PALEO-CHANNEL DELINEATION AS AN INDICATION OF GROUNDWATER ACCUMULATION IN NORTHERN SINAI, EGYPT

Since the last pluvial cycle in the Eastern Sahara ended about 5.5 ka ago, the ancient rivers dried and were concealed under an aeolian sand cover. Although many attempts have been made during the last decades to unveil the courses of these paleo-rivers using space-born radar data, the relationship between these courses and the groundwater remains ambiguous. This research aims at utilizing SAR remote sensing data and field investigations to delineate the paleo-channels of northern Sinai beneath the sand fields, and then correlate them to the hydrological setting of the area. Images from Radarsat-1 (C-band, 12.5 m) and ALOS/PALSAR (L-band, 6.25 m) sensors were used to detect and map the buried rivers. The circular polarization (ѱ = 0° and χ = 45°) of the ALOS/PALSAR was employed to delineate near surface fractures in the study area. Landsat ETM+ and ASTER images were utilized in producing a land-cover map based on supervised classification and field observations. Multi-source data fusion of optical and microwave sensors was performed to extract the texture and compositional characteristics of the wadi bed deposits. Field measurements consisted of measuring the volumetric moisture content of the soil and 1 cm-scale roughness of the surface were applied. In addition we acquired 12 GPR profiles using a 250 MHz shielded antenna to validate the findings of the radar remotely sensed data. A comparative study of the groundwater aquifers was conducted using monitoring records of the piezometric levels and salinity changes of 60 wells in the area, during the period of 1997 to 2011. The results indicate that the recharge of the aquifers near the paleo-streams is relatively high after flash flood events, in comparison to others more distant from the paleo-channels. Moreover, the salinity values decrease toward the buried channel courses west of Gabel Halal and increase in an easterly direction. This could be attributed to the effect of the structural trends that controlled the buried fluvial channels, which probably connect to the tributaries of Wadi El-Arish. Such high density fracture zones may have channeled the runoff to accumulate beneath the paleo-channel courses. These findings may have broad implications to the groundwater exploration for sustainable agricultural development in the region.