Land subsidence in the Nile Delta: inferences from radar interferometry

The Nile Delta formed by progression of a complex system of deltaic fans thought the Pleistocene, with the Modern delta being formed from sediments supplied by at least ten distinct distributaries thoughout the Holocene. With an average elevation of approximately 1 m above sea level within 30 km of the coast and a predicted rise in sea level of 1.8-5.9 mm/yr the subsidence of the northern delta has become a topic of major concern to the Egyptian population and government. The Nile Delta is home to more than 50 million people and the major agricultural production are for Egypt. We evaluated the modern rates of subsidence of sections of the northeastern Nile Delta (a total length of 110 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 promontory, and the nearby Mendesian depocenter that was active up to recent times (to 2500 years ago). The highest subsidence rates (similar to 8 mm/yr; twice average Holocene rates) do not correlate with the distribution of the thickest Holocene sediments, but rather with the distribution of the youngest depositional center (major deposition occurred between similar to 3500 yr BP and present) at the terminus of the Damietta branch. The adjacent, slightly older (8000-2500 yr BP) Mendesian branch depositional center is subsiding at slower rate of 2-6 mm/yr. Results are interpreted to indicate that: (1) modern subsidence in the Delta is heavily influenced by compaction of the most recent sediments, and (2) highly threatened areas are at the terminus of the Damietta and possibly the Rosetta branches, where active deposition is occuring.