comparison and validation of swms 2d and hydrus 2d/3d …...klaus berger: swms_2d & hydrus 2d...

Klaus Berger: SWMS_2D & HYDRUS 2D for Capillary Barriers; HYDRUS Conference Prague 2017

Comparison and Validation of SWMS_2D and HYDRUS 2D/3D for Capillary Barriers

Using Data of a 10-m Tipping Trough

Klaus Berger, University of Hamburg, Institute of Soil Science, Germany

5. HYDRUS Conference30 - 31 March 2017, Prague, Czech Republic

Klaus BergerUniversity of Hamburg, Institute of Soil Science

Outline

1. Introduction

2. Empirical investigations with a 10-m tipping trough (tilt gutter)

3. Simulations with SWMS_2D (1996)

4. Simulations with HYDRUS 2D(/3D) (2017)

5. Comparison of SWMS_2D and HYDRUS 2D/3D results

6. Possible reasons for the mismatch of measured and simulated outflow rates

SWMS_2D & HYDRUS 2D/3D for Capillary BarriersHYDRUS Conference 2017 30.03.2017


Introduction: What is a Capillary Barrier?


Capillary layer (e.g. sand)Relatively fine-grained/porous

Capillary block (e.g. gravel)Relatively coarse-grained/porous


Introduction: Capillary Barriers in Landfill Cover Systems


Mineral liner / Barrier soil layer

Recultivation layer (for vegetation)

Geomembrane (e.g. PEHD)

Lateral drainage layerGeotextile

Standard design of a cover system Alternative design with an ‘extended‘ capillary barrier (schematic profile)

Vegetation

Recultivation layer

Lateral drainage layerBarrier soil layerGeotextileCapillary layer

Capillary block


Introduction: How to Dimension Capillary Barriers? (1)

What does ‘dimension’ mean?

Determine suitable materials and maximum distances to the drain dependent on site specific conditions. Relevant parameters are:

1. Soil hydrological properties of materials for capillary layer and capillary block

2. Slope

3. Slope length / Maximum distance to drain

4. Shape of the slope (convex – concave; convergent – divergent): complex, therefore neglected here

5. Infiltration rate into the capillary layer (dependent on climate and the layers above the capillary barrier)




1. Empirical investigations with large test fields (lysimeters)

Six test fields on the landfill Hamburg-Georgswerder,Germany (50 m long, 10 m wide; profiles see on the right;test field S3 with ‘extended’ capillary barrier)


F1/S1 F2/S2 S3

25

60

20

2540

60

25

F3

75 75

F: 4% slopeS: 20% slope

cmcm

VegetationRecultivation layer / Top soilGeotextileLateral drainage layer; S3: Capillary blockGeomembrane (welded)Geomembrane (not welded)Mineral liner / Barrier soil layerCapillary layer



2. Empirical investigations with tipping troughs (tilt gutters) in pilot plant scale

10-m tipping trough of the Institute of Soil Science ofthe University of Hamburg




Principal methods for dimensioning capillary barriers:

1. Empirical investigations with large test fields (lysimeters)Advantages: Close to reality (field size)Disadvantages: Limited to very few parameter values; time consuming;

very expensive; results not reproducible

2. Empirical investigations with tipping troughs (tilt gutters) in pilot plant scaleAdvantages: Relatively close to reality, results (approximately) reproducibleDisadvantages: Limited to some parameter values; relatively time consuming;

expensive

3. Simulations with 2D or 3D models like SWMS_2D or HYDRUS 2D/3DAdvantages: Many parameter values possible; fast; low costs; reproducibleDisadvantages: Close to reality? Requires sufficient validation of the model!



Empirical Investigations in a 10-m Tipping Trough (Tilt Gutter)


Main characteristics:• 10 m long• 1 m high (capillary barrier)• 0.5 m deep

(0.3 m deep measurement area)• Slope adjustable up to 1:3 (33 %)

by a crank handle• Weighable (empty: ~ 4 t; full: ~ 13 t)• 9 capillary barrier segments,

1 m each, with separate outflows• 1 final capillary layer segment

(1 m long) with separate outflow• Irrigation system on top (uniform

irrigation of the surface)


