Incorporation of Magnetic Resonance Sounding data into groundwater 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

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

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) 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 using MRS Layer 1 w,T 2 *,lt. Layer 2 w,T 2 *,lt. Layer 3 w,T 2 *,lt. MRS model: Simulated by groundwater model

The test model After: Hill, et al., 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

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)

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

GF onlyGWM onlySequentialCoupled Mean pred. Error m3.73 m3.20 m1.12 m Pred. error var m m m m 2 Inversion results (50 models) -Error variance similar / mean error larger -Independent geophysical inversion cannot improve groundwater model prediction Goal: Achieve the most accurate prediction of head at MRS location

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

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

The joint inversion methodology PEST Hydrological parameters Groundwater model Hydrological simulation Hydrological data Geophysical parameters Geophysical model Geophysical simulation Geophysical data Petrophysical relation Petrophysical relation: T mrs = [C p * w a * (T 2 *) 2 ]*lt

Ristrup well field

MRS sounding

Ristrup well field MRS sounding

Coupled inversion Can reduce head prediction error Will only work for unconfined conditions Will be most applicable in remote areas with limited (hydrological) data coverage Joint inversion Expected to increase resolution of hydraulic conductivity inhomogeneity Setup tested and works for a 2d case Using joint inversion MRS can be linked to several types of hydrological data (not only aquifer tests) Perspectives and conclusions