FACULTY OF ENGINEERING CAIRO UNIVERSITY

The Nubian Sandstone Aquifer and the Debates About its Renewability

Introduction To Water Resources Engineering

Presented by Abdulsalam Mohammed Abdulsalam Thabet 1095402

Ahmed Ali Abdullah Mohammed 1073009

Ahmed Mohammed Abdelhamid Ibrahim 1098456

Hassan Yahya Mahmoud Abdulsalam 1101065

Hossam Eldin Mohammed Saied Abdulhamid 1092469

Supervised by

Prof. Dr. Ahmed Emam

Prof. Dr. Hisham Bekhit

I

Abstract

The Nubian Sandstone Aquifer is one of the largest groundwater basins in the world and it was

the subject for a lot of studies since 1920s. The aim of this paper is to give the reader a brief

background about this aquifer and to discuss the debate about its renewability. The report

discussed the aquifer and its renewability using supportive details and demonstrated it by

the aid of graphics, analysis and recommendations of different well-known specialists and

scientists in the field.

II

Acronyms

ANS The Arabian Nubian Sheild

CEDARE Center for Environmental and Development for the Arab region and Europe

NSAS Nubian Sandstone Aquifer System

NAS Nubian Aquifer System

PNAS Post Nubian Aquifer System

III

Table of Contents Table of Contents ..................................................................... III

List of Figures .......................................................................... IV

List of Tables ............................................................................. V

I. Introduction ........................................................................... 1

II. Problem Description .............................................................. 2

A. Geography And Hydrological System ................................. 2

B. Hydrogeological System ..................................................... 5

C. Discharge and Recharge ...................................................... 7

III. Current Study ...................................................................... 9

A. NSAS Ground Water Storage .............................................. 9

B. Environmental Situation .................................................... 11

C. NSAS Groundwater Origin Theories ................................ 12

IV. Discussion ......................................................................... 13

V. Conclusion ........................................................................... 15

VI. References ......................................................................... 16

IV

List of Figures Figure 1 …………………………………………………………………2

Figure 2 …………………………………………………………………4

Figure 3 …………………………………………………………………6

Figure 4 ……………………………………………………..…………11

V

List of Tables Table 1 …………………………………………………………………8

Table 2 ………………………………………………………………...10

Table 3 ……………………………………………………...…………10

Table 4 ………………………………………………………...………10

1

I. Introduction

The importance of searching for new water resources increases as water scarcity

increases globally. In parallel with this, comes the importance of utilization of the existing water

resources to meet our needs and to sustain water supply for the ever increasing demand and for

next generations. In semi-arid and arid regions, Groundwater is considered a vital source for

domestic water supply, agriculture and industry. This directly leads us to the importance of

studying the characteristics of groundwater in these areas, and whether the groundwater sources

we have are considered renewable water resources or nonrenewable resources since each type

has its own and different constraints when we deal with it. The importance of knowing the

renewability of a water resource is also doubled when we are dealing with a Trans Boundary

resources as the water storage in this case can’t be claimed to be owned by only one country, so

studying the renewability of this source is vital to develop a better management and use-

organizing frame for this water resource.

The Nubian Sandstone Aquifer System is a huge water system that lies under and shared

by four countries; Egypt, Sudan, Chad and Libya (CEDARE, 2002). This Aquifer provides a

huge water storage that can be used to satisfy all water needs for the domestic uses of the oasis

lie on the east part of Egypt. That’s why it’s very important to put this aquifer under study and

research to know its boundaries, origin, hydrological/hydrogeological system and renewability.

In this paper we aim to discuss mainly the renewability of the mentioned water resource;

Starting by identifying its boundaries and hydrological system, and then highlighting the

resource’s origin theories as they lead to a better understanding for the way this resource was

formed which leads to a clearer vision about its renewability probabilities.

2

II. Problem Description

A. Geography And Hydrological System

The Nubian Sandstone Aquifer System (NSAS) at the North Eastern part of Africa is

a Trans Boundary Aquifer shared between Egypt, Sudan, Chad and Libya with almost

equal surface area in each four countries (Mirghany, 2012). It’s a large regional

groundwater basin that covers a total area of 2,200,000 with stored water volume of

373,000 (CEDARE, 2002)1. It crosses the major part of Egypt (29%), and eastern

parts of Libya (32%), the northern parts of Sudan (29%) and the northeast parts of Chad

(10%) (MoIWR, 2009). Its area (Figure 1) extends between latitudes - and

longitudes - East. the basin lays in desert, semi-desert and zones with low

rain savanna (Mirghany, 2012). The volume in storage is said to represent the largest

freshwater mass in the whole world (Abuzaid and ElRawady, 2008).

