Compression of Efficiency of MPSIAC and EPM Models to Estimate Soil Erosion and Sedimentated Yield (Case Study: Ghareh Aghach Watershed)

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 Modified Pasific South West Inter Agency (MPSIAC) and Erosion Potential Method (EPM) models and apply GIS to minimize the probable errors in evaluation of soil erosion and sedimentation in Ghareh Aghach watershed extends 8962.25 hectares in Semirom province. The field data used in this study was collected in frequent field visits in 2007-08. To achieve variables models, digitalize topographic map in 1:25000 scale, digital evaluation model, slope map, aerial photos of 1:40000 scales, geological, geomorphologic, vegetation cover, pedagogical and land use maps were used. In frequent field visits all the necessary data from MPSIAC and EPM models were collected, checked and improved in 5 Hydrological units (sampling units). Following of finalizing the information layers, all of them were integrated to create the final soil erosion sensitivity map for each Hydrologic unite and vegetation type. The results of MPSIAC model indicated that 60.8% (5444.28 ha) of the total watershed area was classified at class III of erosion category with medium sedimentation and 39.2% (3510.36 ha) was classified at class IV of erosion category with high sedimentation, respectively. Basin erosion was calculated as 71169.5 and 4222294.2 ton/yr by MPSIAC and EPM models, respectively. The result for basin sediment was 29260.42 and 61725.03 ton/yr, respectively. Thereafter, very high erosion class was found for EPM model under study. The results of statistical compare of erosion of MPSIAC and EPM models in hydrologic unit (sampling unit) by real erosion measure show that, there is no significant different between erosion estimate by MPSIAC model and real erosion measure at level of 1% and 5%, but the erosion estimate by EPM model have a significant different at level of 5%. Thereafter, very high erosion class was found for EPM model under study. Due to not fully compatible tables for EPM model and its subjective nature, one can conclude that MPSIAC model may have better performance.