Dams are usually built to achieve water storage for irrigation, hydropower generation, flood control, navigation, urban water supply, and environmental purposes. But the purpose of dams is affected by a universal phenomenon, called sedimentation. Lack of current data on reservoir capacity loss due to sedimentation is one of the challenges to the sustainable management of reservoirs. This study shows the capacity loss due to sedimentation from 2017 to 2022, and estimated useful life of Ayet Weha reservoir. The main objective of this study was to evaluate the rate of sedimentation and remaining capacity of Ayet Weha reservoir using a bathymetric survey and Arc-GIS 10.3 According to the result of tin difference reservoir capacity decreased from original volume 2.09Mm3 to 1.93Mm3 due to sediment deposition. But In terms of volume, because of 65,216.56m3 volume of clay material is excavated and transported from the reservoir area for dam core material (ANRS Bureau of Water, 2017) during construction due to this the total accumulated sediment between year 2017 and year 2022 is estimated to be in the magnitude of 93,958.44m3 total volume in Six years. Assuming a constant rate over the period, the annual sedimentation rate becomes 15,660m3 per a year. Assuming a constant rate over the period, the annual sedimentation rate becomes 15,660m3/year. As per this rate, the annual reduction in storage capacity due to siltation is about 0.75%. This value is below globally estimated annual rate of siltation of reservoirs (1%). The ASC curve was developed for the two survey periods, to show the spatial distribution of sediment in Ayet Weha reservoir using Arc GIS 10.3 software. Based on bathymetry survey result the sediment yield and specific sediment yield of Ayet Weha watershed are 15,898.20t/yr. and 25.14t/ ha/yr respectively. Also the study indicated dead storage volume will be reached after 10.7-year of reservoir operation whereas reservoir life when 50 percent of the original capacity is filled up by silt remain 60 years starting from 2023. Key words: Bathymetry survey, Sediment yield, Useful life, TIN model, ASC, capacity loss, ARC GIS.