Abstract

In the past decades many different models are used for estimating rates of soil erosion and sediment yield in various watersheds. In this research, for prediction of soil erosion in the Lateshur Watershed, semi-quantitative methods, such as FSM (based on scoring of five factors including lithology, vegetation, topography, gully erosion and the shape of basin) and PSIAC (based on nine factors including surface geology, soil, climate, runoff, topography, vegetation, land use, types of erosion and river erosion and sediment transport) are used. The Lateshur Watershed is a part of Central Iranian drainage basin located in northeast of Tehran Province. This watershed has an elongated form and its surface area is more than 22.2 km². Geologically, It is a part of Central Alborz Zone and consists of marl, limy marl (Neogen red beds) and conglomerate (Quaternary alluvium). Based on these models, the calculated rates of erosion were 318.4 and 779 ton/km²/year, respectively. Also, based on 12 years data, the calculated rate of soil erosion for this watershed is about 498 ton/ km²/ year. Finally, the rates of predicted sediment yields from semi-quantitative methods (FSM and PSIAC models) shows that these models had given a difference results from the real rates of sediment yields in the study area. Our studies show that the FSM model gives close results to the statistical analysis of real than PSIAC model. Therefore, we believe that the FSM model can be used in other drainage basin similar to Lateshur in Iran and similar basin (lithologically and climatologically) in other parts of the world.

Keywords: Soil erosion, Semi quantitative methods, FSM & PSIAC models, Watershed