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Abstract
The central areas of Cross River State is underlain by cretaceous sediments and basement complex rocks with a history of low yield groundwater abstraction wells thus necessitating detailed pre-drilling aquifer characterization and groundwater assessment for siting of drilling locations and appropriate well design. In this study, 20 vertical electrical sounding surveys were carried out across the area and results interpreted for geoelectric layers and parameters, resistivity type curves, subsurface rock lithologies and thicknesses, hydraulic characteristics, groundwater potential and vulnerability. The interpretation infers a 3 ?? 5 geolectric layer subsurface in a lithologic sequence of top lateritic soil, a weathered zone, siltstone,/sandstone/mudstone unit, shales and crystalline rocks. Resistivity type curve were AA, AK, HA, H, KH, QH, HKH. The Layer longitudinal conductance range from 0.0323 ?? 1.514(mhos) while the sun total of the longitudinal conductance of layers overlying the aquifer vary from 0.005 ?? 0.712(mhos) depicting poor ?? weak- moderate groundwater protection capacity. Aquifer hydraulic conductivity varies from 4.65 x 10-6 cm/sec to 7.58 x 10-6 cm/sec in the sandstones, 2.20 x 10-6 cm/sec to 7.72 x 10-6 cm/sec in the saprolites and 7.74 x 10-6cm/sec in shale. The transmissivity of the sandstones range from 4.017 x 10-3 to 6.54912 x 10-2 m 2 /day, fractured saprolite??s from 1.9008 x 10-3 m 2 /day to 6.7219 x 10-3 m 2 /day and fractured shale was 6.668 x 10-3 m 2 /day. Groundwater potential is poor to fair. Results of 135 lineaments interpreted from SRTM and LANDSAT-7 ETM imageries depict lineament density and normalized vegetation index to increase in areas of more improved groundwater potential.
