SPECIAL ISSUE
Localisation and temporal variability of groundwater discharge
into the Dead Sea using thermal satellite data
U. Mallast • C. Siebert • B. Wagner •
M. Sauter • R. Gloaguen • S. Geyer •
R. Merz
Received: 30 December 2012 / Accepted: 28 February 2013 / Published online: 19 March 2013
 The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract The semi-arid region of the Dead Sea heavily
relies on groundwater resources. This dependence is
exacerbated by both population growth and agricultural
activities and demands a sustainable groundwater man-
agement. Yet, information on groundwater discharge as
one main component for a sustainable management varies
significantly in this area. Moreover, discharge locations,
volume and temporal variability are still only partly
known. A multi-temporal thermal satellite approach is
applied to localise and semi-quantitatively assess ground-
water discharge along the entire coastline. The authors use
100 Landsat ETM ? band 6.2 data, spanning the years
between 2000 and 2011. In the first instance, raw data are
transformed to sea surface temperature (SST). To account
for groundwater intermittency and to provide a seasonally
independent data set DT (maximum SST range) per-pixel
within biennial periods is calculated subsequently.
Groundwater affected areas (GAA) are characterised by
DT \ 8.5 C. Unaffected areas exhibit values[10 C. This
allows the exact identification of 37 discharge locations
(clusters) along the entire Dead Sea coast, which spatially
correspond to available in situ discharge observations.
Tracking the GAA extents as a direct indicator of
groundwater discharge volume over time reveals (1) a
temporal variability correspondence between GAA extents
and recharge amounts, (2) the reported rigid ratios of dis-
charge volumes between different spring areas not to be
valid for all years considering the total discharge, (3) a
certain variability in discharge locations as a consequence
of the Dead Sea level drop, and finally (4) the assumed
flushing effect of old Dead Sea brines from the sedimentary
body to have occurred at least during the two series of
2000–2001 and 2010–2011.
Keywords Landsat ETM?  Sea surface temperature 
Submarine groundwater discharge  Groundwater resource
Introduction
The water level of the hypersaline Dead Sea (DS) has been
decreasing significantly for several decades. Main reasons
relate to the high evapotranspiration rates and a decreased
groundwater/surface water contribution (Salameh and El-
Naser 1999). Primarily, increased anthropogenic water
abstraction from groundwater, the main freshwater
resource in the region (Feitelson 2005), followed by the
Jordan River—the only perennial surface water contribu-
tion to the DS have led to the reduction in water level.
Although decisive, groundwater quantity is the most diffi-
cult to assess (Al-Weshah 2000; Gra¨be et al. 2012; Schulz
et al. 2013), which has resulted in numerous and discrepant
estimates of groundwater discharge into the DS (Table 1).
The significant discrepancies in the estimates can be
attributed to the differences in the approaches employed by
Electronic supplementary material The online version of this
article (doi:10.1007/s12665-013-2371-6) contains supplementary
material, which is available to authorized users.
U. Mallast (&)  C. Siebert  S. Geyer  R. Merz
Department of Catchment Hydrology, Helmholtz-Centre
for Environmental Research (UFZ), 06120 Halle, Germany
e-mail: ulf.mallast@ufz.de
U. Mallast  R. Gloaguen
Remote Sensing Group, Institute of Geology, Freiberg
University of Mining and Technology, 09599 Freiberg, Germany
B. Wagner  M. Sauter
Georg-August-University Go¨ttingen, Applied Geology,
Institute of Geology, 37077 Go¨ttingen, Germany
123
Environ Earth Sci (2013) 69:587–603
DOI 10.1007/s12665-013-2371-6
the various authors. They are either based on water/mass
balance calculations or groundwater modelling. Common
to all calculations, however, are rigid ratios of discharge
volumes between the spring areas (Asmar and Ergenzinger
2002; Laronne Ben-Itzhak and Gvirtzman 2005). In
response to the increasing demands on groundwater
resources, the Israel Hydrological Service (IHS) initiated a
measurement program on the western coast of the DS to
monitor discharges from the main spring areas, Ein Fesh-
kha, Kane and Samar either annually or biannually.
While only a fraction (terrestrial springs) of total
groundwater discharge to the DS can actually be monitored
by direct measurements, data of the main spring area (Ein
Feshkha) suggest that the total groundwater discharge rate
is decreasing (Galili 2012) accompanied by changes in the
groundwater flow-system (Hadas 2011; Magal et al. 2010).
Extending the monitoring program along the entire DS
coast (ca. 200 km in 2010) would require extensive tran-
sient modelling supported by costly and labour intensive
field campaigns.
To reduce the extensive efforts and to parallel gain
information on groundwater over large spatial scales in
other study areas, some authors applied thermal remote
sensing (Danielescu et al. 2009; Johnson et al. 2008;
Shaban et al. 2005). This method exploits temperature
contrasts between the inflowing groundwater and the water
body (river, lake, and ocean). The resulting thermal pat-
terns reveal groundwater discharge locations and their
relative importance over large spatial scales. Many studies
took advantage of the high spatial resolution with common
ground sampling distances (GSD) of B1 m provided by
airborne platforms to localise and quantify groundwater
discharge (Mejı´as et al. 2012; Roseen 2002; Torgerson
et al. 2001). While results are impressive and may lead to
an increased knowledge of regional and local hydrogeol-
ogy in many study areas (Mejı´as et al. 2012; Shaban et al.
2005), it provides only a snapshot of the discharge event.
Moreover, the high-cost of acquiring high resolution ther-
mal data is a distinct disadvantage which in most cases
precludes further follow-up campaigns. Especially in
(semi-)arid regions where inflow is often intermittent
(Becker 2006), multi-temporal data sets are required to
obtain a representative reflection of the pattern and spatial
extent of groundwater discharge. A multi-temporal
approach would additionally facilitate an inter-seasonal
comparison of groundwater discharge patterns that can be
further analysed in terms of temporal discharge variability.
Although knowledge of the temporal variability of all
groundwater inflow is central to understand the dramatic
decline of the DS water level and to introduce a sustainable
groundwater management, no study to date has addressed
the temporal variability of groundwater inflow for the
entire Dead Sea.
Hence, the objectives of this study are (1) to identify
groundwater inflow locations along the entire DS coast to
fill the gap of possible unknown discharge locations and (2)
to investigate the spatial and temporal groundwater dis-
charge variability. In this context, we examine the assumed
relationship between the temporal discharge behaviour
deduced from thermal satellite data with the temporal
behaviour of measured spring discharge and recharge along
both coasts. The so-obtained temporal and spatial results
can subsequently be used to improve existing groundwater
models, but may also contribute to sustainable groundwater
management decisions in the wider Dead Sea region.
