SIMULATION OF SEDIMENT YIELD AT THE UPSTREAM WATERSHED OF JEBBA LAKE IN NIGERIA USING SWAT MODEL

Abstract

In this study, we focused on the applicability and suitability of Soil and Water Assessment Tool (SWAT) embedded in Geographical Information Systems (GIS) environment in the prediction of sediment yield of a watershed (12,992km2 ). The watershed is drained by Rivers Niger, Kontagora, Awun and Eku and is located at the upstream of Jebba Reservoir in north central Nigeria . SWAT was run daily for 26 years (1985 to 2010 ) using climatic data representing three weather stations located within the watershed. The model was calibrated and validated using measured flow data from 1990 to 1995. Also due to the unavalilability of observed sediment data for the area, sediment samples were collected from three locations in the watershed from May to December, 2013 using suspended sediment sampler USDH-2A. The sediment samples were analysed and used to spatially calibrate and validate the model. The model was statistically evaluated using coefficient of determination, R 2 and Nasch-Sutcliffe Efficiency, NSE. Evaluation of the model revealed that it performed satisfactorily for stream flow and sediment yield predictions in the watershed. The model predicted the annual sediment yield in the watershed as 255.8 tons/ha/yr producing about 8.31x 109 tons of sediment between 1985 and 2010. Sediment concentration (mg/l) in the reach during the period of simulation showed that the highest sediment concentration was obtained in subbasins 29, 20 and 19 with values 446.3, 376.8 and 365.4 mg/l respectively. However, lowest sediment concentration occurred in subbasin 73 with a value of 108.6 mg/l. The results from the study showed that a properly calibrated SWAT embedded in GIS environment is suitable for modelling the hydrology and predicting the sediment yield in a watershed. In the light of this, SWAT can be adopted by water engineers and hydrologists in Nigeria and other sub sahara Africa countries in the region as a decision support tool to assist policy makers in achieving sustainable sediment and water management at watershed level.