Hydraulic properties at the North Sea island of Borkum derived from joint inversion of magnetic resonance and electrical resistivity soundings

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Munich : EGU

For reliably predicting the impact of climate changes on salt/freshwater systems below barrier islands, a long-term hydraulic modelling is inevitable. As input we need the parameters porosity, salinity and hydraulic conductivity at the catchment scale, preferably non-invasively acquired with geophysical methods. We present a methodology to retrieve the searched parameters and a lithological interpretation by the joint analysis of magnetic resonance soundings (MRS) and vertical electric soundings (VES). Both data sets are jointly inverted for resistivity, water content and decay time using a joint inversion scheme. Coupling is accomplished by common layer thicknesses. We show the results of three soundings measured on the eastern part of the North Sea island of Borkum. Pumping test data is used to calibrate the petrophysical relationship for the local conditions in order to estimate permeability from nuclear magnetic resonance (NMR) data. Salinity is retrieved from water content and resistivity using a modified Archie equation calibrated by local samples. As a result we are able to predict porosity, salinity and hydraulic conductivities of the aquifers, including their uncertainties. The joint inversion significantly improves the reliability of the results. Verification is given by comparison with a borehole. A sounding in the flooding area demonstrates that only the combined inversion provides a correct subsurface model. Thanks to the joint application, we are able to distinguish fluid conductivity from lithology and provide reliable hydraulic parameters as shown by uncertainty analysis. These findings can finally be used to build groundwater flow models for simulating climate changes. This includes the improved geometry and lithological attribution, and also the parameters and their uncertainties. © Author(s) 2012.

Archie equation, Catchment scale, Data sets, Decay time, Electrical resistivity, Fluid conductivity, Geophysical methods, Groundwater Flow Model, Hydraulic parameters, Hydraulic properties, Joint analysis, Joint inversion, Local conditions, Magnetic resonance soundings, North Sea, Petrophysical relationship, Pumping test data, Subsurface model, Aquifers, Catchments, Climate change, Electric conductivity, Groundwater flow, Hydraulic conductivity, Hydrogeology, Lithology, Salinity measurement, Uncertainty analysis, Electric prospecting, barrier island, calibration, catchment, climate change, climate effect, data set, electrical resistivity, flooding, hydraulic conductivity, lithology, porosity, saline intrusion, salinity, uncertainty analysis, vertical electrical sounding, Atlantic Ocean, Borkum, East Frisian Islands, Frisian Islands, Germany, Lower Saxony, North Sea
Günther, T., & Müller-Petke, M. (2012). Hydraulic properties at the North Sea island of Borkum derived from joint inversion of magnetic resonance and electrical resistivity soundings. 16(9). https://doi.org//10.5194/hess-16-3279-2012
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