3d hydrological modeling in a subsurface drained
TRANSCRIPT
Vinicius Ferreira Boico
PhD student in Hydrogeology
Supervisor: René Therrien13 Sept 2018
3D Hydrological modeling in a subsurface drained agricultural area
- Glacial till- low permeable
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Nijland et al. (2005)
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Subsurface drainage in agricultural areas
World Resources Institute
Documented cases of eutrophication (yellow) & hypoxia (red) from 1980 to 2010
Subsurface drainage
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* Most drains are not mapped
- Eutrophication & hypoxia
- Destroy ecosystems
- Impair groundwater and surface water quality
Photo: Fyn County/Nanna Rask
Nutrient contamination of water resources
Since 1987: nitrate loss reduced in 50%
To reach EU water quality criteria:
• Hydrology in drainage areas
• small-scale → catchment-scale
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Nitrate issue in Denmark
62 %
http://trends.nitrat.dk/
✓ Surface
✓ Subsurface (variably-saturated)
✓Drainage
transient & heterogeneous
5Drainage systems in Fensholt catchment
Drainage area
Outlet
Numerical model and study area
• reduce comp. times• similar results
(De Schepper et al., 2015; 2017)
Radom all drains Uniform all over
Uniform drainage areas
a
db
c
Main drainage paths
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Sink nodes distribution - Fensholt
Test Representation Time (d) MAE (L/s) NS
a Main drains 1.0 30 0.62
b Random 1.0 31 0.60
c Uniform drainage areas 2.3 21 0.69
d Uniform all catchment 1.0 36 0.22
Optimal 0 1
0
250
500
750
1000
Stre
am
dis
cha
rge
[L/
s] d
0
250
500
750
1000
Stre
am
dis
cha
rge
[L/
s] a
0
250
500
750
1000
Stre
am
dis
cha
rge
[L/
s] b
0
250
500
750
1000
Stre
am
dis
cha
rge
[L/
s] c
Period: July 2012 - January 2014
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SimulatedObserved
Discharge flow rate - Fensholt
Main drainage paths
8
Similar results
0> 0 – 10> 10
Water depth [m]
Dry period 2013-07-21
Uniform drainage areas
Water table depth - Fensholt
Test Representation Time (h)MAE (L/s)
NS
A Sink - drains 4 0.76 0.50
B Uniform 1 0.80 0.45
C 1D lines 15 0.87 0.34
Optimal 0 1
0
15
30
Dra
ina
ge d
isch
arg
e [L
/s]
A
0
15
30
Dra
ina
ge d
isch
arg
e [L
/s]
B
0
15
30
Dra
ina
ge d
isch
arg
e [L
/s]
CC1D lines
Exchange flow
Wet period2014-01-18
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A
B
SimulatedObserved
Period: July 2012 - January 2014
Drainage area
Field-scaleCatchment-scale
Main drains
Drainage areas
Drains assink nodes
1D lines Improve?
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Position of drains is needed
no position is needed
Future work:- Calibration- Application: different hydrogeological conditions
Conclusions
EXTRAS
Refined mesh Surface Grid
TestDrainage
representationNumber of seepage
nodesnodes elements nodes elements
5 Random 372 3982 7652 75658 137736
6 Main drains 342 3854 7405 73226 133290
7 Uniform drainage areas 318 3867 7436 73473 133848
8 Uniform all catchment 793 4544 8730 86336 157140
Surface GridID nodes elements nodes elements1 1189 2285 24969 457002 1815 3516 38115 703203 4263 8369 89523 167380
Fensholt
Drainage area D5
2D surface and 3D porous medium grid
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Glacial sand
Glacial clay
Tectonic sand
Tectonic clay
Miocene sand
Miocene clay
A horizon
B horizon
C horizon
Clayey till
Geological units Stochastic model
sand
clay
and
lay
sand
clay
A horizon
B horizon
C horizon
Clayey till
Geological units model
He et al. (2014)
Fensholt catchment geological model
Errors
✓ Surface (2D, transient): Saint-Venant
✓ Subsurface (3D, variably-saturated, transient): Richards
−𝛻(𝑤𝑚𝑞) +𝛤𝑒𝑥 ± 𝑄 = 𝑤𝑚𝜕(𝜃𝑠𝑆𝑤)
𝜕𝑡
q = −K kr 𝛻(𝜓 + 𝑧)
✓ Drainage (1D, Hazen-Williams/ Manning)
✓ Nitrate transport (3D)
−𝛻 𝑞𝐶 − 𝜃𝑠𝑆𝑤𝐷𝛻𝐶 +Ω𝑒𝑥 ± 𝑄𝑐 =𝜕(𝜃𝑠𝑆𝑤𝐶)
𝜕𝑡
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✓ Fully-integrated✓ Version 2017
control volume finite element
Numerical model
Baseflow
Groundwater flow
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Wetlands >> nutrient balanceFertilisers
Hansen et al. (2014)
Redox interface
Modeling
