Abstract

The paper presents preliminary results of continuing studies in SE Zimbabwe aimed at understanding the role of fracturing in hard rock aquifers. This is a semi-arid region in which a high proportion of boreholes drilled for water supply are dry or provide minimal yields for hand-pump usage. Remote sensing, using satellite images and aerial photographs, provides a rapid means of identifying potential fracture systems but field evidence of the nature and precise location of such fractures is limited. Ground geophysical techniques such as resistivity, electromagnetic and magnetic surveying have been extensively tested over a few selected sites in an attempt to characterize their response where photolineaments occur. These data reveal the presence of anomalies, predominantly of shallow origin, some of which correspond with the lineaments. Initial results suggest that the lineaments studied do not represent major, open groundwater conduits. Drilling and borehole logging information confirms the view that fracturing is poorly developed in general. An interpretation of pump test data collected as part of hydraulic fracturing tests suggests that drilling itself results in the preferential opening of vertical fissures near the borehole but that background transmissivity is very low. The work is continuing with a programme of core drilling and cross-hole seismic tomography, the results of which will be incorporated in further modelling of the geophysical data.

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