HR: 09:00h
AN: H41B-05    [Abstracts]
TI: Comparison of Transport Parameters derived from Time-Lapse Electrical Resistivity Tomography, TDR and Effluent Break Through Curves
AU: * Koestel, J
EM: j.koestel@fz-juelich.de
AF: ICG-4 (Agrosphere), Forschungszentrum Juelich GmbH, Gebaeude 16.6, Juelich, 52425, Germany
AU: Kemna, A
EM: a.kemna@fz-juelich.de
AF: ICG-4 (Agrosphere), Forschungszentrum Juelich GmbH, Gebaeude 16.6, Juelich, 52425, Germany
AU: Javaux, M
EM: m.javaux@fz-juelich.de
AF: ICG-4 (Agrosphere), Forschungszentrum Juelich GmbH, Gebaeude 16.6, Juelich, 52425, Germany
AU: Vanderborght, J
EM: j.vanderborght@fz-juelich.de
AF: ICG-4 (Agrosphere), Forschungszentrum Juelich GmbH, Gebaeude 16.6, Juelich, 52425, Germany
AU: Binley, A
EM: A.Binley@lancaster.ac.uk
AF: Department of Environmental Science, Lancaster University, Lancaster, LA1 4YQ, United Kingdom
AU: Vereecken, H
EM: h.vereecken@fz-juelich.de
AF: ICG-4 (Agrosphere), Forschungszentrum Juelich GmbH, Gebaeude 16.6, Juelich, 52425, Germany
AB: During the recent years it was shown that time-lapse electrical resistivity tomography (ERT) has potential to image subsurface solute transport processes. In this study we captured the spatio-temporal evolution of an inert salt tracer plume by means of time-lapse ERT in an unsaturated undisturbed soil column (height: 1.4 m, diameter: 1.16 m). The experiment was performed two-fold for 2 different steady state flow conditions, respectively, corresponding to approximately 15 % and 55 % of saturation. The ERT data were inverted with a three dimensional, smoothness-constrained inversion algorithm based on finite-element modelling. Identical error parameters were used for all ERT inversions and experiments. The image time series provides spatially resolved break-through curves (BTCs). Simultaneously, the BTCs in the outflow were measured and local BTCs within the monolith were measured with TDR. Following a stream tube approach, effective transport parameters were obtained by fitting the convective-dispersive equation to all available break-through curves. However, due to the non-uniqueness of the ERT inversion, the parameters derived from time lapse ERT might not be robust. Therefore, we appraised their robustness by comparing them with parameters derived from effluent and TDR measured BTCs. For all break through experiments, the mean ERT derived effective velocities at the TDR positions matched the ones found by TDR with a mean deviation of app. 5 %. The ERT derived dispersivities exceeded the ones found by TDR by a factor of two or more for the upper soil layers. For the deeper soil layers where the electrical contrasts were smoothed by dispersion, ERT and TDR derived effective dispersivities converged. For the four experiments, the effective velocity which was obtained from the effluent BTC matched the mean of the velocities derived from the bottommost ERT voxels with accuracy of 2.5 % to 5.5 %. The dispersivities of the effluent BTCs could be predicted from the variance of the ERT voxel velocities and the mean ERT voxel dispersivities with an accordance of 2.5 % to 23.5 %. The results confirm that smoothness constraint time lapse ERT images can be interpreted quantitatively up to a certain degree. We expect that a greater accuracy could be achieved if time-lapse information was incorporated into the inversion algorithm or a hydro-geophysical joint inversion approach was used.
DE: 1835 Hydrogeophysics
DE: 1859 Rocks: physical properties
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Joint Assembly