Land Subsidence in the Northeastern Nile Delta as Measured by Radar Interfeometry

The Nile Delta was formed by progression of a complex system of deltaic fans throughout the Pleistocene, with the modern delta being formed from sediments supplied by at least 10 distinct distributary channels throughout the Holocene. With an average elevation of only a meter or so above sea level and a predicted rise in sea level of 1.8-5.9 mm/yr, subsidence of the northern Nile Delta is becoming a topic of major concern to the Egyptian population and government. The Nile Delta is the home to more than 50 million people and the major agricultural production area for Egypt. We evaluated the modern rates of subsidence of sections of the northeastern Nile Delta, a total length of 60 km, up to 50 km from the coastline, using persistent scatterer radar interferometry techniques applied to 14 ERS-1 and ERS-2 scenes. The area covered includes the present active depocenter of the Damietta promontories, and the nearby Mendesian depocenter that was active up to recent times (up to 2500 years ago). The highest subsidence rates (~8 mm/yr; twice average Holocene rates) corrolate with the distribution of the youngest depositional centers, where major deposition occurred between ~3500 years bp and the present, at the terminus of the Damietta branch, rather than with the distribution of the thickest Holocene sediments, as suggested earler. The adjacent slightly older (8000 – 2500 years bp) Mendesian branch depositional center is subsiding at slower rates of 2-6 mm/yr. Results are interpreted to indicate that: (1) modern subsidence in the Delta is heavily influenced by the compaction of the most recent sediments, and (2) the highly threatened areas are at the terminus of the Damietta and possibly the Rosetta branches, where the most recent deposition has occured.