of nine effective factors in erosion and sedimentation in the watershed site were obtained by digitalizing and classifying the basic information data in GIS program. In frequent field visits all the necessary data for EPM model were collected, checked and improved in 21 homogenous and uniform sampling units. Following of finalizing the information layers, all of them were integrated to create the final erosion map. The results of EPM model for homogenous and uniform sampling units indicated that 0.19% (16.69 ha) of the total watershed area was classified at class I of erosion category with very low sedimentation and 15.1% (1352.64 ha) was classified at class II of erosion category with low sedimentation and 41.3% (3698.8 ha) was classified at class III of erosion category with medium sedimentation and 13.2% (1175.3 ha) was classified at class IV of erosion category with high sedimentation and finally 30.2% (2711.41 ha) was classified at class V of erosion category with very high sedimentation, respectively. The result of comparing erosion and sediment values by EPM model with measured values showed that no significant difference between estimated and measured values (P<0.05).