Abstract

This research is aimed to modify erosion potential method (EPM) so that its dependency reduces to engineering judgment as well as broadly watershed visit by applying geographic information System (GIS). This study was carried out within acceptance of existing structure and framework of EPM model. In EPM model, the sediment production is evaluated in terms of four parameters including soil and rock resistance to erosion, land use, observed erosion process coefficients and average slope of the surface. The coefficient of soil and rock resistance against erosion is achieved from soil and geology maps and the mean slope is concluded directly from digital elevation method. But, the observed erosion process and land use coefficients are determined based on qualitative approach. Therefore, the parameters are strongly depended upon personal experience and how quality the watershed has been visited. The calculation methods to estimate the last two coefficients can be supported through introducing and applying of new parameters which are derived in our model entitled modified EPM (MEPM). In MEPM, the observed erosion coefficient is quantified based on climatic index, canopy percentage, drainage density and surface geology factors and the land use coefficient is quantified by using canopy percentage and slope. At first stage, the new formulations to derive the modified coefficients including the observed erosion and land use coefficients are adjusted with the same coefficients in existing EPM model and at second stage the results of MEPM model are verified with observed values at "hydrometric station" in the case study. Bakhtiari river watershed was chosen to implement MEPM model. The MEPM model was calibrated in four basins with observed data.

Key words: Erosion, Bakhtiari river watershed, canopy percentage, erosion potential method (EPM), modified EPM (MEPM), geographic information system (GIS).