Effects of Including Hysteresis when Simulating Infiltration

Swen Magnuson

AgE 558

April 13, 2001

Overview

• Background

• Purpose

• Approach

• Results

Radioactive Waste Management Complex

INEEL

LO W M EDIUM HIG H

WAG 7J B97-026

Infiltration Assignment for SDA Modeling

<1 cm/y 4 cm/y 24 cm/y

Purpose

• Determine possible effects of neglecting hysteresis

• Generally neglected as inconsequential compared to spatial variability

• Hysteresis now more commonly included in simulation codes

• HYDRUS-2D (Simunek et al 1999)

Approach

• Select location used in Martian (1995)• NAT-8, middle infiltration range: ~4 cm/yr• Average hydraulic properties from inverse

modeling results at NAT-8• Simulate with and without hysteresis• Difference of >20% in net annual infiltration

may be important enough to investigate

Problem Description• NAT-8 hydrologic properties arithmetically

averaged with weights based on interval thicknesses =>homogenous soil profile

• ~6 meter deep surficial sediments• Free-drainage bottom boundary condition• Initial conditions, h=-30 cm.• Meteorologically driven surface boundary using

site-specific conditions from 1999, used repetitively for 5 years

Average Soil Properties for NAT-8

Parameter Value

Hydraulic conductivity, K 135 cm/day

Porosity, 0.49

Residual moisture content, r 0.11

van Genuchten 0.019 cm-1

van Genuchten N 1.75

Problem Description• NAT-8 hydrologic properties arithmetically

averaged with weights based on interval thicknesses =>homogenous soil profile

• ~6 meter deep surficial sediments• Free-drainage bottom boundary condition• Initial conditions, h=-30 cm.• Meteorologically driven surface boundary using

site-specific conditions from 1999, used repetitively for 5 years

Problem Description• NAT-8 hydrologic properties arithmetically

averaged with weights based on interval thicknesses =>homogenous soil profile

• ~6 meter deep surficial sediments• Free-drainage bottom boundary condition• Initial conditions, h=-30 cm.• Meteorologically driven surface boundary using

site-specific conditions from 1999, used repetitively for 5 years

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

0 50 100 150 200 250 300 350 400

Time [days]

Potential Atmospheric Flux

Cumulative PPT: 19.5 cm Cumulative PET: 127 cm

Snow cover: 0-80 days and 340-365 days

0.2 0.4M oisture Conent

0.1

1.0

10.0

100.0

1000.0

10000.0

- Pressure Head (cm

)

Using hae = 2 * hwe and hae = 1/ results in

hae=50 cm and hwe=25 cm

Treatment of Hysteresis

More on Hysteresis

• Uses something closely approximating the independent domain model: completely specify both wetting and draining curves.

• HYDRUS-2D has options to consider hysteresis in the - relationship and in the K-relationship (both tested)

• Initial conditions must be associated with either the draining or wetting curve.

0.10 0.40 0.15 0.20 0.25 0.30 0.35

time

Moisture Content

DRY WET

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

0 50 100 150 200 250 300 350 400

Time [days]

Actual Atmospheric Flux

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 50 100 150 200 250 300 350 400

Time [days]

Free or Deep Drainage Boundary Flux

Daily flux from bottom boundary in Yr 1 with no hysteresis

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 50 100 150 200 250 300 350 400

Time [days]

Free or Deep Drainage Boundary Flux

Daily flux from bottom boundary in Yr 1 with hysteresis in -in -

Drainage ICs

0

1

2

3

4

5

6

7

8

0 50 100 150 200 250 300 350 400

Time [days]

Free or Deep Drainage Boundary Flux

Daily flux from bottom boundary in Yr 1 with hysteresis only in -

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 50 100 150 200 250 300 350 400

Time [days]

Free or Deep Drainage Boundary Flux

Daily flux from bottom boundary in Yr 2 with hysteresis only in -

0.00E+00

1.00E-02

2.00E-02

3.00E-02

4.00E-02

5.00E-02

6.00E-02

7.00E-02

8.00E-02

9.00E-02

1.00E-01

1 1.5 2 2.5 3 3.5 4 4.5 5

Simulation Year

Dra

inag

e F

lux

(cm

/day

)

without hysteresis

with hysteresis, initial condition assoc w/drainage curve

with hysteresis, initial conditionsassociated with wetting curve

Simulation ResultsEnd-of-year Instantaneous Flux at Bottom of Domain

Simulation Results

SimYr

Base: w/ohysteresis

w/ in both

and K,IC drainage

%diff

w/ in both and K,IC wetting

% diff w/ only in ,IC drainage

% diff

1 3.31E-02 9.44E-02 185 3.64E-02 10 1.17E-02 -65

2 1.36E-02 2.08E-02 53 1.22E-02 -10 2.18E-02 60

3 9.06E-03 1.61E-02 78 8.69E-03 -4 Failed toconverge

4 7.20E-03 1.50E-02 108 7.51E-03 4 -

5 6.27E-03 1.48E-02 136 7.05E-03 12 -

All fluxes given in cm/day

End-of-year Instantaneous Flux at Bottom of Domain

Simulation Results

SimYr

Base: w/ohysteresis

w/ in both

and K,IC drainage

%diff

w/ in both and K,IC wetting

% diff w/ only in ,IC drainage

% diff

1 92.5 70.1 24 44.7 -52 88.3 -5

2 7.36 11.6 58 6.42 -13 19.2 160

3 4.02 6.34 58 3.69 -8 Failed toconverge

-

4 2.95 5.49 86 2.92 -1 - -

5 2.46 5.31 116 2.64 7 - -

All fluxes given in cm

Cumulative Annual Drainage

Observations on Running HYDRUS-2D

• GUI post-processing difficulties

• Do not currently trust result for drainage in case w/o hysteresis

• Problems suspected to be associated with installation

Conclusions

• Premature

• Appears that hysteresis can influence net infiltration by greater than 20%