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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).
7
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.
9
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 .
10
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
11
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)
12
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.
13
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.
15
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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