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Estimating groundwater recharge using the chloridemass-balance method in the West Bank, PalestineA. Marei a , S. Khayat a , S. Weise b , S. Ghannam a , M. Sbaih a & S. Geyer ba Department of Earth and Environmental Sciences, Al Quds University, Jerusalem, PO Box20002, Palestineb Helmholtz Centre for Environmental Research-UFZ, Leipzig/Halle, GermanyVersion of record first published: 05 Jul 2010.

To cite this article: A. Marei , S. Khayat , S. Weise , S. Ghannam , M. Sbaih & S. Geyer (2010): Estimating groundwaterrecharge using the chloride mass-balance method in the West Bank, Palestine, Hydrological Sciences Journal, 55:5, 780-791

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Estimating groundwater recharge using the chloride mass-balancemethod in the West Bank, Palestine

A. Marei1, S. Khayat1, S. Weise2, S. Ghannam1, M. Sbaih1 & S. Geyer2

1Department of Earth and Environmental Sciences, Al Quds University, Jerusalem, PO Box 20002, Palestinemarei@planet.edu

2Helmholtz Centre for Environmental Research-UFZ, Leipzig/Halle, Germany

Received 9 April 2009; accepted 31 March 2010; open for discussion until 1 January 2011

Citation Marei, A., Khayat, S., Weise, S., Ghannam, S., Sbaih, M. & Geyer, S. (2010) Estimating groundwater recharge using thechloride mass-balance method in the West Bank, Palestine. Hydrol. Sci. J. 55(5), 780–791.

Abstract The quantification of natural recharge rate is a prerequisite for efficient and sustainable groundwaterresources management. Since groundwater is the only source of water supply in the West Bank, it is of utmostimportance to estimate the rate of replenishment of the aquifers. The chloride mass-balance method was used toestimate recharge rates at different sites representing the three groundwater basins of theMountain Aquifer in theWestBank. The recharge rate for the Eastern Basinwas calculated as between 130.8 and 269.7mm/year, with a total averagereplenishment volume of 290.3 � 106 m3/year. For the Northeastern Basin, the calculated recharge rate rangedbetween 95.2 and 269.7 mm/year, with a total average recharge volume of 138.5� 106 m3/year. Finally, the rechargerate for the Western Basin was between 122.6 and 323.6 mm/year, with a total average recharge volume of324.9 � 106 m3/year. The data reveal a replenishment potential within the estimated replenishment volumes ofprevious studies for the same area. Also, the range was between 15 and 50% of total rainfall, which is still within therange of previous studies. The geological structure and the climate conditions of the western slope were clearly play animportant role in the increment of total volume. In some cases, such as the geological formations in the NortheasternBasin, the interaction between Eocene and Senonian chalk formations result in minimum recharge rates.

Key words mountain aquifer; chloride-mass balance; recharge rate; groundwater replenishment

Estimation de la recharge hydrogéologique par la méthode du bilan massique des chlorures en Cisjordanie,PalestineRésumé La quantification de la recharge naturelle est un pré-requis pour une gestion efficace et durable desressources en eaux souterraines. Puisque l’eau souterraine est la seule source pour l’alimentation en eau de laCisjordanie, il est primordial d’estimer le taux de renouvellement des aquifères. Nous avons utilisé la méthode dubilan de masse des chlorures afin de calculer la recharge en différents sites du Mountain Aquifer en Cisjordanie,représentatifs des trois bassins hydrogéologiques. La recharge du bassin Est a été estimée entre 130.8 et 269.7 mm/an,avec un volume total de 290.3� 106m3/an. Pour le bassin Nord-Est, la recharge se situe entre 95.2 et 269.7mm/an, avecun volume total de 138.5� 106m3/an. La recharge du bassin Ouest, finalement, s’échelonne entre 125.7 et 323.6 mm/anavec un volume de 324.9 � 106 m3/an. Ces données révèlent un potentiel de renouvellement plus important que lesvolumes estimés lors d’études antérieures dans la même région. La structure géologique et les conditions climatiques surle versant ouest jouentmanifestement un rôle important pour la contribution significative de ce versant au volume total derecharge. Dans certains cas, les formations géologiques, comme la craie Eocène et Sénonienne du bassin Nord-Est, nefavorisent pas la recharge ce qui se traduit par valeurs inférieures.

Mots clefs aquifère de montagne; bilan massique des chlorures; recharge; renouvellement des eaux souterraines

1 INTRODUCTION

Groundwater is themain source of water for Palestiniansin the West Bank; rainfall harvesting is a secondarysource. Limited natural water resources, over-exploitation,salinization and contamination of the groundwaterresources are critical management issues. Three

hundred springs and 60 groundwater wells drain fresh-water from carbonate rocks of Upper Cretaceousand Tertiary age, with a total discharge of about130 � 106 m3/year (GTZ report, 1995; Nasser Eddin& Nuseibeh, 1995; Palestinian Water Authority,2003).

