Modelling of streamflow before and after dam construction in the Mono River Basin in Togo-Benin, West Africa

The sub-tropical region of West Africa is not only vulnerable to the negative effects of climate change but also to the changes in land management. The goal of this study was to model streamflow in the Mono River Basin (MRB) for the period before (1964-1986) and after (1988-2011) dam construction. The Soil and Water Assessment Tool (SWAT) using input data such as a digital elevation model, soil and land use, and daily climate data model was set up, calibrated and validated for the period before dam construction (SIM1) and after dam construction (SIM2). The model sensitivity analysis, calibration and uncertainty analysis were performed based on daily observed streamflow using the Sequential Uncertainty Fitting procedure (SUFI-2) algorithm. The change in seasonal and annual streamflow between SIM1 and SIM2 was assessed and linked with land use/cover change between 1975 and 2000. The SWAT model shows satisfactory performance with Kling-Gupta Efficiency (KGE) >= 0.60 and percent bias vertical bar PBIAS vertical bar <= +/- 20 during calibration and KGE >= 0.50 and vertical bar PBIAS vertical bar <= +/- 15 during validation of SIM1 and SIM2. The results further showed that the construction of the dam affected the hydrological system of the catchment with a change in annual average streamflow between SIM1 and SIM2 of -14.13%, -19.86% and 3.66% at Athieme, Tetetou and Corrokope stations, respectively. The simulated average streamflow amplitude of SIM2 has decreased globally compared to SIM1. Therefore, the changes detected in land use/cover may have affected the average streamflow in response to the difference in amplitude simulated streamflow of SIM1 and SIM2. The finding of this analysis demonstrated that the impacts of dam construction on streamflow are challenging and crucial for water resource management in MRB.