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Effects of Including Hysteresis when Simulating Infiltration

Effects of Including Hysteresis when Simulating Infiltration. Swen Magnuson AgE 558 April 13, 2001. Overview. Background Purpose Approach Results. Radioactive Waste Management Complex. Infiltration Assignment for SDA Modeling. <1 cm/y. 4 cm/y. 24 cm/y. Purpose.

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Effects of Including Hysteresis when Simulating Infiltration

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  1. Effects of Including Hysteresis when Simulating Infiltration Swen Magnuson AgE 558 April 13, 2001

  2. Overview • Background • Purpose • Approach • Results

  3. Radioactive Waste Management Complex

  4. Infiltration Assignment for SDA Modeling <1 cm/y 4 cm/y 24 cm/y

  5. 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)

  6. 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

  7. 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

  8. Average Soil Properties for NAT-8

  9. 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

  10. 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

  11. Cumulative PPT: 19.5 cm Cumulative PET: 127 cm Snow cover: 0-80 days and 340-365 days

  12. Treatment of Hysteresis Usinghae = 2 * hwe and hae = 1/a results in hae=50 cm and hwe=25 cm

  13. 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.

  14. time Moisture Content DRY WET

  15. Daily flux from bottom boundary in Yr 1 with no hysteresis

  16. Daily flux from bottom boundary in Yr 1 with hysteresis in q-y in q-K Drainage ICs

  17. Daily flux from bottom boundary in Yr 1 with hysteresis only in q-y

  18. Daily flux from bottom boundary in Yr 2 with hysteresis only in q-y

  19. Simulation Results End-of-year Instantaneous Flux at Bottom of Domain

  20. Simulation Results End-of-year Instantaneous Flux at Bottom of Domain All fluxes given in cm/day

  21. Simulation Results Cumulative Annual Drainage All fluxes given in cm

  22. 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

  23. Conclusions • Premature • Appears that hysteresis can influence net infiltration by greater than 20%

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