Effect of hydrologic soil groups on runoff generation in reservoir catchments in Northern Ghana

Abstract

The study was carried out in northern Ghana to estimate surface runoff in nine (9) reservoir catchments for a period of 20 years (1999–2018) using the United States Department of Agriculture Natural Resource Conservation Service-Curve Number (USDA-NRCS-CN) method. The key input parameters of the method were hydrologic soil group, antecedent moisture condition, rainfall amount, landuse/landcover, weighted curve number and potential maximum soil moisture retention. The annual rainfall within the reservoir catchments was found to vary between 617.2 and 1,382.3 mm. The estimated annual runoff depths ranged from 68.5 ± 7.5 to 98.0 ± 13.3 mm and the percentage annual rainfall converted into runoff varied between 9.8 ± 0.7 and 13.7 ± 0.9 %. Hydrologic soil groups accounted for about 67.2 % and 62.5 % of the variation in runoff depth and percentage runoff respectively, in the reservoir catchments. Catchment size accounted for only 2.7 % and 3.9 % of the variation in runoff depth and the percentage of the amount of rainfall converted into runoff respectively, in the reservoir catchments. Therefore, hydrologic soil groups should be used by reservoir managers as a primary indicator of the potential runoff generation in reservoir catchments.