Simulations with SWMS_2D (Vs. 1.1) in 1996

Simulations were performed for:• One material combination (capillary layer: ‘METHA’ sand; capillary block:

gravel 1 – 3 mm; both well sorted; assumption: homogeneous and isotropic)• Two slopes: Steep, i.e. 1:5 (20 %); flat, i.e. 1:25 (4 %)• Only periods with (assumed) stationary flow (constant irrigation from top;

maximum weighing difference of the entire tipping trough of 5 kg)Preliminary simulation series to check the impact of the FE net (4 nets from 392 nodes & 347 rectangular elements to 1118 nodes & 1039 rectangular elements).Refinements of the FE nets along the upper boundary, the interface, and the outflows of capillary layer and capillary block (seepage faces).Four simulation series with the same FE net, reflecting the statistical variation of soil hydrological parameters; one outflow each for capillary layer & capillary block.



1 10 100 10000.0

0.1

0.2

0.3

0.4

Water content Sand Gravel

Wat

er c

onte

nt θ

(1)

0.0

0.2

0.4

0.6

0.8

Equivalent pore diameter (µm)

Pore density Sand Gravel

Pore density (-d θ(h)/d log10 h)

30000 3000 300 30 3

1 10 100 1000-24

-18

-12

-6

0 0.1

α (cm-1) n Sand 0.0302 5.113 Gravel 0.2057 3.75

Pressure head h (cm)

Hydr

aulic

con

duct

ivity

log 10

(k (

m/s

))

0.1

Simulations with SWMS_2D (2)Van Genuchten Mualem model for METHA sand and 1/3 gravel (average values)


METHA sand Mean 95 % confidence interval

α (cm-1)n (1)

0.030185.11346

0.02834.2778

0.03215.9491

θs (1)θr (1)

0.30560.0400

--

--

ks (m s-1) 1.3 e-4 - -

1/3 gravel

α (cm-1)n (1)

0.205703.75010

0.19723.4224

0.21424.0778

θs (1)θr (1)

0.37460.0330

--

--

ks (m s-1) 1.2 e-2 - -


Simulations with SWMS_2D: Results


Validation attempt for SWMS_2D failed!(Possible reasons will be discussed at the end.)

Break for 20 years …

0.0 0.5 1.0 1.50.0

0.5

1.0

1.5

Out

flow

rate

(see

page

face

s) (c

m 2/m

in)

Inflow rate (upper boundary) (cm2/min)

Measured dataSeries of simulation runs:

best fit ks capillary layerbest fit hydrological(separation layer - block)best fit kscapillary blockAverage values of the van-Genuchten-Mualem parameters

0.0 0.5 1.0 1.5

0.0

0.5

1.0

1.5

Slope 1:250.0 0.5 1.0 1.5

0.0

0.5

1.0

1.5 Capillary layer

Slope 1:5

0.0 0.5 1.0 1.50.0

0.5

1.0

1.5 Capillary block

0 5 10 15 20Inflow rate (mm/d)

0 5 10 15 20


Simulations with HYDRUS 2D/3D (Vs. 2.05) in 2017Possible reason for the mismatch: assumption of homogeneous materials.Due to spatial inhomogeneity, breakthrough of the capillary barrier may occur in fingers.Question: Will HYDRUS 2D/3D with scaling lead to a better match?Three simulation series were performed with a 2D general geometry for the same materials, slopes and periods with stationary flow as 20 years before:1. Preliminary simulation series to check the impact of FE net (1:5, 14.2 mm/d)2. Average values of the van Genuchten Mualem parameters; no scaling3. Scaling option with Miller-Miller similitudeRefinements of the FE nets along the interface and the outflows of capillary layer and capillary block (seepage faces); stretching along the length of tipping trough.Different FE nets compared to SWMS_2D simulations; Slightly different nets for slopes 1:25 and 1:5 generated by HYDRUS.



Simulations with HYDRUS 2D/3D: FE net, slope 1:5


Entire tipping trough

Detail: Sump and seepage faces ofCapillary layer & capillary block (arrows)

FE mesh statistics:• Nodes 367• 1D-elements 115• 2D-elements 670


Simulations with HYDRUS 2D: Results


Validation attempt for HYDRUS 2D/3D failed, too!

