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Saturated hydraulic conductivities (Ks) and textural characteristics of soil have been determined by infiltration and particle size distribution tests, respectively, at 56 sites. These soil tests were conducted in the B-horizon during a groundwater resources survey in the Tarkwa area, Ghana. It was observed, in general, that extremely poorly sorted soils exhibited low porosity and relatively higher Ks, while relatively better sorted soils revealed high porosity and low Ks values. The range of Ks of the soils is from 10-5-10-8 m s-1, although the overwhelming majority is in the 10-6-10-7 m s-1 range. Tarkwaian soils are mainly silty sands with minor lateritic patches, which are located on hilly terrain underlain by Banket Series and Tarkwa Phyllite rocks. Banket soils are located mainly on hills, which act as groundwater recharge areas and exhibit the most favourable characteristics for infiltration in the area, in terms of both particle size distribution and Ks values. The preponderance of the Banket soils implies that they are the best medium for groundwater recharge in the area and can be expected to act as fair-yielding regolith aquifers in favourable areas. Huni and Kawere soils located in low-lying areas display characteristics suggesting that the Huni, with a much better sorting coefficient and Ks value, will admit more precipitation for recharge compared to the Kawere. Baseflow indices, determined for four catchments in the area, all reveal low storage characteristics in the range of 17-33%, reflecting a strong influence of the textural properties of soil. The moisture content of the soils varies from about 10% in the Banket gravels to 22% in dykes, while field capacity and permanent wilting point are estimated at 20-25% and 7-9% by volume, respectively. The pH of the soils varies from very acidic to moderately acidic, that is 1.72-5.01. The lowest pH values are associated with felsic dykes and are caused by the presence of welldisseminated fine pyrite crystals, which are expected to be a potent source for acid rock drainage when found in the unsaturated zone. Inference from Atterberg limits suggests that the soils are kaolinitic, the area is wed drained and water is likely to exhibit relatively dilute concentrations of major solutes. © 2002 Elsevier Science Limited. All rights reserved.
Author(s): Kuma JS, Younger PL
Publication type: Article
Publication status: Published
Journal: Journal of African Earth Sciences
ISSN (print): 1464-343X
ISSN (electronic): 1879-1956
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