8th Annual Meeting of DWRIP 2014 JANUARY 30

1. Incorporation of Magnetic Resonance Soundingdata intogroundwater models through coupled and joint inversion 8th Annual Meeting of DWRIP 2014 JANUARY 30 T.N. Vilhelmsen, A.A. Behroozmand, S. Christensen, E. Auken, and A.V. Christiansen

2. Outline • Coupled vs. Joint inversion (MRS and groundwater model) • Mapping the groundwatertableusing MRS • Results from coupled inversion tests (synthetic model) • Perspectives for 3d joint inversion

3. Joint vs. coupled inversion Joint inversion • Inversion setup is linked through shared parameter characteristics • Here: Transmissivity derived from MRS (using petrophysical relation) is linked to transmissivity in a hydrological model (through regularization) Coupled inversion • Tight link directly through model forward responses • Here: Groundwater flow model is used to simulate the thickness of the upper layer in an MRS model (unsaturated zone)

4. Coupled inversion using MRS MRS model: Simulated by groundwater model Layer 1 w,T2*,lt. Layer 2 w,T2*,lt. Layer 3 w,T2*,lt.

5. The test model • Two aquifers separated by an aquitard • Two recharge zones • Well pumping from lower aquifer • Flow in from adjoining hill side • Flow out through river • Model observations generated using heterogeneous parameter fields After: Hill, et al., 2000

6. Reference model (50 realiazations): • Heterogeneous k-fields (calculated from water content and decay time fields) • 10 head obs. • 1 river discharge obs. • 1 MRS sounding (located at prediction point)

7. The inversion setup: PEST • Groundwater model parameter files: • Hydraulic conductivity zones • River bed conductance • Recharge • Groundwater model • (MODFLOW-2005) • Simulated heads • Simulated river flow Thickness of unsat. zone • Geophysical model parameter files: • Holds all geo. phys. par. Except for layer 1 thick (unsaturated zone) • Geophysical model • (AarhusInv) • Simulated MRS resp. • Simulated TEM resp.

8. Inversion results (50 models) Goal: Achieve the most accurateprediction of head at MRS location • Error variance similar / mean error larger • Independent geophysical inversion cannot improve groundwater model prediction

9. 3d joint inversion of MRS and groundwater models • Goal: • Use MRS to improve estimate of hydraulic conductivity heterogeneity in groundwater flow models • Estimate parameters pertaining to the petrophysical relation together with MRS/TEM and hydrological parameters using a regularized coupling

10. The joint inversion methodology PEST Hydrological data Hydrological parameters Hydrological simulation Groundwater model Geophysical simulation Geophysical data Geophysical parameters Geophysical model

11. The joint inversion methodology PEST Hydrological data Hydrological parameters Hydrological simulation Groundwater model Petrophysical relation Geophysical simulation Geophysical data Geophysical parameters Geophysical model Petrophysical relation: Tmrs= [Cp * wa * (T2*)2]*lt Regul. Obj. Fun.

12. Ristrup well field

13. Ristrup well field MRS sounding

14. Ristrup well field MRS sounding

15. Perspectives and conclusions • Joint inversion • Expected to increase resolution of hydraulicconductivityinhomogeneity • Setup tested and works for a 2d case • Using joint inversion MRS canbelinked to several types of hydrological data (not onlyaquifer tests) • Coupled inversion • Canreduce head predictionerror • Will onlywork for unconfinedconditions • Will be most applicable in remoteareas with limited (hydrological) data coverage