ASSESSMENT OF RATES AND FACTORS CAUSING SUBSIDENCE ACROSS THE NILE DELTA FROM RADAR INTERFEROMETIC TECHNIQUES

The Nile delta region of Egypt is the economic and social hub of Egypt. Throughout the Holocene period, the delta landscape evolved due to flooding, sediment accumulation and compaction, recent tectonics, and re-distribution of Nile Delta channels and distributaries. We monitored the current deformation of the Nile delta landscape and identified the factors controlling the observed deformation: (1) using radar interferometric techniques (persistent scatterer interferometry and small baseline subset technique), we extracted deformation rates across the entire delta landscape using 108 level 0 Envisat Advanced Synthetic Aperture radar scenes in four adjacent tracks, (2) we developed and applied procedures to map the distribution of River Nile streams and sub-basins throughout the Holocene using high resolution (spatial resolution: 30 m; vertical resolution: 0.1 m) digital elevation model (DEM), (3) we simulated flooding events and sediment distribution using Arc hydro tool in ArcGIS, and (4), we compared the output of the flood delineation model to outputs of persistent scatterer interferometric applications to investigate the spatial relationship between the extent and depth of the flooding events of the Nile River and the measured deformation. Our analysis revealed the following: (1) the spatial extent and depth of the flooding is highly pronounced on the north eastern part of the delta especially near Lake Manzalah, an area that exhibits high subsidence rates (up to 9 mm/yr.), (2) the southern outskirts of Lake Burulus and the terminus of the Damietta branch are also highly affected by the simulated flooding; these areas experience high subsidence rates (mean value of 4.5 mm/yr), and (3) lateral movements across E-W as well as NW-SE trending faults throughout the Holocene, obstructed the river Nile channels, diverted surface flow and controlled sediment distribution during flooding events. To conclude, areas showing high subsidence rates across the delta correlate with the distribution of thick and relatively young sediments that are largely controlled by topographic and tectonic factors.