Geophysical investigation of a weathered terrain for groundwater exploitation: a case study from Huidong County, China

Abstract

2D electrical resistivity tomography (ERT) coupled with electrical resistivity profiling, induced polarisation, and self-potential (ER-IP-SP) measurements and pumping-test data has been used to acquire subsurface electrical properties for the assessment of groundwater reserves in weathered terrains of Huidong County, China. In this investigation, ERT was performed using a pole-dipole array with 305 measurements, and ER-IP-SP with 127 stations, both along three profiles. A least-squares inversion technique is used for the post processing of the ERT data to generate 2D models of the subsurface geologic units. The following deductions are made based on the 2D ERT modelling. The average depth of fresh basement is generally 10–30 m. Three distinct layers were interpreted, i.e. 5–10 m thick topsoil cover with resistivity <1800 Ωm (above the water table), 5–25 m thick weathered layer with resistivity <900 Ωm (below the water table), and fresh bedrock with resistivity >900 Ωm (below the water table). These layers comprise the 50 m thick overburden revealed by the inverted sections. The ERT models were incorporated with ER-IP-SP to delineate various discontinuities. Groundwater resources enclosed in the weathered/fractured zones were estimated by hydraulic conductivity (K) and transmissivity (T) into three different aquifer zones with specific ranges of T and K (i.e. high, medium, and low yield aquifer). The results suggest that the best potential groundwater resources are contained within fractures/discontinuous zones. The results are well in line with the hydrogeological information available for the investigated area. This geophysical approach is useful to assess the groundwater potential where the weathering has hydrogeological significance.