Impacts of Land-Use Change, Associated Land-Use Area and Runoff on Watershed Sediment Yield: Implications from the Kaduna Watershed

An uncontrolled sediment influx from the watershed upstream is a known threat to dam stability, while the pattern and amount of sediment yield are influenced by the predominant upstream land-use and land cover (LULC) types, precipitation amount, and intensity. Hence, the need to monitor sediment yield accumulation and its controlling factors in dam operation becomes crucial. In this paper, the Soil and Water Assessment Tool (SWAT) was used to assess the roles of land-use change, land cover area, and runoff on watershed's sediment yield based on change detection analysis between 1975 and 2013 in the Kaduna Watershed (Nigeria), Western Africa. The SWAT standard procedures for the simulation of hydrological characteristics and sediment yields prediction were adopted. The datasets were calibrated for a period of 46 years and validated using 2015-2017 measured flow data, and suspended sediments concentration (SSC) acquired between March and October 2018. The model function was statistically determined using the Nash-Sutcliffe (NS), the coefficient of determination (r(2)) and the percentage of observed data (p-factor). The evaluation results of the SWAT model yielded NS, r(2) and p-factor of 0.71, 0.80, and 0.86, respectively. These data suggest that the model performed satisfactorily for streamflow and sediment yield predictions. Findings suggest that the extinction of evergreen forests and a significant change in land-use from range grasses and forest to agriculture generic and residential types between 1975 and 2013, which resulted in surface runoff, sediment yield, and flow alteration. Evapotranspiration increased by 22.40% between 1975 and 2013. These changes have negatively impacted the watershed runoff by 56.00% and model sediment yield by 68.00% at the end of 2013. Thus, these variations can influence various human activities in the watershed, such as food security, livestock, energy production and water supply. It is hypothesized from the presented data that land use types exact a more dominant control on runoff and sediment yield than land cover area, although climatic influence may not be ruled out.