Compiling geophysical and geological information into a 3-D model of the glacially-affected island of Föhr

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Date
2012
Volume
16
Issue
10
Journal
Series Titel
Book Title
Publisher
Munich : EGU
Abstract

Within the scope of climatic change and associated sea level rise, coastal aquifers are endangered and are becoming more a focus of research to ensure the future water supply in coastal areas. For groundwater modelling a good understanding of the geological/hydrogeological situation and the aquifer behavior is necessary. In preparation of groundwater modelling and assessment of climate change impacts on coastal water resources, we setup a geological/hydrogeological model for the North Sea Island of Föhr.

Data from different geophysical methods applied from the air, the surface and in boreholes contribute to the 3-D model, e.g. airborne electromagnetics (SkyTEM) for spatial mapping the resistivity of the entire island, seismic reflections for detailed cross-sections in the groundwater catchment area, and geophysical borehole logging for calibration of these measurements. An iterative and integrated evaluation of the results from the different geophysical methods contributes to reliable data as input for the 3-D model covering the whole island and not just the well fields.

The complex subsurface structure of the island is revealed. The local waterworks use a freshwater body embedded in saline groundwater. Several glaciations reordered the youngest Tertiary and Quaternary sediments by glaciotectonic thrust faulting, as well as incision and refill of glacial valleys. Both subsurface structures have a strong impact on the distribution of freshwater-bearing aquifers. A digital geological 3-D model reproduces the hydrogeological structure of the island as a base for a groundwater model. In the course of the data interpretation, we deliver a basis for rock identification.

We demonstrate that geophysical investigation provide petrophysical parameters and improve the understanding of the subsurface and the groundwater system. The main benefit of our work is that the successful combination of electromagnetic, seismic and borehole data reveals the complex geology of a glacially-affected island. A sound understanding of the subsurface structure and the compilation of a 3-D model is imperative and the basis for a groundwater flow model to predict climate change effects on future water resources.

Description
Keywords
3D models, Borehole logging, Catchment area, Climate change impact, Climatic changes, Coastal aquifers, Coastal area, Complex geology, Data interpretation, Electromagnetics, Freshwater bodies, Geological information, Geophysical methods, Glacial valleys, Groundwater Flow Model, Groundwater modelling, Groundwater models, Groundwater system, Hydrogeological structures, Integrated evaluation, North Sea, Petrophysical parameters, Quaternary sediments, Saline groundwater, Sea level rise, Seismic reflections, Spatial mapping, Subsurface structures, Thrust faulting, Aquifers, Catchments, Climate change, Data processing, Electromagnetism, Geophysics, Glacial geology, Groundwater flow, Hydrogeology, Iterative methods, Sea level, Sediments, Structural geology, Three dimensional, Water supply, Groundwater resources, aquifer, borehole logging, calibration, climate effect, climate variation, coastal water, electromagnetic method, geological survey, glaciation, glaciotectonics, groundwater resource, hydrogeology, hydrological modeling, sea level change, seismic reflection, subsurface flow, three-dimensional modeling, thrust, Fohr, Frisian Islands, Germany, North Frisian Islands, Schleswig-Holstein
Citation
Burschil, T., Scheer, W., Kirsch, R., & Wiederhold, H. (2012). Compiling geophysical and geological information into a 3-D model of the glacially-affected island of Föhr. 16(10). https://doi.org//10.5194/hess-16-3485-2012
License
CC BY 3.0 Unported