density dependent groundwater flow at the island of texel, the netherlands introduction computer...
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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
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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
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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
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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
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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
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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]
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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
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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
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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:
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--->---> 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
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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:
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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
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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
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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
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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
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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
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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
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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]
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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
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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