Hydrochemistry and environmental isotopes of spring water and their relation to structure and lithology identified with remote sensing methods in Wadi Araba, Egypt [original]

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Hydrochemistry and environmental isotopes of spring water

and their relation to structure and lithology identified

with remote sensing methods in Wadi Araba, Egypt

Manal Wannous

&Barbara Theilen-Willige

&Uwe Troeger

1,2

&Marianne Falk

&Christian Siebert

&Florian Bauer

Received: 6 July 2020 /Accepted: 24 March 2021

#The Author(s) 2021

Abstract

Springs located at the historical sites of Wadi Araba (Eastern Desert of Egypt) and emerging from the escarpments of the

Northern and Southern Galala Plateaus were investigated. A combination of methods, including hydrochemistry, stable and

radioisotope composition, and structural analyses based on satellite data, provided information about the structure of the sub-

surface and the derived groundwater flow paths. Satellite images reveal karst features within the northern plateau, e.g. conical

landforms. Karstic caves were documented along both escarpments. Chemical analysis of floodwater from Wadi Araba indicates

higher concentrations of terrestrial salts compared to floodwaters from central and southern parts of the desert. δ

Oandδ

signatures in spring waters resemble those of floodwater and fall on the global meteoric water line, confirming their fast

infiltration with minor influence of evaporation. The aquifer feeding the springs of the Northern Galala Plateau has low retention

and the springs dry out quickly, even after heavy rainfall. Contrastingly,

H activities in springs emerging from the Southern

Galala Plateau refer to much slower subsurface passage. With respect to

H content (3.8 TU) in recent flood waters, the spring

water at Southern Galala Plateau contains about 40% recently recharged groundwater. However, its largest spring—the St.

Antony spring—discharges water with a radiocarbon age of about 15,000 years. In combination with this spring’sconstant

and high discharge over a period of several months, that age estimate suggests a large reservoir with moderate to high retention.

Keywords Groundwater recharge .Egypt .Stable isotopes .Mean residence time .Lineaments

Introduction

In the Eastern Desert of Egypt, as in most arid regions

worldwide, groundwater is the only noteworthy source

for water supply. Since ancient times, the establishment

of settlements and agricultural areas has relied on that

source, particularly on perennial discharging springs.

That situation is observable in Wadi Araba, a 110-km

long and about 20-km wide arcuate valley, which is

flanked by the Northern and Southern Galala Plateaus,

and finally opens into the Gulf of Suez in the north-

western part of the Red Sea (Fig. 1). In the Wadi Araba

Valley, groundwater is abstracted from springs and

wells scattered over a wide area (Fig. 2). The springs

predominantly originate from the fractured aquifer

forming the Galala Plateaus (El-Sadek et al. 1998).

The northern part, which extends up to the Suez

Governate, contains several thermal springs. Previous

studies investigated their stable isotope composition,

mineralization, the source of the enhanced temperatures

andenergypotential(Sturchioetal.1996; Abouzied

et al. 2020). Nassim (1990) applied aerial images to

analyse lineaments that focus the surface water drain-

age, mapped springs in the region, and classified

*Manal Wannous

manal.wannous@tu-berlin.de

Water Engineering Department, Central Institute El Gouna,

Technische Universität Berlin, Acker Str.76, 13355 Berlin, Germany

Institute of Applied Geoscience, Technische Universität Berlin,

Ernst-Reuter-Platz 1, 10587 Berlin, Germany

Museum of Natural History, Leibniz Institute for Evolution and

Biodiversity Science, Invaliden Str. 43, 10115 Berlin, Germany

Department of Catchment Hydrology, Helmholtz Centre for

Environmental Research –UFZ, Theodor-Lieser Str. 4,

06120 Halle, Germany

Karlsruher Institute of Technology Campus Nord,

Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen,

Karlsruhe, Germany

https://doi.org/10.1007/s10040-021-02343-x

/ Published online: 4 June 2021

Hydrogeology Journal (2021) 29:2245–2266

groundwater aquifers in Wadi Araba. Following local

knowledge, a number of springs has been documented

along the northern flank of Wadi Araba, usually flowing

insmallpondsusedbysmallcommunities.

Particularly in the Southern Galala Plateau region, produc-

tive springs have been used since ancient times to provide

water for settlements such as the two >1,500-year-old monas-

teries—St. Anthony’s Monastery (SAM), located at the south-

ern flank of Wadi Araba, and St. Paul’s Monastery (SPM),

located some 20 km further SE (Fig. 1). Within the area of

SAM several springs emerge along an 800-m-long lineament

and are intended as emergency source of water supply for 350

residents and for irrigation purposes. Unlike SAM, in the area

of SPM a single spring emerges, intended to serve the same

purpose.

Except for a few quality data of the main springs of

St. Anthony and St. Paul (Nassim 1990), neither re-

charge mechanisms nor discharge dynamics of the

springs that emerge in Wadi Araba and in these histor-

ical sites have been adequately investigated yet.

According to the authors’own measurements, the larg-

est of the SAM springs yields an average discharge of

87 m

/day and is flowing all year round, while many of

the small springs along the northern rim of the valley

fall dry. Thus, this study aims at mapping and charac-

terizing the groundwater springs in Wadi Araba, with a

special emphasis on the springs at SAM and SPM. The

evaluation of satellite image data can contribute to: (1)

the detection of fault and fracture zones influencing the

groundwater flow and fluid permeability of rocks, (2)

Fig. 1 aMap indicating the location and morphology of Wadi Araba,

which opens into the Gulf of Suez at the north-western end of the Red

Sea. bTopographic cross section perpendicular to thevalleyaxis.