0.0 0.5 1.0 1.50.0

0.5

1.0

1.5

Out

flow

rate

(see

page

face

s) (c

m 2/m

in)

Inflow rate (upper boundary) (cm2/min)

Measured dataSeries of simulation runs:

Scaling, Miller-Miller similitudeAverage values of the van-Genuchten-Mualem parameters

0.0 0.5 1.0 1.5

0.0

0.5

1.0

1.5

Slope 1:250.0 0.5 1.0 1.5

0.0

0.5

1.0

1.5 Capillary layer

Slope 1:5

0.0 0.5 1.0 1.50.0

0.5

1.0

1.5 Capillary block

0 5 10 15 20Inflow rate (mm/d)

0 5 10 15 20


Simulations with HYDRUS 2D: Results (2)


Final water content without scaling

Final water content with scaling (MMS)


Average relative deviation of simulated and measured outflow rates:

Simulation series:• Avg vGM: with average values of the van Genuchten Mualem parameters• Best fit ks Layer: Best fit of saturated hydraulic conductivity of capillary layer• Best fit ks Block: Best fit of saturated hydraulic conductivity of capillary block• Bfit hydSep Lay – Block: Best fit of the hydrologic separation of capillary layer and

capillary block• Scaling MMS: Scaling with Miller-Miller similitude (parameters 0.125; 0; 0)

Comparison of SWMS_2D and HYDRUS 2D Results


Slope SWMS_2D HYDRUS 2D/3D

Avg vGMParam

Best fitks Layer

Best fitks Block

Bfit hydSepLay – Block

Avg vGM Scaling MMS

Steep 1:5 0.498 1.39 3.24 3.61 2.63 3.14

Flat 1:25 0.495 1.62 2.69 2.94 1.48 1.48


Errors in the empirical investigation:• Typical flow pattern with distinct inflow rates designating the effectiveness of

the capillary barrier (specific materials, slope) is well confirmed.

Errors in the application of the models:• Parameters of the interface capillary layer – capillary block: not isotropic• Hysteresis neglected • Parameters of the van Genuchten Mualem model ok? (see also below)• Spatial inhomogeneity of material properties modeled with scaling;

Fingering would require 3D simulation

Errors in the models (incompleteness, unsuitable approaches, FEM problems, …):• Van Genuchten Mualem model suitable for these materials?• FEM: Material properties assigned to the nodes, not to the elements; does not

allow a sharp interface between two layers (Heiberger 1996)

Possible Reasons for the Mismatch of Measured and Simulated Outflow Rates



The METHA Sand in the van Genuchten Mualem Model


1 10 100 10000.0

0.1

0.2

0.3

0.4

0.1

Measured data

Wat

er c

onte

nt θ

(1)

Different fits of the van-Genuchten Mualem modelfor the METHA sand

0.1

1 10 100 1000-18

-12

-6

0

Measured data (IfB) kr(h) characteristic of

10-m tipping trough (tensiometer data)

θr: 0.040, θs: 0.3056 (total pore volume: 0.382)θr: 0.005, θs: 0.34 (TU Berlin)

α n Source0.03018 5.11346 θ(h) fit with RETC0.04895 4.50385 kr(h) fit

(tension infitrometer data)0.069 2.51 kr(h) fit of TU Berlin

(data from transient evaporation experiment)

Pressure head h (cm)

Rela

tive

cond

uctiv

ity lo

g 10 k

r (1)


FEM: Modeling of the Interface between Two Layers


From Heiberger 1996, p. 52


Errors in the empirical investigation:• Typical flow pattern with distinct inflow rates designating the effectiveness of

the capillary barrier (specific materials, slope) is well confirmed.

Errors in the application of the models:• Parameters of the interface capillary layer – capillary block: not isotropic• Hysteresis neglected• Parameters of the van Genuchten Mualem model ok? (see also below)• Spatial inhomogeneity of material properties modeled with scaling;

Fingering would require 3D simulation

Errors in the models (incompleteness, unsuitable approaches, FEM problems, …):• Van Genuchten Mualem model suitable for these materials?• FEM: Material properties assigned to the nodes, not to the elements; does not

allow a sharp interface between two layers (Heiberger 1996)

Possible Reasons for the Mismatch of Measured and Simulated Outflow Rates


Thank you for your attention!

Any idea to overcome the mismatch of measured and simulated outflow rates is welcome!

comparison and validation of swms 2d and hydrus 2d/3d …...klaus berger: swms_2d & hydrus 2d...

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