Evaluation of WEPP and EPM for improved predictions of soil erosion in mountainous watersheds: A case study of Kangir River basin, Iran

In the current study, WEPP and EPM models were used to estimate the amount of soil erosion and sediment in the basin of Kangir. The required data for implementation of the WEPP model were prepared in six categories including soil, climate, management, slope, drainage and reservoir based on which we took the information needed to build soil and management files. Some information such as texture, cation exchange capacity, organic matter, sand content, effective hydraulic flow and critical shear stress was used. After production of all the layers, the WEPP model was implemented using the GEOWEPP software. In this software, erosion and sediment amounts were estimated by three methods: domain, watershed and flow path methods. In the Kangir River watershed, the sediment content was 7.64 t/ha/year, 6.13 t/ha/year and 11.87 t/ha/year. Thus, the two methods of domain 7.64 t/ha/year and flow path 11.83 t/ha/year were closer to the observed sediment 10.5. Based on the EPM model, the sedimentation coefficient of the Kangir basin was 0.81. The results of the research indicate the high erodibility rate of the watershed basin. The erosion-sensitive units were located in the western and southwestern regions of the basin. In the EPM model, the erosion rate (Z) was 0.6 indicating moderate to high erodibility rate in the watershed. Furthermore, the highest erosion rate was in the western and southwestern parts of the watershed. Finally, the results of estimating soil erosion and sediment production in the watershed of Kangir illustrated that the WEPP model has a more accurate estimation of soil erosion and sediment production, and in this model, the flow path method used to estimate the amount of soil erosion and sediment production was close to the observed sediment at the hydrometric station.