Reservoir sedimentation evaluation using remote sensing and GIS approaches for the reservoirs in the upper Blue Nile Basin

Abstract

The present study aimed to evaluate the temporal dynamics of water stored in a reservoir using satellite remote sensing data integrated with a GIS application. The study is carried out in three reservoirs, which include Koga, Shina, and Selamko reservoirs located in the upper Blue Nile Basin. The techniques used to carry out this study have been pre and post-processing of Landsat images, modeling and identifying water pixels, evaluating reservoir capacity, and compression of results with recent bathymetric survey data. The Normalized Difference Water Index (NDWI) has been also employed to determine open water features and to improve the presence of water pixels in satellite imagery. Percentage Difference Area Index (PDAI) and Normal Difference Area Index (NDAI) techniques have been used to assess the deviation of storage area from satellite remote sensing, topo of bed elevation, and bathymetric survey. Results indicated that the Koga reservoir storage capacity has reduced from 83.10 to 81.179 Mm3, showing an annual storage loss of 0.33% (2009–2016). For Shina and Selamko reservoirs, annual storage loss due to sediment depositions is found to be 2.53% and 2.13% in a span of 9 and 11 years, exceeding the annual average worldwide rate for reservoir sedimentation of 1%. The findings of the study showed that the sedimentation problem was relatively severe as compared with the findings of most other studies of similar reservoirs in other parts of Ethiopia. The area needs some intensive soil and water management strategies for sustainable use of the reservoirs in the Blue Nile Basin. To regain the storage capacity of the reservoirs, it would be proposed to adopt manual and or mechanical dredging with flushing for de-silting the deposited sediments, especially in Shina and Selamko reservoirs.