Tracking The GER Dam Impoundment Stages Using SWOT and Other Radar Altimetry Products

Monitoring of inland water bodies is considered crucial for effective water resource management. In this study, a combination of satellite imagery and altimetry products was utilized to monitor changes in water level and surface extent during the different operational filling phases of the Grand Ethiopian Renaissance (GER) Dam. The primary objective was to utilize diverse remote sensing products to provide an accurate estimation of water volume changes over time. Sentinel-1 data were processed using an unsupervised edge Otsu algorithm to map reservoir extents. These output maps were validated against Planet and Sentinel-2 water masks, and a high level of agreement was observed, with overall accuracy values ranging from 0.97 to 0.99. Furthermore, various Surface Water and Ocean Topography (SWOT) satellite products were evaluated for the estimation of reservoir extents. It was found that the SWOT Lake Single Product performed poorly, with an Intersection over Union (IOU) value of approximately 0.33 being recorded. In contrast, moderate agreement with validation sets was demonstrated by the SWOT water mask raster and pixel cloud products, with overall accuracy values ranging from 0.78 to 0.89 being observed. Volume variation across different dam operational phases was estimated through the application of satellite-based observations and a DEM contouring method. Although a high correlation (R² value of 0.98) was exhibited by both methods, significant differences in absolute values were identified (RMSE value of 2736.35 km³). These discrepancies are attributed to a potential scaling error and the inherent water slope present within the GER Dam reservoir.