APPLICATIONS OF REMOTE SENSING AND GIS IN GROUNDWATER RESOURCES ASSESSMENT AND DEVELOPMENT CASE STUDY, GEDAREF STATE, EASTERN SUDAN

Abstract

ABSTRACT The study area lies in Gedaref State in the eastern Sudan, the area suffers from acute shortage of water supply especially during summer seasons, due to the over exploitation of groundwater and the high rate of runoff as a result of clayey overburden and relatively high slopes. Integrated methods of Remote Sensing (RS) and Geographic Information System (GIS), geological, geophysical and hydrogeological investigations have been carried out to assess and develop the water resource in the area under consideration. Remotely sensed data of the Landsat 7 ETM+ multi-spectral images and SRTM (Shuttle Radar Topographic Mission) interferometry elevation data have been used in this study. Different digital image processing techniques were applied to the satellite images to reveal the geological, structural, hydrogeological, and hydrological aspects. The enhanced imageries had been pre-processed by new technique of vegetation suppression in order to minimize the masking effect of vegetation spectra over the geological ones. DEM (Digital Elevation Model) derived from SRTM data is used to delineate the hydrological catchment areas and the major lineaments. Nine sub-basins have been delineated with their hydrological aspects, where River Atbara and Abu Fargha sub-basins are the largest sub-watershed in the Gedaref area. Lineaments have been spatially and structurally analyzed, which revealed that most fractured basaltic and sandstone aquifers lie in tensional fractures zones related to the formation of Gedaref basin, whereas in basement terrains the fractures were classified based on the paleao - stresses during old geological events. The electrical geophysical methods identify three main aquifer types, sandstone, fractured basalts, and the unconsolidated superficial aquifers. The thickness of sandstone aquifer extends between 47 m to 150 m, where the groundwater occur at depths range from 30 m to more than 100 m blow surface. The sandstone aquifer parameters were calculated from pumping tests revealed that the average transmissivity is about 280 m2 day"', whereas the average hydraulic conductivity is 0.75m day", and the storativity varies from 6.3 x 10'2 to 2.0 x 10'7. However, the fractured basaltic aquifers are of average transmissivity values of 100 m2 day'l. l-lydrochemical data disclosed that the total dissolved solids (TDS) varying from 151 to 5210 ppm due to the lithological variations in the study area. Spatial analysis of these data indicates the presence of the highly TDS concentration zones in basaltic terrains. Surface geological investigations coupled with the geophysical data confirmed the presence of a thick widespread clayey layer capping the sandstone and basaltic aquifers, which preventing the infiltration of water to the underling aquifers. A number of fourteen potential dams and eighteen injections wells as artificial recharge facilities have been proposed in order to enhance the groundwater storage based on RS and GIS, geological, hydrological, and structural criteria.