For calculating subsidence rates along the Nile Delta coastal margin, archaeological site data provide more accurate temporal and elevation control relative to Holocene sea levels than chronostratigraphic analyses of radiocarbon-dated sediment cores. Recently acquired data on the depth and age of 11 buried and/or submerged levels of human activity at seven ancient sites serve to calculate average annual rates of subsidence along the northern Nile Delta margin during the middle to late Holocene. Subsidence rates range from 0.9 to 4.3 mm/yr, varying irregularly from west to east along the northern delta coast, and averaging ∼2.5 mm/yr for 11 data points on the margin as a whole.
Subsidence rate is directly related to thickness of sediment section, with highest values in the eastern part of Manzala lagoon and at coastal promontories of the Damietta and Rosetta branches. This, in large part, is a function of underlying sediment compaction plus sediment loading and readjustment of strata at depth. Short-term natural events such as earthquakes, tsunamis, Nile floods, and winter storm surges also serve as triggers of subsidence. An additional important factor is human activity, such as construction of large structures on water-saturated substrates. Most modern towns along this increasingly populous delta margin are located in low-lying vulnerable settings presently subject to subsidence, a phenomenon that warrants close monitoring and increased implementation of protective measures.