Modelling the water balance of Ouémé catchment at the Savè outlet in Benin: contribution to the sustainable water resource management

Abstract

The present modelling study carried out on the water balance of Ouémé catchment at the Savè outlet (23,000 km 2 ), had its main objective as to assess the water availability of the basin. To achieve, the agro hydrological model SWAT (Soil and Water Assessment Tool) was used. With this model the Hydrological Response Units (HRUs) were generated and used as spatial units for the evaluation of all water balance components and transport of soil particles. Within the SWAT model, surface runoff has been estimated by the runoff curves number method. Soil water was measured by the method of routing with storage and the actual evapotranspiration has been quantified using Penman - Monteith method. Meanwhile, the erosion in this catchment has been estimated with the modified universal soil loss equation. Digital elevation model (DEM), soil characteristics, vegetation parameters, climate data and farming practices were the principal data of the study area that have been integreated into the model. After the model calibration and validation, it was realised that runoff, actual evapotranspiration and the total groundwater recharge represent respectively 7.8 % ; 73 % and 18.8 % of the total annual rainfall. Regarding erosion, an average value of 4.4t/ha/a was obtained for the watershed with a maximum value for the croplands with ridges parallel to the slope (20/ha/a) whereas plots with ridges perpendicular to the slope have showed 9.3t/ha/a. Using these results some suggestions have been made for a sustainable water resources management.