Geophysical investigation of a badger sett located in a flood embankment on the River Ouse

White, A.; Boyd, J.; Wilkinson, P.; Chambers, J.. 2022 Geophysical investigation of a badger sett located in a flood embankment on the River Ouse. Nottingham, UK, British Geological Survey, 27pp. (OR/22/058) (Unpublished)

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Abstract/Summary

Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) are two nearsurface geophysical methods that are well suited to mapping air-filled cavities (e.g. burrows) in the shallow subsurface. They both have the advantage that they are non-intrusive, so can image the subsurface targets without disturbing them, which is advantageous for detecting, characterising, and monitoring animal burrows. GPR is a very rapid technique that can survey large areas relatively quickly; however, flood embankments often have a clay component that can limit the depth of investigation of GPR surveys, with tunnels beyond the penetration depth of the instrument. ERT surveys are typically slower but are not limited by clay-rich ground. Both techniques are affected by metal objects in the ground, such as sheet piling and wire mesh, which are installed at the stie to prevent animal burrowing. A desk study of badger sett morphology found that: • Badgers rarely dig beyond 10 m from an entrance • The tunnels are 30 cm wide and 20 cm tall • Tunnels rarely go deeper than 2 m below the surface. At the badger sett north of Drax power station, entrances were found within an area extending along 75 m of the flood embankment. The location of the sheet piling was confirmed using the GPR, and all badger tunnel entrances were found to be within this reinforced section of the embankment. However, the entrances at the site's eastern end were very close to the end of the sheet piling, making this area the focus of the geophysical survey. In summary, the results of the geophysical survey (Figure 5) are as follows: • Two areas of extensive tunnelling were found in the GPR data, matching tunnel entrances' locations. • GPR could only detect tunnels in the first three lines, beyond which the tunnels likely continued but were over 1.5 m deep, deeper than the penetration depth of the GPR signal. • Most of the tunnelling seems to be concentrated in the floodplain and embankment toe. • ERT focused on the eastern area but was partially affected by sheet piles, especially the lines perpendicular to the embankment. • Tunnels interpreted from the ERT data head towards the crest of the embankment close to where the sheet pilling ends. • We are unsure if we imaged the full extent of the tunnels or if they continued in to the embankment, but they were beyond the detectability of the instruments at these depths. Furthermore, the proximity of sheet piling at these locations caused significant noise in the data. This report concludes that ERT and GPR could successfully image areas of tunnelling in the embankment northwest of Drax power station. Useable data could be collected despite the sheet piling, which makes interpretation of the data significantly more difficult. While GPR could only find tunnels in the first three lines, it provided some confidence to the ERT interpretation and was able to investigate a much larger area. This highlights the potential benefits of combining ERT and GPR for future badger investigations.

Item Type:	Publication - Report
Funders/Sponsors:	British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed.
Date made live:	13 Sep 2022 13:20 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/533207

Item Type:

Publication - Report

Funders/Sponsors:

British Geological Survey

Additional Information. Not used in RCUK Gateway to Research.:

This item has been internally reviewed, but not externally peer-reviewed.

Date made live:

13 Sep 2022 13:20 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/533207