USE OF RADAR DATA TO UNVEIL THE STRUCTURALLY CONTROLLED PALEOLAKES ALONG THE ANCESTRAL CHANNEL OF WADI EL-ARISH, SINAI, EGYPT

The folded belt in the northern part of the Sinai Peninsula had significant influences on the shape and direction of Wadi El-Arish, the largest ephemeral drainage system in Sinai. Anticlinal ridges appear to have formed natural barriers that block runoff across the main drainage course during humid periods, and forced the wadi to deviate from its course. Several temporary paleolakes developed behind the folded ridges, and extended 10 to 4 km across the main course. The wadi pushed its water overload through three gorges (500 to 150 m wide), which incised the crest of massive carbonate anticlines (Gebels) and followed the predominant fault plains that trend in NE-SW and NW-SE directions. This obstruction of Wadi El-Arish caused the abnormal shape of the main stream channel that deviated from its course twice toward NE, and once to the NW before reaching the outlet at the Mediterranean Sea. Radarsat-1 and SRTM data, with the aid of high resolution multi-spectral images, were utilized to depict the ancestral course of Wadi El-Arish and delineate its associated paleolakes. These data were used to define the relation between surface structure and groundwater recharge. The analysis showed that the defunct branch drained west of the current course, headed to the NW between Gebels Halal and Yelleg, then to the north between Gebels El-Maghara and Libni. Four paleolakes have been identified and reconstructed to estimate the size and the water volume of each. Three of them were located behind gorges at G. Kharim, G. Tal'at El Badan and Deigat El-Halal, from south to north, respectively. Such geological structure setting plays indispensable role in recharging Quaternary groundwater aquifers, because it is still acting as natural dames during flash flood events. However, the gorges near the Wadi outlet expedite the flow velocity and increase the flood threats. Accordingly, these gorges should be dammed. The fourth paleolake formed between G. Halal and Yelleg along the old wadi course and connected to the present drainage course by NW-SE subsurface faults. By damming the gorges, such connection could be used to direct excess runoff to rejuvenate the paleorivers and recharge local near-surface reservoirs for development purposes. This is particularly timely due to the pressing need to develop the Sinai Peninsula in the post-revolution era.