Hydrological Sciences Journal – Journal des Sciences Hydrologiques, 55(5) 2010780

ISSN 0262-6667 print/ISSN 2150-3435 online© 2010 IAHS Pressdoi: 10.1080/02626667.2010.491987http://www.informaworld.com

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The amount of water used for domestic purposes inthe West Bank in 2003 was estimated at 64.7� 106 m3

(Palestinian Water Authority, 2003). The PalestinianCentral Bureau of Statistics estimated the population ofthe West Bank as 2 313 609 in 2003 (PCBS, 2004),which means an average water share at 86 L per capitaper day, assuming zero water losses. This volume issmall in comparison with the 150 L per capita dayrecommended by the World Health Organization. Inaddition to this shortage, 257 Palestinian communitiesare still not connected to the water networks. Taking intoconsideration the natural population growth, additionalwater networks need to be constructed. The annual watershortage in the West Bank reached 60� 106 m3 in 2003(Palestinian Water Authority, 2003). To satisfy theincreasing demand, new wells have been drilled duringthe last 10 years, in addition to many illegal shallowwells (up to 150 m depth) that were drilled in theNortheastern and Eastern basins, in the Jenin andJericho areas in particular. While the natural replenish-ment of the aquifer systems in theWest Bank depends onthe recharge rate from rainfall, identifying this compo-nent is of key importance to the aquifer’s sustainability.The objective of this study is to estimate recharge rates atdifferent sites of the West Bank by using the chloridemass-balance method.

2 HYDROGEOLOGY

Groundwater recharge is defined as the movementof moisture downwards through the unsaturated zoneto the saturated zone. It can influence the groundwaterbody and can, in certain circumstances, also bededuced from the discharge rate of local springs(Freeze & Cherry, 1979). Quantification of therecharge rate in different geographical locations isone of the basic requirements for proper managementand protection of groundwater resources.

The West Bank Mountain Aquifer extends fromnorth to south and is mainly composed of limestone,dolomite and chalk of Upper Cretaceous to Tertiaryage (Fig. 1). The Jordan Rift Valley is the largeststructural feature in the area. Tal A’sur is the highestpoint in the northern West Bank, with an elevation of1022 m above sea level (ARIJ, 1996). The Dead Sea isthe lowest part and has an elevation of 410 m belowsea level. The surface water divide runs parallel to thenorth–south axis of the mountain ridge. The change inclimate from semi-humid on the western slopes of themountains to semi-arid and arid on the eastern slopesand on the Dead Sea shore, respectively, reflects therainfall distribution that exceeds 600 mm/year on themountain ridge and is less than 100 mm/year on the

Fig. 1 Geological map of the West Bank (source Rofe and Raffety, 1963).

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Dead Sea shore (Arad &Michaeli, 1967; Husary et al.,1995; Palestinian Water Authority, 2006). Rain occursmainly during the winter and spring seasons, while theintensity of rainfall varies from 1 year to another. Ingeneral, 75% of the rain falls between November andMarch. When the rainfall intensity exceeds 50 mm perday or reaches 70 mm in 48 hours there is surfacerunoff (Rofe and Raffety, 1963, 1965).

Based on the groundwater movement in the moun-tain area, three groundwater basins were identified in theWest Bank: theWestern Basin, the Eastern Basin and theNortheastern Basin (Fig. 1). The surface catchment areaof the Eastern Basin is about 2473 km2 extending fromthe top to the foot of the mountain in the Jordan Valley(Table 1). The rainfall ranges from650mmat the summitto 150 mm in the Jericho area (Arad & Micheali, 1967;Husary et al., 1995; Palestinian Water Authority, 2006).Limestone, dolomite, chalky limestone and chalk ofUpper Cretaceous to Tertiary age cover the catchmentarea. The Plio-Pleistocene aquifer system in the JordanValley is part of this basin and consists of gravel, sand,silt, clay and evaporites (Begin, 1974). In places withless than 200 mm annual rainfall, the direct recharge isneglected as most of the rainfall evaporates due to thehigh temperatures. Recharge to this aquifer depends onthe occurrence of wadi flooding, where floodwatercrosses the alluvial deposits of the wadi floor duringthe winter months (Marei & Vengosh, 2001).

The Northeastern Basin, which is shared betweenthe Palestinians and Israelis, has a catchment areaof about 976.8 km2 inside the West Bank boundary.Upper Cretaceous limestone, and chalky limestone,and Tertiary chalky limestone and chalk cover thecatchment area, which receives an annual rainfall of500–600 mm. There are two aquifer systems in thisbasin: the Eocene and the Turonian-Cenomanian aquifer.

The catchment area of the Western Basin extendswestward from the mountain ridge to the coastal areaover the political boundaries of the West Bank. Thecatchment area covers about 1771.9 km2 inside theWest Bank (Table 1). Limestone and dolomite cover

most of the catchment area, which receives an annualrainfall of 650 mm on the mountain top to 450 mm inthe coastal area.

Blake & Goldschmidt (1947) made the first esti-mate of recharge for the region; their estimate rangesbetween 22 and 25% of annual rainfall. Rofe andRaffety (1965) estimated the West Bank recharge bysubtracting the average annual runoff and evapotran-spiration from the total rainfall, resulting in valuesranging from 20 to 55% of total rainfall (Table 2).

