SWAT based evaluation of the effect of land use/ land cover change on reservoir sedimentation (Case study in watershed of Ribb reservoir, Ethiopia)

Abstract

The land and water resources of the watershed and the ecosystem are in danger due to the rapid growth of population, deforestation, overgrazing, soil erosion, sediment deposition, water logging and flooding. The upper Ribb watershed is one of the most affected areas by soil erosion, sediment transport and land degradation. The lack of decision support tools and limitation of data concerning weather, hydrological, topographic, soil and land use; are factors that significantly hinder research and development in the area. There is a need for hydrological and sediment transport research on the RIBB watershed that can improve catchment’s management programs and increase effective use of RIBB irrigation dam which is under construction. In this paper the influence of land use changes on catchment’s hydrology is observed particularly on sediment yield. By putting sediment yield estimation in the Lake Tana basin, at Ribb reservoir catchments and sediment yield analysis of Ribb catchment under different land use scenarios as a main objectives. To carry out this, using modeling tools will help to save the physical quantity of the land under study and time. So SWAT MODEL, one of the common models in this area was used for simulation. Two scenarios are developed to observe the impact of land use changes on reservoir sedimentation. Then Watershed delineation, Model calibration and validation were done at upper Ribb gaging statin by using the model. In addition to this the model efficiency was checked at this station. Based on this values for coefficient of determination (r²) and Nash– Sutcliffe model efficiency (ENS) were found to be in the acceptable range i.e. greater than 0.75 for all cases. The result obtained from the model based on the above method was the annual sediment load at RIBB irrigation dam site increase by 24% from 1986 to 2006 because of the land use change. So to use the Ribb irrigation dam as per the design land use management practices are mandatory in the future to prevent further increase of sediment yield of the catchment.