In-situ loading experiments reveal how the subsurface affects coastal marsh survival
Z. Hosseini, E. Raeizi
Department of Earth Science, School of Science, Shiraz University, Shiraz, Islamic Republic of Iran
I. Abdollahifard
Exploration Bldg., NIOC, Tehran, Iran
P. Teatini
Department of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
ABSTRACT
The Nubian Aquifer System (NAS) is one of the largest known deep aquifers, with an area of 1.7 Mkm2 and a
maximum depth of 4000 m. It is located in North-East Africa and shared between Egypt, Libya, Chad, and Sudan
countries. The sediments deposited inside intra-cratonic basins from the Precambrian to the Quaternary. The
NAS consists of the Nubian sandstone aquifer (NSA) overlain by the Post Nubian limestone aquifer (PNLA) in
northern portion of the basin.
This study provides a comprehensive review of the NAS including sedimentary basin evolution, geology,
geomorphology, current and past climate, hydrogeology, general flow direction, water balance, hydrochemistry,
water resources management and permissible exploitation period. The primary mechanisms behind the forma
tion of the deep NAS involve the weathering of granitic igneous rock around the basin, low compressibility
sandstone and displacement of saline water trapped during deposition by precipitation since one million years
ago. The general flow direction is from the southern heights northward, reaching to a depth of 3500 m below sea
level, eventually discharging into the Qattara Depression and the Mediterranean Sea during the pre-development
period and in local low-lying oases. The NAS has discovered through hydrocarbon exploration. The Total
Freshwater Storage Volume (TFSV) is estimated to be about 500 trillion m3 before exploitation. In 2006,
groundwater extraction was 2.17 billion m3. Overexploitation without a scientific plan resulted in drying springs,
decreasing water levels and quality, land subsidence and intrusion of saltwater from the Mediterranean Sea. The
groundwater age is between 4,000 and 50,000 years at a depth fewer than 750 m and up to one million years at
lower depth. Therefore, the majority of the aquifer's TFSV is nonrenewable. The lack of systematic, reliable,
locally and timescale distributed data are the main challenge of hydrological studies, especially in water balance
estimation. TDS varies from 70 to 8500 mg/l, with the NSA water quality generally better than the PNLA. Some
parts of the aquifer have reported heavy elements, including lead, manganese, cadmium, chromium and iron.
As the NAS is predominantly nonrenewable, only a small percentage of the TFSV, termed the Permissible
Exploited Storage Volume (PESV), can be safely exploited in the future. However, determining the extent,
location, and implementation plan for the PESV raises critical questions. In addressing these urgent inquiries, the
comprehensive review presented in this paper should be regarded as an initial and crucial step in developing a
reliable physics-based numerical model of the NAS aquifer system. This model will allow to explore sustainable
management practices that effectively address potential challenges.
