Comparative assessment of aquifers in a typical karst sedimentary system, South-West Nigeria

The necessity of hydraulic assessment of groundwater system for practical application in any lithospheric environment cannot be overemphasized. The subject matter includes formulae to quantitatively appraise the hydraulic parameters influencing the water-yielding capacity of boreholes which tap a typical sedimentary karst rock mass. Pumping test was carried in a total of 25 boreholes each from different autonomous residential communities around 4 towns within Ewekoro Local Government Area to quantitatively appraise the hydraulic parameters influencing the water-yielding capacity of boreholes abstracting water from a typical sedimentary karst rock mass. The measurements were carried out at a controlled rate and water-level response was measured separately from Wasinmi, Itori, Ewekoro and Papalanto. The rise in water levels was recorded as residual drawdowns΄, and the water level measured at a residual time t΄ after the pump has been turned off. Hydraulic properties were estimated with discharge, drawdown and specific capacity data. The values of the hydraulic parameters are consistent with what obtains in the sedimentary aquifer. The average measured values of the basic and estimated hydraulic parameters are: borehole depth, 51, 50.36, 60.32, 95.36 m; specific discharge, 4.0 × 10-2 , 5.0 × 10-2 , 4.0 × 10-2 , 5.0 × 10-2 l/s; specific capacity, 6.3 × 10-3 , 7.0 × 10-2 , 6.0 × 10-3 , 5.0 × 10-2 m 2 /s; well loss constant, 5.98 × 104 , 4.30 × 105 , 6.16× 102 , 5.19 × 103 s 2 /m5 ; transmissibility, 94.8 m2 /s respectively recorded for Wasinmi, Itori, Ewekoro and Papalanto. Further research should employ precise, quantitative data concerning requisite geologic information about sedimentary rock aquifer system.