Sedimentation assessment using hydrological simulation and bathymetry survey: The case of river Amissa drainage basin, Ghana

Studies on freshwater bodies in Ghana for their sustainability are mostly concentrated on a few large rivers. However, other equally important rivers that do not attract research attention provide varied services and benefits to inhabitants and living organisms in their riparian communities. The basin of River Amissa as a major source of freshwater supply for several communities within its catchment has undergone various changes due to rapid socioeconomic and increasing anthropogenic disturbances. This consequently has led to increased sediment yield on the reservoir beside the river and the river basin itself. Hence the need to estimate the amount of sediment accumulated in the reservoir and in the river's catchment for their sustainability and management purposes. Sediment yield in the reservoir and the river basin were estimated using a bathymetric survey integrated with Geographic Information System (GIS) and the Soil and Water Assessment Tool (SWAT) hydrological model respectively. Results from the bathymetric survey estimated the current capacity of the reservoir to be 4,321,060 m³. Reservoir storage capacity lost to sedimentation was 1,438,940 m³ representing 25% of the reservoir volume. Additionally, the SWAT (Arc SWAT) performance was very good with Nash-Sutcliffe efficiency coefficient (NSE) for calibration and validation being 0.88 and 0.84 respectively. For the entire 28-year period, simulated sediment yield increased by 10,263 tons per kilometer square.