Modelling the hydrological balance of the Okpara catchment at the Kaboua outlet in Benin

Abstract

Rapid population growth and industrial development create problems with water management that can lead to contamination and scarcity of water resources. The primary aim of the modeling in this study was to assess annual renewal rates of water resources and erosion rates in the Okpara catchment at the Kaboua outlet. The SWAT 2003 model was selected as the most appropriate for the purpose of this study; it was calibrated and validated for the study basin. Digital elevation model, daily climatic data for 1968-2007, soil and land use maps, physical characteristics of soil, physical parameters of crops were all incorporated in the model that divided the whole catchment in to sub-basins and Hydrological Responses Units (HRU). Calibration and validation of data demonstrated that precipitation in the watershed was 1,075.8 mm/a. Surface runoff was 106.6 mm/a (10% of precipitation), and the total recharge of aquifers was 225.4 mm/a (21% of precipitation). The actual rate of evapotranspiration was 759.8 mm/year (71% of precipitation). The total volume annually produced in the catchment was about 4 billions m3 ; this amounted to more than 500 times the needs of the population, but paradoxically it still suffered from severe water scarcity. Regarding erosion, an average value of 7t/ha/year was obtained for the watershed with a maximum value for cropland (16.85t/ha/a) and the minimum value for bushed savannah (0.64t/ha/a). Moreover, agricultural practices most susceptible to reduce soil loss were those ridges perpendicular to a slope. Based on these results, some suggestions were made for more sustainable use of land and water resources in the catchment.