Use of radar data to delineate palaeodrainage flow directions in the Selima Sand Sheet, Eastern Sahara

Palaeodrainage directions in the Selima Sand Sheet (centered on 22.5 degree s N, 29 degrees E) were determined using high-resolution, multi-wavelength, multi-polarization Spaceborne imaging Radar (SIR-C) data and the Global La nd One-km Base Elevation (GLOBE) Project Digital Elevation Model (DEM). The combined use of these two data sets shows that both large;flood features a nd later superimposed drainage channels of variable morphology all drain NE and ENE from northwest Sudan toward the Kharga depression in southern Egyp t. This is supported by drainage directions deduced from the USGS Global To pography (GTOPO) DEM. These directions are opposite to those of the Trans-A frican Drainage System (TADS) model in which the large flood features are c onsidered to flow southwest across northeastern Africa into the Chad Basin. Instead, the results show that an internal drainage basin operated in the gently undulating terrain of the Selima Sand Sheet (probably during the Cen ozoic period), and that the slope of the North African plate remained gener ally northeastward during those times. Further, the northeastern parts of t he Selima Sand Sheet are likely to be the primary area for ground-water acc umulation in southern Egypt.