GEOPHYSICAL INVESTIGATION FOR GROUNDWATER POTENTIAL ASSESSMENT AT THE UPPER TULL RIVER CATCHMENT, ADET, ETHIOPIA

Abstract

This study is intended to assess the groundwater potential in the upper Tull river catchment near Adet town, North West Ethiopia. The study area is situated in Amhara National Regional state west Gojam Administrative Zone with UTM (zone 37N) coordinate between latitudes of 1229912 m and 1259379 m, Northing, and longitudes of 316477m and 337551m Easting. Geologically the study area is covered by volcanic rocks of both acidic and basic rock units. The main objective of the study is to assess the groundwater potential of the Tull river catchment. Geophysical surveys involving electrical resistivity and magnetic methods have been carried out over the area to investigate subsurface structures that may control the movement of groundwater. The data acquired from seventeen (17) Vertical Electrical Soundings using Schlumberger electrode array with maximum half current electrode spacing (AB/2=500m) and 330 magnetic data with station intervals of 100m and 50m were interpreted both qualitatively and quantitatively in order to understand the local geology and identify groundwater bearing horizons. Different maps are prepared from the data and results are presented in slice depth sections, geoelectric section, pseudo-depth sections, total magnetic field anomaly map, analytic signal map and Euler Deconvolution map. The Vertical Electrical Sounding data were processed using Ipi2win software and the magnetic data using Oasis montaj software. The Vertical Electrical Sounding result differ in degree of weathering, fracturing, composition and depth of burial. The geo-electric sections enabled to identify the thickness and the depth to the water bearing (aquifer) zones along the survey lines. The vertical electrical sounding survey helped to identify groundwater potential areas and determine the depth to the aquifer. Moreover, the pseudo-depth sections and the geoelectric sections further suggested the presence of shallow and deep potential zones of groundwater saturation. The magnetic data effectively map, structural features like faults, fractures and/or contact zones which often serve as potential hosts for a variety of minerals and/or conduits for movement of groundwater. From these maps result the N-S and E-W oriented structure intersected with NE-SW oriented structure. The N-S and E-W structures are the main controlling factor of groundwater moment and storage in the study Area