3 METHODOLOGY

3.1 Data collection and analysis

An average rainfall contour map generated by thePalestinian Water Authority indicates the evolution overthe last 20 years during which rainfall was measured at63 weather stations in the study area (PalestinianWater Authority, 2006). This map was used to estimatethe recharge rate as an input component (Fig. 2).

A total of 118 rainfall samples were collected forchemical analyses during the hydrological years from2001/02 to 2004/05 at the weather station at AQU, andother samples from Ramallah, Hizma, Hebron andNablus in the years 2006, 2007 and 2008. Water sam-ples were collected directly during the rainfall eventsand filtered through 0.45-mm filters and then stored at4�C. Table 3 presents the weighted average of chlorideconcentration at the different stations. Additionalinformation about chloride contents in rainwater wasextracted from Herut et al. (1994) who state that theaverage chloride concentration in the rainwater of theJudea area is 9.06 mg/L.

Groundwater samples were collected from59 sampling sites across the three groundwater basins(Fig. 3). Within each basin, areas of different rockformations were distinguished and the related areawas calculated using ArcGIS 9.0 software (Table 1).The recharge rates and volumes were calculated for

Table 1 Formation outcropping in the three groundwaterbasins in the West Bank (km2).

EasternBasin

NortheasternBasin

WesternBasin

Total

Eocene andQuaternary

178.3 560.2 139.3 877.8

Senonian 890.9 169.3 202.0 1262.2Cretaceous 1403.8 247.3 1430.6 3081.7Total 2473.0 976.8 1771.9 5221.7

Table 2 Recharge rates estimated by different studies.

Study % of rainfall

ANTEA (1998) 20CDM & Morganti (1997) 20–30Tahal (1995) 25–60Scarpa (1994) 20Arad & Michaeli (1967) 6–48Rofe and Raffety (1963, 1965) 20–55Goldschmidt & Jacobs (1959) 34Blake & Goldschmidt (1947) 22–25Our calculation (2008) 15–50

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each formation, after which the recharge volume wasestimated for each basin. Impermeable chalky forma-tions of Senonian age and the Quaternary Lisan for-mation were excluded from the calculation.

Chloride and bromide values were measuredby ion chromatography. Nitrate concentration wasmeasured in groundwater samples using the spectro-photometric method, in order to identify pollutionsources. Sodium concentration in groundwater wasmeasured by flame photometry. In the case of thepresence of high NO3

- concentrations (indicative of

contamination), additional chloride was excludedusing the Cl-/Br- molar ratio, as Br- is a conservativeanion in the water cycle. Excess chloride values werecalculated using the Cl-/Br- molar ratio for both rain-water and groundwater, where the ratio for the latterwas estimated to be 300 (Rosenthal, 1987).

Variations in the amount of rainfall from one yearto another have a slight impact on the average chloridecontent because it depends on the intensity and dura-tion of the rainfall events, rather than the precipitationtotal for the hydrological year.

Fig. 2 Average annual rainfall (mm/year) distribution in the West Bank (source Palestinian Water Authority, 2006).

Table 3 Weighted average of chloride concentration in rainwater in the West Bank.

Weather station Date Chloride (mg/L) No. of samples

Al-Quds Univ. 2001/2002 6.95 23Al-Quds Univ. 2002/2003 9.12 28Al-Quds Univ. 2003/2004 12.81 24Al-Quds Univ. 2004/2005 11.54 21Kefar ha wardim1 Herut et al. (1994) 7.87 1Qazrin Herut et al. (1994) 4.08 1Akhziv Herut et al. (1994) 12.34 2Bet Yannay Herut et al. (1994) 6.38 2Mizpe Ramon Herut et al. (1994) 11.56 1Ramallah 2006/2007 9.30 6Hizma-Jerusalem 2006/2007 6.62 6Nablus 2008 8.53 5Hebron 2008 9.57 5Average 8.97

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3.2 Recharge estimation

3.2.1 Chloride mass-balance method Chlorideis regarded as a suitable environmental tracer since itis highly soluble, conservative and not substantiallyabsorbed by vegetation. The chloride mass-balancemethod is convenient and inexpensive because of itssimple data requirements. Recharge can be estimated by:

R ¼ P � Cl-PCl-gw

(1)

where R is recharge (mm/year); P is rainfall (mm/year);Cl-P is weighted average chloride concentration in rain-fall (mg/L); and Cl-gw is average chloride concentrationin groundwater (mg/L).

The weighted average (Cl-P) is calculated accord-ing to the following equation:

Cl-P ¼ P1 � C1 þ � � � þ Pn � Cn

P1 þ � � � þ Pn

where P1 is the first rainfall event (mm) and C1 is thecorresponding chloride concentration in the rainfall(mg/L), for 1 to n events.

To determine the weighted chloride average foreach hydrological year, the chloride concentration ofeach rainfall event is first multiplied by the amount ofrainfall. The summation of these individual compo-nents is then divided by the total annual rainfall.

Table 3 shows the weighted average chloride con-centrations for each hydrological year from 2001/02 to2004/05 at AQU station, with values ranging between6.95 and 12.81 mg/L, and for the stations Ramallah,Hizma, Nablus, and Hebron, which are 9.30, 6.62, 8.53and 9.57, respectively.

