Effects of watershed delineation on the prediction of water quality parameters in Gaa Akanbi area, Ilorin

Abstract

Watershed delineation is a required step when conducting any spatially distributed hydrological modelling. The prediction of water quality parameters in a basin entails delineation of watershed into different number of sub-basins. Thus, this research evaluated effects of watershed delineation on the prediction of water quality parameters in Gaa Akanbi area of Ilorin, Kwara state, Nigeria. The objectives are to model and predict water quality parameters in the watershed; delineate the selected watershed in various numbers of sub-basins and study the effects of watershed delineation in the prediction of water quality parameters of the basin. For proper implementation of this study, Geographical Information System (GIS) software, physically based watershed model - Soil and Water Assessment Tool (SWAT) and other data processing software were used. Since the model is physically based, the surface properties (i.e. Digital Elevation Model (DEM), stream network, digital soil map, digital land use and land cover map, climatic and hydrological data) served as input in the model. The model was daily for a period of 30 years (i.e. January 1991 to December, 2020). The results showed that the watershed was successfully delineated to 3,7,11,21,32,53 sub-basins. Also, it was noted that the predicted values of water quality parameters (Nitrate, organic phosphorus and sediment concentration) are directly proportional to increase in the number of sub-basins delineated in the watershed.