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Salt tracer and 3-D time-lapse electrical resistivity tomography imaging – a field test for optimum spatial and temporal resolution

Kennedy O. Doro1, Carsten Leven1, Arno Patzelt2, Olaf A. Cirpka1
1 Zentrum für Angewandte Geowissenschaften, Universität Tübingen
2 Terrana Geophysik, Mössingen

O 15.5 in Forum Junge Hydrogeologen (H 36, NW III)

28.05.2014, 13:20-13:40, H36, NWIII

 

Recent studies have shown that the distribution of aquifer hydraulic parameters can be obtained by a fully coupled inversion of electrical resistivity and hydraulic head data obtained from tracer or aquifer recharge experiments monitored via electrical resistivity tomography (ERT). This however opens up a practical challenge on how well and fast ERT can be used to image such dynamic processes mostly at field scale. In this study, we explored the possibility of an improved spatial and temporal resolution of a tracer - time lapse ERT imaging in three dimensions with optimum tradeoffs. For this purpose, we conducted salt tracer experiments at the Lauswiesen test site of the University of Tübingen. The aquifer at the site consists of a 6 m thick, heterogeneous alluvial sand and gravel deposit with an average hydraulic conductivity of 3 x 10-3 m/s. Tracer experiments were conducted using a dipole injection-extraction approach to keep high transport velocity, maximize the tracer recovery within a short time span and minimize influence of changing boundary conditions on test, e.g. from river stage changes. Imaging of the tracer experiment was done within a 10 m × 10 m domain using both cross-hole and surface ERT measurements to obtain 3D images of the tracer distribution in space and time. Initial results show that we could capture the tracer breakthrough using a measurement cycle of 20 minutes for each cross-hole measurement consisting of 4650 data points and 25 minutes for surface measurements with 1976 data points. Results of this work will be further analyzed using a fully coupled hydrogeophysical inversion approach after Pollock and Cirpka [2010] to obtain the hydraulic conductivity distribution of the study site.



Pollock, D., and O. A. Cirpka (2010), Fully coupled hydrogeophysical inversion of synthetic salt tracer experiments, Water Resour. Res., 46, W07501, doi: 10.1029/2009WR008575.



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Letzte Änderung 01.11.2013