Swat based soil erosion modeling Case study nashe watershed, ethiopia

Abstract

Soil erosion modeling is a significant tool for viable conservation of natural, agricultural and built up environments. In this thesis, Soil Erosion modeling of Nashe watershed was done to assess where and when soil erosion potentials has occurred. The study was carried out using SWAT model with GIS interface.. The general objective of this study was to estimate spatial and temporal patterns of soil erosion of Nashe watershed physical based SWAT model. The SWAT (Soil and Water Assessment Tool) with GIS interface which is used to delineate the watershed and extract networks for sub basin watershed. This study assess sediment yield from Nashe watershed at outlet. The stream flow was calibrated for eleven years (1991- 2001) and validated seven years (2002-2008) at Nashe station using SWAT-CUP to estimate performance of the model. The suspended sediment was generated by rating curve to compare with sediment suspended simulated by SWAT and showed that acceptable result. In addition, from simulated suspended sediment by SWAT, sediment yields simulated for sub-watershed. Based on simulated sediment yields prone soil erosion of watershed were identified. The model was successfully calibrated and validated for flow to estimate sediment yield. The model performance for calibration and validation also has been evaluated by using statistical parameters. Flow calibration gave coefficient of determination (R2 ) and Nash-Sutcliffe simulation efficiency (ENS) 0.79 & 0.75 respectively. Flow validation gave 0.71 and 0.65 for R2 and ENS values respectively. Both calibration and validation results indicate that the observed values show good agreement with simulated flow. The SWAT model yields average annual sediment of 60.97 ton/ha for study area. The annual sediment yield of Nashe sub basin has been obtained from stream flow simulated results. Sediment yield from each sub watershed were also determined and prone soil erosion area has been identified. The erosion prone area which needs immediate soil and water conservation measure in Nashe watershed was identified. The sub watershed (75-150 ton/ha sediment yield) has been identified as Severe soil erosion prone area, priority were needed for conservation measures