Previously average chloride concentrations in theprecipitation in the Judea area was estimated at9.06 mg/L (Herut et al., 1994). Table 4 shows Cl-,Na+ and NO3

- concentrations as well as Na/Cl Br/Clmolar ratios of the groundwater sampling sites in thedifferent West Bank locations.

Fig. 3 Groundwater sampling sites.

784 A. Marei et al.

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Tab

le4Groundw

ater

samplingsites,hydrochemicalvalues,rainfalland

correspondingcalculated

recharge

estim

ates

fortheWestB

ank.

Sam

plingsite

Type

No.

ofsamples

Date

Eastin

gNorthingAquifer

Groundw

ater

basin

Cl-

(mg/L)

Cl-

(meq/L)Na+

(meq/L)

Br+

(meq/L)Cl

excess

(meq/L)

CalcCl

(meq/L)

CalcCl

(mg/L)

Clin

rainfall

(mg/L)

P (mm/year)

R (mm/year)

Ham

deh

S1

10/03/20

0617

0544

166622

Low

erCenom

anian

Northeastern

29.00

0.80

0.83

0.0023

0.11

0.69

24.39

9.18

550.00

207.07

Zakaria

S1

10/03/2006

167800

191100

Eocene

Northeastern

35.00

1.00

0.91

0.0029

0.14

0.86

30.49

9.18

475.00

143.06

Zaw

ateh

S1

10/03/2006

171650

183940

Eocene

Northeastern

25.00

0.70

0.61

0.0020

0.10

0.60

21.34

9.18

550.00

236.65

BeitE

baS

110/03/2006

170015

182665

Eocene

Northeastern

32.00

0.90

0.80

0.0026

0.13

0.77

27.44

9.18

550.00

184.06

Saqi

S1

10/03/20

0617

1000

166000

Low

erCenom

anian

Northeastern

34.00

1.00

1.00

0.0029

0.14

0.86

30.49

9.18

550.00

165.65

Ras

Al-Ein

S1

12/03/2006

174310

180210

Eocene

Northeastern

25.00

0.70

0.70

0.0020

0.10

0.60

21.34

9.18

500.00

215.13

Harun

S1

12/03/2006

169500

185780

Eocene

Northeastern

23.00

0.60

0.60

0.0017

0.08

0.52

18.29

9.18

500.00

250.99

Al-Sharqiyah

S1

12/03/20

0617

4080

176620

Eocene

Northeastern

20.00

0.60

0.30

0.0017

0.08

0.52

18.29

9.18

550.00

276.09

Ein

Sidra

S27

28/12/20

02–

30/07/20

05179950

185490

Eocene

Northeastern

36.00

1.00

0.90

0.0029

0.14

0.86

30.49

9.18

550.00

165.65

Ein

Baida

S36

26/03/20

04–

30/07/20

05180120

185320

Eocene

Northeastern

37.90

1.10

0.90

0.0032

0.15

0.95

33.54

9.18

550.00

150.59

Ein

Ham

adS

3626

/03/20

04–

30/07/20

05180110

185325

Eocene

Northeastern

36.90

1.10

0.80

0.0032

0.15

0.95

33.54

9.18

550.00

150.59

Ein

Qudeeri

S36

26/03/2004–

30/07/20

05180130

185280

Eocene

Northeastern

38.00

1.10

0.80

0.0032

0.15

0.95

33.54

9.18

550.00

150.59

Ein

Al-Jeser

S36

26/03/20

04–

30/07/20

05180370

185100

Eocene

Northeastern

38.60

1.10

0.90

0.0032

0.15

0.95

33.54

9.18

550.00

150.59

Ein

Tabb

anS

3626

/03/20

04–

30/07/20

05180420

184820

Eocene

Northeastern

37.40

1.10

0.80

0.0032

0.15

0.95

33.54

9.18

550.00

150.59

Ein

Sub

ian

S35

8/01

/200

4–30

/07/20

05180440

184420

Eocene

Northeastern

39.60

1.10

0.80

0.0032

0.15

0.95

33.54

9.18

550.00

150.59

Ein

Dlaib

S36

26/03/20

04–

30/07/20

05182000

187950

Eocene

Northeastern

59.40

1.70

1.20

0.0049

0.24

1.46

51.83

9.18

550.00

97.44

Ein

Faria

S40

28/12/20

02–

30/07/20

05182400

188400

Eocene

Northeastern

55.70

1.60

1.10

0.0046

0.22

1.38

48.78

9.18

550.00

103.53

16-19/012

W1

10/04/20

0716

9460

193410

Upp

erCenom

anian

Northeastern

37.00

1.00

1.00

0.0029

0.14

0.86

30.49

9.18

550.00

165.65

17-11/002

W1

10/04/2007

175000

198320

Eocene

Northeastern

27.00

0.80

0.70

0.0023

0.11

0.69

24.39

9.18

550.00

207.07

Mesleh

S1

14/04/20

0616

0364

1109

37Albain

Eastern

38.00

1.10