Episodic floods formed erosional fluvial landforms including large dry

beds and a meandering bed in the central part of Wadi Araba

2246 Hydrogeol J (2021) 29:2245–2266

deriving the youngest fault pattern cutting the most re-

cent sediments as preferable infiltration pathways, (3)

mapping of structural features and lithologic units which

play a role in storing and transporting groundwater, and

(4) monitoring of morpho-dynamic processes influencing

the infiltration of surface water such as sediment flow,

accumulation and erosion.

The chemical analyses of water samples from spring

locations detected in the area clarify which kind of

aquifer is discharging to these springs and what kind

of water/rock interactions take place in the subsurface.

The stable isotope signatures of

Oand

Hcontribute

to the understanding of (1) climate conditions at which

the water was recharged and (2) whether their isotope

signatures indicate contributions of groundwater from

the Nubian Sandstone aquifer, which springs elsewhere

in the region. The radio isotope analyses of

Hand

were used to calculate the mean resident time of

groundwater in the aquifer, which also allows insight

into whether or not the emerging groundwaters are at

least partially recharged recently by occasional rainfall

or flash floods.

Study area

Climate

The climate in the Eastern Desert of Egypt is arid and gener-

ally characterized by hot summers and moderate winters.

Sporadic and short precipitation events take place in winter

months (between October and April) and their spatial

extension and intensity are extremely variable, e.g. the

event on 27 October 2016 produced more than 100 mm

of precipitation and caused a destructive flash flood in

the town of Ras Ghareb (Saber et al. 2020), while north

(Suez) and central (El Gouna) (Fig. 1), less than 20 mm

of precipitation occurred.

Fig. 2 Map indicating the locations of sampling points in the Wadi Araba area. Inset maps focus on the: aspring group along the northern rim of the

Wadi; bthe Monastery of St. Anthony at the southern rim; cthe Monastery of St. Paul, outside the Wadi on the Southern Galala Plateau

2247Hydrogeol J (2021) 29:2245–2266

The orographic influence of the Galala Plateaus on cloud

distribution in Wadi Araba may lead to rain-bearing cloud

concentration above the Northern and Southern Galala

Plateaus. Observations in Suez, which has the closest climate

station to Wadi Araba, show erratic precipitation events with

usually low amounts, less than 6 mm/day, while only a few

events produced more than 10 mm/day (Fig. 3).

The climate data presented in Fig. 4were obtained from El

Gouna climate station, situated at the Red Sea coastal plain

(27.43 E, 33.66 N). The monthly averages and standard devi-

ations are calculated using the data measured in the period

between March 2014 and January 2019 with a time interval

of 10 min. The range between average ± standard deviation

represents 68% of the data.

The highest temperatures are recorded between June and

August (>30 °C) and the lowest in December/January

(<20 °C). The relative humidity with an annual average of

47% shows a weak seasonal variation with a minimum be-

tween May and August (average 45%) and a maximum be-

tween October and December (average of 50%). Evaporation

data from the region were reported by Awad et al. (1996)with

a maximum annual mean value in June with 10.11 mm/day

and a minimum in December with 6.11 mm/day.

Geomorphology

The geomorphological units of the landscape that are impor-

tant for recharge and precipitation runoff can be differentiated.

The Northern Galala Plateau shows typical conical landforms

related to weathering of limestones and dolomites during more

humid conditions in the past. The uncovered, flat, exposed

fractured carbonate rocks show good properties for recharge.

The Southern Galala Plateau is block-wise intersected by

distinct visible escarpments related to fault zones (Fig. 1). This

area shows traces of an intense erosion such as deeply incised

valleys. Sand and gravel sediments are accumulated in small

depressions. While the northern escarpment is forming an al-

most continuous line, the southern border of the Wadi Araba

basin is characterized by dissected front lines, intersected by

larger N–S-oriented valleys. Along the northern escarpments,

block gliding and rockfall towards the southern direction are a

common feature. This morphology enables recharge in the

hollows and fissures left behind and the steep slopes promote

more surface runoff. The drainage network indicates a rela-

tively flat bedding of the rocks and is probably the result of

parallel tectonic structures.

The interaction between fluvial and tectonic processes is

evident as the development of channels is influenced by sub-

surface structures and geotectonic movements related to plate

tectonic rifting activity in the Gulf of Suez area and northward

movements of the African Plate.

Geology and tectonic

Wadi Araba is a structurally controlled tectonic basin (Fig. 5).

The major force of the structural development in this area was

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Precipitaon [mm]

Fig. 3 Precipitation depth for the period Jan 2006 to Dec 2016 at Suez climate station (source: National Water Research Center (Egypt), Rainfall data of

the Suez climate station, obtained through personal communications, 2020)

2248 Hydrogeol J (2021) 29:2245–2266

the opening processes of the Red Sea, which started in the

Miocene and continues today (Bosworth and Durocher

2017). The stratigraphy is divided into three major units,

which are related to the evolution of the Red Sea/Gulf of

Suez, i.e. the pre-rift (Pre-Oligocene), syn-rift units (Late

Oligocene–Middle Miocene) and post-rift units (Late

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Relative humidity [%]

Average relave humidity

± Standard deviaon

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Temperature [°C]

Average temperature

± Standard deviaon

Fig. 4 Air temperature and relative humidity records at El Gouna climate station (based on 10 min time series data)

2249Hydrogeol J (2021) 29:2245–2266

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