1 Although the NSAS has been the subject of too many studies, the information about the total volume of water

stored is still limited and we found that the value varies in a very wide range (from 15,000 KM3 to 457,550 KM3). We have chosen this value as it has a valid proof that we can build on as we will discuss later in this paper.

Figure 1 The NSAS is one of the largest aquifers in the world and spans approximately 2 million square

kilometers across Libya, Egypt, Chad and Sudan (International Waters Learning Exchange and Resource

Network, 2014)

3

The Aquifer is considered to be a closed system. It has natural boundaries (Figure

2) to the east and the southeast formed by the mountains of the Nubian Shield2. It is

bounded from the south and west by Kordofan Block, Ennedi, and Tibesti mountains.

The aquifer is bounded by the groundwater divide located between Tibets and Ennedi

Mountains in the southwestern part of the basin. From north; the boundary is the Saline-

Freshwater Interface, Whose location is considered spatially stable, although sometimes

there are slight movements (Thorweihe and Heinl, 1999, Cited in: SEFELNASR, 2007).

Low irregular rainfall is the main characteristic of the climate in this region.

Persistent of drought led to land degradation with time and desertification. The average

annual precipitation according to records is less than 25 mm. Rainfall in the northern

parts is the least and it increases as we move to South where the average annual

precipitation hits 200 mm at Khartoum but it its distribution is very erratic. The average

temperature in the area is very high and more than 〖40〗^OC during summer months.

The maximum temperature is usually between May and September. The minimum is

usually between December and March. The wind in this area is, most of the time, from

north to south (Mirghani, 2012).

The main recharge sources are occasional rainfalls, flash floods and groundwater

flow from southern and eastern mountainous belt but the recent annual recharge is very

small and negligible (Müller, Dengler and Leicht, 2006).

2 “The Arabian-Nubian Shield (ANS) is an exposure of Precambrian crystalline rocks on the flanks of the Red Sea.

The crystalline rocks are mostly Neoproterozoic in age. Geographically - and from north to south - the ANS includes the nations of Palestine, Jordan. Egypt, Saudi Arabia, Sudan, Eritrea, Ethiopia, Yemen, and Somalia. The ANS in the north is exposed as part of the Sahara Desert and Arabian Desert, and in the south in the Ethiopian Highlands, Asir province of Arabia and Yemen Highlands.” (Wikipedia)

4

Figure 2 Natural boundaries of NSAS (SEEFLNASR, 2007)

5

B. Hydrogeological System3

Because of the geology of the region, The Nubian Sandstone Aquifer System is

divided into two different parts (Figure 3). The greatest and oldest part is the Nubian

Aquifer System (NAS) which is unconfined. The other part is the Post Nubian Aquifer

System (PNAS) which lies under Libya and Egypt. A low permeability layers are

separating the two systems. (Bekhbakhi, 2006)

According to a paper published by Dr. Muna Mirghani in February, 2012; the Nubian

basin itself is composed of hydraulically connected groundwater sub-basins where

different uplifts subdivide the aquifer system and contribute in shaping it (Wycik, 2004,

Cited in: Mirghani, 2012). The problem is that these boundaries of sub-basins are not

well known and are overlapping in different places. But till now we that they include:

1) Kufra Basin in Libya, Chad and Sudan.

2) Dakhla Basin in Egypt.

3) Sarir Basin in Libya.

4) North Darfur Basin in Sudan.

5) Main Nile Basin in Sudan and Egypt.

Also the NSAS is covered by a number of surface drainage basins that, unfortunately, are not

clearly defined. (Mirghani, 2012).

3 In this paper we wanted to differentiate between the geography and the hydrogeology of the NSAS as in most of

the papers, researches and articles we found that both are considered one part sometimes which may cause some confusion. In this paper; we considered that geography is related to the location and horizontal boundaries but hydrogeology is related to vertical boundaries, soil properties, depth and earth shape in the different parts.

