Density dependent groundwater flow at the Density dependent groundwater flow at the island of Texel, The Netherlandsisland of Texel, The Netherlands

IntroductionIntroduction Computer codeComputer code Model designModel design DiscussionDiscussion ConclusionsConclusions

Gualbert Oude EssinkGualbert Oude Essink

Earth SciencesEarth Sciences

Utrecht UniversityUtrecht UniversityThe NetherlandsThe Netherlands

Utrecht University

Great Geohydrologic Research Texel

Interfaculty C entreHydrology Utrecht

Salt water intrusion at TexelSalt water intrusion at Texel

IntroductionIntroduction

polder areadunes

salt water intrusion

saline

seepage

naturalgroundwater recharge

brackish

infiltration

sea

extractioninfiltration

freshwater lenssea

aquitard

Present ground surface in the NetherlandsPresent ground surface in the Netherlands

IntroductionIntroduction

0 25 50 75 100 km

Den Haag

Island of

Germ any

Belgium

Rotterdam

10-20

0 - 2-2 - 0-4 - -2< -4 m M.S.L.

2 -10

20-40>40

lowest point:-6.7 m M.S.L.

highest point:+322 m M.S.L.

Amsterdam

Texel

North Sea

The island of TexelThe island of Texel

IntroductionIntroduction

Tourist island in summer timeTourist island in summer time

Land surface: 130 kmLand surface: 130 km22

Polder areas:Polder areas: 1. Eijerland1. Eijerland 2. Waal en Burg2. Waal en Burg 3. Dijkmanshuizen3. Dijkmanshuizen 4. Hendrik polder4. Hendrik polder

Sand-dune area at western sideSand-dune area at western side

‘ ‘De Slufter’ is a tidal salt-marshDe Slufter’ is a tidal salt-marsh

North Sea surrounds the islandNorth Sea surrounds the island

0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

1. E ijerland

2. Waal en Burg

3. D ijkm anshuizen

De Slufter

4. Hendrik po lder

Nor

th S

ea

San

d-d

un

e a

rea

Present phreatic water level in top layerPresent phreatic water level in top layerIntroductionIntroduction

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

-1.25-

-1.00-

-0.75

-0.75-

-0.50

-0.50-

0.00

0.00-

0.50

0.50-

1.00

1.00-

1.50

1.50-

2.00

2.00-

3.00

3.00-

4.00

4.00-

-1.00

6.50

-2.50-

-1.50-

-1.25

-1.50

[m M.S.L.]20002000

Present chloride concentration in top layerPresent chloride concentration in top layerIntroductionIntroduction

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15

.0-1

7.5

-20

.0-2

2.5

-25

.0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

20002000

300-

1000

1000-

2500

2500-

5000

5000-

7500

7500-

10000

10000-

12500

12500-

15000

15000-

18630

150-

300

50-

150

0

50

-Concentration [mg Cl /l]

density dependent groundwater flowdensity dependent groundwater flow DarcyDarcy continuitycontinuity

solute transportsolute transport

advectionadvection

hydrodynamic dispersionhydrodynamic dispersion

displacement of fresh, brackish and saline groundwaterdisplacement of fresh, brackish and saline groundwater

linear relation between density & concentrationlinear relation between density & concentration

Computer codeComputer code

MOCDENS3D = MOC3D (MOCDENS3D = MOC3D (Konikow et al.Konikow et al., 1996), 1996) but adapted for density differences but adapted for density differences

Groundwater flow equation (MODFLOW, 1988)Darcy

Continuity

Freshwater head

Advection-dispersion equation (MOC3D, 1996)

Equation of state: relation density & concentration

q kx

q ky

q kzx x

fy y

fz z

f f

f

; ;

C

t n Rd

xinDij

C

xj

1

Rd

ViC

xi

W C'-C

n Rd

C

1 [ ( )]

i, j,k i, j,kf

( )1 C

-q

x

q

y

q

zS

tWx y z

s

f

f

pz

g

Computer codeComputer code

Effective porosity: 0.3Effective porosity: 0.3

Anisotropy: 0.4Anisotropy: 0.4

Hydrodynamic dispersion:Hydrodynamic dispersion: LL=2 m, =2 m, THTH=0.2 m, =0.2 m, TVTV=0.2 m=0.2 m molecular diffusion=10molecular diffusion=10-9-9 m m22/s/s

Density groundwater: Density groundwater: freshfreshff=1000 kg/m=1000 kg/m33, saline, saliness=1024 kg/m=1024 kg/m33

Boundary conditions:Boundary conditions: No flow at sea sideNo flow at sea side Neumann in dunes: natural recharge of 1 mm/dayNeumann in dunes: natural recharge of 1 mm/day Dirichlet in polder area: constant phreatic water levelDirichlet in polder area: constant phreatic water level

Model designModel design

Subsoil parameters:Subsoil parameters:

--->---> aquifer 1: aquifer 1: kkhh=~5 m/day (intersected by aquitards)=~5 m/day (intersected by aquitards)

--->---> aquifer 2: aquifer 2: kkhh=~30 m/day (intersected by aquitards)=~30 m/day (intersected by aquitards)

--->---> aquitard 1: aquitard 1: kkhh=0.01 to 1 m/day=0.01 to 1 m/day

--->---> aquifer 3: aquifer 3: kkhh=~30 m/day (intersected by aquitards)=~30 m/day (intersected by aquitards)

--->---> aquifer 4: aquifer 4: kkhh=2 m/day=2 m/day

--->---> aquifer 5: aquifer 5: kkhh=10 to 30 m/day=10 to 30 m/day

Model designModel design

Subsoil composition (simplified):Subsoil composition (simplified):0

m M

.S.L

-202

-102

-72

-302

-22

-62

Number of elementsNumber of elementsnnxx=80, n=80, nyy=116, n=116, nzz=23=23

total number of active elements: ~125000total number of active elements: ~125000

Sizes of elements:Sizes of elements:x=250 m, x=250 m, y=250 m, y=250 m, z=1.5 to 20 mz=1.5 to 20 m

