Estimation of Reservoirs Sedimentation Using Bathymetry Survey:  Case Study on Tagel Night Storage Reservoir, Lake Tana Sub Basin, Ethiopia

Reservoir sedimentation is a serious problem that affects the life of reservoirs. Because it reduces the original capacity of the reservoir significantly which in turn affects irrigation, hydropower, and drinking water supply activities. This study was conducted in the Tagel night storage reservoir in the Upper Blue Nile basin to estimate reservoir sedimentation and life of the Tagel night storage reservoir using a bathymetric survey. Comparison of initial reservoirs capacity and present capacity were done to estimate reservoir sediment deposition. The present capacity was obtained by a bathymetry survey developing of TIN surface and analyzing the volume of the reservoir. Sedimentation reduced reservoir capacity from an initial value (design storage) of 32294 in 2012 to 27054 in 2020. The result showed that Tagel Night Storage Reservoir has lost on the average 16.2% of its capacity due to sedimentation in 8 years of operation period. Based on the bathymetry survey result, the average sedimentation rates in live storage zones are found to be 655 m 3 /year with a 2.1% annual rate of loss. At the current rate of sedimentation, the storage of the Tagel Night Storage Reservoir will be completely lost by sedimentation in 49 years.