Characterization of aquifers in Offa and environs, southwestern Nigeria, and implications on productivity
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Date
2021
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Water Utility Journal, E.W. Publications
Abstract
Borehole water is currently the most important source of water both for irrigation and domestic uses due to limitations such as inconsistency in availability and impaired quality associated with other sources of water. However, efficiency of boreholes is dependent on several factors that vary in space. 30 boreholes within Offa and environs have been evaluated with a view of determining their properties and relate them with borehole efficiency, establishing regional classification of boreholes and defining groundwater flow pattern(s). This was achieved through analysis of drilling
and pumping test data of existing boreholes. 30 Vertical Electrical Soundings (VES) were conducted using Schlumberger array in order to determine geoelectric layers and fracture attributes. Geophysical investigation revealed three to four geoelectric layers which are inferred to be sand, laterite, weathered aquifer, and basement rocks. The frequency of curve types obtained are KH (50.00%), H (36.67%), QH (10.00%), and K (3.33%). Results of borehole aquifer characteristics showed that the depth of well varies from 23.86 - 46.17 m, static water level ranges from 2.04 -11.22 m, discharge rate varies from 15.74 - 93.57 m3/day and drawdown varies from 3.5 - 19.98 m. Pumping test results revealed that transmissivity vary from 0.33 m2/day to 19.45 m2/day, with an average value of 2.84 m2/day, indicating aquifer of negligible to high potentials, hydraulic conductivity value vary from 1.13x10-2 m/day to 1.0x10-1 m/day, while the specific capacity value ranges from 1.07 m3/day/m to 21.89 m3/day/m which shows that the performance of boreholes in the study area varies from good to moderate. From the statistical evaluation, it was inferred that there are strong relationships between the following pairs of parameters; specific capacity and discharge, drawdown and depth of borehole, hydraulic conductivity and transmissivity. Pearson’s correlation revealed that specific capacity against drawdown has a negative correlation which suggests an inverse relationship between the parameters.
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Keywords
Borehole; groundwater; Offa; geophysical; aquifer; hydraulic conductivity.