Erosion and Sediment Yield Modeling- Application of Soil and Water Assessment Tool (A Case Study of Bilate Watershed-SNNPR)

Abstract

Abstract Land degradation caused by soil erosion has become one of the major constraints-of agricultural development in Ethiopia threatening the well being of many people living in rural areas under subsistence agriculture. Moreover, erosion has become one of the most serious problems in areas of water development due to silt loads in irrigation canals, diversion structures and storage reservoirs. Effective watershed planning requires understanding of runoff and erosion rates at the plot, on hill slopes, and at small catchments scales and how these vary spatially and temporally in the watershed. Therefore to account for this spatial and temporal variability of the watershed hydrologic characteristics, Soil and Water Assessment Tool (SWAT) has been used to model the hydrologic variables (suface run off, sediment yield, sediment load, etc.) at Bilate watershed. Therefore the main aim of this thesis is to identify the potential erosion sensitive areas that have critical sediment generating sub watersheds that actually demand immediate management treatment to minimize or even to stop the risk of erosion. The model was calibrated and validated against measured flow and sediment data at Alaba Kulito outlet of Bilate watershed. Except manual stream flow calibration where the calibration efficiencies are found to be poor, the overall calibration and validation results showed model efficiencies within the permissible limit, and this in turn showed a good match between measured and simulated flow as well as suspended sediment load of the watershed (See sections 4.4 and 4.5). simulated flow as well as suspended sediment load of the watershed (See sections 4.4 and 4.5). identified and three management scenarios, i.e., using field filter strips, foresting or planting grass and contour bands have been suggested to minimize or alleviate erosion hazards of these critical sub watersheds in particular and the watershed in general. Therefore the sediment yield reduction due to 5m filter strips is 59.2%; due to 1 Om filter strip is 72. 7%; that due to contour bands is about 50% and 100% land Lise improvement (afforestation) could yield ne9ligible sediment.