SUMMARYThe study area of Mashhad-Chenaran, measuring 223989.7 acres, is the largest and most important subbasin of Kashafrood. This area consists mostly of mountains and plains with variable slopes. The study area is an uneven land type and thus prone to soil erosion. Various practical methods have been developed to study soil erosion both qualitatively and quantitatively, but most of them do not accurately process information regarding soil erosion. Therefore, it is essential to confirm the credibility of these methods by investigating the results yielded by examinations compared with measured quantities taken from watersheds of Iran. The importance of the practical role of soil maps in evaluating erosion and sedimentation must also be considered. In this study, both MPSIAC and EPM were used to estimate erosion and sediment yield. Sediment measuring stations showed a rate of 2.74 t/ha per year; however, the MPSIAC model showed a rate of 1.56 t/ha per year and the EPM model showed a rate of 5.73 t/ha per year. Both the EPM and MPSIAC models were created in countries with climates and geology attributes that differ from those of Iran. Hence, the coefficients and factors affecting erosion do not correspond precisely to the conditions in Iran.

In most parts of Iran, due to population growth, deforestation, over-grazing of pastures and other factors, soil erosion is more than the world's average and increase as time passes. Therefore, its correct evaluation is very important. The Mashhad-Chenaran is the biggest and most important sub-basin of Khorasan, with an extension of about 223989 acres. Two models, the MPSIAC and the Erosion Potential Method-EPM (Gavrilovic, 1972), used for evaluation of sediment amounts and soil erosion stations showed 2.74 t ha-1 per year. However, the MPSIAC model showed 1.56 t ha-1 ; whereas the EPM model showed larger amounts of 5.73 t ha-1 per year. In soil erosion studies in watersheds, researchers have often introduced hydrological units of work. In this research, physicalgeographical factors such as geological factors, soil type, vegetation, slope were utilized in the erosion estimation models used in addition to the hydrological units in the land components. The present study attempted to measure the erosion and sediment in hydrological units (sub-basins) and land components. The accuracy of estimates of erosion was tested; in order to ensure that the accuracy of the results or possibly the superiority of the homogeneous units to the hydrological units is ensured, it can be used in the same areas in the future.