INTEGRATION OF OPTICAL IMAGES AND RADAR DATA REVEAL PALEOHYDROLOGICAL PROCESSES WEST OF THE NILE, EGYPT

The geomorphology of the Egyptian Nile region south of the Qena Bend is unlike that north of it. Sizable area of the Cretaceous/Tertiary sedimentary rocks were denuded and transported by strong river actions. The expanse of this region reflects long term hydrodynamic processes, as well as tectonic movements. Interpretation of Radarsat-1 and Shuttle Radar Topography Mission (SRTM) data of the Gallaba Plain revealed vestiges of paleochannels and probable flutes of tectonic events across the plain. The depth, distribution, and direction of these flutes suggest tectonic origin. Large masses of the eastern edge of the Western Desert plateau such as Gebel El-Barqa, approximately 16 km in diameter, have slide to form a barrier that blocked the earlier channel at the present Wadi Abu Dommi. This forced the channel to find a new path to the east. The tectonics damming of the region south of the Qena Bend allowed accumulation of water to facilitate hydrodynamic processes, including erosion and down-cutting. The water had accumulated in a lake-like depression until breached northward through the tectonic barrier. Tectonic movements are preserved as cracks, landslides, uneven surfaces and block dislocations. There are also numerous fractures and forms of compressive stress. The curved cracks and fractures divide the plateau into round masses on its eastern edge. In addition to these findings, radar images revealed that the Gallaba Plain was as lake, received water from the Red Sea hills and from the Nile system through Wadi Kubbaniya, although, the latter has been interpreted as the downstream continuation of Wadi Abu Subeira. Relics of Wadi Kubbaniya have been detected in the south along the present Nile, masked by its channel, which makes them difficult to identify. The dimension and geomorphology of Wadi Kubbaniya are compatible with the earlier Nile system more than Wadi Abu Subeira, as confirmed by the geomorphic evidences extracted from Radarsat-1 data. Previously published work and field investigations confirm most interpretations of the radar images that the region was shaped by a sequence of tectonic and hydrodynamic processes. The presence of paleochannels and fossil rivers provide significant evidence for the recent drainage dislocations.