Regional Sediment Yield Estimate for Abbay River Basin

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Addis Ababa University


Abbay basin is one of the largest basins of the western drainage system located in the north west of Ethiopia. It accounts 17.5% of land area and 50% of annual average surface water resources of Ethiopia. It is also characterized by high population pressure, improper land-use planning, over dependency on agriculture as source of livelihood, which is causing deforestation, overgrazing, expansion of agriculture to marginal lands and steep slopes. These have resulted in declining agricultural productivity and resources use conflicts in many parts of the Abbay basin. As a consequence of poor land use practices and improper management systems there are high soil erosion rates, sediment transport, and loss of agricultural nutrients. The total soil eroded within the landscape in the Abbay Basin is estimated to be 302.8 million tones per annum. In contrary, currently the government has multitude plan to implement development projects with regard to Irrigation, Hydropower and water supply to ensure food security and sustainable development. Therefore, knowing the estimate of annual sediment withdrawal is important in the planning, design and operation of water resources development projects. Generally, this study is aimed at conducting regional sediment yield estimates for Abbay River basin using statistical multiple regression relationships based on catchment characteristics and Rainfall. Sediment yield of about 27 selected sub basins/stations are computed from suspended sediment concentration (SSC) and daily flow records. Other factors affecting sediment yield (catchment area (A), precipitation (P) is obtained from rainfall data of the station, whereas vegetation index (VIDX), slope index (SLDX), soil index (SIDX) are catchment characteristics determined by running SWAT2005 for the basin. The statistical multiple regression models, for estimating the regional sediment yield is applied, using sediment yield, precipitation and catchment characteristics data once the selected sub basins are regionalized. Hence the regression parameters are obtained for the regression equation with coefficient of determination near to unity. Generally the equation developed will give preliminary sediment yield estimate for concerned individuals, institutions, stakeholders, etc for any water resource development project.



Regression relationships