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Increased Land Subsidence and Sea-Level Rise are Submerging
Egypt’s Nile Delta Coastal Margin
Jean-Daniel Stanley, Mediterranean Basin (MEDIBA) Program, 6814 Shenandoah Court, Adamstown, Maryland 21710, USA,
stanleyd1@outlook.com; and Pablo L. Clemente, Dept. of Geographic and Environmental Systems, University of Maryland,
Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, USA, clempa1@umbc.edu
ABSTRACT
Egypt’s Nile delta, only ~1 m above
mean sea level at the Mediterranean
coast, is subject to uneven rates of sub-
mergence. This is a response to several
factors leading to increasing land lower-
ing (subsidence) of the northern delta and
adjacent seafloor, plus an accelerating
rise in eustatic (world) sea level in the
Mediterranean. An average eustatic sea-
level 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 low-
ering, 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 dis-
tributed 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 pov-
erty 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.
INTRODUCTION
Recent submergence of many world
fluvial-marine deltaic margins is generally
attributed to increased eustatic (world)
GSA Today, v. 27, no. 5, doi: 10.1130/GSATG312A.1.
4 GSA Today | May 2017
sea-level rise responding largely to Figure 1. Map of the Nile Basin indicating relative
increased polar glacial ice melt and ther- percentages of fresh-water flow contributed by
mal expansion of seawater associated the Blue Nile, Atbara River, and the White Nile to
with global warming (Hansen et al., 2016). the Main Nile in the Sudan and Egypt. GERD—
Less attention has been paid to other Grand Ethiopian Renaissance Dam.
mechanisms that could presently play a
substantial, or even greater, role in a del- political stability (La Guardia, 2016), must
ta’s coastal submergence. The Nile delta’s already import much of its food to feed its
margin in northern Egypt is examined growing population concentrated in the
here with regard to its ongoing submer- Nile delta and valley.
gence by rising sea level (Shaltout et al.,
2015), combined with the effects of land BACKGROUND
subsidence near its Mediterranean coast-
line and seafloor offshore (Fig. 1). The latter The Nile Basin covers 3,250,000 km2
include (1) effects of recent neotectonic and extends northward across 36° of lati-
lowering of the delta surface associated tude. The delta forms at the mouth of the
with substrate displacement; (2) ongoing Nile, the world’s longest river (~6700 km),
compaction of the Holocene sedimentary whose water in Egypt is derived from two
sequence; and (3) diminished sediment north-flowing branches, the Blue and
replenishment by the Nile River at the White Niles, that merge as the Main Nile
delta coast and adjacent shelf. We propose in the northern Sudan (Fig. 1). Interpreta-
that these three phenomena have triggered tions regarding Holocene depositional
a greater amount of subsidence of the
low-elevation delta margin (~1 m above
mean sea level [msl]) and consequent
landward coastline retreat during the past
few thousand years than could have been
produced during this time span by the
increased rate of eustatic sea-level rise
alone. Factors triggering land subsidence,
interacting with increased rise in eustatic
sea level, account for what is generally
termed relative sea-level rise.
This survey highlights increased anthro-
pogenic pressures that augment the impact
of these factors and have negative conse-
quences for populations in the northern
delta. Of major concern is the ongoing
reduction of useable land and fresh water
needed for agricultural production in this
small but vital breadbasket, one that has
previously accounted for 60% of the coun-
try’s food production. This continued
coastal margin submergence occurs at a
time when Egypt, facing increased eco-
nomic stress and diminished internal