The Nubian Sandstone Aquifer Systems (NSAS) underlies an area in excess of 2.5 million km2 within The Eastern Sahara in North-East Africa (Figure 1).

Ground Waters
Aquifer Renewable resources

The Phanerozoic succession ( Figure 6 ), having cumulative thickness in excess of 15 kilometers, is distinct into two major units: a lower unit dominated by sand facies mainly ofepicontinental origin,and an upper unit dominated by carbonate facies of marine origin.

There is 6 reservoirs:

ةيرابونلا ةعرت

Geomorphology and Hydrography
The surface of the
Project Area is developed into a number of five mega-watershed areas and mega drainage basins (Figure 4).

At the close of the Paleozoic era, several geosynclinals seas were formed since the beginning of tile Mesozoic (Late Jurassic times). Such seas accounted for two major transgressive phases in N. Africa:
*during the Middle Mesozoic (Cenomanian), and
*during the Late Mesozoic (Upper Senonian) A main regressive~ phase
(with minor ingressions) took place at the beginning of the upper
Mesozoic (Turonian and Lower Senonian).
In the Project Area the surface exposures of the Mesozoic
(Figure 5 and 6 ) occupy much of the southern portion
(South of Latitude 27 ْ N). The exposed section, having a maximum thickness of about 2000m, is differentiated into two main units:
*a thick lower unit (about 1500m); dominated by epicontinental sediments, and
* an upper unit. having a thickness of about 500 m and is developed into marine carbonates and shales, with thin phosphatic horizons.

The oldest rocks exposed in the Project Area belong to the Precambrian and are referred to as the
Basement rocks (Figure 5 & 6).
These outcrop immediately to the south, east and southwest of the Project Area. Local exposures are also found at Oweinat area at the border between
Egypt, Libya and Sudan. These Basement rocks are dominated by granites and grano-diorites, in addition to an association of meta-sediments, metavolcanics, meta-gabros and serpentines.

The Phanerozoic succession ( Figure 6 ), having cumulative thickness in excess of 15 kilometers, is distinct into two major units: a lower unit dominated by sand facies mainly ofepicontinental origin,and an upper unit dominated by carbonate facies of marine origin.

Paleozoic rocks are exposed in SE Libya, SW Egypt, NW Sudan and
NE Chad ( Figure 5 ). The maximum reported thickness is of the order of 1500m in Ennedi in NE Chad. A thinner section of about
500m outcrops in Gebel Haweesh (Dahna) in SE Libya. The succession in both locations is dominated by fluviatile sand facies.
Paleozoic rocks are reported in the subsurface, attain a maximum thickness of about 000m. and are also dominated by sand facies.
Paleozoic rocks are expected, from aero-magnetic surveys to exist in some other localities. Reference is especially made to SE Egypt (in the vicinity of Aswan), where the expected thickness is of the order of
3000m (lssawi, 1999). Figure 9 is a regional isopach map of the
Paleozoic.
From base to top the Paleozoic is differentiated into:
~ The Cambro-Ordovician
~ The Silurian
~ The Devonian
~ The Carboniferous, and
~ The Permean.
The details are indicated in (Table1 ).

Geology
The Basement relief, as outlined by the long term geological and geophysical surveys is fairly well understood (Figure
7 ). Such rocks are overlain by a thick sedimentary section, which is here referred to as the Phanerozoic. The details about the stratigraphy of this section is given here below.

In the northern portion of the Project Area (north of latitude27 o N) the Mesozoic sediments are wide spread in the subsurthce. Local exposures are only tbund in the domal structures of Abu Roash in the vicinity of Cairo City and of Bahareya, 300 km to the southwest. The Mesozoic section, having a cumulative subsurface thickness, in excess of
7000m is developed essentially into marine facies.
Figure 10 is an isopach map of the Mesozoic sediments in the Project Area.
From base to top the Mesozoic is differed into:
~ The Triassic,
~ The Jurassic and
~ The Cretaceous

The Cretaceous is divided into the major units, titled the Lower
Cretaceous, and the Upper Cretaceous. This comprises the
Cenomanian, the Turonian, the Lower Senonian and the Upper
Senonian. Table 2 gives more details about Mesozoic section.