0.70

0.0032

0.15

0.95

33.54

9.18

600.00

164.28

BeitJalah

S1

14/04/20

0616

7299

124114

Upp

erCenom

anian

Eastern

34.00

1.00

0.80

0.0029

0.14

0.86

30.49

9.18

600.00

180.71

Wayko

kiS

116

/03/20

0615

8804

103710

Low

erCenom

anian

Eastern

37.00

1.00

0.60

0.0029

0.14

0.86

30.49

9.18

550.00

165.65

Al-Balad

S1

14/04/20

0616

0014

1143

43Upp

erCenom

anian

Eastern

37.00

1.00

0.70

0.0029

0.14

0.86

30.49

9.18

600.00

180.71

Al-Liban

ashrqiya

S1

20/02/20

0617

3000

164000

Albain

Eastern

23.00

0.60

0.60

0.0017

0.08

0.52

18.29

9.18

550.00

276.09

Turmusava

S1

20/02/2006

177000

161000

Low

erCenom

anian

Eastern

23.00

0.60

0.60

0.0017

0.08

0.52

18.29

9.18

550.00

276.09

Saleh

S1

20/02/20

0616

5900

121000

Low

erCenom

anian

Eastern

28.00

0.80

0.60

0.0023

0.11

0.69

24.39

9.18

550.00

207.07

Jaljo

ulia

S1

20/02/20

0517

0500

155400

Albain

Eastern

22.50

0.60

0.50

0.0017

0.08

0.52

18.29

9.18

550.00

276.09

Al-kabeerah

S1

25/02/20

0617

1600

151200

Albain

Eastern

21.00

0.60

0.50

0.0017

0.08

0.52

18.29

9.18

500.00

250.99

Al-magharah

S1

25/02/20

0617

1550

151050

Albain

Eastern

21.00

0.60

0.50

0.0017

0.08

0.52

18.29

9.18

500.00

250.99

Al-daraj

S1

25/02/20

0617

1600

151150

Albain

Eastern

22.00

0.60

0.50

0.0017

0.08

0.52

18.29

9.18

500.00

250.99

Majur

S1

25/02/20

0616

8150

150550

Albain

Eastern

22.00

0.60

0.50

0.0017

0.08

0.52

18.29

9.18

550.00

276.09

(Contin

ued)

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Tab

le4(Contin

ued)

Sam

plingsite

Type

No.

ofsamples

Date

Eastin

gNorthingAquifer

Groundw

ater

basin

Cl-

(mg/L)

Cl-

(meq/L)Na+

(meq/L)

Br+

(meq/L)Cl

excess

(meq/L)

CalcCl

(meq/L)

CalcCl

(mg/L)

Clin

rainfall

(mg/L)

P (mm/year)

R (mm/year)

18-15/001

W6

12/11/20

01–

23/04/20

0518

1550

155250

Upp

erCenom

anian

Eastern

29.60

0.80

0.60

0.0023

0.11

0.69

24.39

9.18

450.00

169.42

Al-Jummaizah

S1

14/02/20

0617

9070

137770

Turon

ian

Eastern

30.20

0.90

0.70

0.0026

0.13

0.77

27.44

9.18

400.00

133.86

Fara

S1

14/02/20

0617

8720

137860

Turon

ian

Eastern

30.10

0.80

0.70

0.0023

0.11

0.69

24.39

9.18

400.00

150.59

Jadu

rS

114

/02/20

0616

1000

1150

00Low

erCenom

anian

Eastern

24.00

0.70

0.70

0.0020

0.10

0.60

21.34

9.18

600.00

258.16

17-11/00

1W

113

/04/20

0717

0900

1183

00Upp

erCenom

anian

Eastern

29.00

0.80

0.80

0.0023

0.11

0.69

24.39

9.18

450.00

169.42

16-11/00

6W

113

/04/20

0716

9460

1140

80Low

erCenom

anian

Eastern

25.00

0.70

0.70

0.0020

0.10

0.60

21.34

9.18

500.00

215.13

17-11/00

3W

113

/04/20

0717

1850

1172

20Low

erCenom

anian

Eastern

28.00

0.80

0.70

0.0023

0.11

0.69

24.39

9.18

450.00

169.42

Shalal

S1

04/03/20

0616

3400

164600

Upp

erCenom

anian

Western

34.00

1.00

0.80

0.0029

0.14

0.86

30.49

9.18

550.00

165.65

Marda

S1

04/03/20

0616

8571

169085

Upp

erCenom

anian

Western

29.00

0.80

0.70

0.0023

0.11

0.69

24.39

9.18

550.00

207.07

Ibween

S1

04/03/20

0616

8808

159893

Albain

Western

20.00

0.60

0.50

0.0017

0.08

0.52

18.29

9.18

600.00

301.19

Ras

Karkar

S1

04/03/20

0616

0148

149901

Low

erCenom

anian

Western

23.00

0.60

0.60

0.0017

0.08

0.52

18.29

9.18

550.00

276.09

Darah

S1

05/03/20

0616

8000

159000

Albain

Western

19.00

0.50

0.50

0.0014

0.07

0.43

15.24

9.18

550.00

331.31

Mazara’

