Resistivity imaging and self-potential applications in groundwater investigations in hard crystalline rocks

Despite massive river diversion schemes there is a shortage of water in most areas of the dry zone of Sri Lanka. Therefore, prospecting for groundwater in the hard crystalline rocks is a top priority. A geological and geophysical study was therefore carried out to investigate groundwater accumulations in the hard rock terrain in Moneragala, using the resistivity imaging and self-potential techniques. This possibly is the first time that the above technique is used in the country, in prospecting for groundwater.

Interpretations using aerial photographs and geological maps carried out prior to the field survey indicate significant lineaments and fracture zones in the study area. These locations, which are favourable for groundwater accumulations, were tested using the resistivity imaging and self potential methods in 8 transects up to 200 m in length with an electrode spacing of 5 m.

The results obtained show areas of low resistivities and negative self potential anomalies, which correlate well with the geological structures identified from maps or field observations. These are possibly areas with groundwater accumulations. More work, including bore holes are required to confirm the findings. However, this study shows that these simple methods show promise and may be used to improve accuracy to locate groundwater wells in the dry zone.

Keywords: Crystalline rocks, resistivity imaging, self potential, Sri Lanka.

doi: 10.4038/jnsfsr.v37i1.454

J.Natn.Sci.Foundation Sri Lanka 2009 37(1): 23-32