Use of geoelectrical techniques for monitoring the structural integrity of earthen flood embankments

River embankments are constructed to protect areas of high economic and societal value from water inundation. It is therefore vital to ensure that their integrity is maintained to prevent embankment failure, damage to protected infrastructure, disruption to society and risk to human life. River embankments encompass large areas across many countries. In the United Kingdom they span 34,000 km in length, making comprehensive coverage through monitoring challenging. Traditionally, embankments have been monitored with visual inspection and geotechnical investigations. However, these are limited by lack of sensitivity to internal structure during walkover surveys and limited spatial coverage of boreholes. Geophysical techniques can provide a non-invasive means to identify potential concerns within river embankments. It is impossible to cover the entirety of embankments upon surveying, but targeted deployment of such techniques can give coverage of large areas. Electromagnetic induction (EMI) and electrical resistivity tomography (ERT) are particularly useful because of their sensitivity to changes in moisture content, which may indicate potential seepage issues within an embankment. ERT and EMI have therefore been utilised to monitor embankments at three sites in the Humber region, United Kingdom: 1) Haweswater Way; 2) Boothferry Bridge; 3) Paull Holme Strays, where monitoring was required to gain insight to potential issues and visualise subsurface conditions. ERT and EMI surveys across these sites were able to successfully visualise embankment structure, geology and identify regions where water content was high. Analysis of the geophysical data, with use of geological knowledge of the area, enabled identification of potential seepage areas for further investigation. This has showed the potential for geoelectrical techniques to be used in conjunction, in order to visualise the internal structure of embankments in river and estuarine settings. In combination with geotechnical data such surveys can provide useful interpretations and identifications of structural flaws within embankments.