Modeling-Impact of Land Use/Cover Change on Reservoir Sedimentation (Case Study on Omo-Gibe Basin, Gilgel Gibe III Watershed, Ethiopia)

Abstract

Impacts of land use/cover change on water resources are the result of complex interactions between diverse site-specific factors and offsite conditions; standardized types of responses will rarely be adequate. The knowledge of how land use/cover change influence watershed hydrology will enable local governments and policy makers to formulate and implement effective and appropriate response strategies to minimize the undesirable effects of future land use/cover change or modifications. In this research SWAT model was used for analyzing the land use and land cover change of the watershed and its impact on reservoir sedimentation. The main objective of the research was to model the hydrological processes that will predict the impact of land use/cover changes on soil erosion and sedimentation in the Omo-gibe basin. In this paper the influence of land use changes on catchment’s hydrology is observed particularly on sediment yield. The delineated watershed was divided into 62 sub basins and 372 HRUs by the model. Model calibration and validation was done at Abelti station. In addition to this the model efficiency was checked at this station. Based on this values for coefficient of determination (r²) , Nash–Sutcliffe model efficiency (NSE) and percentage of bias (PBIAS) were found to be in the acceptable range for 1990 and 2010 land use land cover maps in both calibration and validation period. To analyze the impact of land use change on sediment yield different comparison criteria were applied. The first was selecting sub basins having higher sediment yield and found around the main course of the river. The second was selecting and analyzing sub basins having lower sediment yield and the third criterion was based on availability of varied land use classes specially sub basins covered by forest land. While analyzing the impact of land use/cover in all criteria using 1990 and 2010 land use/cover map, it shows an increase in sediment yield. SWAT estimated the sediment yield from the watershed to the reservoir for both 1990 and 2010 land use/cover maps. Therefore 1.1 Mtons annual sediment load was entered to the reservoir during 1990 and 1.3 Mtons annual sediment load was entered to the reservoir during 2010 land use/cover data. This shows that there is 16.57% increment of sediment yield in 2010 as compared to 1990 land use/cover data.