Response of the groundwater system to a Base Level Drop: The Dead Sea Case

Response of the groundwater Response of the groundwater system to a Base Level Drop: The system to a Base Level Drop: The

Dead Sea CaseDead Sea Case

Yael Kiro, Yoseph Yechieli, Vladimir Lyakhovsky, Yael Kiro, Yoseph Yechieli, Vladimir Lyakhovsky, Eyal Shalev, Abraham Starinsky Eyal Shalev, Abraham Starinsky

Hebrew University of Jerusalem

Geological Survey of Israel

The Dead Sea level during the past 70 years

-420

-410

-400

-390

1930 1950 1970 1990Time (year)

Ele

vatio

n (

m)

IntroductionInstantaneous drop

gw responseInstantaneous drop

TZ responseContinuous drop

gw responseContinuous drop

TZ response

Location map

maps.google.com





TZ response

Groundwater levels in the Tureibe region

The rate of the groundwater level drop is smaller than the rate of the DS level drop

Yechieli et al., 2004





TZ response

Groundwater levels in Wadi Arugot

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2002 2003 2004 2004 2006 2007 2008Year

elev

atio

n (

m)

EG

11 a

nd

DS

-411

-409

-407

-405

elev

atio

n (

m)

EG

6

DS EG11 EG6

Groundwater levels drop at the same rate as the Dead Sea in all boreholes





TZ response

The transition zone during the Dead Sea level drop

The transition zone drops and widens over time





TZ response

The response of the groundwater system involves two aspects:

The response of the groundwater level

The response of the transition zone

• an instantaneous lake level drop

• a continuous lake level drop





TZ response

Problem settings

Constant inflow

no flow

no flowspecified pressure according to the lake level at each time step

W-SW E-NE

1400 1200 1000 800 600 400 0m200160018002000

EG-9 EG-10

AR-2

EG-6

EG-11

EG-17

E G-16

-390

-370

-360

-350

-380

-410

-420

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-440

-450

-460

-470

-400EG-12

EG-8AR-3

22020050

<0.5

10

25

100

150

WATER TABLE

Equal Chloride concentration (gr/l)

1

EG-7EG-13

EG-19

AR-1

Low permeability layer





TZ response

Dead Sea salinity 340 g/L

t

h

T

n

x

h

2

2

Bear, 1979

00,

0,

,0

xh

tLx

h

hth

0

2/0

222

,0k

tknL

T

eL

hKhtQ

n porosity B[L] aquifer thickness

h[L] groundwater head h0[L] flow section at x=0

T[L2/T] transmisivity (T=KB) L[L] aquifer length

K[L/T] hydraulic conductivity

An instantaneous lake level drop





TZ response

Freshwater discharge

4/

0

2/

0

2

2

/

eA

eAQQ

gw

k

tk

gw

0

0max

2

2

s

gw

L

hhKA

FKB

nL

Simulations:

An instantaneous lake level drop





TZ response

0.0E+002.0E-064.0E-066.0E-068.0E-061.0E-051.2E-051.4E-051.6E-05

0 10 20 30 40 50 60 70time (year)

Q-Q

0 (m

2/s)

simulation with salinewaterbest fit for the salinewater simulation

fresh water simulation

analytic solution

τgw

A

The response of the transition zoneThe response of the transition zone depends on

• The response rate of the fresh water (τgw)

• The horizontal density gradient

Depends on the transition zone slope

Depends on the hydraulic gradient





TZ response


•Saline water circulates in steady-state

• As the lake level drops, the saline water flows towards the lake

• When the groundwater reaches a new equilibrium, the saline water circulation reappears





TZ response


N

Q

hLnBC

LQ

hBK

TLTL

gwTZ

25.00

25.05.10

2max

Transition zone characteristic time

τgw[T] groundwater characteristic time L[L] aquifer length

Kmax[L/T] hydraulic conductivity αL[L] longitudinal dispersivity

Δh[L] lake level drop αT[L] transversal dispersivity

B[L] aquifer thickness n porosity

Q0[L3/T] inflow C, N factors





TZ response

A continuous lake level drop

t

h

T

n

x

h

2

2

00,

0,

,0

xh

tLx

h

Rtth

0

2/

20

0

2

12/

1)(

k

tk

s gwek

nRLQtQ

n porosity Kmax[L/T] hydraulic conductivity

h[L] groundwater head B[L] aquifer thickness

T[L2/T] transmisivity (T=KB) L[L] aquifer length

τgw[T] groundwater characteristic tine F factor

R [L/T] rate of lake level drop t [T] Time

Q[L3/T] discharge at x=0 ρs[M/L3] saline water density

Q0[L3/T] inflow ρ0[M/L3] fresh water density

FBK

nLgw

max

2





TZ response

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0 10 20 30 40 50 60

time (years)

Q-Q

0 (k

g/se

c)

simulation

analysis

τgw

A quasi-equilibrium is reached, in which the groundwater level drops but the discharge to the lake and the hydraulic gradient remain constant


0

2/

20

0

2

12/

1)(

k

tk

s gwek

nRLQtQ

FKB

nLgw

2





TZ response

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-415

050100150200250300350400

distance from the Dead Sea (m)

elev

atio

n (m

)

EG7

EG17

EG11

EG16DS

Oct-05

Jul-04

May-05

May-06

simulationborehole

Field measurements and simulation results

Simulation results and field data both indicate that the hydraulic gradient remained constant during the past few years.

The groundwater level maintained a quasi-equilibrium





TZ response

The response of the transition zone to a continuous lake level drop

The saline water circulation reappears during the lake level drop





TZ response

The effect of bathymetry

The transition zone widens when the bathymetry slope is larger





TZ response

mm TL 01.010

Seasonal changes in the fresh-saline interface

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01/05 03/05 05/05 07/05 09/05 11/05 01/06 03/06 05/06 07/06 09/06 11/06 01/07 03/07 05/07date

elev

atio

n (

m)

EG

17

-423.5

-422.5

-421.5

-420.5

-419.5

-418.5

-417.5

elev

atio

n (

m)

DS

groundwater level 100mS/cm 150 mS/cm 75 mS/cm DS





TZ response

Summary• We defined two characteristic times that

describe the groundwater response rate:

(i) A groundwater characteristic time (τgw) which depends on the aquifer diffusivity and its length.

(ii) A transition zone characteristic time (τTZ) which depends on τgw, and the hydraulic gradient.

• During a continuous lake level drop after a time interval proportional to τgw, the discharge to the lake and the hydraulic gradient attains a constant value.

• At this stage, the saline water circulation reappears

The hydraulic gradient increases until it attains quasi-equilibrium and remains constant


Quasi-equilibrium





TZ response

Response of the groundwater system to a Base Level Drop: The Dead Sea Case

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