Combining implicit geological modeling, field surveys, and hydrogeological modeling to describe groundwater flow in a ka
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PAPER
Combining implicit geological modeling, field surveys, and hydrogeological modeling to describe groundwater flow in a karst aquifer Fernando M. D’Affonseca 1,2 & Michael Finkel 1 & Olaf A. Cirpka 1 Received: 12 February 2020 / Accepted: 22 July 2020 # The Author(s) 2020
Abstract In three-dimensional (3-D) implicit geological modeling, the bounding surfaces between geological units are automatically constructed from lithological contact data (position and orientation) and the location and orientation of potential faults. This approach was applied to conceptualize a karst aquifer in the Middle Triassic Muschelkalk Formation in southwest Germany, using digital elevation data, geological maps, borehole logs, and geological interpretation. Dip and strike measurements as well as soil-gas surveys of mantel-borne CO2 were conducted to verify the existence of an unmapped fault. Implicit geological modeling allowed the straightforward assessment of the geological framework and rapid updates with incoming data. Simultaneous 3-D visualizations of the sedimentary units, tectonic features, hydraulic heads, and tracer tests provided insights into the karst-system hydraulics and helped guide the formulation of the conceptual hydrogeological model. The 3-D geological model was automatically translated into a numerical single-continuum steady-state groundwater model that was calibrated to match measured hydraulic heads, spring discharge rates, and flow directions observed in tracer tests. This was possible only by introducing discrete karst conduits, which were implemented as high-conductivity features in the numerical model. The numerical groundwater flow model was applied to initially assess the risk from limestone quarrying to local water supply wells with the help of particle tracking. Keywords Implicit geological modeling . Numerical model . Karst . Conduit flow paths . Groundwater risk
Introduction Understanding the geology is the backbone of any groundwater management project, since hydraulic heads and velocities, as well as flow trajectories and residence times, are strongly controlled by the properties and arrangement of lithological entities. The hydraulic connection between aquifers depends on their shape, arrangement, and internal structure (Raiber et al. 2015). Regional flow systems can be segmented by faults, which may form either barriers or preferential flow Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10040-020-02220-z) contains supplementary material, which is available to authorized users. * Olaf A. Cirpka [email protected] 1
Center for Applied Geoscience, University of Tübingen, Hölderlinstr. 12, 72074 Tübingen, Germany
2
TIMGEO GmbH, Hölderlinstr. 29, 72074 Tübingen, Germany
paths (Caine et al. 1996; Moya et al. 2014; Raiber et al. 2015). Groundwater models that are merely developed on hydraulic interpretations, while disregarding geological insights, are likely to be erroneous or untrustworthy (Fogg 1986). Shaped by dissolution, internal
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