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THINKING SCALE IN UNSATURATED FLOW PARAMETER ESTIMATION

NHC Røros, 2002. THINKING SCALE IN UNSATURATED FLOW PARAMETER ESTIMATION. Thorgeir Holm , Nils-Otto Kitterød and Lars Gottschalk. Dept. of Geophysics, University of Oslo, P.O.Box 1022 Blindern, N-0315 Oslo, Norway. thorgeih@geofysikk.uio.no , nilsotto@geofysikk.uio.no

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THINKING SCALE IN UNSATURATED FLOW PARAMETER ESTIMATION

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  1. NHC Røros, 2002 THINKING SCALE IN UNSATURATED FLOW PARAMETER ESTIMATION Thorgeir Holm, Nils-Otto Kitterødand Lars Gottschalk Dept. of Geophysics, University of Oslo, P.O.Box 1022 Blindern, N-0315 Oslo,Norway thorgeih@geofysikk.uio.no, nilsotto@geofysikk.uio.no Lars.Gottschalk@geofysikk.uio.no

  2. Background The Oslo Airport Gardermoen Pollution hazard Different scales NHC Røros, 2002

  3. Problem NHC Røros, 2002 Forecasts based on unsaturated flow models indicate safe conditions for the groundwater In real life pollution breakthrough to the groundwater do occur Why? real sediment/soil flow model discrete heterogeneous at all scales volume averages finite resolution

  4. Purpose NHC Røros, 2002 Use inverse modelling to estimate (homogenized) flow parameter conditioned on different data sets, and compare calculated breakthrough curve to ”observed” breakthrough curve. Different data sets? What is best, lot of observations with low sensitivity, or few observations with high sensitivity?

  5. Method p47 Delta topset Delta foreset Generate realizations (a,b,c) with high spatial resolution (0.2 m x 0.05 m) Based on observed sedimentological architecture And simulation of ks, 1/a and nvg based on ”hard” physical observations

  6. Method NHC Røros, 2002 Simulate ”real” (Søvik and Alfnes et al.) tracer experiment Infiltration time series: 2.5 mm/day from -¥ to day 0 42 mm/day from day 0 to day 16 day (»¥)

  7. Flowpattern in synthetic realizations NHC Røros, 2002 a b

  8. Flowpattern in synthetic realizations NHC Røros, 2002 a c

  9. Breakthrough curves based on syntetic data from all over the Gardermoen area 1.00 0.80 -2.95 m (Br) -3.09 m (Br) 0.60 -3.30 m (Br) F(x) for [Br] and [HTO] -2.95 m (HTO) -3.09 m (HTO) 0.40 a b -3.30 m (HTO) c 0.20 0.00 0.00 5.00 10.00 15.00 20.00 25.00 30.00 time <days> NHC Røros, 2002 Observed breakthrough curves (Søvik and Alfnes et al, 2001)

  10. Recall database NHC Røros, 2002 Oslo Airport Gardermoen foreset sand top- set Glacier fronts: foreset silt borehole locations

  11. Purpose with conditional homogenization heterogeneous isotropic 0 -1 -2 -3 homogeneous anisotropic 12 6 10 8 4 2 NHC Røros, 2002 How to get same response (breakthrough)?

  12. findmodel parameters The answer is Inverse modelling that minimize | cal. – obs. | kp,kt, 1/a, nvg NHC Røros, 2002 homogeneous flow parameters to estimate:

  13. Conditional data sets (synthetic) ”observations”: |qcalc – qobs | |qcalc – qobs | |pcalc – pobs | |pcalc – pobs | and |c(t)calc – c(t)obs | NHC Røros, 2002 1) soil moisture (or saturation) 2) pressure 3) pressure and soil moisture 4) the breakthrough curve (for the future)

  14. Results breakthrough curves (42 mm/d infiltration) 15 10 number of particles 5 heterogeneous isotropic (case a) 10 11 12 7 8 9 homogeneous anisotropic saturation (all) time (days) pressure (all) pressure and saturation saturation (no dip2) pressure (no dip2) NHC Røros, 2002

  15. Conclusion NHC Røros, 2002 structure is crucial internal arrangment of heterogeneity is important (cf. flowpaths in realization a,b and c) difficult to compare breakthrough curves from a,b,c with homogenous model Future work: evaluate importance of boundary conditions are effective parameters possible to derive or is equvalent parameters the only realistic result? is reliable forecasts (of NOE) possible without conditioning on observations (of noe)?

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