Abstract
Kennedy O. Achilike
The aim of the study was to estimate the hydraulic characteristics of aquifers in Owerri and some selected towns in Imo State from surface geophysical techniques. Sixteen (16) Schlumberger vertical electrical soundings (VES) were carried out with maximum current electrode separation (AB) of 400 m. The data was acquired using R-plus resistivity meter and processed with Resixtm Interpex Software.
The results of the VES interpretation identified 3-5 geoelectric layers overlying the aquiferous layers: surface soil, lateritic earth, the fine-medium-coarse grained sands with intercalations of clay which constitute the water bearing zone. The curves identified in the study area include HK, KHK, KQQQ, KQHK, AAKH, HKHK, AKHK and HAAK. The results of the qualitative interpretation indicate that majority of the field curves terminated as Kshaped and Q-shaped type curves.
The general shapes suggest that the transverse resistance of the aquifers can be considered as the dominant parameter for the estimation of transmissivity in the study area. The main aquiferous zones occur between the 4 th and 6th geoelectric layers with a resistivity range of 409.5 - 12704.7 ohm-m, depths range varying from 39.37 – 207.30m, and layer thickness range between 28.14 and 176.70m.
The hydraulic characteristics of the aquifer estimated from the geoelectric parameters revealed that the aquifer has protective capacities of between 0.008 and 0.085 mhos, transverse resistance ranges from 39573.3 – 1.911E + 06 ohm-m2 , transmissivity values from 1132.26 - 105211.12 m2 /day and hydraulic conductivity ranges from 11.72 – 2448.77 m/day.
The estimated aquifer transmissivity values suggest that aquifer materials are highly permeable to fluid movement within the aquifer. This study has demonstrated the efficacy of surface geophysics in estimating hydraulic characteristics of an aquifer where pumping test data are not available and also its vulnerability to surface contaminants.
PDFShare this article