Study area and groundwater flow
The DS is a terminal lake situated in the Jordan-Dead Sea
Graben surrounded by 300–500 m high escarpments
(Fig. 1) formed by normal faults (Gardosh et al. 1990). Due
to a left lateral displacement of 105 km along the Arabian
with respect to the African plate boundary, the aquifer
bearing strata are different (Ben-Avraham and Ten Brink
1989). Along the western side, the Cretaceous limy Judea
Group is identified in most of the sub-catchment area with
an upper and a lower subaquifer (U-JGA and L-JGA)
separated by the clayey Bet Meir aquiclude (Yechieli et al.
2010; Guttman 2000). On the eastern flank, identified
aquifers include the Jurassic Zarqa limestone and Creta-
ceous Kurnub sandstone aquifers and the overlaying Upper
Cretaceous Ajloun- and Belqa Group (Salameh and
Table 1 Assessments of annual groundwater discharge rates into the
DS
Author Q
(106 m3 a-1)
Considered area
Stiller and Chung
(1984)c
[30 Western coast (only some
springs)
Lensky et al. (2005)b 60 Western and eastern coast
Asmar and Ergenzinger
(2002)b
80 Western and eastern coast
Laronne Ben-Itzhak and
Gvirtzman (2005)a
84 Western coast
Salameh (1996)b 90 Eastern coast
Guttman (2000)a 93 Western coast
Salameh and El-Naser
(1999)b
140 Western and eastern coast
Chan and Chung
(1987)b
150 Western and eastern coast
Israel Hydrological
Service (2008–2011)c
82–96 Only Ein Feshkha, Kane,
Samar (western coast)
a Groundwater modelling
b Water/mass balance calculation
c Measured volumes
588 Environ Earth Sci (2013) 69:587–603
123
Bannayan 1994). Bounded by the escarpment and along
both sides of the DS, a Quaternary coastal aquifer exists.
This aquifer comprises intercalated aragonite, gypsum and
clay varves that are interlayered with gravel, sand and
pebbles at wadi mouths (Gardosh et al. 1990).
Groundwater flow is controlled by the structural geom-
etry, i.e. faults zones and folds with mainly E-W and SW-
NE orientations along the western side of the DS and W-E
and SE-NW orientations on the eastern side (Mallast et al.
2011). The identified control also applies to the coastal
aquifer whereby the general flow-direction partly changes
as Holocene structural features display ESE-WNW orien-
tations with extensional directions of NNE-SSW (Enzel
et al. 2000; Gardosh et al. 1990). Groundwater emerges at
distinct locations as a consequence of the structural control.
Several authors describe the spring areas of Ein Feshkha,
Kane/Samar, Qedem and Ein Gedi (Fig. 1) indicated by
terrestrial springs and abundant vegetation along the wes-
tern coast (Guttman 2000; Laronne Ben-Itzhak and
Gvirtzman 2005; Mallast et al. 2011). In contrast (and with
the exception of Wadi Zara), vegetation that could indicate
shallow groundwater availability directly is not observed
along the eastern coast. Nevertheless, Closson et al. (2010)
and Akawwi et al. (2008) indirectly demonstrated the
occurrence of groundwater discharge via landslide occur-
rences and airborne thermal remote sensing along the
mouths of the Wadis Suweimeh, Zarka Ma’in, Zara and
Wadi Mujib, respectively.
Different spring types, which predominantly occur as
spring clusters, are common to all discharge locations.
Along the western coast, terrestrial springs emerge along
faults or sedimentary discontinuities, subsequently forming
erosion channels due to the lowering of the DS (Fig. 1b, c).
This spring type is included in the afore-mentioned IHS
discharge monitoring program since the setting provides
favourable measuring sites. The second spring type, sub-
marine springs, is generally located along both coasts and
emerges at the lake’s bottom. A density difference between
emerging groundwater (1.06–1.19 g cm-3) and DS water
(1.24 g cm-3) triggers buoyancy of the emerging ground-
water that surfaces in circular patterns at the DS surface
(Munwes et al. 2010) (Fig. 1d). Due to their complex
Fig. 1 Study area overview (a blue area represents DS in the year
2000; small white areas represent spring areas (Ein Feshkha,Kane/
Samar, Qedem Ein Gedi); solid blue arrows show general ground-
water flow-paths after Mallast et al. 2011; solid white lines indicate
50 m contour lines of the bathymetry after Hall (2000); Subset: light
grey coloured area represents catchment of the DS, dark grey area DS
area of the year 2000; IL Israel PA palestine authorities, JO Jordan, SY
Syria); Pictures: all illustrate spring types representative for the study
area—b shows an aerial photograph of the northern Ein Feshkha area
from 01/2011 with several erosion channels discharging into the DS;
c shows a similar erosion channel of an upstream located terrestrial
spring in the Kane area and d shows a submarine spring in the Qedem
area (source picture d Munwes et al. 2010)
Environ Earth Sci (2013) 69:587–603 589
123
nature, their discharges are difficult to quantify and hence
not included in the IHS measurements (Ionescu et al. 2012;
Munwes et al. 2010).
Spring temperatures vary along both coasts. On the
western coast, measured spring discharge temperatures
range from *25–28 C (Ein Feshkha), to *25–30 C
(Kane), to*28–30 C (Ein Gedi), to*41–44 C (Qedem-
Shalem) independent of spring type (Siebert et al. 2011).
On the eastern coast, the only direct spring water temper-
ature is reported by Akawwi et al. (2008) with *24 C in
the Zara area. Rimawi and Salameh (1988) and Salameh
and Hammouri (2008) report further springs from the
eastern slope of the Dead Sea with varying temperatures of
22–38 C in the Wadi Muijb, Ibn Hammad and Sweimah
area and also thermal springs (34–62 C) in the Zarka Ma’
in area. However, it has to be assumed that some of the
groundwater feeding the springs, that are not directly
located at the DS, discharge into the DS too.
Groundwater temperatures remain rather stable during the
course of the year and they are only minimally influenced by
ambient air temperature changes (Mallast et al. 2013). In
contrast, the general temperature of the DS underlies a clear
atmospherical influence resulting in minimum temperatures
of *22 C between December and March and maximum
temperatures of *33 C between July and September (Hact
and Gertman 2003). The thermal contrast between ground-
water and DS water approaches a maximum in high summer
and winter periods, and hence represent promising periods to
identify and analyse groundwater inflow using multi-tem-
poral thermal analyses. This fact is even enhanced by the
density difference between fresh to brackish groundwaters
(1.06–1.19 g cm-3) and lake water (1.24 g cm-3). The
difference establishes a buoyant layer at the DS surface, in
which native groundwater temperatures remain largely
unchanged and which further contributes to the suitability of a
thermal remote sensing approach for groundwater detection.
