Investigating reservoir sedimentation for two micro earth dams in the Ethiopian Highlands.

Abstract

Reservoirs serve multiple purposes, such as providing water for irrigation and domestic use, flood control, and hydropower generation. However, they are prone to sediment accumulation due to watershed erosion. Understanding erosion and sedimentation processes is essential to determine sedimentation rates and identify factors contributing to these issues. Various methods exist for estimating sediment delivery, and this study employed a bathymetric survey to assess sediment deposition and erosion in the Anjeb and Abrajit reservoirs. Additionally, RUSLE was used to simulate watershed sedimentation. The findings revealed significant differences in sediment impoundment between the reservoirs, with noticeable bathymetric changes due to sedimentation. Both reservoirs were found to be heavily silted before reaching their intended lifespans.

The RUSLE analysis estimated annual soil loss at 1374.71 t/km²/y for Abrajit and 1518.23 t/km²/y for Anjeb, much lower than the bathymetric results of 9362.29 t/km²/y and 12889.61 t/km²/y, respectively. The soil loss rates and spatial patterns align reasonably well with records and prior studies. In 2013 and 2021, Anjeb's capacities and sediment volumes were 1.0720 and 0.9534 Mm³, respectively, with an estimated live storage capacity loss of 0.119 Mm³. The long-term average annual sedimentation rate was 12,889.61 t/km²/y for Anjeb (8 years) and 9,362.29 t/km²/y for Abrajit (13 years). Bathymetric surveying revealed average annual storage losses of 11.12% for Anjeb and 4.5% for Abrajit.