Geophysical mapping of badger tunnels in levees

Rivers provide freshwater, food, and transport routes but can also cause floods. Flood defences are often long piles of earth and rock, forming embankments or levees. In the UK over 38,000 km of flood defences have been built. Failure of these structures during flood events could cause disruption, property damage and even loss of life. It is therefore essential that levee failure is minimised. These manmade structures make ideal homes for many burrowing animals as they provide sloping ground raised above the surrounding water table. Over several years, animals such the European badger (Meles meles) can build extensive burrow networks through these structures, dramatically compromising their integrity. During flood events the network of tunnels can provide preferential flow paths for flood water, increasing the risk of seepage and piping failures. Piping failure is one of the main causes of levee failure and are commonly associated with animal burrows. European Badgers are a protected species in the UK, so badger setts cannot be disturbed without a license making remediation challenging and expensive. Geophysical methods can provide non-intrusive information about the subsurface so are particularly well suited to imaging tunnel networks. Only sites where badger activity was compromising structural integrity would remediation be needed. Ground Penetrating Radar (GPR) is commonly used to detect cavities, but penetration depth can be limited in clay rich and/or saline environments, often associated with levees. Electrical Resistivity Topography (ERT) is sensitive to voids due to their high resistivity contrast with the surrounding ground and may complement GPR. Unlike GPR, ERT is effective in electrically conductive environments. GPR and ERT have been used to investigate two badger setts located next to levees in the Humber region, United Kingdom. Co-located surveys were undertaken with the aim to image and map the extent of the burrow networks. Each method was interpreted independently to identify potential tunnel networks, before being combined to create a single ground model of each site. The results validate ERT as a suitable methodology for cavity detection in levees. The results will inform remediation plans for each site, allowing further ground truthing of the geophysical results.