Besides groundwater contributions the Dead Sea
receives additional fresh water inputs from the Jordan
River as perennial flux and ephemeral fluxes from flash-
floods through Wadis during the months of November to
March. A third, but so far unobserved contribution may
exists in the form of the flushing effect (Kiro et al. 2008;
Yechieli and Sivan 2011). Rapid drops in the Dead Sea
level enforce the hydraulic gradient between groundwater
head and lake level and result in an increased groundwater
discharge (flushing) until the new dynamic equilibrium is
reached (Kiro et al. 2008). This response system causes a
significant increase in discharge if the rate of lake level
drop and the respective local hydraulic gradient are small.
Consequently, a significantly increased groundwater dis-
charge occurs in times in which the DS level drops at an
above average rate.
Data and methodology
Hundred Landsat ETM ? band 6.2 (high gain) data (path
174/row 38) covering the years 2000 to 2011 with a cloud
cover of less than 15 % are analysed (Appendix 1 in ESM).
Although ground sampling distance (GSD) of band 6 is
60 m, all data delivered by the US Geological Survey are
resampled to 30 m using cubic convolution (USGS 2011).
Data are recorded at approximately 10 a.m. local time
(GMT ? 2). First processing steps include a co-registration
to UTM WGS 84 Zone 36 N and a gap fill, since images
recorded after the 05/31/2003 contain gaps due to scan line
failure of Landsat (USGS 2012). The authors applied the
‘‘gap fill’’ function of Envi 4.7 that is based on a triangu-
lation method with linearly interpolated values between
surrounding pixel. Note that the NADIR region with no
gaps was located almost parallel and right above the wes-
tern coast of the DS with a corridor of *10 km to each
side where subsequently no interpolation is necessary. To
exclude land pixels, the normalised difference water index
(NDWI) of ETM ? band 4 and 2 is calculated from the
earliest image of the series. On the resulting NDWI image,
a threshold of -0.2 is applied, where values [-0.2 rep-
resent land features while values \-0.2 are explicitly
water features (McFeeters 1996). The further processing of
data is explicitly elucidated in Mallast et al. (2013) and is
subsequently only summarised.
To convert digital numbers (DN) to sea surface tem-
peratures (SST), the authors follow the method presented
by Chander et al. (2009). As emissivity value for water, the
lower 0.97 value is applied following Wenyao et al. (1987),
who proposed this value at higher salinities ([34 %).
Atmospheric transmissivity, upwelling and downwelling
radiances needed for the atmospheric correction of the
thermal data are obtained through the web-based Atmo-
spheric Correction Tool that is based on MODTRAN
(Barsi et al. 2003; Barsi et al. 2005).
The resulting atmospherically corrected SST data rep-
resent temperatures with an error of \1.3 K for the tem-
perature range of 270–330 K (Barsi et al. 2005). This error
applies to the accuracy of SST values during the conver-
sion from DNs with the normal atmosphere thickness,
where the sea surface is at mean sea level. The larger
atmosphere column for the present case of the DS (-400 m
msl.) causes a non-linear reduction of the absolute SST of
*2–4 K (Mallast et al. 2013; Stanhill 1990). Note that the
temperature represents the skin temperature of the water
and, therefore, less than 1 mm of the uppermost water
layer. This layer tends to be ca. 0.1 K colder than lower
water masses due to evaporative heat loss, sensible heat
flux and longwave radiation (Wloczyk et al. 2006; Donlon
et al. 2002).
590 Environ Earth Sci (2013) 69:587–603
123
Further data processing included the identification and
extraction of images with surface-runoff influence using the
influence factor (IF) of Mallast et al. (2013) (see Appendix 2
in ESM for a detailed explanation). This factor describes the
difference of normalised mean SST within a radius of
1,000 m off wadi mouths and the central area of the DS
(defined by a 5 km distance perpendicular to any point of
the coastline). If surface-runoff as flash-floods with consis-
tent temperatures below the minimum temperature of the DS
occurs, the SST lowers significantly at wadi mouths while
the SST of the central area remains uninfluenced. This
results in a negative IF where values B-0.053 indicate an
influence through surface-runoff. In a first step, all data
below this value are excluded from further groundwater
studies. The second step includes the visual reassessment of
the images with IF values between -0.053 and 0 as small
negative values can be caused by both declining surface-
runoff influence and natural variability (Mallast et al. 2013).
The two-step IF analysis allowed the identification of 48
SST images influenced by surface-runoff, but also 51 SST
images that are not influenced (Appendix 1 in ESM).
The subsequent multi-temporal analysis to identify
groundwater inflows and the inter-seasonal groundwater
discharge variability is performed on the not-influenced
data as they represent an adequate basis for groundwater
investigations.
Within the multi-temporal analysis, two aspects have to
be considered to ascertain an optimal analysis. First, the
lateral retreat of the DS shoreline amounts to several tens
of meters per year in areas with minor sea bed inclination
such as at Ein Feshkha. This process possibly causes a
relocation of groundwater flow and hence of springs as
observed by Magal et al. (2010) and hinders an analysis
over the entire investigation period of 2000–2011. Sec-
ondly, groundwater flow is intermittent, thus requiring to
base the analysis on multiple SST data to assure reliable
and most of all representative results (Becker 2006; Mallast
et al. 2013). To account for both, minimal effect of the
natural retreat of the DS shoreline and a maximum of
available SST data, the authors consider biennial series.
Each series comprises 5–12 SST images (Fig. 2) on which
the maximum temperature range (DT) per-pixel is calcu-
lated. DT is defined as the difference between the maxi-
mum and minimum SST value. Previous investigations
showed this statistical measure to be most suitable to
investigate SST variability over time (Mallast et al. 2013).
The reason to analyse the temporal SST variability derives
from the fact that groundwater discharge affected areas
exhibit only a minor SST variability over time. The minor
variability derives from a thermal stabilization induced by
a spatial and temporal constant groundwater flux that
encompasses negligible water temperature variability
throughout the year. This continuous groundwater flux that
is enhanced by a constant density driven buoyancy estab-
lishes a floating layer at the DS surface. As groundwater is
permanently supplied, this floating layer gets continuously
Fig. 2 Temporal distribution of SST recordings (one grey section represents one SST image) and number of SST images (n) compiled to
biennial series
Environ Earth Sci (2013) 69:587–603 591
123
regenerated. At the surface of this layer, the native
groundwater temperatures remain largely unchanged and
distribute up to tens of meters around the respective spring
outlet that in turn can be exploited to identify groundwater
discharge locations and temporal discharge variability.