6

Figure 3 Nubian System and Post Nubian System (Bekhbakhi, 2006)

Nubian formation is lying flat to gently dipping rocks consist of continental sediments

including sandstone, gravel, clay and conglomerates, topped with alluvial deposits (Mirghani,

2012). NAS includes Paleozoic and Mesozoic deposits and complex overlies Precambrian

basement; PNAS includes continental deposits in Libya, Egypt and carbonate rocks in Egypt;

there is separator layer belongs to the Upper Cretaceous and the lower Tertiary (CEDARE,

2008).

The Nubian Sandstone Aquifer System reaches a maximum depth of 4,500 m. The

Hydraulic head ranges from 570 m above sea level west to Darfur to 78 m in the Qattara

Depression (Alker, 2009).

Based on radiocarbon dating the groundwater stored in the NSAS dates from 100,000 to

1,000,000 years ago and up to 2,000,000 years in the deeper zones (Zektser and Everett, 2004).

Water quality in the NSAS varies from excellent in the parts to the south, with 500 ppm

total dissolved solids (TDS), to high salinity in the parts to the north. The part contains high

salinity of the aquifer lies mostly under Libyan lands (Alker, 2009).

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C. Discharge and Recharge

The discharge from the studied system can be divided into two types. The first one is

the natural discharge. The second one is the discharge due to the groundwater

withdrawal.

In the oases and depressions at the Nubian Sandstone Aquifer System, the

groundwater level occurs close to the surface immediately or even above the ground as a

condition of artesian groundwater, and also flows naturally as springs in some locations.

Because of the surrounding arid areas, groundwater discharge occurs either by natural

evaporation of the springs, and high capillary of underground water and transpiration

from wild plants. The estimation of the natural discharge of NSAS by evapotranspiration

in the depressions is about 10-15 mm/a4 (Sonntag Et al, 1987 Cited in: SEEFLNASR,

2007). The average groundwater loss from storage was estimated to be some 109

m3/year. (SEEFLNASR, 2007)

According to SEEFLNASR research; the total present extraction (discharge) from

NSAS equals 2.177 /year (Table 1).

4 It has to be mentioned that during our search we have founded that an approximation of the evapotranspiration

can be given by Thornthaite method that can be expressed in the following formula:

. Where Et is

the possible evapotranspiration [cm/month], T is the monthly average temperature [Co], I and a are parameters that depend on many variables. It means that once the monthly average temperature is known for a point we can use this equation to calculate the evapotranspiration. (Zhou etal, 2003 Cited in: SEEFLNASR, 2007)

8

Table 1 Present extractions from NSAS (SEEFLNASR, 2007)

Country Present extraction (

PNAS NAS Total

Egypt 0.306 0.2 0.506

Libya 0.264 0.567 0.831

Sudan - 0.84 0.84

Chad - 0.0 0.0

Total 0.57 1.607 2.177

The recharge of the NSAS has three possible ways according to the transient

theory of the groundwater origin:

Seepage of Nile water.

Regional groundwater influx from areas with modern groundwater

recharge.

Local infiltration through precipitation during wet periods in the past

It has to be mentioned here that the theory disbelieved the quantity of the recharge and

the significance of such kind of recharge for the Nubian Sandstone Aquifer System

(Thorweihe and Heinl 2002, Cited in: Abuzaid, 2008).

Since that approach is still under evaluation and study there is no need to dig into it

now and we can assume that recharge from the mentioned above resources is negligible.

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III. Current Study

Although that most of the studies tend to neglect the recharge to the NSAS from

infiltration and seepage and this accordingly should lead to the conclusion that we are dealing

with a nonrenewable resource, it can’t be determined that easy whether it’s a renewable or

nonrenewable water resource. Scientists and water resources engineers have conducted too

many researches using technology and advanced tools to get to know whether the NSAS is a

renewable water resource or not. In this part we will highlight the origin theories of the

NSAS and the studies made by other scientists using satellites and GIS techniques to get to

understand this water resource in a better way.

A. NSAS Ground Water Storage

Generally, the lack of area-wide data concerning geological structures, porosity, and

the various thicknesses of water-bearing strata throughout the basin has led to a relatively

high level of uncertainty. The issue of ground water storage in the NSAS has been

published frequently. The most known studied we found are from Ambroggi (1966), who

estimated the total groundwater volume at 15,000 , And from Gischler (1976), who

considered it to be at least 60,000 . Thorweihe and Heinl (1996) estimated the

groundwater volume of the Nubian Sandstone Aquifer System to be 150,000 , with a

very large amount of water largely exceeding the previous estimates.

