Estimation of aquifer productivity and groundwater recharge from single - well pumping test

Abstract

Due to the abrupt variations in lithology and structures associated with crystalline basement terrains of southwestern (SW) Nigeria, reliable evaluations of aquifer properties are essential for the management and protection of groundwater resource. For this purpose, single-well pumping and recovery tests were carried out in wells within the various bedrock terrains of Ibarapa region of SW Nigeria to evaluate the discharge, drawdowns, storage capacity, transmissivity, recovery rate and other well inventory with the aim of evaluating sustainable groundwater yield within the diverse geological terrains of the region of study. From the results, the average (av.) groundwater discharge (in m³/day) for wells in areas underlain by amphibolite was 72.05; 53.45 in gneisses; 68.27 in migmatite and 64.33 in granitic terrains. In the respective order of geological settings, the total drawdowns in wells were 10.70 m, 21.99 m 17.69 m and 15.58 m and transmissivities (in m²/day) were 6.85, 2.57, 0.76, 1.72, while specific capacity values (in m³/d/m) were correspondingly; 7.67, 3.10, 4.00 and 5.54.  The recovery tests showed that wells in granitic terrains were characterized by better water recharge than in other terrains. However, groundwater yield in amphibolite and to a lesser extent in gneisses were quite sustainable and the rates of groundwater recovery though moderate sustained continuous discharge for hours of continuous pumping. It is therefore mandatory to develop a reticulation system in this region so as to cater for water supply in areas underlain by granite and migmatite at the central and north-eastern part of the study area.