Results and discussion
Identification of groundwater inflow
The authors focus on areas where groundwater discharge
can most likely be expected to investigate the influence of
groundwater discharge on the thermal distribution of the
DS. Those discharge areas are indicated in a previous study
during which Mallast et al. (2011) derived groundwater
flow-paths. Extending the flow-paths towards the DS
reveals six areas on each coast of the DS (Figs. 3, 4) where
proposed flow-paths intersect the shoreline and hence
where groundwater inflow occurrence is most likely. As the
surface-runoff was excluded during the pre-processing
step, all thermal anomalies with low DT values are
assumed to reflect groundwater affected areas (GAA). The
visually identifiable extent thereby directly mirrors
groundwater discharge volume at the respective location
(Mallast et al. 2013). The DT value most likely is a measure
for the emergence depth, ranging from terrestrial/very
shallow to deep spring discharge. Due to the intermittent
character of the groundwater discharge and the rather
coarse GSD of the SST data, especially small GAAs can
visually disappear over different biennial series. To present
the most complete result, the authors choose to depict the
biennial series, which best reflects the groundwater inflow
locations. Additionally, GAAs are classified by continuous
coast-parallel extent into: (1) large GAAs ([1 km in length
parallel to the coast), (2) small GAAs/single spots (\1 km
Fig. 3 Identification of inflow locations along the western DS
coast—colours indicate DT values per pixel for biennial periods
where blue represents small DT values, which indicates stable
groundwater inflow while red indicates high DT values caused by
external forces or the retreat of the DS shoreline—letter a–f refer to
respective discharge areas; the number behind indicates the chosen
biennial DT image which shows groundwater inflow best
592 Environ Earth Sci (2013) 69:587–603
123
in length parallel to the coast) and (3) assumed/diffuse
GAAs to distinguish discharge magnitudes per GAA. All
sites with GAAs are subsequently coded with the area
where they occur and a running number.
Large GAA
From the observation of DT data along the entire coast, the
authors identify two locations representing large GAAs. Both
are located at the western coast of the DS (Fig. 3). The first
site (A1), located in discharge area A, exhibits DT values of
6.9–8.5 C and a continuous area of*3.4 km length parallel
to the coast and *300 m orthogonal to it. The second site
(C7), located in discharge area C, is characterised by small
DT values of 6.3–8.5 C. The extent parallel to the coast is
*2 km with an orthogonal extent of *200 m. A1 and C7
correspond to the spring areas of Ein Feshkha and Samar,
respectively, which are known to have several terrestrial
springs (white dots) discharging 82–94 9 106 m3 a-1 for
Ein Feshkha and 19–35 9 106 m3 a-1 for Samar (note that
the numbers originate from the IHS measurements and rep-
resent the minimum and maximum numbers between 2004
and 2011) (Guttman 2000; Laronne Ben-Itzhak and Gvirtz-
man 2005; IHS 2012). The fact that both thermally detected
sites spatially correspond to locations of in situ spring mea-
surements distinctively validates thermally inferred ground-
water discharge sites. This observation is further supported
by similar DT values derived for areas with a stabilised SST
through groundwater (Mallast et al. 2013). In fact, as the
relationship between in situ groundwater measurements and
thermal anomalies appears to be valid, the authors deduce
that at both northern ends of site (A1) and (C7) further
groundwater discharge occurs. No in situ measurements were
conducted at these locations, but DT slightly increases to
values \9.4 C over ambient groundwater uninfluenced
temperatures ([10 C). The authors presume that the
Fig. 4 Identification of groundwater inflow locations along the
eastern DS coast—colours indicate DT values per pixel for biennial
periods where blue represents small DT values, which indicates stable
groundwater inflow while red indicates high DT values caused by
external forces or the retreat of the DS shoreline—letter g–l refer to
respective discharge area; the number behind indicates the chosen
biennial DT image which shows groundwater inflow best
Environ Earth Sci (2013) 69:587–603 593
123
observation of low DT values possibly shows an additional
groundwater discharge location of possibly submarine origin.
Small GAA/single spots
All discharge areas contain small or single spot GAAs with
similar DT values of 6.4–8.5 C as the afore-mentioned
large GAAs on the western coast (Fig. 3). Thermally
indicated sites B6, D10 and D11 spatially match in situ
measurements of spring discharge (note that B6 corre-
sponds to Kane spring area while D10 and D11 correspond
to the Qedem spring area). This verifies the spatial infor-
mation of inferred thermal anomalies for small GAAs also.
The GAA extents (B6 and D11: length *400 m/orthogo-
nal extent *150 m; D10 length 150 m/orthogonal extent
90 m) suggest less discharge compared to the afore-men-
tioned group and is verified by in situ measurements
(B6 * 6–9 9 106 m3 a-1 (IHS 2012 for 2004 to 2005);
D11 * 10 9 106 m3 a-1 (Shalev et al. 2007 for 2005);
D10 0.6 9 106 m3 a-1 (own measurements in 2011). The
latter discharge volume reflects only a minimum since
several field observations exhibited at least three submarine
springs (Fig. 1d) with an estimated sea surface diameter of
*10 m that probably contribute significantly to the ther-
mally indicated extent of site B6.
Further small GAAs are located at sites A2, B5 E14,
E15 and F16. All sites generally exhibit smaller extents
except for site A2 that is similar in extent to site D10.
Hence, taking site D10 as reference, a similar volume can
be assumed for site A2 and that the remaining sites (B5,
E14, E15, F16) groundwater discharge is lower by an order
of magnitude. On the other hand, the groundwater dis-
charge appears to be mainly of terrestrial/shallow origin,
applicable to all of these GAAs, since DT values
(8.1–9.0 C) are similar to afore-mentioned DT values
induced by terrestrial springs.
Despite being noticeable from the DT data, these loca-
tions remain unconfirmed as neither terrestrial springs are
reported nor could field observations in the years
2010–2011 directly confirm their existence. Sites E14 and
E15 could correspond to the Ein Yesha springs that are
mentioned in Guttman (2000) and Vengosh et al. (1991).
Site F16 seems also reasonable as Shalev et al. (2009)
suggest a NE-orientated hydraulic gradient from the
Ye’elim area towards the thermally indicated location at
the northern DS basin.
