Exacerbation of levee failure with climate change: Insights from ERT monitoring

Adrian White, Paul Wilkinson, James Wookey, John-Michael Kendall, Ross Stirling, James Boyd, Joel Smethurst, Jonathan Chambers

Climate change is bringing hotter, drier summers and warmer, wetter winters, intensifying winter floods and causing larger seasonal variations in soil moisture. These shifts place increasing stress on levees – many of which were constructed decades or centuries ago – making their current performance challenging to assess. Levee performance depends on limiting water ingress, as increased seepage can trigger piping and slope failure, potentially leading to catastrophic breaches. Hydraulic conductivity strongly controls water ingress, but is challenging to measure directly and can change as the materials deteriorate. To investigate how environmental loading affects levee performance, a clay levee in northern England was monitored for four years every 48 hours using electrical resistivity tomography (ERT) – a geophysical technique sensitive to fluid changes – alongside environmental sensors (soil moisture, river stage, and meteorological data). Two zones showed clear responses to climatic and hydrological forcing: the foundation strata, where groundwater levels rose with river levels, and the active layer (upper ~1.5 m), which seasonally dried in summer and rewetted in winter. These zones may therefore be particularly vulnerable to future climatic extremes and flood events. Analysis of annual drying-front depths indicates that average summer desiccation depths could increase from ~0.6 m to >1 m in northern England by the late 21st century (UKCP18 data, RCP8.5). This enhanced desiccation may reduce their performance, especially in early autumn when open shrinkage cracks can act as seepage pathways during subsequent floods. Forward planning using geophysical methods will help guide remediation and mitigate the effects of potential failure in levees.