An integrated approach for aquifer characterization and evaluation in a complex geologic terrain (Cross River State, Nigeria): A contribution to support sustainable development and management of groundwater

Abstract

Increasing agriculture, industrial and urban growth have resulted in the rapid and an haphazard development of groundwater resources through indiscriminate abstraction in the Cross River State (CRS), Nigeria. This has resulted in stress on groundwater, especially in areas with complicated geologic formations where reliable data are lacking. This paper focuses on understanding the hydrogeological characteristics of the different aquifers using an integrated approach. The methods applied are hydrogeological surveys together with interpretation of geological, geoelectrical and hydrochemical data. The results reveal six hydrogeological zones (HZs): HZs 1 (igneous and metamorphic rocks), 2 (sandstone and siltstone), 3 (massive, baked and fractured shale), 4 (sand, gravel, silt and clay), 5 (carbonate rocks) and 6 (basic intrusive rocks). Estimates of groundwater reserves indicate that the HZ 1 has the largest reservoir of stored fresh groundwater, estimated at 332,637.00 × 106 m3, while the highest yield is estimated to be 1085.53 m3/d from HZ 4. Groundwater chemistry showed that Na+ and Ca2+ dominated the cations, while Cl− and HCO3− dominated the anions. In general, major chemistry of the water is controlled by atmospheric input, weathering of silicate, carbonate minerals and ion exchange. In terms of drinking and irrigation quality, the groundwater showed low values of total dissolved solids, pH, hardness, dissolved oxygen and NO3− at few locations, while more than 50% of the samples have excellent quality for irrigation use. However, higher values were recorded in HZ 2, due to occurrence of brackish water.