On the eastern coast, all discharge areas except for area F
show evidence of small GAAs/single spots. Descriptions of
groundwater occurrence from literature are not as exact as
on the western coast. This is most likely connected to the
steeper coastal morphology and bathymetry which might
predominantly result in submarine springs due to the
induced increased hydraulic pressure conditions. Closson
et al. (2010) and Akawwi et al. (2008) could prove the
occurrence of groundwater discharge at some locations that
spatially correspond to the thermally indicated small GAAs/
single spots with DT values of 6.3–8.7 C at sites G18, G19,
H24, I26-27, J28-29, and J34, respectively (see white dots
in Fig. 4). The spatial extents of site H24 (160 m parallel
and 70 m orthogonal to the coast, respectively) are similar
to site D10 on the western coast and thus a discharge vol-
ume of similar magnitude ([0.6 9 106 m3 a-1) is assum-
able. The two low DT value spots at site G19 have slightly
smaller extents (100 m parallel and 70 m orthogonal to the
coast). Consequently, the discharge volume appears to be
slightly smaller than for site H24. Site H27 on the other
hand has a spatial extent of 300 m parallel and 120 m
orthogonal to the coast indicating a higher discharge vol-
ume. All three mentioned GAAs (G19, H24, H27) are
characterised by DT values of 6.9–8.7 C and a direct
connection to the coast. Both aspects commend to a shallow
or terrestrial emergence that applies for sites G18, I28 and at
least the northern end of site I29 also. Most parts of sites I29
and J34 display similar DT values (7.5–8.4 C) but do not
have a direct connection to the coast, which suggests a
deeper submarine emergence. For these locations, it is dif-
ficult to approximate discharge magnitudes, since neither
the required thermodynamic mechanisms and parameters
nor the exact emergence depth are known.
Beside the GAAs that spatially correspond to reported
groundwater occurrences, sites G20, G21, G23 and K37
reflect thermal anomalies with DT values of 6.9–8.5 C that
point at continuous groundwater discharge. Yet these sites
are not mentioned in literature. The near-shore location
suggests these sites to have a shallow/terrestrial emergence.
Site G23 represents an exception since it has no direct
connection to the coast and is probably of submarine ori-
gin. However, the extents differ considerably. Whereas
sites G20, G21 and G23 display small spatial extents with
\100 m parallel and \60 m orthogonal to the coast and
hence a small discharge magnitude, site K37 has a similar
extent (parallel to the coast 150 m and orthogonal to it
90 m). This extent is comparable to site G19 why the
authors assume a similar magnitude of discharge also. The
authors furthermore suggest that all of these GAAs reflect
groundwater discharge. Nonetheless, these GAAs are
unconfirmed due to missing ground information.
Moreover, it should be mentioned that site G17, which
falls into the group of small GAA, probably does not reflect a
GAA. Instead, it represents discharge from the Jordan River
as the coordinates correspond to the location of its mouth.
Assumed/diffuse GAAs
This class contains all GAAs that cannot clearly be distin-
guished based on homogenous small DT values and yet
594 Environ Earth Sci (2013) 69:587–603
123
display certain peculiarities noteworthy to mention. Based
on these peculiarities they can be allocated into three groups.
The first group contains hardly visible GAAs. Sites B3,
B4 and C9 are located on the western coast and I30-32 on
the eastern coast. All GAAs of this group on the western
coast are characterised by extents \4 pixel (pixel size:
30 9 30 m) and DT values of 8.9–9.5 C emphasised by
high ambient DT values ([10 C). The slightly higher
DT values might indicate low groundwater discharge. The
small contrast to ambient SST represents an unfavourable
condition. Thus, the authors suggest these sites to be
allocated to ‘‘assumed GAAs’’ requiring further ground-
truth data. This is in contrast to the GAAs on the eastern
coast (sites I30-32). Here, GAAs are also characterised by
similar DT values of 8.1–9.2 C, exhibiting, however, lar-
ger connected extents ([6 pixel). Additionally, all of these
sites are verified by already confirmed groundwater dis-
charge locations (Akawwi et al. 2008). Hence, the authors
suggest the eastern GAAs of this group to truly reflect
groundwater discharge. The emergence is probably sub-
marine with very low discharge magnitudes causing
DT values of 8.5–9.5 C.
The second group comprises heterogeneous GAAs with
large extents (1–2 km parallel and *500 m orthogonal to
the coast, respectively). Site D12 on the western coast
and sites G22, H25, and F38 on the eastern coast belong to
this group. Akawwi et al. (2008) report a submarine
groundwater inflow for site H25 that verifies our finding.
The same applies to site F38, where extensive studies of
Closson (2005) and Closson et al. (2010) report landslides,
subsidence and sinkhole occurrences that directly or indi-
rectly depend on shallow groundwater flow and dynamics.
Both verifications indicate these GAAs to have a ground-
water origin. The question remains why these GAAs dis-
play slightly increased and heterogeneous DT values
(8.2–8.9 C). The missing direct connection to the shore of
all (except for site G22) indicates a submarine origin. At all
locations (except for site F38), the bathymetry is unequally
steep. These GAAs are located at the -450 m msl. isoline
on both coasts (Fig. 1), which means a water depth of
around \35 m (taking the DS level of -415 m msl. of
2001 and -417 m msl. of 2005). Ionescu et al. (2012)
describe the occurrence of submarine springs up to a depth
of *30 m. Hence, from a hydrostatical perspective, this
observation indicates these GAAs to be generally reason-
able. The slightly higher DT values that characterise this
group could have two origins. First, as the groundwater
ascents due to different densities, a heat exchange between
the DS water and the discharging and ascending ground-
water occurs. This partly changes the original temperature
of the groundwater to the DS water. Most of the DT data
are recorded in summer months, during which the DS has a
temperature of 32-35 C. The resulting DT between DS
water and groundwater amounts to 4-7 C. The density
driven buoyancy of the groundwater yields a velocity of
*0.4 m s-1 and hence a travelling time of *75 s for
emerging water at a depth of 30 m (deepest observed
submarine spring) (Ionescu et al. 2012; Mallast et al. 2013).
Complete temperature equilibrium within the short travel-
ling time is, therefore, unlikely. A certain temperature
adaption, however, can be assumed.
Second and probably more decisive is the influence of
different limno-physical mechanisms (e.g. currents, tem-
perature diffusion, etc.) on the ascending groundwater.
These mechanisms might influence the vertical flow caus-
ing the circular pattern at the sea surface to move in hor-
izontal dimensions by some meters over a longer time
period. The movement could be repeatedly observed in the
field and may explain why springs with submarine origin
are thermally unequally clearly visible on the sea surface
compared to groundwater that discharges in shallow areas.
The third group encompasses GAAs that are character-
ised by a near-shore cluster of high DT with values of
10.5–12.2 C, which differ from ambient SSTs. This is in
contrast to the aforementioned analysed characteristic that
steady groundwater discharge with large discharge volume
stabilizes ambient SSTs that subsequently cause low
DT values.
