Groundwater investigation using electrical resistivity imaging technique at Sg. Udang, Melaka, Malaysia

Electrical resistivity imaging surveys have been conducted in order to locate, delineate subsurface water resource and estimate its reserve. The resistivity imaging surveys carried out basically measures and maps the resistivity of subsurface materials. Electrical imaging is an appropriate survey technique for areas with complex geology where the use of resistivity sounding and other techniques are unsuitable to provide detailed subsurface information. The purpose of electrical surveys is to determine the subsurface resistivity distribution by making measurements on the ground surface. The resistivity imaging measurement employing Wenner electrode configuration was carried out using an ABEM SAS 1000 terrameter and electrode selector system ES464. In this survey, electrodes were arranged in a straight line with constant spacing and connected to a multicore cable. A 2-D geoelectrical resistivity technique was used. The field survey was conducted along four profiles which provide a continuous coverage of the resistivity imaging below surface. Colourmodulated sections of resistivity versus depth were ploted for all lines, giving an approximate image of the subsurface structure. The surface soil material is mainly clayey silt. The results showed that the layers associated with the low resistivities (Ω.m) are located at depth ranging from 2 to 28 m. This low resistivity values are associated with zone of water saturated weathered layer and fractures. The results showed that the thickness of residual soil is about 0.5-2.55 m. Borehole data indicated that the depth of bedrock is about 10m and the groundwater level is ranging from 8.73 m to 8.54 m.