Stanley, J.-D. and Clemente, P.L., 2014. Clay distributions, grain sizes, sediment thicknesses, and compaction rates to interpret subsidence in Egypt's northern Nile Delta.
This study focuses on the role of clay on subsidence of Holocene sedimentary sequences in the northern Nile Delta. Proportions of clay in 1262 samples from 87 cores are much higher here than elsewhere in the delta and along the Nile in Egypt. The northern third of the delta lies at a low, near-horizontal elevation (∼1 m above mean sea level), but clay content and total thickness of Holocene deposits in subsurface vary considerably in time and space. Greatest clay content (to >60%) and mud-rich thickness (to 47 m) are concentrated near Manzala lagoon. The volume of Nile water and sediment discharged annually on the delta diminished during the past two millennia as a result of climate change and intensified human activity. During the past two centuries, barrages and dams placed across the Nile and increased water diversion activities further reduced Nile flow and sediment delivery to the northern delta. Lowering at the coastal margin has also resulted from interplay of sediment compaction, regional sea-level rise, and intermittent readjustment of strata at depth. These events are ongoing, as indicated by increased erosion of extensive stretches of delta coast, salinization that affects large areas of agricultural land and groundwater, and major changes in recent sediment textural patterns as mapped in the present survey. Formerly dominant fluvial S-to-N transport during much of the Holocene has become distinctly shore parallel, recording landward shoreline advance and W-to-E sediment displacement along the delta margin. Implementing extensive coastal protective measures should take into account zones most prone to effects of subsidence, where (1) clay-rich subsurface sequences are thickest, (2) these strata are subject to high compaction rates, (3) sediment replenishment is insufficient, and (4) readjustment at depth of pre-Holocene sequences is continuing. These factors will cause the delta's NE and north-central sectors to experience continued significant surface lowering.