The Cenozoic is differentiated into the following lithostratigraphic units (from base to top):
~ the Paleocene,
~ the Eocene,
~ the Oligocene,
~ the Miocene,
~ the Pliocene,
~ the Pleistocene, and the Hoiocene
The details about each unit is given in Table 3 .

The Mediterranean Depression acted as a major discharging area. An early
Pleistocene event occurred in NE Africa, characterized by a variety of structural features, best represented by the swarm of E-W faults detected in the eastern porlion of the Project Area. The pluvials of the Pleistocene and the sub-pluvials of the Holocene have also significant impressions on the landscape, as well as in the
Nubian Sandstone Aquifer System.
The sediments of the Cenozoic cover large tracts of the
Project Area south of Latitude 26 o . These are represented by extensive and rather thin sand sheets and elongate dunes and also by scattered lacustrine deposits and calcareous tufa. To the north of that Latitude the Cenozoic is represented by thick marine deposits, dominated by carbonate traces, having a thickness in excess of 4000 m. in the Nile Delta Region the marine deposits are overlain by at least 1000m of fluviatile and fiuviomarine deposits assigned to the Quaternary. Figure 11 is an isopach map of the Cenozoic in the Project Area.

The type and magnitude of unconformity differs in the regional tectonic provinces viz the Hinge Belt in the liar northern portion, the Unstable Shelf Belt in the central portion and eventually the Stable Shelf Belt in the southern portion. In the Stable
Shelf Belt, no major breaks in deposition are detected between the Upper
Cretaceous and the Lower Cenozoic.
In the Unstable Shelf Belt the relationship is governed by the paleo-relief inherited from the Late Cretaceous. In the positive areas of the paleo-relief great breaks are known as a result of the non-deposition of the total units of the
Cenozoic. This relationship played a significant role in determing the hydro geological characteristics of the
Nubian Sandstone Aquifer System and the influence of the inland seawater intrusion. Reference can especially be made to major positive areas, which became manifested along the Mediterranean Region between the Nile Delta and Gebel El Akhdar, and which became morphologically developed in Post-Upper Cretaceous times. The details about the techtonical elements are indicated in figure 12 .

Fig.12

The Nubian Aquifer System (NAS); underlying almost all the area of Egypt, Eastern Libya,
Northern Sudan and Northern Chad (Figures 13,
14 and 15 ). This consists of continental clastic sediments, mainly sandstone.
It includes all the aquifers, the confining units and
These comprise: the aquicludes. This system overlies the Pre-
Cambrian Basement Complex. The Strata forming the Nubian Aquifer System range in age from Cambrian to the Pre-Upper Cenomanian.

For the present study the above hydrogeological units, constituting the multi layered aquifer system, have been assumed on a regional basis hydraulically connected and lbr all practical purposes to behave as a one layer aquifer system. This aquifer is under unconfined conditions south of
25th parallel and under confined conditions north of it (Figure 15)

1. Hydrogeological Units
The Pre-Upper Cenomanian geological succession, referred to in this study as the
Nubian, comprises the oldest and the most extended reservoir of supreme hydrogeological interest in Northeast Africa. This succession, having a thickness ranging from less than 500 meters, to more than 5000 meters, shows a marked lateral change of facies, which plays a significant role in determining the hydraulic characteristics of the water bearing horizons.
The succession can be differentiated into three distinct hydrogeological units
( Table 4 ):

a) an upper unit, dominated by clastic facies, changing in the basinwide ward direction into carbonate facies and is assigned to the
Lower and Upper Cretaceous. This unit is extensive and is also highly productive.
b) a middle unit, dominated by sand facies with interbeds of carbonates beds. It is extensive and is also moderately to very low productive; it is assigned to Late Paleozoic and to the Early
Mesozoic.
c) a lower unit, dominated by sand facies with inter-beds of clays, assigned to the Cambro-Ordovician, and is extensive and is also highly productive.

