Sedimentation is a major problem of Dam reservoir service life reduction. Ayet-Wuha reservoir is located in Delanta Woreda, South Wollo Zone, Amhara region, Ethiopia for a purpose of irrigation development. This reservoir has no pervious study on its sediment deposition. Now, the amount of sediment deposition in reservoir has been surveyed using range line bathymetry survey system. The reservoir topography data was collected that surveyed in 2014 G.C year before dam construction and bathymetry survey data surveyed in January, 2023 G.C. The number of bathymetry data and pervious topography data is 2861 points and 891 points respectively. Those collected data processed, TIN Model surface developed and volume difference executed for amount of sediment deposition in the reservoir under ArcGIS 10.1.The reservoir has accumulated 9.02*104 m3 volume of sediment during six year service time. If the sedimentation runs according to the above rate of sediment; the estimated 22.82*104 m3 dead storage volume will be reached after 9.3-year service. However, the excavated material from reservoir is 6.52*104 m3 volume and this will raise the service life to 13.64 year. The reservoir catchment area has 31.28 t/ha/yr specific sediment yields. This deposition has 0.72% annual storage loss rate of the reservoir and this value falls within global estimated range. KEY WORDS: Sediment, Reservoir, Deposition, Bathymetry, Arc GIS.