Streamflow and sediment yield prediction using AnnAGNPS model in upper ebonyi river watershed, South-eastern Nigeria

Abstract

Sediments resulting from soil erosion are the major non-point source pollutant of surface waters in agricultural watersheds. Annualized Agricultural Non-Point Source Pollution Model (AnnAGNPS) is a computer-based watershed model that predicts non-point source pollutants and runoff loadings within agricultural watersheds. AnnAGNPS v5.2 was used in conjunction with ArcView 3.2 GIS to predict streamflow and sediment discharges from a 1700 ha or 17 km² Upper Ebonyi River watershed located at Obollo-Etiti in Udenu Local Government Area in Enugu State, South-eastern Nigeria. AnnAGNPS predictions were compared with two months (September and October) of streamflow and sediment discharge field measurements from the study watershed. The September data were used to calibrate the model to a reasonable agreement with predicted data (R² = 0.9341 for streamflow and R² = 0.7066 for sediment yield). Statistical performance evaluation of the model was carried out on the validation results. The model performed very well in following the trends, peaks and volumes of the measured hydrograph and sediment graph, with R² = 0.9908 for hydrograph and R² = 0.9675 for sediment graph. The results show that the model performed better in predicting runoff than predicting sediment yield.