The Post Nubian succession can be differentiated into four different lithostratigraphic units, which form the following hydrogeological units Table 7 :

The Aquifer Boundaries:
The lateral boundaries of the aquifer (Figure 15); determined on the eastern side by the impervious Pre-Cambrian basement complex of the mountain ranges of the Red Sea and northwards the Suez Canal. The
System eastern boundary is designed as a no-flow boundary. On the southern side it is determined by the outcrops of the Basement rocks of
Southern Sudan (Kordfan and Darfur blocks) and Chad (Tibesti and
Ennedi), which represents also a no-flow boundary. In the southeastern
The Aquifer boundary. On the western side there is a groundwater divide extending from Tibesti mountains in the south and continuing northwards along the
19 o Meridian. This boundary represents a no-flow boundary.
The aquifer northern boundary coincides with the Mediterranean coastline, representing a fixed-head boundary the base of the aquifer is taken at the surface of the Pre-Cambrian Basement complex. The Basement surface elevations thll regionally from Sea level in the southern part of the NAS to over 5000m b.s.l, along the northern boundary, as shown in Figure 7.
Figure 15 show the bottom of the confining bed. It also shows that the confining bed is missing north of a lat. 30 ْ between Marsa Matruh and
Alexandria where the NAS and PNAS are in direct contact.

Aquifer Potentiometry
The data obtained from a good number of observation wells, assisted in the preparation of the initial potentiometric surface map
(pre-development) Figure 16 .
This map gives indication to:
*the groundwater divide between Kufra and Chad basins,
*the northwest flow of groundwater from Kufra to Tazerbo and
Sarir (Post Nubian),
*steep northeast flow of groundwater from Kufra to Farafra,
*a northeast flow from W. Howar area to East Oweinat area and
Kharga,
*a complicated flowportion in the Nile Valley area to the north of
Qena Bend (faulted),
*the lack of reliable information about the flow pattern at the border area between Libya and Egypt to the south of Siwa-Jagboub area.

Groundwater from the Nubian Aquifer System has been utilized since centuries in the Oases all over the area through springs and shallow wells. Intensive groundwater development for different purposes (Irrigation, mining, medical tourism and water supply) was initiated in 1960 in the Western Desert Oases of Kharga,
Dakhla, Bahareya and Farafra while it started in 1990 in Siwa
Oasis and East Oweinat areas, and lately in Darb EI-Arbain area.
In Libya, large-scale groundwater extraction from the Nubian
Aquifer System started in 1970 in Kufra Production Project
(KPP) and later in Kufra Settlement Project (KSP).
No historical data regarding water extractions from the NAS was available for Sudan and Chad development areas. Figure 17 shows the locations of the extraction zones from the aquifer in
Egypt, Libya and Sudan.

The total extraction from the Nubian Aquifer System within the study area in 1998, is about 1376 mcm, of which 683 mcm in Egypt, 286 mcm in Libya and 407 mcm in Sudan. In Sudan, the figure includes extraction east of the study area i.e. east of The iNile River in Dongola area and may be even further south. Historical groundwater extraction in the different development areas from the Nubian Aquifer System is indicated in Table 6 .

Aquifer Response to Extraction
Data of water level fluctuations in piezometers, (Egypt: 26 piezometers, Libya: 7single piezometers and 42 dual piezometers) as a response to groundwater extraction from the NAS in the development areas were collected, reviewed and stored in the project database. Well hydrographs for some of the observation wells in two NAS development areas in Egypt and Libya, are presented and discussed in the following:
Figure 18 and Figure 19 show the groundwater extraction in Kharga
(Egypt) and the relevant changes in the water level respectively. They indicate that the groundwater extraction rate increased from 51.0 mcm/y in 1960 to 118 mcm/y in 1998. This created two groundwater depressions in the northern part of the Oasis with a maximum drop of water level of
60 m., while another depression occurs surrounding Bullaq-Garmashin zone with a maximum drop in water level of 35m. In 1960 the groundwater was extracted mainly from naturally flowing shallow wells and springs, while now 97% of the extracted water is pumped from deep wells.

Jalu / Ojla development areas in Libya while a limited datfi is available for the rest of the Aquifer extraction zones in both countries. The historical groundwater production from the PNAS in the different development areas during the period 1976-1998, are given in the Table 9 , which indicates a total of 911 mcm/year is extracted from the aquifer in 1998, and as well be detailed here below:
~ In Egypt 346 million m3/y was extracted ~om this system mainly in El Farafra,
Sewa and W. El Fareigh.
~ In Libya a sum of 565 million m3 were extracted in 1998 mainly from Sarir,
Jalo, Ojla, Marada, Yazerbo and Jabal Al Akhdar.