CEDARE/IFAD in 2002 and based on the most updated database and the GIS

technique estimated the groundwater storage volume to be 372,950 .

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The author made this estimation using the modeled saturated volume and calibrated

hydraulic parameters of the system. And this volume to some extent is for academic uses

and interests only5. The following tables (2,3 and 4) summarize the data collected by

CEDARE/IFAD (2002) and taken from a paper published in 2006 by UNESCO and

Bekhbakhi.

5 This volume is considered of academic interest only since it is economically unreasonable and infrastructurally

impossible to obtain groundwater from great depths over broad areas of the aquifer system.

Table 2

Table 3

Table 4

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B. Environmental Situation

Based on researches published in 2006 by Margat etal; the non-renewability is

never strictly expressing groundwater resources, but in many cases, especially in the

arid regions, the time span required for aquifer replenishment is normally too long in

relation to the normal time frame of human activities in general and of water

resources planning in particular. In cases where groundwater is available for

extraction from the reserves of an aquifer which has a very low current rate of

average annual recharge but a large storage capacity, this ground water resource can

thus be termed “non-renewable” (Alker, 2009). And this exactly can be applied on the

NSAS (Figure 4).

Figure 4 The concept of non-renewability of the Nubian Sandstone Aquifer System. Typically, recharge area, transmission area and discharge area (SEEFLANASR, 2007)

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C. NSAS Groundwater Origin Theories

The ground water origin in the NSAS has been the subject of too many discussions

by several authors since the 1920s. In general, there are two main concepts that have

presented the origin of groundwater in the NSAS (Thorweihe and Heinl, 2002):

The allochthonous6 concept. It is an old theory adopted mainly by Ball (1927) and

confirmed by Sandford (1935). The theory claims that there’s a flow of

groundwater from precipitation in the most southern mountains parts of the

system to provinces of discharge in the aquifer. The concept was justified from

the regional piezometric map and flow direction of the aquifer, which illustrates a

general flow direction from southwest to the northwest of the aquifer. According

to this theory the groundwater is renewable, and the basin is receiving some

recharge at intake areas estimated to be about 1.6 /year. This concept is still

valid till now, though rejecting the steady state idea.

The autochthonous7 concept. This concept is based mainly on the chemical

analysis of the groundwater or what is called interpretation of the isotopes. From

this analysis scientists concluded that no age gradient along the stream lines was

detected; on the other hand, no flow direction could be seen. The theory

concluded that the bulk of the groundwater mass within the basin was formed in

situ in the area surrounding the present discharge areas during the humid pluvial

periods of the Holocene (Sonntag 1986, Pachur 1999).

6 Scientific term that is used by geologists to describe something found in a place other than where they or their

constituents were formed. 7 Scientific term that is used by geologists to describe something that is originating or formed in the place where

found.

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IV. Discussion

Based on the previously mentioned facts and theories about the Nubian Sandstone

Aquifer System and its renewability; we find ourselves in front of a very large debate

about its renewability; Especially that each theory is based on a valid data and

assumptions about the renewability of the studied basin. But we are still don’t see that

each of the points of view included all the parameters that could be included to lead to a

valid decision whether it’s a renewable or nonrenewable water resource.

When Ball and Sandford developed the origin theory that concluded that the NSAS is

renewable water resource there was an obvious matching among the slope of

groundwater level, the gradient of precipitation in the southern parts of the basin, and the

general flow direction to the northeast. We see that such matching might have led them to

a false conclusion that the aquifer is renewable and gets continuous recharge from the

south regions. They also ignored the groundwater velocity, the permeability of the aquifer

layers and the climatic changes which may have misled them to that conclusion.

Based on this we tend to believe that NSAS is a non-renewable water resource. This

tendency is not based on the difference between the discharge and recharge rates from the

basin, as most of the studies neglected the recharge since it’s very small, But this

tendency is based on the fact that until now we can’t find the source of the groundwater

formed in this area and no possible main recharge source was found and there are no

clues for the possibility of existence of one in the past, and taking into consideration that

no rainfall has occurred in the area during the last 80 years.

14

It also has to be mentioned that during our searches we found published articles

about researches made by Dr. ElBaz and Dr. Eman Ghoneim in which they claim that

there was an old river in the area of the basin during the ice ages that got buried later and

the great sand sea was formed instead of it where the river water turned to be great

groundwater basin. But, we couldn’t get the full paper and we didn’t find any articles for

other authors that got to the same approach.