Al

Nou

ban

S1

05/03/20

0616

6023

161853

Albain

Western

27.00

0.80

0.70

0.0023

0.11

0.69

24.39

9.18

550.00

207.07

ElB

alad/

Ibwein

S1

06/03/20

0616

9100

160300

Albain

Western

25.00

0.70

0.50

0.0020

0.10

0.60

21.34

9.18

550.00

236.65

Marrashah

S1

06/03/20

0616

4700

149900

Albain

Western

25.00

0.70

0.60

0.0020

0.10

0.60

21.34

9.18

550.00

236.65

Al-Balad

S1

06/03/20

0616

3000

154500

Albain

Western

24.00

0.70

0.60

0.0020

0.10

0.60

21.34

9.18

500.00

215.13

DairAmmar

S1

07/03/20

0616

2000

156500

Albain

Western

22.00

0.60

0.60

0.0017

0.08

0.52

18.29

9.18

550.00

276.09

Um

Al-Enain

S1

20/03/20

0616

4370

147800

Albain

Western

24.00

0.70

0.50

0.0020

0.10

0.60

21.34

9.18

550.00

236.65

Um

al-

Rum

man

S1

20/03/20

0616

4400

147800

Albain

Western

24.00

0.70

0.50

0.0020

0.10

0.60

21.34

9.18

550.00

236.65

Kurta

S1

20/03/20

0615

2082

101123

Low

erCenom

anian

Western

29.00

0.80

0.70

0.0023

0.11

0.69

24.39

9.18

475.00

178.83

Abu

Hum

mus

S1

20/03/20

0615

8150

94664

Upp

erCenom

anian

Western

39.00

1.10

0.80

0.0032

0.15

0.95

33.54

9.18

475.00

130.06

Al-Jame’

S1

02/04/20

0616

2590

125470

Upp

erCenom

anian

Western

26.00

0.70

0.70

0.0020

0.10

0.60

21.34

9.18

550.00

236.65

Udah

S1

02/04/20

0616

3000

124000

Upp

erCenom

anian

Western

21.00

0.60

0.50

0.0017

0.08

0.52

18.29

9.18

550.00

276.09

Fares

S1

02/04/20

0615

9500

122050

Upp

erCenom

anian

Western

23.00

0.60

0.50

0.0017

0.08

0.52

18.29

9.18

550.00

276.09

Ein

Areek

Alofouq

aS

311/12/20

02–

14/08/20

0616

3630

145880

Albian

Western

24.10

0.70

0.60

0.0020

0.10

0.60

21.34

9.18

550.00

236.65

15-17/015

W1

04/05/20

0715

0280

171840

Upp

erCenom

anian

Western

43.00

1.20

1.00

0.0034

0.17

1.03

36.58

9.18

500.00

125.50

15-15/004

W1

04/05/20

0715

5200

153000

Albian

Western

30.00

0.80

0.70

0.0023

0.11

0.69

24.39

9.18

550.00

207.07

15-18/015

W1

04/05/20

0715

6800

181200

Albian

Western

38.00

1.10

0.90

0.0032

0.15

0.95

33.54

9.18

550.00

150.59

15-17/008

W1

04/05/20

0715

1160

170100

Upp

erCenom

anian

Western

38.00

1.10

1.00

0.0032

0.15

0.95

33.54

9.18

500.00

136.90

14-17/002

W1

04/05/20

0714

8700

174780

Upp

erCenom

anian

Western

44.00

1.20

0.70

0.0034

0.17

1.03

36.58

9.18

500.00

125.50

15-18/007

W1

04/05/20

0715

2350

189000

Upp

erCenom

anian

Western

32.00

0.90

0.70

0.0026

0.13

0.77

27.44

9.18

500.00

167.33

0.11

0.69

24.39

9.18

550.00

207.07

S:spring;

W:w

ell;P:annualp

recipitatio

n;andR:estim

ated

recharge

ofthesamplingsite.

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The assumptions necessary for successful appli-cation of the chloride mass-balance method are:

1 The absence of additional chloride sources such asdissolution of minerals, use of road salts and anypotential source of pollution like wastewater.

2 Chloride is of a conservative nature in the systemmeaning that the ion neither leaches from, nor isabsorbed by, aquifer sediments and does not parti-cipate in any particular chemical reaction.

3 The depth of the groundwater table should be deepenough to prevent groundwater evaporation.

4 Surface runoff should be minimal.

The first assumption is almost impossible, espe-cially in the case of the Western and Northeastern basinareas. A large amount of wastewater is generated by thecommunities in the upper mountains and drains downthrough wadi flow, which makes the opportunity forfresh sewage water mixing high. Moreover, the Jordanrift valley formations, which cover a large part of theEastern basin, contain a high quantity of salty rocks. Allof the previous factors make the presence of excesschloride unavoidable, and this amount of excess chlor-ide should be taken into account in calculations. In ourstudywe used the Br/Clmolar ratios in rain and ground-water to calculate any addition of chloride to therecharged water during its pathway. Both Cl- and Br-

behave conservatively. Rosenthal has suggested theCl-/Br- molar ratio in the groundwater of the studyarea is 300 (Rosenthal, 1987). The relative ratio forthe rainwater in our data was taken into account,where these values were used to approximate theamount of any additional chloride compared to themeasured values in the rainwater, and the valueassumed for groundwater by Rosenthal (1987).