Kharga

Figure 20 & Figure 21 show the groundwater extraction in Kufra
(Libya) and the relevant changes in water level respectively. Less than 2 mcm/y was extracted in the sixties through shallow wells and springs. In 1973 the extraction has jumped to over 150 mcm and mainly from deep wells to grow progressively to over 284 mcm/y in
1998.
This has lead to a decline in water level ranges between 10-20 m in
Kufra production Project and to less than 5 m in Kufra Settlement
Project during the period 1972-1998, creating a drawdown circle around the pumping centers of less than 25 km in radius.

kofra oasis

1. For the Nubian Aquifer System reference is made to Table
10 which shows the calculated NAS storage capacity in both its unconfined and confined parts, in the fbur sharing countries: Egypt, Libya, Chad and Sudan. It indicates that the total volume of groundwater in storage in the unconfined part is about 9 3 x 10 -11 .

Table 11 shows the results of estimating the volumes of exploitable groundwater from the NAS in Egypt, Libya, Chad and Sudan, which indicates that under the above constraints, a total of about 8.9 xl ()~z m3. can be recovered from the aquifer, representing 2.4% of the volume in storage. If the annual groundwater extraction of 1380 mcnU year presently extracted in the aquifer tbur sharing countries would be kept constant, the recoverable reserves would last tbr a period of about 4860 years.

Potential Ground water Resources
1. In the approach to this subject differentiation, is made between:
* the storage capacity and
* the recoverable amounts of water.
while the total groundwater volume stored in tile confined part is about 265 x l0~z m3. of which 151 xl0~: m~ is hyper saline occurring north of salt water-flesh water interface ( Figure 22 ) and the rest of
114 xl0~z m~ is fresh groundwater. Therefore, it can be concluded that the total volume of fresh groundwater stored in the NAS is about 373 xl0l-" m3.

. For the Post Nubian Aquifer System Table 12 shows calculated PNAS storage
Capacity and Groundwater recoverable volume. It indicates that the total volume of Groundwater in storage is 84.60 x 10i2m3 and the Groundwater recoverable volume of 6.443 x 1012m3. If we limit the fresh water occurrence to the North by the depression marked by several sabkhas along the parallel 3()~ N. the recoverable volume of freshwater is about 5.57 x l02 m3.

Ground water Quality
Water quality in the unconfined part of the Nubian Aquifer System is good (TDS less than 1000 ppm) to excellent (TDS less than 500 ppm) all over the area.
For the confined part of this system particularly in the area up to
Lat. 30 o in Egypt and Lat. 26 o in Libya, the water quality changes laterally and vertically where the upper part of the aquifer system
(Mesozoic) contains fresh water (TDS less than 2000 ppm), while the lower part of the aquifer system (Paleozoic) becomes saline very rapidly north of the Lat. 26 o and west of the Long. 27 o till it reaches the freshwater- saline water interface where the whole aquifer becomes saturated with hyper saline water. The data obtained from
Drill Stem Tests (DST) or calculated from SP logs for a good number ofoil wells, in Libya and Egypt, tapping the upper most horizons of the Nubian Aquifer System, shows the groundwater chloride salinities ( Figure 22 ).

Extent and Boundaries of the Aquifer
The Post Nubian Aquifer System (PNAS) overlies the Nubian Succession north of the 26.h parallel in the study area (Figure 23 ), and assigned to the Mesozoic-
Cenozoic (Post Lower Cenomanian), having a cumulative thickness of the order of
5000 m.
This group is regionally missed in the southern part of the study area(with the exception of its southeastern extension in Sin E1-Kadab plateau west of Aswan), due to non-depositional conditions and is also locally missed in the northern part due to erosion.
The PNAS is bounded by:
*In the south by the 26 th parallel demarking the limit of the deposition, forming a no flow boundary.
*In the west by the 19 Meridian north of Tibesti, as a no-flow boundary.
*In the east, the Red Sea basement mountains and the Suez Canal, which represents a no-flow boundary.
*In the north by the Mediterranean sea.
The vertical boundaries of the aquifer are represented by its base, which coincideswith the top of the confining bed to the underlying Nubian aquifer ( Figure 23 ), while the top of the aquifer is represented by its water table.