Particles per element: 8Particles per element: 8

Flow time step: 1 yearFlow time step: 1 year

Convergence criterium: 10Convergence criterium: 10-5-5 m m

Model designModel design

Model parameters:Model parameters:

Calculated present seepage and infiltration at -1.5 m M.S.L.Calculated present seepage and infiltration at -1.5 m M.S.L.DiscussionDiscussion

-1.00-

-0.75-

-0.50

-0.50-

-0.25

-0.25-

-0.10

-0.10-

0.00

0.00-

0.10

0.10-

0.25

0.25-

0.75

0.75-

1.20

>1.20

-0.75

-3.50-

-1.50-

-1.00

-1.50

seepage infiltration [m m /day]

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15

.0-1

7.5

-20

.0-2

2.5

-25

.0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

20002000

Calculated present salt load at -1.5 m M.S.L.Calculated present salt load at -1.5 m M.S.L.DiscussionDiscussion

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

Salt load [kg/ha/year]

-500-

-100-

0

0-

500

500-

1000

1000-

2500

2500-

5000

5000-

7500

7500-

15000

15000-

75000

>75000

-100

-50000-

-2500-

-500

-2500

20002000

Modelling of two sea level rise scenarios:Modelling of two sea level rise scenarios:

I.I. Present mean sea level during 200 years Present mean sea level during 200 years

II.II. Relative sea level rise of 0.75 m/century during 200 years Relative sea level rise of 0.75 m/century during 200 years

Interest is focused on:Interest is focused on:

A.A. Change in concentration in top layer Change in concentration in top layer

B.B. Change in seepage in polders Change in seepage in polders

C.C. Change in salt load in polders Change in salt load in polders

DiscussionDiscussion

A.A. Change in concentration in top layer Change in concentration in top layerScenario Scenario II: present mean sea level during 200 years: present mean sea level during 200 years

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

300-

1000

1000-

2500

2500-

5000

5000-

7500

7500-

10000

10000-

12500

12500-

15000

15000-

18630

150-

30050

-150

0

50

-Concentration [m g C l /l]

20002000

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

22002200

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

Scenario Scenario IIII: relative sea level rise of 0.75 m/c during 200 years: relative sea level rise of 0.75 m/c during 200 years

300-

1000

1000-

2500

2500-

5000

5000-

7500

7500-

10000

10000-

12500

12500-

15000

15000-

18630

150-

30050

-150

0

50

-Concentration [m g C l /l]

20002000

A.A. Change in concentration in top layer Change in concentration in top layer

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

22002200

Scenario Scenario IIII: relative sea level rise of 0.75 m/c during 200 years: relative sea level rise of 0.75 m/c during 200 years

300-

1000

1000-

2500

2500-

5000

5000-

7500

7500-

10000

10000-

12500

12500-

15000

15000-

18630

150-

30050

-150

0

50

-Concentration [m g C l /l]

A.A. Change in concentration in row 76: East-West profile Change in concentration in row 76: East-West profile

W

20.00 .0 5 .0 10.0 15.0 km

0-1

00-2

00-3

00km O

20.00 .0 5 .0 10.0 15.0 km

0-1

00-2

00-3

00km W O

20002000

22002200

Scenario Scenario IIII: relative sea level rise of 0.75 m/c during 200 years: relative sea level rise of 0.75 m/c during 200 years

B.B. Change in seepage Change in seepage

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

22002200

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

20002000

-1.00-

-0.75-

-0.50

-0.50-

-0.25

-0.25-

-0.10

-0.10-

0.00

0.00-

0.10

0.10-

0.250.25

-0.75

0.75-

1.20>1.20

-0.75

-3.50-

-1.50-

-1.00-1.50

seepage infiltration [m m /day]

Scenario Scenario IIII: relative sea level rise of 0.75 m/c during 200 years: relative sea level rise of 0.75 m/c during 200 years

C.C. Change in salt load Change in salt load

Salt load [kg/ha/year]-500

--100

-0

0-

500

500-

1000

1000-

2500

2500-

5000

5000-

10000

10000-

30000

30000-

90000

>90000

-100

-50000-

-2500-

-500-2500

Salt load [kg/ha/year]-500

--100

-0

0-

500

500-

1000

1000-

2500

2500-

5000

5000- - -

-100

-50000-

-2500-

-500-2500

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

22002200

0.0 2 .5 5 .0 7 .5 10.0 12.5 15.0 17.5 20.0 km

0.0

-2.5

-5.0

-7.5

-10.

0-1

2.5

-15.

0-1

7.5

-20.

0-2

2.5

-25.

0-2

7.5

km

Eijerland

Waal en Burg/Het Noorden

Dijkmanshuizen/De Schans

De S lufter

Prins Hendrikpolder

20002000

Conclusions:Conclusions: numerical dispersion is limited (no Peclet number problems)numerical dispersion is limited (no Peclet number problems)

initial density distribution is difficult to determineinitial density distribution is difficult to determine

present situation is not in a dynamic equilibriumpresent situation is not in a dynamic equilibrium

salinisation during coming 200 years is significant due to:salinisation during coming 200 years is significant due to: the present difference in polder level and sea levelthe present difference in polder level and sea level tthe sea level risehe sea level rise

effect of sea level rise:effect of sea level rise: accelerates the salinisation processaccelerates the salinisation process salt load and seepage in polders increases substantialsalt load and seepage in polders increases substantial