Estimation of borehole yield using vertical electrical sounding data: a case study from Kwabre District
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Date
May, 2017
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Abstract
Groundwater has been identified as the world’s largest resource that can be easily accessed especially when confronted with water shortages as a result of low river discharges. Successful execution of groundwater exploration using geophysical methods requires knowledge on the relationships that exist between hydrogeological and geophysical parameters. This makes data interpretation and delineation of groundwater zones easier, thereby avoiding the drilling of marginal holes. This study was carried out in the Kwabre District and was aimed at establishing a relationship between airlift yields and electrical resistivity parameters. Three methods, viz. borehole log analysis, cumulative resistivity method and the drilling rate with respect to formation analysis, were employed to obtain resistivity (rho) and thickness of the saturated zones from borehole logging and vertical electrical sounding data. The obtained resistivity and saturated thickness were used to compute transverse resistance (Tr) and longitudinal conductance (Sc). Each of these parameters (i.e. Tr and Sc) including the resistivities of the saturated zones were further correlated with airlift yields of the boreholes to evaluate their relationships. Also, the airlift yields were used to create a yield map of the district. Correlation results obtained from the borehole log analysis and cumulative resistivity method suggest there is no relationship between the airlift yield and the resistivity parameters. On the other hand, results obtained from the drilling rate with respect to formation analysis showed that the yield versus resistivity, longitudinal conductance and transverse resistance are related by 60.85%, 57.16% and 50.25% respectively. However, validations of the associated models were very poor in predicting measured airlift yield values. Thus, further studies may be required to improve and validate the method. This study also provided useful information on the variation of airlift yields in the district.
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A Thesis submitted to the Department of Geological Engineering, College of Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the degree of Master of Science.