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

5. Infiltration Assignment for SDA Modeling <1 cm/y4 cm/y24 cm/y

6. 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)

7. 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

8. 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

9. Average Soil Properties for NAT-8

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. 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

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

13. Using h ae = 2 * h we and h ae = 1/  results in h ae =50 cm and h we =25 cm Treatment of Hysteresis

14. 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.

15. time Moisture Content DRYWET

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

18. Daily flux from bottom boundary in Yr 1 with hysteresis in  -  in  -  Drainage ICs

19. Daily flux from bottom boundary in Yr 1 with hysteresis only in  - 

20. Daily flux from bottom boundary in Yr 2 with hysteresis only in  - 

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

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

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

24. 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

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