Effects of Including Hysteresis when Simulating Infiltration

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Effects of Including Hysteresis when Simulating
Infiltration

• Swen Magnuson
• AgE 558
• April 13, 2001

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Overview

• Background
• Purpose
• Approach
• Results

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Radioactive Waste Management Complex
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Infiltration Assignment for SDA Modeling
lt1 cm/y
4 cm/y
24 cm/y
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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)

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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 gt20 in net annual infiltration may
  be important enough to investigate

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Problem Description

• NAT-8 hydrologic properties arithmetically
  averaged with weights based on interval
  thicknesses gthomogenous 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

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Average Soil Properties for NAT-8
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Problem Description

• NAT-8 hydrologic properties arithmetically
  averaged with weights based on interval
  thicknesses gthomogenous 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

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Problem Description

• NAT-8 hydrologic properties arithmetically
  averaged with weights based on interval
  thicknesses gthomogenous 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

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Cumulative PPT 19.5 cm Cumulative PET 127
cm Snow cover 0-80 days and 340-365 days
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Treatment of Hysteresis
Using hae 2 hwe and hae 1/a results
in hae50 cm and hwe25 cm
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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 q-y relationship and in the K-y relationship
  (both tested)
• Initial conditions must be associated with either
  the draining or wetting curve.

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time
Moisture Content
DRY
WET
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(No Transcript)
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Daily flux from bottom boundary in Yr 1 with no
hysteresis
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Daily flux from bottom boundary in Yr 1 with
hysteresis in q-y in q-K Drainage ICs
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Daily flux from bottom boundary in Yr 1 with
hysteresis only in q-y
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Daily flux from bottom boundary in Yr 2 with
hysteresis only in q-y
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Simulation Results
End-of-year Instantaneous Flux at Bottom of Domain
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Simulation Results
End-of-year Instantaneous Flux at Bottom of Domain
All fluxes given in cm/day
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Simulation Results
Cumulative Annual Drainage
All fluxes given in cm
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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

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Conclusions

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