I. HYDROGEOLOGY OF ARID REGIONS
21
A. NUBIAN AQUIFER
The Nubian Aquifer underlies a large part of northeastern Africa (Fig.
11). Similar rocks are also important aquifers in part of the northeastern
Arabian Peninsula (Naimi, 1965). In general, the aquifer contains potable
water in the Sudan, the northeastern part of Chad, southeastern part of
Libya, and the southern two-thirds of the United Arab Republic. The
water grades from brackish to salty north of the Qattara Depression.
To date, little significant development has taken place in the aquifer
except in the New Valley Project and near the various oases such as
Dakhla, Farafra, and Bahariya in the United Arab Republic and near
Khartoum in the Sudan. Natural discharge has been largely in the oases
of the Western Desert and in the Qattara Depression. Nubian sandstone
does not crop out in the Qattara Depression, but slow, upward leakage
through overlying rocks probably takes place.
The Nubian Aquifer is designated as a sandstone in much of the geologic
literature. Its lithology in detail, nevertheless, is quite varied. In the Sudan,
conglomerate, coarse-grained sandstone and medium-grained sandstone are
abundant in the Nubian Aquifer. Lesser amounts of mudstone, and hard
ferruginous and siliceous layers are also present. Most of the coarser strata
have abundant quantities of cement and clays. Lateral variations of lithology are abrupt (Rodis et al, 1968). To the north, in the United Arab
Republic, the finer-grained units appear to dominate in the upper part of
the unit. The maximum thickness of the Nubian Aquifer in the Sudan is
about 500 meters (El Boushi and Whiteman, 1967) and roughly 700
meters in the west central part of the United Arab Republic (Said, 1962).
The exact age of the Nubian Aquifer is unknown. Most of the aquifer
materials have a continental origin and lack fossils. Largely through dates
on underlying and overlying beds, the Nubian Aquifer is assumed to be
largely Lower and Middle Mesozoic. In other words, it was deposited during the period from roughly 200 to 100 million years ago. Owing to this
great age and the fact that it is presently exposed at or near the surface,
ample opportunity must have existed for flushing out the original pore
water in all except the northernmost part of the aquifer. Water is, therefore, for the most part, probably less than a few hundred thousand years
old.
One of the most interesting aspects of the Nubian Aquifer is the origin
of the fresh to brackish water presently within the aquifer. Hydraulic gradients of today suggest that the water is flowing outward from the general
region where the countries of Chad, Sudan, Libya, and the United Arab
Republic join together (Jones, 1966). The climate in this region is, nevertheless, arid and could not produce much recharge under present condi-
21
A. NUBIAN AQUIFER
The Nubian Aquifer underlies a large part of northeastern Africa (Fig.
11). Similar rocks are also important aquifers in part of the northeastern
Arabian Peninsula (Naimi, 1965). In general, the aquifer contains potable
water in the Sudan, the northeastern part of Chad, southeastern part of
Libya, and the southern two-thirds of the United Arab Republic. The
water grades from brackish to salty north of the Qattara Depression.
To date, little significant development has taken place in the aquifer
except in the New Valley Project and near the various oases such as
Dakhla, Farafra, and Bahariya in the United Arab Republic and near
Khartoum in the Sudan. Natural discharge has been largely in the oases
of the Western Desert and in the Qattara Depression. Nubian sandstone
does not crop out in the Qattara Depression, but slow, upward leakage
through overlying rocks probably takes place.
The Nubian Aquifer is designated as a sandstone in much of the geologic
literature. Its lithology in detail, nevertheless, is quite varied. In the Sudan,
conglomerate, coarse-grained sandstone and medium-grained sandstone are
abundant in the Nubian Aquifer. Lesser amounts of mudstone, and hard
ferruginous and siliceous layers are also present. Most of the coarser strata
have abundant quantities of cement and clays. Lateral variations of lithology are abrupt (Rodis et al, 1968). To the north, in the United Arab
Republic, the finer-grained units appear to dominate in the upper part of
the unit. The maximum thickness of the Nubian Aquifer in the Sudan is
about 500 meters (El Boushi and Whiteman, 1967) and roughly 700
meters in the west central part of the United Arab Republic (Said, 1962).
The exact age of the Nubian Aquifer is unknown. Most of the aquifer
materials have a continental origin and lack fossils. Largely through dates
on underlying and overlying beds, the Nubian Aquifer is assumed to be
largely Lower and Middle Mesozoic. In other words, it was deposited during the period from roughly 200 to 100 million years ago. Owing to this
great age and the fact that it is presently exposed at or near the surface,
ample opportunity must have existed for flushing out the original pore
water in all except the northernmost part of the aquifer. Water is, therefore, for the most part, probably less than a few hundred thousand years
old.
One of the most interesting aspects of the Nubian Aquifer is the origin
of the fresh to brackish water presently within the aquifer. Hydraulic gradients of today suggest that the water is flowing outward from the general
region where the countries of Chad, Sudan, Libya, and the United Arab
Republic join together (Jones, 1966). The climate in this region is, nevertheless, arid and could not produce much recharge under present condi-