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22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesCOUPLED HYDROGEOPHYSICAL INVERSION FOR A SALT WATERINTRUSION MODEL AND TIME-DOMAIN ELECTROMAGNETIC (TDEM)DATAHERCKENRATH, Daan; DUQUE-CALVACHE, C.; NENNA, V.; ODLUM, N. J.;KNIGHT, R.; BAUER-GOTTWEIN, P.daah@env.dtu.dkTECHNICAL UNIVERSITY OF DENMARKMiljovej; building 113; Kgs. Lyngby; 2800; DenmarkAbstract. Coupled hydrogeophysical inversion approaches (CHI) have been increasinglyused to extract hydrological information from geophysical datasets. In a CHI hydrogeologicalparameters are estimated by translating hydrologic model simulations into geophysicalimages using petrophysical relationships. This is done by varying hydrological modelparameters until the observed geophysical data is fit. CHI has a potential for improving themapping and simulation of saltwater intrusion since large-scale Time-DomainElectromagnetic (TDEM) datasets have become available. These datasets can provide threedimensionalelectrical resistivity models of the subsurface, which can be correlated with thedistribution of saltwater and freshwater within coastal aquifers. For our scoping study, weperform a CHI for a field site in California. We estimate five uniform aquifer properties for across-sectional salt water intrusion model using observed TDEM data. In addition to thehydrologic parameters, we estimate one petrophysical and one geophysical parameter. Theseseven parameters could be well resolved by fitting more than 300 apparent resistivities thatcomprise the TDEM dataset. Except for 4 soundings the TDEM data could be fit close to anRMSE of 1. The poor data fit of these 4 soundings is likely due to the assumption of spatialuniformity and 3D effects in the TDEM forward responses. The electrical resistivity modelsthat resulted from the CHI provided a large improvement in spatial resolution, which wouldbe difficult to obtain with traditional geophysical inversion approaches as the complex spatialcorrelation between geophysical parameters cannot be captured with standard regularizationconstraints. To summarize, our study emphasizes the potential of CHI to improve thesimulations of salt water intrusion models. In combination with such models, this couldprovide an opportunity to use TDEM data as a non-invasive real-time monitoring tool tosupport groundwater management.Keywords: geophysics;modeling;parameter estimation; coupled inversion172