Hydraulic Parameters
Table 8 represents the results of the interpretation of the pumping tests conducted in those wells tapping different aquifers of the PNAS (48 wells in Sarir well field in Libya and 18 wells in the Western Desert of Egypt). It indicates that the Post Nubian Aquifer Hydraulic conductivity ranges between 3.6 x 10.5 m/s. in the area between West Delta and Qattara
Depression, 6.4 x 10-5 m/s. in northwestern Western Desert and 3.1 x 10-4 m/s to 8 x 10.5 m/s in Sarir.

The aquifer transmissivity ranges between 1.6 x 10.2 m2/s. in Sarir area, 2.8 x 10 -4 to 2 x 10 -3 m 2 /s. for the moghra aquifer in West Delta - Qattara depression Zone and 6 xl0 -5 to 8 xl0 -4 m 2 /s. for the middle Miocene limestone aquifer in
EI-Diffa plateau. Figure (24) shows the Post Nubian aquifer transmissivity map.
Aquifer Potentiometry
Based on the available data about depth to water of those wells tapping the PNAS and their site elevations, a potentiometric surface map was prepared (Figure 24 ).

Aquifer Response to Extraction
Based on the observed decline in water levels in the Sarir water production projects during the period 1975-1977 to
1998, a contour map showing the drop in the water levels tbr the same period, is prepared.
Figure 26 indicates a decline of water level ranging between 5-8m. within the North Sarir project, 3-8 in the
South Sarir project and from l-4m in the well field of the
Sarir Water Transport Scheme. The map also shows that the cones of depression are connected and form a unique large depression enclosed by the I m. iso-decline contour line due to the effect of the three well fields.
No reliable data are available for the other areas.

The Post Nubian reservoir exists only in Egypt and Libya but it is definitely more important in
Libya in term of development potential. It was assumed to be under unconfined conditions all over its domain. In Sarir and Jalu-Awjilah areas, the Libyan development programmes increasing the discharge from 9.70 m3/s (306 Mm3/yr) today to 36.28 m3/s (1145 Mm3/yr) in
2010 then keeping it constant until 2060, were simulated.
In Siwa,, the present discharge in that area 8.37 m3/s (264 Mm3/yr) has not been increased. The model calculated an additional drawdown of some 20 m in Siwa area, similar to that calculated with the constant discharge everywhere, and of some 20 to 65 m in Sarir well fields. ( Figure 27 ).

ايبيل
رصم

Model of deceasing discharge of reservoir during 60 years

The Pre-Upper Cenomanian deposits, (Nubian Aquifer System) called Nubian, extend over the four countries but is intensively exploited in Egypt and Libya only.
South of the 26th parallel, the Nubian Aquifer System is under unconfined condition. As anticipated, the unconfined part of the Nubian aquifers includes the most important groundwater potential of the whole basins: the extension of the cones of depression resulting from the water abstraction in existing and planned well fields in that part of the Nubian domain is always limited and makes it possible to multiply the centers of extraction. North of the 26th parallel, on the contrary, where the Nubian is under confined condition, the aquifer response to water abstraction from the various oases (essentially New Valley and Siwa), makes up a unique large cone of depression, though deeper in correspondence to the abstraction zones. This behavior of the Nubian aquifers, north of the 26th parallel made it necessary to limit the future groundwater abstraction in the simulated highest scenario ( Simulation 11 ) much lower than proposed by the Egyptian authorities. In the case of Siwa in Egypt and the symmetric Jaghbub referred to the political border, from where the Libyan authorities are planning to develop a water transport system to the most eastern Libyan coast, the reciprocal interference between-the two development areas is so strong that the planned abstraction had to be limited to 68 Mm3/yr from both areas, also in view of the slight reliability of the model in that area and of ther risk of deterioration of the water quality.

Recommendations to the Regional Programme
Steering Committee (RPSC):
*The findings of the project, the developed database and the calibrated model may be used by the [bur countries lbr thrther simulation of scenarios on both regional and local scales.
*Further studies and modeling should be carried out to tackle the water quality is sties including saline water intrusion as well as the environmental impacts related to water use.
*To enhance the cooperation among the countries sharing the Nubian Basin, the existing cooperative framework should be reint brced by both legislative and institutional mechanisms.
*Regional monitoring network to be augmented particularly in the New Valley and Siwa in order to improve the reliability of the model in these areas.
*Regular monitoring for checking the possible interference across the boundaries, particularly in Siwa and Jaghboub as well as in East Oweinat and Selima is necessary.