Detection of the filling phases of the Grand Ethiopian Renaissance dam using sentinel-1 SAR data

The Grand Ethiopian Renaissance Dam (GERD) is regarded as one of the most critical water issues in downstream countries. While the GERD offers hopeful development chances for Ethiopia, the reduced flow of the Nile would exacerbate Egypt's current water shortage. Many stress factors are of particular interest for Egypt include population growth, global warming, economic expansion, and groundwater depletion. These factors represent significant challenges in the use and management of the primary water resource of the Nile Basin. The purpose of this study was to monitor the two phases of filling the GERD reservoir using VV polarized SAR data and ALOS global DEM. To achieve this aim, 14 scenes of Sentinel-1A imagery were processed using SNAP Toolbox. To automatically extract water bodies, a histogram of backscatter values (dB) in the VV band was developed to determine the optimal threshold value that separates water from non-water features. From our analysis, we observed that the pixels of backscatter values (dB) in the VV band lower than −18 dB were classified as water pixels. Also, the results showed that the volume of water at the GERD reservoir increased by approximately 4.12 billion m3 during the period from August 2, 2020, to July 28, 2021. Our findings demonstrated that the overall accuracy for Sentinel-1 SAR data was 97% and the kappa coefficient was 0.94. This study confirmed the efficiency of using SAR data to monitor the changes in the water volume during the filling process of the GERD reservoir and its impacts on downstream countries.