Sediment Yield Estimation Using SWAT, Case Study of Upper Awash Basin, Ethiopia

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Sediments are very important parameter component in many water resource projects for studies of reservoir sedimentation, river morphology, soil and water conservation planning, water quality modelling and design of efficient erosion control structures. High sediment rates leads to filling of reservoirs and loss of live storage, which eventually commanding to loss of production potential. Furthermore, evacuation of sediments from reservoirs is a costly process that can have large environmental impacts. The Soil and Water Assessment Tool model, a physically based distributed hydrological model, was used to estimate sediment yield and runoff in the upper awash basin measuring of 11073 km 2 catchment area. The basin shows large heterogeneity in terms of hydrological parameters, land use land cover and soil features. This research has been undertaken to analyse the sediment yield at the outlet of the catchment and effects of LULC changes on sediment yield and flow values. The model has been calibrated and validated using observed runoff and sediment yield data of 11 years at the basin outlet. The average values for RSR and Nash-Sutcliffe efficiency (NSE) for sediment yield are found to be 0.67 and 0.66 and the average values for RSR and Nash-Sutcliffe efficiency (NSE) for run-off are found to be 0.71 and 0.71, which are within good limits for sediment and good limits for runoff respectively. So the overall average annual output for sediment at the out let point was estimated, which is 5167400Met ton/month or 0.046667 ton/ha/month is model monthly output. High sediment reduction was observed when agricultural land changed to cropland/savanna/bush land and the value of sediment is 0.03182 ton/ha from overall catchment because cropland/savanna/bush lands are denser than agricultural land. Here appropriate mitigation measures were recommended to reduce sediment yield of the catchment. As land development is a continuous process, for the optimum use of the land and water resources of the area, it is recommended that soil and watershed conservation practice should be undertaken in order to keep the sustainability of the reservoir conserning sediment reduction.



Sediment Yield, runoff, land use/land cover change, SWAT Model, Upper awash watershed, Ethiopia