Abstract:
This study employs integrated geophysical approaches for groundwater investigation at Dijil
catchment. Dijil is located in East Gojjam, Amhara Regional state, Ethiopia. The main
objective of this research is to investigate and ensure the potentiality of groundwater resource
of Dijil catchment. Geologically the study area is covered by recent alluvial deposits, volcanic
rock units both acidic and basic in composition. Geophysical approaches specifically regional
satellite gravity data has been used as reconnaissance survey, and magnetic methods have been
carried out over the study area to verify the presence of possible subsurface geological
structures that are important for the occurrence, storage and movement of groundwater in the
study area. Electrical resistivity (VES) method was applied following inferred structures
mapped from both satellite gravity and magnetic data; to determine the nature of the subsurface
geological units, identify possible depth and thickness of expected aquifer zone of the study
area. Ten magnetic profiles at every 100m station spacing with a total of 228 magnetic data
points have been collected and analyzed and a total of twenty four vertical electrical soundings
along seven profiles using schlumberger electrode array with maximum half current electrode
spacing (AB/2=700m) were also conducted. The magnetic and bouguer gravity anomaly maps
revealed structures mainly orientating NE-SW, NW-SE, E-W and N-S directions. These
structures may control the groundwater movement at Dijil river catchment emanating from the
Choke shield volcano extension which makes the deep wells with high discharge. However,
abandoned wells (Fendika and Debre Markos well no.2) and low yield (Debre markos well no
1) missed those inferred geological structures. The apparent resistivity pseudo-depth sections
and the true resistivity geoelectric sections show the presence of shallow as well as deeper low
resistivity horizons which are potential zones of groundwater saturation. As a result, high
productive zone are found in the eastern direction of the study area along Dijil and Wonka
Perennial rivers. The comparison of the geophysical result with the available geological
information showed that the results of the integrated geophysical survey were in a very good
agreement with the borehole logging results. As a result of these, geologic structures and
groundwater potential zones (aquifer) are detected and also preferred drilling sites for
productive boreholes are recommended.
