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Influence of Bedrocks on Hydraulic Characteristics of Weathered Basement Aquifers: A Case Study from Ibadan, South-Western Nigeria

Analyses and interpretation of aquifer tests carried out on 21 boreholes drilled into the weathered regolith aquifers within Ibadan metropolis, SW-Nigeria were carried out with emphasis on aquifer characterization on one hand and assessment of the influence of bedrock types (i.e. banded gneiss, augen gneiss, and quartz-schist) on the hydraulic characteristics on the other hand. The study approach involved assessment of borehole data inventory as well as evaluation of pumping and sludge tests data, based on which principal hydraulic properties (such as transmissivity, hydraulic conductivity, and specific capacity) of the weathered regolith/fracture crystalline aquifer were estimated. The borehole data revealed varied regolith thickness of 21.6 – 60m (mean 36.2m) in banded gneiss, 12.1 – 68m (mean 47.7m) in augen gneiss, and 60 – 87m (mean 66.4m) in quartz-schist. The average saturated thickness varies from 30m in banded gneiss to 42.2m in augen gneiss and 62.6m in quartz-schist, while the observed yield is generally low with average value of about 80.8m3/d in all the three bedrock settings. The estimated average specific capacity (Sc), range from 5.6m3/d/m in the banded gneiss to 13.8m3/d/m in the augen gneiss and 5.2m3/d/m in the quartz-schist. However, the estimated transmissivity (T) range from 1.1 – 4.2m2/d (mean 2.8m2/d) in banded gneiss, 0.76 – 27.2m2/d (mean 7.3m2/d) in augen gneiss, and 0.41 – 10.6m2/d (mean 2.7m2/d) in the quartz-schist. Further evaluation of overall measured and estimated aquifer parameters show that the augen gneiss setting exhibits higher hydraulic potentials compared to banded gneiss and quartz-schist settings. Nonetheless, weak correlations (R =<0.1) of the yield and Sc with respect to saturated aquifer and total regolith thicknesses are indications of the dominant influence of the interplay of bedrock geology and hydraulic characteristics on the infiltration process and aquifer recharge characteristics of the weathered basement aquifer.

Auteur(s) : Moshood N. Tijani, Alichi U. Alichi and Seybatou Diop
Pages : 23-33
Année de publication : 2018
Revue : Journal of Mining and Geology
N° de volume : 54(1)
Type : Article
Mise en ligne par : DIOP Seybatou