GROUNDWATER POTENTIAL ASSESSMENT USING INTEGRATED ELECTRICAL RESISTIVITY TOMOGRAPHY AND GRAVITY METHODS, A CASE OF FANGO LOME CATCHMENT, HUMBO DISTRICT, SOUTHERN ETHIOPIA.

Abstract

The search for groundwater is vital as an immediate and sustainable solution to the scarcity of water for drinking and other domestic uses in heavily populated areas like Fango Lome catchment of Southern Ethiopia. The current study was therefore conducted to assess the groundwater potential in Fango Lome catchment, found in Humbo district. The study used two non-destructive geophysical techniques, Electrical Resistivity Tomography (ERT) and Gravity Methods to assess the aquifer bearing potential structures. A total of 427 gravity points and six ERT profiles were collected in the current study. SYSCAL Pro Earth Resistivity Meter was used to obtain the electrical resistivity imaging data and RES2DINV software was used to process the data. Gravity data were recorded using GPS and analyzed using Geosoft Oasis Montaj (Version 8.4) interpretation software. The analysis of the results obtained from the ERT method revealed that the study area is characterized to have four distinct layers of soil with different texture and apparent resistivity: The first layer with very low apparent resistivity value was identified to represent silty clay soil, the second layer has relative low apparent resistivity value is correlated to represent slightly weathered and fractured basalt materials, the third layer has moderate apparent resistivity value is characterized by highly fractured and weathered basalt, and the fourth layer has indicated massive bedrock materials with higher apparent resistivity. The third layer is expected to be a good source of ground water or aquifer horizons. Similar result was also found from the Gravity method which was employed to depict the lateral and depth variation in density. Accordingly, the result revealed that the subsurface geologic structure of the study area consists of four main density layers: the first density layer associated with silt and clay soil, the second density layer likely representing slightly weathered and fractured basalt, the third density layer characterized by highly weathered and fractured basalt - which is expected to be a good source of ground water or aquifer zone- and the fourth density layer probably composed of massive base bade rock. The overall discussion was done by integrating all the above results together with the topographic map, geologic and borehole information. Finally, based on these results, geological structures and groundwater aquifer potential zones were identified and drilling sites are recommended