3D Hydrological modeling in a subsurface drained

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

1

Nijland et al. (2005)

2

Subsurface drainage in agricultural areas

World Resources Institute

Documented cases of eutrophication (yellow) & hypoxia (red) from 1980 to 2010

Subsurface drainage

3

* 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

4

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

6

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

7

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

9

A

B

SimulatedObserved

Period: July 2012 - January 2014

Drainage area

Field-scaleCatchment-scale

Main drains

Drainage areas

Drains assink nodes

1D lines Improve?

10

Position of drains is needed

no position is needed

Future work:- Calibration- Application: different hydrogeological conditions

Conclusions

vinicius.ferreira-boico.1@ulaval.ca

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

14

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

16

✓ Fully-integrated✓ Version 2017

control volume finite element

Numerical model

Baseflow

Groundwater flow

17

Wetlands >> nutrient balanceFertilisers

Hansen et al. (2014)

Redox interface

Modeling