Evans UF, Okiwelu AA, Udoinyang EP
Geoelectrical measurement using Schlumberger electrodes array was conducted to assess the impact in-stream sand mining on hydrological system of coastal aquifers. A total of 15 VES was carried out and results were interpreted using manual curve plotting and computer software. The VES results as well as the fluctuations in groundwater level for mining and non-mining sites were compared. The variation of in-situ resistivity of geounit shows that mining sites produced mostly AK and K curve types with comparatively higher values (1042-12827 Ωm). This was contrary to the HQ and H curves with relatively lower resistivity values (162-4736 Ωm) obtained for geolayer of non-mining sites. HQ and H curve types with the associated low resistivity values, complemented with observed
low percolation groundwater level (0.22 mmd-1), and productive 4 m depth well indicate balance in hydrological level. However, AK and K curves, associated high resistivity values earth layer, high groundwater percolation (0.56 mmd-1) and non-productive 10 m deep-hand-dug wells within mining site, were pointers to
unsaturated geolayer and groundwater imbalance. This means that, groundwater could only be abstracted from deeper aquifers in locations with intensive sand mining especially during dry season.To maintain balance in hydrogeological system of mining sites, a well-planned sand mining programme should be employed
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