We believe that when it comes to the definition of non-renewability of a water

resource there’s some confusion as it’s not defined clearly till now and we don’t know

how to consider a water resource as renewable or non-renewable. For example during our

searches we found that many scientists believe that a state of “zero recharge” is extremely

rare. That’s why the other point of view related the definition of renewability to the

period needed for replenishment of a water basin as it gets bigger in comparison with the

normal time-frame of human activities in general it means that it could be considered as a

nonrenewable water resource. Also, the closest term that is defined in the International

Glossary for Hydrology, 1992 is “Fossil groundwater”. It’s defined as “water that

infiltrated usually millennia ago and often under climatic conditions different to the

present, and that has been stored underground since that time” (Abuzaid and ElRawady,

2008).

It means that if we decided to depend on the definition of the fossil groundwater as a

definition for the non-renewable water resource, we have to deal with NSAS as a non-

renewable water resource neglecting Margat et al point of view for example that depend

on the time span of replenishment. This can’t be considered as a valid approach since we

could have non-renewable water that is not fossil water too.

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V. Conclusion

When assessing groundwater aquifers, the term “non-renewable” is totally relative.

The term has always been associated with aquifers underlying arid areas where no surface

recharge is applied. The Nubian Sandstone Aquifer has too many parameters that should be

taken into consideration before deciding whether it’s renewable or not. Till now and based on

the current studies and researches we can’t say that the NSAS has a continuing recharge

source so that it could be considered a renewable resource, and it’s probably a basin that was

formed during the wet/ice ages where this arid area had a high rainfall. But now it’s an arid

area with very low annual average rainfall precipitation. That’s why we should decide to deal

with NSAS as a non-renewable resource till we can prove the opposite. It’s very important to

make that decision since it’s a Trans Boundary water basin and determination of the

renewability issue is very important to organize and utilize its use between the sharing

nations and generations.

16

VI. References

Abuzaid, K. M., & Elrawady, M. H. (2008). Sustainable Development of Non-renewable Groundwater.

CEDARE, 1-10.

Abu-zeid, K., & El-Meguid, A. A. (2008). Pioneering Action in Managing the Transboundary Nubian

Sandstone Groundwater Aquifer. CEDARE, 4-12.

Alker, M. (2009). The Nubian Sandstone Aquifer System: A case study for “Transboundary groundwater

management in africa”. German Development Institute Journal, 237-248.

Bekhbakhi, M. (2006). Regional Cases: Nubian Sandstone Aquifer System. In S. Foster, & D. P. Loucks,

Non-renewable Groundwater Resources (pp. 69-75). Saint-Denis, France: United Nations

Educational, Scientific and Cultural Organization.

CEDARE. (2002). Regional Strategy for the Utilization of the Nubian Sandstone Aquifer System Volume II.

Cairo, Egypt: CEDARE.

Michel, D., & Pandia, A. (2009). Troubled Waters: Climate Change, Hydropolitics, and Transboundary

Resources. STIMSON, 1-14.

Mirghani, M. (2012). GROUNDWATER NEED ASSESMENT - Nubian Sandstone Basin. Watertrac, 1-7.

MoIWR. (2009). SADA Country Report. Sudan.

Müller, M., Dengler, C., & Leicht, F. (2006). The Nubian Sandstone Aquifer System. Berlin, Germany:

Martina Müller.

SEFELNASR, A. M. (2007). DEVELOPMENT OF GROUNDWATER FLOW MODEL FOR WATER RESOURCES

MANAGEMENT IN THE DEVELOPMENT AREAS OF THE WESTERN DESERT. In A. M. SEFELNASR.

Halle: Martin Luther University Halle-Wittenberg.

Thorweihe, & Heini. (1999). Groundwater Resources of the Nubian Aquifer System. Regional Aquifer

Systems - Managing Non-renewable resources (pp. 42, 58-67). Tripoli: UNESCO-IHP V Technical

Documents in Hydrology.

Zektser, I. S., & Everett, L. G. (2004). GROUNDWATER RESOURCES OF THE WORLD AND THEIR USE. Saint-

Denis: United Nations Educational, Scientific and Cultural Organization.

Zwirn, M. (2014, February 14). Nubian Sandstone Aquifer System (NSAS) . Retrieved May 23, 2014, from

IW:Learn: http://iwlearn.net

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