However, several of these GAAs are observed at both
coasts (sites C8, E13, J33, J35 and J36) that match inde-
pendent groundwater discharge observations and in situ
measurement locations (Figs. 3, 4). It is known from the
IHS measurements in 11/2004 that at the location of site C8
several springs exist with minor discharge volumes of
\0.015 9 106 m3 a-1, while only two springs exhibit
discharge volumes of 0.3–0.5 9 106 m3 a-1, respectively.
Due to these very small discharge volumes that are dis-
tributed along a shore strip of [1 km and mostly along
coarse grained wadi fans the authors hypothesise that these
rather diffusely discharging springs with low flow
dynamics (Fig. 5) and quantity stabilize only a small fringe
along the DS coast. This fringe cannot be resolved by the
coarse GSD of the SST data. In periods with increased
discharge, due to, e.g. the flushing effect, the thermally
stabilised area increases and is captured by the SST data
subsequently, despite the coarse GSD. As a consequence,
the alternation of both discharge situations could lead to
higher observed DT values.
Akawwi et al. (2008) reported groundwater discharge
locations for two of the GAAs on the eastern coast (sites
J35 and J36) that validate our findings. Hence, the authors
suggest that this thermal pattern potentially indicates
groundwater discharge, with mostly diffuse emergence and
small discharge magnitudes.
Environ Earth Sci (2013) 69:587–603 595
123
Hence, on the positive side the authors conclude that
(i) All discharge areas (A-L) indicated through previ-
ously inferred groundwater flow-paths exhibit GAAs.
(ii) 37 exact locations could be identified, where ground-
water discharge occurs along both coasts.
(iii) The findings spatially match available in situ mea-
surement locations or ground observations.
(iv) 15 concrete indications for spring locations could be
provided where so far groundwater discharge was
unknown to occur.
(v) GAA extents and location with respect to the coast
and DT values provide an indication of discharge
magnitude and probable origin.
Also noticeable are 8 IHS measurement locations between
sites B5, B6 and 8 own spring measurements in 2011 south of
site E12, where neither low nor distinctive high DT values at
the same longitude are present. Most of these show discharge
volumes of 0.02–0.18 9 106 m3 a-1. Only two springs in
discharge area B and two in discharge area E exhibit values of
0.23–0.41 9 106 m3 a-1. From this fact, the authors would
argue that the applied thermal analysis based on coarse GSD
satellite data has a clear limitation if it comes to the identi-
fication of discharge volumes with a magnitude of
\0.4 9 106 m3 a-1. If the intention is to identify all
groundwater inflow independent of quantity, the authors
suggest using airborne thermal imaging as it is applied in the
study of Akawwi et al. (2008). For the detection of larger
discharge volumes, the applied multi-temporal thermal
satellite data prove a successful applicability.
Inter-biennial groundwater discharge variability
With the exact spring locations identified, the temporal
discharge variability is being analysed for the years 2000 to
2011. Due to the variability in discharge volume, some
discharge areas display no visually delimitable GAAs.
Hence, the focus is set on GAAs that are continuously
distinguishable throughout the entire investigation period.
These GAAs are located in discharge areas A-C on the
western coast and H and J on the eastern coast.
The SST data included in all series are recorded between
March and October (Fig. 2). Hence, the results reflect the
same hydrological time of the year and imply compara-
bility between biennial series. Within each series, the
DT values are Gaussian distributed where the groundwater
caused lower DT values display below the 95 percentile of
the normalised DT. This threshold and the constraint for the
GAAs to have a minimum Euclidian distance of 120 m (4
pixels) to the coast are taken to delineate the GAAs in the
respective series. Both parameters allow the determination
of the temporal evolution of groundwater discharge quan-
titatively in which GAA extents are proportional related to
groundwater discharge volume.
Western coast
The GAA extent and hence the groundwater discharge
derived from the DT data indicate a significant but unsteady
decrease in all discharge areas during the observation span
(Fig. 6). For discharge area A, which corresponds to the
spring area of Ein Feshkha, the behaviour of the GAA extents
exhibits a three-steps change. From 2000 to 2001 to 2002 to
2003, the GAA decreases from 2.41 to 0.68 km2. It then
remains constant for the subsequent 2004–2005 series
(0.69 km2). The following two series again show a signifi-
cant decrease to [0.14 km2 before the GAA increases to
0.83 km2 during 2010–2011 (Fig. 6). For the years
2004–2011, IHS spring measurements show an identical but
less pronounced behaviour except for the last increase that
will be discussed later. Mean total measured groundwater
discharge decreases almost linearly from 71.0 9 106 m3 a-1
during 2004–2005 to 60.2 9 106 m3 a-1 during 2008–2009
series (Fig. 6).
Discharge area B/C (lower row in Fig. 6) shows a dif-
ferent behaviour. The changeover from 2000–2001 to
2002–2003 demonstrates a similar GAA decrease from
3.24 to 0.08 km2 as in discharge area A (Fig. 6). The fol-
lowing series (2004–2005) unlike discharge area A exhibits
an increase to 0.42 km2. This surface remains stable during
2006–2007, but unlike discharge area A, it decreases to
0.05 km2 until the 2008–2009 series. The last changeover to
Fig. 5 Observed groundwater
inflow at the tip (a) and a
northern section (b) of the Wadi
Darga fan (GAA site C8/Samar
spring area)
596 Environ Earth Sci (2013) 69:587–603
123
the 2010–2011 series behaves similarly as it exhibits an
increase. Comparing the total GAA to the IHS spring
measurements reveals an analogous behaviour. The mean
total spring discharge (QKane and QFeshkha accumulated) of
37.6 9 106 m3 a-1 during 2004–2005 is similar to
41.1 9 106 m3 a-1 during the 2006–2007 series, before it
decreases to 30.4 9 106 m3 a-1 during 2008–2009 (Fig. 6).
These numbers suggest that if one takes the IHS measured
terrestrial spring discharge into account only the always
reported rigid discharge ratio of 2:1 between Ein Feshkha
(discharge area A) and Kane/Samar (discharge area B/C) is
true. In contrast, our results that also include submarine
springs suggest that the discharge ratio between both areas
can vary inter-annually between 8:1 and 1:3 (Fig. 6).
There is a further interesting observation next to the
variation in groundwater discharge rates. Our temporal
comparison suggests variable groundwater discharge
locations across time. In discharge area A, for example, an
inflow is apparent along the entire bay structure during
2000–2001 (Fig. 6). During the following two series inflow
only occurs along the northern and central part of the bay.
