Estmation of aquifer hydralie parametes from surficus electrical resistivy capabilite in ne part of khartoum basin

Abstract

ABSTRACT Abu Deleig is a transitional area between Butana basement terrain to the east; and Khartoum and Shendi sedimentary basins to the west and northwest directions, respectively. Geologically, it is covered by Cenozoic sediments and sandstone of Cretaceous age unconforrnably overlying the Precambrian basement rocks. The main objective of the present study is to use the application of the geophysical methods in combination with pumping tests data for some boreholes to provide a cost—effective and efiicient alternative tool to estimate aquifer parameters. The study used an integrated approach‘s, Satellite images have been used for delineation of lineaments and drainage systems, followed by a structural analysis and geophysical investigations including gravity and resistivity methods. The interpretation of the remotely sensed data revealed that the drainage pattem is structurally controlled and Wadi Al I-lawad is the southem continuation of the Keraf Shear Zone with trend N-S, the related minor fractures in a NE—SW direction exhibit nomial faults goveming the geometry of the basin. The geophysical investigations confirmed the findings of structural analysis and portrayed the subsurface geometry of the sub-basin. The interpretation of the gravity data revealed that the depth to the basement increases from 20 m at Abu Deleig in step form to more than 400 m and extends to 40 km in NW direction in a prism-like shape with its apex occurring at Abu Deleig toum and extends 40 km in NW direction. Electrical resistivity survey confirms the existence of two groundwater aquifers. An upper aquifer composed mainly of alluvial sediments and shallow sandstone is found at depths ranging between 20-30 m; while the lower aquifer is predominantly Cretaceous sandstone found_at depths below 50 m, each of these aquifers shows a wide range of variable hydraulic parameters, due to the high in-homogeneity of the sedimentary formations. An integrated approach of estimating aquifer parameters from electrical resistivity and pumping test data is a good altemative to drilling more wells and conducting pump tests. A relationship has been established between electrical and hydraulic parameters for the area where borehole information is very sparse and grain size data is not available. The study area has thick beds of coarse sand with sufficient transmissivities to act as good aquifer in the northwestem part, whereas the eastem and south eastem pan is dominated by shallow basement depth and variable hydraulic conductivities. Thick alluvial strata with high hydraulic conductivity qualify for drilling a production well in the northwestem part of the study area. ll