Resistively and Self-Potential Investigations of Sub-surface Water Seepage Phenomenon at Omdurman

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Fahal,Mohsin Ali Elhag
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University of Khartoum
The Omdurman suhsurface water seepage problem constitutes a serious phenomenon at present because of the high-density population and lavish use of water. The Omdurman region is covered by rather flat Cretaceous Nubian sandstones with gentle centripetal clips that hinder the outflow of the groundwater into the River Nile. The sandstone bands are intercalated with mudstone layers or lenses, and injected by Tertiary basalts along the bedding planes. Both rock types are impervious and retard the infiltration of the surface water, hence over-flooding. Plastic clay soil (Banat east, Al-Abassia and AL-Ahlya square) when present may also hamper vertical water seepage; cause swelling potential and consequent damage. Geophysical investigations applying resistively potential (SP) methods are conducted to reveal the occurrence and distribution or the impervious layers underneath, and to detect characteristic features of the subsurface streamlines. The results obtained indicate the presence of significant almost horizontal bands and lenticular bodies of mudstone intercalated with the standstills or the Nubian formation. Some of these bands are situated close to the land surface e.g. at Bait elmal, Al-Mullazlmean, AI-Abasia, Banat east and Al-Arda districts. These layers have been successfully delineated by the electrical resistively method. Geo-electrical sections and maps were constructed to show their locations, thicknesses, attitudes and inclinations. The mudstone layers being impervious prevent water infiltration from natural and artificial sources and can therefore, create temporary perched aquifers located at the interface between the superficial deposits and the top very layer or lens of the mudstones. From these aquifers water is expected to rise up and seep into the surface land and cause damage. Negative SP anomalies show the occurrence and variable intensities of the subsurface streamlines. The distribution of the SP contour lines indicate the haphazard orientation of water flow, hence, the phenomenon appears to be of local nature.
Self Potential Investigations;Sub surface Water Seepage ;Omdurman