ABSTRACTThe El‐Shawak area in eastern Sudan lies within a large synclinal basin known as the Gedaref Basin, composed principally of elastic sediments of the Nubian Sandstone Formation which are overlain by sheets of basalt and dolerite and underlain by a metamorphic Basement Complex.As a part of a hydrogeological research project in the area, gravity and seismic refraction techniques were combined to locate the extent of the basaltic flow and to determine the thicknesses of the sedimentary formations.The results of these studies show that the topography of the Basement Complex is undulating and characterized by two troughs separated by subsurface ridges. The thicknesses of the Nubian Formation sediments range from 50 m (164 ft) to greater than 250 m (820 ft). Although the thicknesses of the Nubian Formation are favorable for ground‐water occurrence, the yield is very limited because the sediment succession is composed largely of compact mudstone.The application of the gravity method in the El‐Shawak area has shown that a polynomial trend‐surface fit can be used to separate the regional and the residual components to reflect local geological f