The chloridemass-balancemethod has been appliedby various authors (Allison & Hughes, 1978; Edmunds& Walton, 1980; Allison & Stone, 1985; Sharma, 1989;Lerner et al., 1990; Abdulghaffar et al., 1996; Selaolo,1998; Simmers & de Vries, 2002). Note that Edmundset al. (1988) conclude that the amount of chlorideremoved through vegetation is usually balanced by theamounts released by plant decomposition.

Subyani (2004) used the chloride mass-balancemethod in Wadi Tharad, western Saudi Arabia, andestimated that the recharge rate was around 11% of theeffective annual rainfall. Bazuhair & Wood (1995)also used the method in the wadi systems of the Asirand Hijaz mountains. In general, recharge was foundto be between 3 and 4% of precipitation. They con-clude that the chloride mass-balance method appears

to be a useful technique to rapidly estimate ground-water recharge, or constrain estimates of groundwaterrecharge in certain arid areas.

In their paper, Simmers & de Vries (2002) summar-ize the current understanding of recharge processes,identify recurring recharge-evaluation problems, andreport on some recent advances in estimation techniques.Emphasis is placed on semi-arid regions because this iswhere the need for information is greatest. The paperconcludes that multiple tracer approaches (Cl-, 3H) prob-ably offer the best potential for reliable results in localstudies that require “at-point” information.

Kerh et al. (1998) adopted the chloride mass-balance method to estimate groundwater recharge inthe Pingtung Plain, Taiwan. Based on the measuredand calculated results for all sites, groundwaterrecharge was estimated at 15% of the annual rainfall,excluding recharge from additional irrigation water.They conclude that this information can improve theaccuracy of future groundwater simulation and man-agement models in the plain.

Unfortunately, few studies were found to haveapplied this method in Palestine. According to theCoastal Aquifer Management Program in theIntegrated Aquifer Management Plan (PalestinianWater Authority, 2000) the Water Resources ActionProgram estimated recharge coefficients in areas ofdune sand and clayey soil. The coefficients obtainedwere 55–65% and 15%, respectively. Using thesevalues and applying long-term average rainfall datafor various stations in Gaza, the total estimatedrecharge was calculated to be 46 � 106 m3/year inthe Gaza Strip. Another study (Ghanem, 1999) usedthemethod to calculate the annual recharge in the FariaDrainage Basin in the West Bank. The estimatedrecharge was found to be 77.2 mm/year in the phreaticaquifer and 76.2 mm/year in the confined aquifer.

3.3 Empirical relations

The natural recharge of aquifers is a function of pre-cipitation, along with many other factors such as geol-ogy, soils, vegetation, land use, climatic conditions,topography, land form and groundwater conditions.Based on studies of the correlation between rainfalland natural recharge, a number of empirical relationshave been identified. Goldschmidt & Jacobs (1959)developed a relationship between rainfall and baseflow data in the period between 1943/44 and 1953/54.Since there was very little well abstraction at the time,

Estimating groundwater recharge using the chloride mass-balance method in the West Bank, Palestine 787

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the total annual spring flow was considered equal to theannual recharge to the basin. The formula applied is:

R ¼ 0:86� P � 360ð Þ (2)

where R is the recharge in mm/year; P is the annualrainfall in mm/year.

Instead of 0.86, Mandel & Shiftan (1981) used0.90 as a coefficient in equation (2) for recharge inMediterranean climates.

The following equations were used as the basisfor the development of annual recharge estimates byGuttman & Zukerman (1995):

R ¼ 0:8� P � 360ð Þ P> 650mm (3)

R ¼ 0:534� P � 216ð Þ 300 < P< 650mm (4)

R ¼ 0:15� P P < 300mm (5)

These equations were later modified by the SUSMAQproject team (Abu Sa’da et al., 2004) to give:

R ¼ 0:6� P � 285ð Þ P > 700mm (6)

R ¼ 0:46� P � 159ð Þ 456 < P < 700mm (7)

R ¼ 0:3� P P < 456mm (8)

Other more complicated formulas for empiricalrelationships between precipitation and recharge havealso been developed. For example, Sinha & Sharma(1988) developed an equation better known as theCheeturvedi formula:

R ¼ 50:8� P

25:4� 15P> 380mm=year (9)

Fig. 4 Recharge rates estimated for the West Bank using the chloride mass-balance method.

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Note that in equation (9) there is a lower rainfall limitbelow which recharge is zero. The lower rainfall limitin equation (9) may account for the soil moisturedeficit, interception losses and potential evaporation.

4 RESULTS AND DISCUSSION

The weighted average of chloride contents in the rain-water samples collected at the five sampling sitesrange between 6.95 and 12.81, with an average9.30 mg/L. This value is close to the value of9.06 mg/L estimated by Herut et al. (1994). We imple-ment a new chloride average value of 8.97 mg/Ltaking into consideration our measurements and thevalues of Herut et al. (1994). Table 4 and Fig. 4summarize the recharge rate estimation results afterapplication of the chloride mass-balance method.

