MODELING WATER YIELD AND WATER BALANCE OF LOWER BENUE RIVER BASIN FOR SUSTAINABLE WATER MANAGEMENT

The use of hydrologic models to predict the relevant processes occurring within a catchment will serve as a veritable tool for water managers and planners for a sustainable management of water resources especially in the absence of quality and reliable data. The Soil and Water Assessment Tool (SWAT), a physically based semi-distributed hydrological model interfaced with MapWindows GIS software was used to simulate the different components of water balance and estimation of water yield of the Lower Benue River Basin in Nigeria. Climate data of three weather stations; Lokoja, Makurdi and Ibi located close to the catchment were used to simulate the stream flow of the catchment. The model was calibrated and validated using measured streamflow at Makurdi gauging station and subsequently used to predict the water balance and water yield of the catchment. Model evaluation gave R2 value of 0.79 and RSR of 0.45 for the calibration period, while R2 of 0.74 and RSR of 0.51 were recorded for validation of the model indicating a reasonable agreement between the measured and simulated flows. The prediction of water balance showed that more than a third of the water loss from the catchment is due to evapotranspiration. Sub-surface flow accounted for over 50% of the water balance simulation, while stream flow yielded only 10% as a result of the shallow slopes of the study area. The maximum water yield recorded in the study area occurred in 2009 with a value of 162,862mm representing 8.74% for the 20 year period while the lowest water yield for the period occurred in 2015 with 45,458mm representing 2% of the total water yield for the period. Overall, results show a progressive reduction in streamflow and precipitation since 2012 in the catchment and 2015 recorded the least values for the period of study. These findings show that SWAT is a viable tool for predicting future scenarios for water resources management in the catchment.