Emergence gradually starts to disappear from the north
over the subsequent two series leaving only inflow loca-
tions at the bay centre. Magal et al. (2010) report similar
findings and describe the gradual drying out of northern
springs at the Ein Feshkha Nature Reserve. In contrast,
during the last series (2010–2011) the springs seem to
reappear along the entire bay. The same phenomenon takes
place in discharge area B/C where a shift of groundwater
inflow locations from north to south is visible between
2004 and 2007. The dis- and reappearance of springs along
this strip of discharge area B/C was also observed during
several field observations during the years 2009–2011,
which supports the results obtained from the multi-tem-
poral thermal analysis.
The authors hypothesise that this change is not only a
result of different recharge amounts and areas. It might
additionally indicate the formation of new preferential
Fig. 6 Temporal variability of discharge behaviour per biennial
series between 2000 and 2011 at the example of identified areas A and
B/C. DT values per pixel of the SST data in the respective series
shown are with bluecolours indicating low DT values and hence GAA
and red colours indicating high DT values with highly variable
temperatures and no groundwater influence. Numbers in the lower
right corner represent the total area of the GAA while the numbers in
the upper left corner represent IHS mean measured spring discharge
in the respective series. Red, Yellow and blue dots represent IHS
measured spring discharge of B0.1 3 106 m3 a-1 (blue), [0.1–
B1.0 3 106 m3 a-1 (yellow) and[1.0 3 106 m3 a-1 (red). Note that
the white solid line represents the coast line of the last image of the
series
Environ Earth Sci (2013) 69:587–603 597
123
flow-paths triggered by the lowering of the DS and the
location of narrow fault- and folding zones described by
Enzel et al. (2000). Groundwater potentials adjust to the
dropping of the DS level. This could lead to the activation
of a lower lying fault zone as preferential flow-path, which
could slightly differ in orientation than overlying fault
zones. Or, the internal folding of this zone governs the
flow-direction and hence the discharge location.
The fact that the 2000–2001 and 2010–2011 series differ
in appearance from the remaining series 2002–2003 until
2008–2009 is also striking. While DT data of the latter
series show distinct discharge points that mostly corre-
spond to high quantity spring discharge (see red points in
Fig. 6), the 2000–2001 and 2010–2011 series show a spa-
tially continuous discharge over large areas. This phe-
nomenon is probably due to the flushing effect (Kiro et al.
2008) that will be discussed later.
Plotting the GAA of the respective series against the
calculated recharge (Fig. 7) using the empirical formula
given in Guttman (2000) (Appendix 3 in ESM) reveals a
similar curve progression with a delayed response time of
one series. This similarity is supported by high index of
agreement (d) values (index varies between 0 and 1, where
1 indicates a perfect fit of curve progression and 0 indicates
no fit (Willmott 1981)) of d = 0.71 for Ein Feshkha and
d = 0.66 for Kane/Samar (Appendix 4 in ESM). Recharge
curve and spring discharge from IHS measurements for
Kane/Samar also display a conform behaviour. In contrast,
the recorded Ein Feshkha groundwater discharge rate
shows an almost linear decrease and hence a non-conform
behaviour with respect to the average biennial recharge.
This might indicate a different hydrological system with
multiple input sources than only recharge from the Judean
mountains.
The GAA curve and recharge curve are dissimilar dur-
ing 2000–2001 and 2010–2011. It is striking that concur-
rently, the lake level drops at a maximum of 1.5 m and
1.6 m during these series. Both numbers are above the
long-term average drop of 1 m. For this situation with
above average drops of the lake level, Kiro et al. (2008)
and Yechieli and Sivan (2011) propose an increased dis-
charge due to the contribution of old brines (flushing
effect) that could explain the larger GAAs.
Hence, the authors hypothesise that the larger GAAs
during both periods are a consequence of the so far
unobserved flushing effect. The flushing of old brines is
Fig. 7 Comparison of GAA per
identified areas A (equivalent to
Ein Feshkha) and B/C
(equivalent to Kane/Samar)
against the mean recharge
amount calculated using rainfall
information [mm a-1] of
Jerusalem station and the
empirical equation from
Guttman (2000) and the mean,
maximum and minimum DS
level drop per series
598 Environ Earth Sci (2013) 69:587–603
123
connected to the availability of void spaces to temporarily
store water. With the recently exposed Quaternary uncon-
solidated sandy and clayey lake sediment areas along the
entire coastline, this possibility is given and in turn induces
an increased discharge over large areas rather than at dis-
crete points. Observations based on the thermal GAA
indications show that both discharge areas A and B/C
exhibit theses assumed continuous discharge appearance.
This supports the hypothesis of an occurring partial flush-
ing mainly during the 2000–2001 and 2010–2011 series.
Eastern coast
Unlike at the western coast, the discharge areas H (Wadi
Zarka Ma’in and Zara) and J (Wadi Mujib) along the eastern
coast do not display a homogeneously decreasing trend.
Instead, area H (upper row in Fig. 8) shows a sinusoidal
course of decreasing and increasing GAA, whereas the GAA
in area J (lower row Fig. 8) increases until 2004–2005 and
decreases from thereon. Striking is the GAA in discharge
area H in the 2000–2001 series that is with 0.6 km2 signif-
icantly higher than GAAs of the subsequent series. The same
series provides an indication that the flushing effect of old
brines occurs on the eastern coast also. The reason is the
continuous appearance of GAAs in contrast to remaining
series with rather distinctive discharge locations analogously
to the discharge areas A and B/C on the western coast during
the same 2000–2001 series.
In discharge area J, higher DT values can be observed
along the entire coastline. As this observation indicates
diffuse discharge with minor volumes (see Sect. 4) and as it
occurs over a continuous spatial extent along the coast, the
authors assume this pattern to be caused by the flushing
effect. The topography may be responsible for the low dis-
charge quantities. Unlike the western coast, the eastern coast
exhibits steep slopes that extend offshore, with generally
non-existent or less developed Quaternary lake sediments
(Closson et al. 2010). This, in turn, means less void spaces
compared to the western coast, and hence lower quantities of
groundwater which are temporarily stored and available for
flushing from unconsolidated sediments.
Plotting the derived GAA against the calculated recharge
depth (Fig. 9) with the empirical formula given in Guttman
(2000) (Appendix 3 in ESM) reveals a similar curve
Fig. 8 Temporal variability of discharge behaviour per biennial
series between 2000 and 2011 demonstrated on areas H and J.
