Sediment Yield and Soil Erosion Assessment by Using an Empirical Model of MPSIAC for Afjeh & Lavarak Sub-Watersheds, Iran

Watershed degradation due to soil erosion and sedimentation is one of the major environmental problems in Iran. With respect to the relatively suitable compatibility of MPSIAC model to the arid and semiarid conditions of Iran and lack of hydrometric station in region, we employed the "modified PSIAC model" to estimating of sediment yield and providing sediment yield map in these sub-watersheds. The MPSIAC method incorporates nine environmental factors that contribute to sediment yield of the watershed, this factors are: surface geology, soil, climate, runoff, topography, ground cover, land use, channel and upland erosion. Open-source Geographic Information System (GIS) was used to facilitate the spatial interpolation of the nine model factors and interpretation of predicted sediment yield for the entire watersheds. At first, to enter the available raw data into the GIS framework we digitized the nine factors of maps. In the second stage, digitized maps were encoded with respect to the values of each factor and then these factors of maps were summed together, and finally sedimentation score map was provided. We applied (QS) equation on the sedimentation score map and finally related map was obtained. Various formations basically contain Shaly, Sandstone, Conglomerate and tuff lithology, covered this region more than igneous rocks. The results show that the most values of erosion are in Shaly, Marly, weathered Tuff and alluvial diposites parts of sub-watersheds correlated with sensitive formations such as Karaj and Quaternary sediments. Based on sediment yield map of MPSIAC model, more than 75% of the total sub-watersheds area was classified at class IV of erosion category with high sedimentation. Sub-basin’s erosion were calculated as 769.3 and 583.21 m2/km3 per year for each Afjeh and Lavarak sub-basins by MPSIAC model, respectively. Linear regression analysis between MPSIAC model results and two of most influencing factors on erosion, the geology and soil erodibility indicated that there was a significant correlation. The results of this paper suggested that the model is suitable for predicting yearly average sediment yield of the Iranian watersheds with similar conditions.