4.1 Eastern Basin

A total of 19 groundwater samples were collectedfrom this basin. The chloride concentration rangedfrom 21 to 38 mg/L (values from the Plio-Pleistoceneaquifer in the Jordan Valley are excluded), and theNa+/Cl- ratio ranged from 0.86 to 1.0, which isclose to the marine value. The nitrate concentrationranged from 4.0 to 16 mg/L. The excess chloridewas calculated using the Cl-/Br- molar ratio, andranged from 15 to 20% of the measured chloride forthe three basins. The land use in the recharge area isprimarily grazing, with some rainfed crops, includingwheat and olive trees. However, it is mostly used as

rangeland. Recharge rates calculated by various authorsrange between 130.2 and 259.3 mm/year. The chloridemass-balance method shows that the annual rechargerate is between 130.8 and 269.7 mm/year (Table 5), anda recharge volume of 290.3 � 106 m3/year (Table 6).

4.2 Northeastern Basin

A total of 19 groundwater samples were collected fromthis basin. The chloride concentration Ranges from20.0 to 59.4 mg/L and the Na+/Cl- ratio ranged from0.86 to 1.0. The nitrate concentrations were5.3–19.5 mg/L. The high chloride contents in somesamples can be ascribed to the low permeabilitychalky limestone formation and the thick soil horizonin some areas (Rofe and Raffety, 1963); the percentageof excess chloride reached 2% of measured chloride inthese samples. Most of the land is used for agriculturalpurposes (mainly olive trees) and relies on rainfall. Inthe northern part of the basin, some of the land is alsoirrigated and vegetables are cultivated. The source ofnitrate in groundwater samples is related to nitrifica-tion of organic matter in the soil horizon as well aspercolation of irrigation water (Hem, 1970).

Rofe and Raffety (1965) calculated the averageactual recharge to range between 50 and 250 mm/year(Table 2). Our calculation of the recharge rate using thechloride mass-balance method shows slightly differentresults. According to this method, the average annualrecharge rate of the Northeastern Basin lies between95.2 and 269.7 mm/year (Table 5), and a rechargevolume of 138 � 106 m3/year (Table 6).

Table 5 Recharge rate in mm/year in groundwater basins of the West Bank.

Study Western Basin Northeastern Basin Eastern Basin

Goldschmidt & Jacob (1959) 263.7 247.7Mandel & Shiftan (1981) 276.0 259.3Tahal (1995) 245.3 230.7Cheeturvedi (Sinha & Sharma, 1988) 133.7 130.2Our estimation 122.6–323.6 95.2–269.7 130.8–259.7

Table 6 Estimated recharge volume (106 m3/year).

Study Northeastern Basin Eastern Basin Western Basin Total

WRAP (1994) 140.0 125.0 335.0 600.0Rofe and Raffety (1963–1965) 124.0 213.3 375.9 713.2Our estimation 138.0 290.3 324.9 753.2

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4.3 Western Basin

A total of 19 groundwater samples were collected fromthis basin. The general groundwater flow direction iswest (Fig. 3). The chloride concentration ranged from19.0 to 43.0 mg/L, and the Na+/Cl- ratio rangedbetween 0.86 and 1. The highest chloride concentra-tions were found in the coastal area, where the soilhorizon is a few metres thick and irrigation activitiesare widely distributed. The average nitrate content con-centration ranged from 2.0 to 39.0 mg/L. According toour chloride mass-balance calculation, the estimatedrecharge rate in this area ranges from 122.6 to323.6 mm/year (Table 5), and a recharge volume of324.9 � 106 m3/year (Table 6).

4.4 Comparison with previous estimation

Table 6 shows our estimates of recharge volume for theWest Bank Mountains aquifers, and the previous esti-mation frommany other studies. The data reveal higherreplenishment potential volume (753.2 � 106 m3/year)than previous studies for the same area (Table 6). Also,the range was between 15 and 50% of total rainfall,which is still within the range of previous studies.

5 CONCLUSIONS

Recharge in semi-arid regions like theWest Bank can beestimated using the chloride mass-balance method. Anaverage chloride concentration in rainfall of 8.97 mg/Lwas applied for the calculations. Recharge areas coveredin impermeable chalk and Quaternary formations alongthe Jordan rift valley were excluded from the calculationof the total recharge volume. Recharge rates range from15 to 50% of rainfall, which is still within the range ofprevious studies records. Low recharges rates werefound in areas of chalky limestone in the NortheasternBasin, and along the western margin of the easternslopes of the Mountain Aquifer.

In most of the samples the Na+/Cl- ratio is lessthan 1 and close to the marine ratio, and the NO3

-

concentration ranges from 5.3 to 24.0 mg/L. Thesetwo parameters were applied to identify pollutionsources. The Br-/Cl- ratio was used to calculate excesschloride, which was excluded in the recharge estima-tion. According to this method the total estimatedrecharge volume in the three groundwater basins(without the shallow Plio-Plistocene aquifer in thelower Jordan Valley) is 753.73 � 106 m3/year.

Acknowledgements This research was conducted aspart of the Groundwater Availability and the Fate ofPesticide Input research project (GAPI) funded by theGermanMinistry of Education and Research (BMBF).

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