DT values per pixel of the SST data of the respective series are shown
with blue colours indicating low DT values and hence GAA and red
colours indicating high DT values with highly variable SSTs and no
groundwater influence. Numbers in the lower right corner represent
the total area of the GAA. Note that the white solid line represents the
coast line of the last image of the series
Environ Earth Sci (2013) 69:587–603 599
123
progression and the same response time-shift of one series as
on the western coast. The similarity is supported by good-
ness-of-fit values of d = 0.67 for area H and d = 0.86 for
area J (Appendix 4 in ESM). These numbers correspond to
those derived on the western coast and indicate that the
recharge-GAA relationship is applicable. Figure 9 also
reveals the flushing effect to occur in the earliest series
2000–2001 for discharge area H due to the above average
drop of the DS level of 1.5 m. As observed on the western
coast, a shift of discharge locations is also partly visible on
the eastern coast at the example of discharge area J. There,
the inflow varies from the tip of the Wadi Mujib fan to the
north and to the south. Similar to the western coast, the
hydro-geological system may change locally with the drop
of the DS level establishing new flow-paths and inflow
locations.
Remarks on the temporal behaviour and quantification
of groundwater discharge
The congruency between curve progressions of recharge
and GAA extents suggests a direct relationship. Hence, it
once again confirms our hypothesis that it is possible to
derive information on the temporal groundwater discharge
behaviour using thermal satellite data (2013).
Following Ou et al. (2009), who proved a direct rela-
tionship between area of discharge plume (in the present
case GAA) and discharge quantity, it appears to be possible
to derive absolute volumetric quantities based upon the
GAAs. However, for the present case, the authors consider
the absolute quantification to be unfavourable due to the
following reasons:
1. GAAs comprise discharge from terrestrial springs and
an unknown discharge dimension from submarine
springs and old-brine flushing.
2. Diffuse groundwater discharge with discharge\1–5 9
106 m3 a-1 as shown in Fig. 4 cannot be reliably
resolved due to the coarse GSD of the satellite data.
3. The GAA delineation might miss areas induced by
groundwater where the thermal contrast is insufficient
or which are not directly located at the coast.
All points influence a reliable and concrete statement
regarding absolute quantities. Hence, the authors suggest
applying satellite data at unmonitored locations only semi-
quantitatively as pursued during this study.
Fig. 9 Comparison of GAA per
identified areas H and J against
the mean recharge amount
calculated using rainfall
information [mm a-1] of
Amman station and the
empirical equation from
Guttman (2000) and the mean,
maximum and minimum DS
level drop per series
600 Environ Earth Sci (2013) 69:587–603
123
Our results reveal that
1. Rigid ratios of discharge volumes between different
spring areas (e.g. ratio of 2:1 for Ein Feshkha 60–70 9
106 m3 a-1 to Kane/Samar 30–40 9 106 m3 a-1) have
to be reconsidered if discharge from submarine springs
and old-brine flushing is included
2. A hydraulic change in the existing hydro-geological
system as a result of the drop of the DS level likely
induces changes in the discharge location.
3. The response time between recharge area and dis-
charge locations is less than two years.
4. The so far unobserved flushing effect occurred at least
during 2000–2001 and 2010–2011 along both coasts.
This confirms the proposed and modelled additional
water contribution of old DS-brines as a consequence
of an above average DS level drop (Kiro et al. 2008;
Yechieli and Sivan 2011).
Conclusion
Six potential groundwater discharge areas were identified on
each coast, where general groundwater flow-paths (Mallast
et al. 2011) intersect the DS coastline. All discharge areas
exhibit thermal anomalies with different extents at the sea
surface and hence represent groundwater discharge. This
causality proves the structural control of groundwater flow in
this area similar to the results of Shaban et al. (2005) in
Lebanon. Based upon the abundance of thermal anomalies
(termed groundwater affected areas—GAA) so far reported
general spring areas could be concretised to 37 specific
groundwater discharge sites along the entire coast. These
sites spatially correspond to available discharge observations
from field campaigns, in situ measurements or literature
reports that validate our findings. Beyond that, our results
provide indications for further groundwater discharge sites,
spring types and discharge magnitudes along the entire coast
that are so far not reported.
The temporal variability of the GAAs suggests a direct
relationship to natural groundwater recharge as both display
an analogous curve progression over the investigated period
of 2000–2011. This proves our hypothesis that thermal
satellite data are suitable to analyse discharge variability
over defined time units despite the coarse GSD. It also
reveals reported rigid ratios of discharge volumes between
different spring areas not to be true at all times. Partially
significantly different ratios exist if the total discharge (ter-
restrial, submarine and flushing of old brines) is considered.
Moreover, the drop of the DS level provokes a change of
the hydrogeological system that leads to changes in
groundwater discharge locations. During periods with
above average DS level drop, an increased groundwater
discharge over large areas can be observed. This is in
contrast to periods with below average DS level drops
during which discharge is limited to discrete locations. The
increased continuous discharge is probably a consequence
of the temporarily stored flushing of old brines from sed-
iment-voids. This flushing effect matches assumptions of
Yechieli and Sivan (2011) and modelling results of Kiro
et al. (2008) who describe the same causality.
Although GAA and discharge quantities have a direct
relationship, absolute discharge quantities cannot be reli-
ably deduced. This is mainly due to the fact GAAs contain
an unknown discharge dimension from submarine springs
and old-brine flushing. A further reason applies to the
coarse GSD of the satellite data set. This allows localising
and assigning discharge magnitudes to larger GAAs, but
groundwater discharge magnitudes \1 9 106 m3 a-1 can
only be qualitatively localised.
Hence, from our perspective, the obtained discharge
locations subsequently can be used as detailed boundary
condition within groundwater modelling of this region or
for further applications aiming at a sustainable groundwa-
ter management. The possibility to infer relative discharge
variability might also be valuable for management con-
cerns as it represents a cost-effective and fast method to
monitor groundwater discharge behaviour over time. If it is
intended to obtain absolute groundwater discharge quanti-
ties by means of remote sensing, the authors suggest using
data with higher GSD, from, e.g. airborne platforms, and to
parallel measure in situ groundwater discharge volumes
(Danielescu et al. 2009) or to determine the discharge
through mass balances (Johnson et al. 2008).
Acknowledgments The authors greatly acknowledge the grant for
this study from the German Federal Ministry of Education and Research
(BMBF) within the multilateral IWRM-project SUMAR (grant code:
02WM0848). We are also very grateful to the Israel Hydrological
Service for the intense support and for providing spring discharge data.
Further thanks are addressed to Prof. John Laronne and Yaniv Munwes
(Ben Gurion University), Megilot Dead Sea, Omar Cohen and Yossi
Guttman (Mekorot), and the Ein Feshkha National Park Rangers for
their intense support during the course of this study. Helmholtz Impulse
and Networking Fund through Helmholtz Interdisciplinary Graduate
School for Environmental Research (HIGRADE) kindly supported this
study. The authors are grateful to two anonymous reviewers for their
helpful comments that significantly improved the manuscript.
Open Access This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, dis-
tribution, and reproduction in any medium, provided the original
author(s) and the source are credited.
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