Estimation of Groundwater Potential in Njikoka, Anambra State, Southeastern Nigeria Using Resistivity and Pumping Test Method

Abstract

Onyenweife, Geraldine Ifesinachi and Mgbolu Charles Chinedu

The research, which is focused on the prediction of aquifer parameters was carried out in order to highlight the essence of better knowledge of the groundwater sustainability of Njikoka and environs using a geophysical approach (Cooper-Jacob’s method modified by David, 1959). Two (2) vertical electrical sounding (VES) in all the six (6) towns that made up Njikoka and environs, which resulted in twelve (12) VES locations. From VES obtained, geoelectric sections of the locations were modelled and aquifer information of the study area was inferred as thus; hydraulic conductivity, transmissivity, longitudinal conductance, transverse resistivity, thickness, depth to water table from mean sea level (MSL), and resistivity. Suitable software IPI2WIN was used to plot the apparent resistivity against the electrode spacing values obtained from the litho units of the subsurface. The VES curve types produced from the area show thus; A, H, K, AK, and KH, which was very useful to calculate the spatial percentages of the aquifer distribution in the study area. The geoelectric section delineated three (3) to five (5) layers of different lithology and aquifer depth from the surface level ranging from 15 m to 100 m with prevalently unconfined water saturated sands. The aquifer average resistivity value varied from 37 Ωm to 3451 Ωm throughout the study area. Two locations were chosen for pumping test exercises VES 3 and VES 9 whose data helped to calculate the proportionality constant K�? = A, needed to estimate the transmissivity and hydraulic conductivity quantity. The two important aquifer parameters were calculated to be thus; transmissivity values ranged from 0.28 m2/ day to 22.54 m2/day and the hydraulic conductivity varied from 0.003 m/day to 0.9 m/day. Only part of Enuguagidi showed evidence of little groundwater potential with 8.33% whose transmissivity and hydraulic conductivity rating were low fairly good and well-structured clay respectively, while the majority of the aquifer layers with 91.67% were classified as poorly structured clayey in transmissivity and hydraulic conductivity hence poorly productive aquifer zones. This is in consonant with the geology of the area under study.

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