Detailed knowledge of the hydraulic characteristics of an aquifer system is very essential for the management of groundwater resources. Conventionally these characteristics are determined through the conventional pumping test method often carried out in water wells. However, there is a dearth of accurate and reliable pumping test data in the study area as carrying out pumping tests at a number of sites may be costly and time consuming. The application of geophysical methods in combination with pumping test using the Dar-zurrock parameters therefore provides a cost effective alternative to the estimation of hydraulic parameters from wells. For this reason, surface geosounding data have been used for evaluation of the hydraulic characteristics of the aquifer system of the Middle Imo River Basin, Southeastern Nigeria. Forty (40) Schlumberger Vertical Electrical Soundings (VES) were carried out in various parts of the study area using a maximum electrode separation of 1000metres. Four of the soundings were made at existing boreholes for parametric purposes. The VES data were processed using a combination of curve matching techniques and computer iterative modeling using the OFFIX software. Aquifer hydraulic characteristics were estimated using the concept of Dar-Zarrock parameters. Results of the study revealed that the hydraulic conductivity ranges from 1.08m/day to 37.04m/day in areas underlain by the Benin Formation; and 0.409m/day to 5.21m/day in areas underlain by the Ameki Formation. Transmissivity values on the other hand ranges from 61.9m2/day to 1558.4m2/day in areas underlain by Benin Formation: and 1.41m2/day to 413.89m2/day in areas underlain by the Ameki Formation.
Keywords: Hydraulic characteristics, geo-sounding data, Dar- zurrock parameters, aquifers, Nigeria,
Over the years, access to safe drinking water has posed a major challenge to developing countries of the world. More than half of the rural populace in Nigeria owes their source of drinking water to untreated rain and surface water sources. Groundwater however remains the only realistic and affordable source of potable water across much of the country.
The sedimentary sequences of Southeastern Nigeria including those of the Imo River basin are known to contain several aquiferous units (Uma, 1989). However several boreholes in the area have become unproductive due to complexity in the geology of the area. Although numerous boreholes abound in the Imo River Basin, there has not been any systematic and comprehensive study to establish the nature and distribution of the aquifers beneath the basin (Uma, 1989).
An accurate groundwater resource assessment and a quantitative description of aquifers have become imperative in other to address several hydrological and hydro-geological problems associated with groundwater management. Fluid transmissivity, transverse resistance, longitudinal conductance, hydraulic conductivity and aquifer depth are fundamental properties describing subsurface hydrology. As a result, many investigation techniques are commonly employed with the aim of the estimation of spatial distribution of the above mentioned hydraulic parameters. Field estimations of the above parameters are not always available. Hydraulic conductivity appears to be the most problematic to obtain because of either the great range of observed values or the unsatisfactory laboratory measurements.Traditionally, one of the most effective ways …
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