Citation:

PANGAEA.974990

Name: Near surface geophysical data (Electromagnetic Induction and Electrical Resistivity Tomography) from the Ahr floodplain at Mayschoß, Germany
Published: 2025-02-17
License: https://creativecommons.org/licenses/by/4.0/
Keywords: Ahr floodplain; Ahr river; Electrical Resistivity Tomography; electromagnetic induction; EMI; ERT; Near surface geophysics

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Published: 2025-02-17 • DOI registered: 2025-03-18

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Abstract:

The dataset was used to explore the spatial distribution of fluvial deposits in the area of the Ahr valley floor southwest of Mayschoß. The objective of this investigation was to extrapolate the findings of a chronological classification of an embedded floodplain cross-section, thereby underscoring the significance of fluvial geomorphological records in reconstructing past high-magnitude flood events. In detail, we used geophysical prospection methods (Electromagnetic Induction and Electrical Resistivity Tomography) to map the distribution and thickness of floodplain sediments as both methods provide proxy information on grain size distribution.

Electromagnetic induction (EMI) was measured with a CMD-Mini Explorer and a CMD Explorer (both GF Instruments s.r.o., Brno, Czech Republic) in June 2022. We used the vertical dipole (VDP) at coil spacings of 0.32 m (VDP1, CMD Mini Explorer), 0.71 m (VDP2, CMD Mini Explorer), 1.18 m (VDP3, CMD Mini Explorer), 1.48 m (VDP4, CMD Explorer), 2.82 m (VDP5, CMD Explorer) and 4.49 m (VDP6, CMD Explorer). With the existing coil spacings, effective penetration depths of 0.5 m (VDP1), 1.0 m (VDP2) and 1.8 m (VDP3) for the CMD Mini Explorer and 2.2 m (VDP4), 4.2 m (VDP5) and 6.7 m (VDP6) for the CMD Explorer could be achieved. According to the manufacturer, 70 % of the signal originate from above these depths. The EMI sensors measured the apparent electrical conductivity (ECa, in mS/m). Measurements were taken by carrying the instrument about 0.2 m (CMD Mini Explorer) respectively 0.9 m (CMD Explorer) above the ground while being directly connected to Differential -GPS (Leica GPS1200) for positioning. The acquisition rate was five measurements per second. Data quality was checked by measuring a reference line before and after each measurement. The maximum offset of the EMI values between the two time points was 1.2 mS/m. A correction of the data was not necessary. We removed the reference lines and single outliers. In addition, two interference areas were removed from all EMI data sets. (1) a L-shapped area, running from north to the center and then to east, in which an underground power cable runs. (2) an area on the north-eastern part of the measurement area. Information on the location and extent of the removed interference areas can be found in the enclosed explanation of the EMI measurements.

The Electrical Resistivity Tomography (ERT) data were acquired by using a PC controlled DC resistivity meter system (RESECS, GeoServe, Kiel, Germany) in October 2022. We measured a total of four transects with an electrode spacing 1 m. Transect 1 has a total length of 255 m, transect 2 a total length of 207 m, transect 3 a total length of 136 m and transect 4 a total length of 158 m. For all transects we applied a Wenner alpha and Dipole-Dipole configuration. The coordinates and the height of the electrodes were measured with a Differential-GPS (Leica GPS1200).

Further information on the measurement setup and data structure can be found in the explanation of the specific ERT transects.

Keyword(s):

Ahr floodplain; Ahr river; Electrical Resistivity Tomography; electromagnetic induction; EMI; ERT; Near surface geophysics

Related to:

Zielhofer, Christoph; Rabiger-Völlmer, Johannes; Westermann, Henriette; Fischer, Markus Lothar; Schneider, Birgit; Khosravichenar, Azra; Bauch, Martin; Pohle, Marco; Werban, Ulrike (in prep.): Fluvial deposits of the Ahr River reveal recurring high-magnitude flood events during the last 1400 years.

Coverage:

Median Latitude: 50.515486 * Median Longitude: 7.016484 * South-bound Latitude: 50.513374 * West-bound Longitude: 7.015018 * North-bound Latitude: 50.517027 * East-bound Longitude: 7.018185

Date/Time Start: 2022-06-22T00:00:00 * Date/Time End: 2022-10-19T15:36:39

License:

Creative Commons Attribution 4.0 International (CC-BY-4.0)

Size:

7 datasets

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Pohle, Marco; Bauckholt, Matteo; Werban, Ulrike (2025): Near surface geophysical data (Electromagnetic Induction and Electrical Resistivity Tomography) from the Ahr floodplain at Mayschoß, Germany [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.974990

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