Groundwater recharge using baseflow recession analysis in Southwestern Nigeria

Abstract

Baseflow recession analyses of Yewa and Ona rivers were carried out with a view to determining and comparing groundwater recharge in parts of the sedimentary and Basement Complex terrains of Southwestern Nigeria. Daily discharges of the rivers for ten years (1988 – 1997) were analysed. Groundwater recharge in Yewa Basin, located in a sedimentary area was 27.3 mm while that in Ona Basin, which is mostly urban and located within the Basement Complex, was 63.6 mm, representing 2.3% and 5.3% of the annual precipitation of the study area respectively. Baseflow were 21.5 mm and 65.3 mm, representing 34% and 8% of the average annual total runoff of Yewa and Ona rivers respectively. Ona Basin had a comparatively lower groundwater recharge than Opeki Basin (with 137.4 mm), which is in a similar terrain but in a rural environment of Southwestern Nigeria, indicating the negative effects of vegetation clearing and developmental activities, typical in urban environments, on infiltration and consequent increase in direct runoff and reduction in groundwater recharge. Identification and preservation of groundwater recharge areas, especially in urban environments, is therefore imperative in the sustainable management of groundwater in the study area.

 Keywords: Groundwater Recharge, Baseflow Recession Analysis, Yewa Basin, Ona Basin, Opeki Basin, Southwestern Nigeria