Case Studies

Detecting Tunnels of Badger Setts

Techniques employed:- Ground probing radar (GPR)

Client: RPS Consultants, Ashford

GPR is frequently the most successful technique in mapping the extent of badger setts. Badgers often excavate their sets beneath access roads causing concern to the stability of the road and the safety of the badgers themselves. GPR allows a high resolution survey to locate the extent and depth of the tunnels so that an investigation strategy can be planned.

A particular example in Kent involved a contractor inadvertently running construction traffic over a badger sett. The survey was undertaken to assess what damage, if any, had been sustained to the sett.

  

                                                                                                                                 		                                                                                                                                                                                                     

A general view of the site showing the extent of the intrusion into the area of the sett

The radar being drawn over an entrance to the sett

 

                                  
The interpretaion of the radar survey showing the extent of the sett tunnels and nest site in red. The green areas are where the tunnels may have been abandoned in the past or possibly collapsed as a result of the construction traffic.   This 'time slice of the radar data shows in plan the main area of the sett. Note the good correlation between the known locations of the tunnel entrances and the tunnel posions along the right hand side of the image. 

 

 

Locating land drains

Geophysics can be used to detect and map the layout of land drainage. This relies on the geophysical characteristics of the site being altered by the installation of the drain. These characteristics could include the following:

  • The drains were installed using clayware pipes which have thermoremanent magnetic properties as a result of the firing.
  • The back fill to the trench into which the drain was installed may be more or less magnetic than the natural sub-soils.
  • The backfill of the trench having either higher or lower moisture content which can be detected by a resistivity survey.
  • Where the drain has been laid using plastic the void within the pipe is detectable using ground probing radar.    

Often the best technique is magnetometry where the first two characteristics listed above are detected. The example below is from a magnetic gradiometer survey of a school sports field where a comprehensive land drainage system had been installed with a classic herring bone layout. The nature of the magnetic response suggests the backfill to the trenches is markedly more magnetic than the parent soils - possibly boiler clinkers or ash.

land drain data  

 

land drain interp