Impact of Landuse Changes on Soil Erosion and Sedimentation in the Tono Reservoir Watershed Using GeoWEPP Model

Abstract

Sediment delivery from the Tono Reservoir watershed in the Upper East Region of Ghana is of major concern, necessitating the need to estimate the rate of siltation of the reservoir. This study determined the current volume of silt in the reservoir, mapped landcover changes using Landsat images and employed Water Erosion Prediction Project (WEPP) model, to simulate hydrology and sediment dynamics for three landuse/landcover scenarios. The Geo-spatial interface for WEPP (GeoWEPP) was used to characterize upland overland flow elements based on their landuse/landcover, soil, and slope profiles. Using characteristics obtained from GeoWEPP as inputs for the WEPP model runoff fluxes, soil loss rates, and sediment delivery ratio (SDR) for three environmental scenarios: landuse/landcover with agricultural lands under fallow tilled management (Scenario 1), landuse/landcover with agricultural lands under corn, soybean no till management (Scenario 2), landuse/landcover with non-agricultural lands under shrub-perennial (Scenario 3) were estimated. Over the simulated 29-year period; runoff depth, soil loss rate and SDR were estimated to be 118.4 mm, 22.8 t/ha, and 0.68 for Scenario 1; 94.6 mm, 2.8 t/ha, and 0.31 for Scenario 2; and 57.7 mm, 0.6 t/ha, and 0.92 for Scenario 3. Shrubland had decreased by 8 %, bareland area had increased by 9.1 %, and the reservoir area had also decreased by 3.7 %. The study indicates landuse/landcover change impacts significantly on land degradation and hydrology of the Tono reservoir and subsequently accounts for the reduction in reservoir capacity by about 1.74 % on annual basis observed through the bathymetric survey.