Increased Land Subsidence and Sea-Level Rise Are Submerging Egypt’s Nile Delta Coastal Margin

Abstract

Egypt's Nile delta, only ~1 m above mean sea level at the Mediterranean coast, is subject to uneven rates of submergence. This is a response to several factors leading to increasing land lowering (subsidence) of the northern delta and adjacent seafloor, plus an accelerating rise in eustatic (world) sea level in the Mediterranean. An average eustatic sealevel rise of ~3 mm/yr represents only ~26% to 45% of total relative sea-level rise measured along this margin. Three factors leading to subsidence are neotectonic lowering, compaction of Holocene sequences, and diminished sediment replenishment by much reduced Nile flow to Egypt's coast. Subsidence accounts for variable average land lowering of ~3.7 mm/yr of section in the NW delta, ~7.7 mm/yr in the N delta, and ~8.4 mm/yr in the NE delta, based on compaction rates of strata thicknesses that decrease down-core between top and base of Holocene sections in 85 drill cores distributed along the delta margin. Among present critical challenges are marked reduction of Nile water and sediment below the High Aswan Dam that can now reach the delta coast. It is expected that problems of fresh water and energy poverty in the lower Nile Basin are likely to be seriously exacerbated in years ahead by construction of Ethiopia's Grand Renaissance Dam (GERD). Completion of this, the biggest hydroelectric structure in Africa, is this year. Egypt, the Sudan, and Ethiopia must resolve the looming crisis of diminished Blue Nile water and sediment distribution to the lower Nile Basin and Egypt's delta margin.

Minimizing the Residual Topography Effect on Interferograms to Improve DInSAR Results: Estimating Land Subsidence in Port-Said City, Egypt

“…Thus, the construction of the Dam and barrages not only control the water flow, but also the sediment load delivered to the Nile Delta. In addition, future dams such as the construction of Ethiopia's Grand Renaissance Dam (GERD) are expected to diminish Nile flow and sediment supply to Egypt's delta region even further [26].…”

“…The average vertical ground movement rate was recorded as over 4 mm/year across the Nile Delta, while the maximum rates of subsidence were estimated at the east of the Damietta promontory (the eastern down-stream branch of the River Nile). Recently, Stanley and Clemente [26] reported that the maximum subsidence rates have been estimated as 8.4 mm/year in the NE Delta. The highest subsidence velocities were attributed to the major eastern Mediterranean fault system with accelerated velocities attributed to the thick belt of Holocene sediments ( Figure 1).…”

“…The combination of land subsidence and sea level rise in Hereher [22] stated that around one quarter of the Nile Delta's area would be flooded if the sealevel raises 1 m. Consequently, over two million people would be enforced to abandon their homes and around 214,000 jobs and over US $35 billion in land value, property, and tourism would be lost [27]. Furthermore, Stanley and Clemente [26] add that the construction of new dams in the upper Nile Basin will only exacerbate the problem of subsidence by reducing Nile water and sediment supply to the lower Nile Basin and Egypt's delta margin. Consequently, updated maps of the Nile Delta and coastal cities of Egypt provide decision makers with useful information for integrated development and sustainable use of natural resources.…”

“…This unique geological setting has important implications on subsidence rates in Port-Said City and will be discussed in a later section. The top map shows the average thickness of Holocene sediments in the northern delta (modified after Stanley and Clemente, [26]) and the bottom map shows the regional structural setting of the northern Nile Delta (modified after Mosconi et al [42]). …”

“…Numerous studies have recorded the vertical land subsidence velocities of the Nile Delta by using in situ observations [23,26,[28][29][30][31][32] as well as remote sensing techniques [15,19,[33][34][35][36][37][38][39][40]. Across the northern Delta, about 87 continuous sediment drill cores from the National Museum of Natural History (NMNH) of the Smithsonian Institution were used to provide estimates of its subsidence [41].…”