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The double whammy of increasing human water consumption and the effects of warming world is poised to further shrink large lakes, especially in arid and semi-arid regions. Further, reservoir sedimentation remains a critical challenge to global water security, causing a progressive loss in storage capacity and disrupting the ecological balance of downstream river systems. The motivation of the present study is based on the fact that at present reservoir managers are dependent upon expensive hydrographic surveys to locate the sedimentation impacted area, which cannot be conducted as and when required due to financial constraints. Further, the recent floods in the Indian state of Punjab (August 2025) were related to intense rainfall, sudden sediment inflow, resulting in drastic reduction in the storage capacity of the reservoirs.This study presents a comprehensive geospatial framework on assessment of elevation-area-capacity relationships of Ukai reservoir. The method uses multi-temporal optical and SAR satellite imageries (Landsat-9, Sentinel-2 and Sentinel-1) and corresponding altimetry water level data to delineate the water spread areas (contours) at varying elevations. Two different time-periods (historical, 2008-2010 and 2021-2022) were compared to assess the change in contours. The results of sedimentation assessment clearly show an expansion in water boundary extent in recent years compared to that in the past decade. Additionally, the findings reveal that over the last decade Ukai reservoir’s live storage capacity has significantly declined by ~200 MCM, indicating ~20 MCM annual sedimentation rate. The spatial analysis distinctly maps the geographical areas of sediment accumulation or erosion and show that the sediment change is not uniform.