Runoff and sediment yield modeling using WEPP in a semi-arid environment (Case study: Orazan Watershed)

Water erosion is a major environmental problem in many parts of the world. Majority of semi-arid countries are concerned because of their specific climate and soils sensitivity, but also because of the recent intensification of human activities and agricultural practices. Accurate estimation of water erosion for various land-use and climate scenarios is so an important key to define sustainable management policies. In the last decades, several studies have been carried out to build models suitable for quantifying sedimentation. Among these models, the Water Erosion Prediction Project (WEPP), is a physically based, distributed-parameter model that has been developed and mainly validated in America. Only few studies have investigated its applicability to environmental conditions that differs from those where the model was developed. The aim of this work is to test the efficiency of WEPP model to predict runoff and sediment yield at catchment scale in a semi-arid area. Continuous simulations have been conducted between 1996 and 2005 in Orazan Watershed. Comparison between predictions and measurements indicates that WEPP under-estimates sediment volumes of 23% and over-estimates runoff volumes of 27%. Results shows that sediment yield and Runoff outputs are relatively well predicted but lack of input data to run WEPP model is an important challenge in Iran conditions.