Impacts of climate change mean that engineers must be “vigilant and adaptable to change” when designing flood embankments, according to Royal Haskoning DHV technical director Philip Smith.
“Most failures are due to internal erosion of uplift, rather than rotational slips, which can be hard to predict,” he said.
“There is a mixed history of poor performance of flood embankments and the impacts of climate change means that engineers must think beyond the current situation.”
Smith made the comments during an evening lecture delivered to the British Geotechnical Association on the subject of Levees and Flood Embankments: Geotechnical Challenges in the Anthropocene Epoch.
“Man’s biological, chemical and physical impact on earth’s surface now characterises a new geological epoch,” he said. “To put it into context, man is now responsible for moving 57Bn.t of rock and soil each year, while only 26Bn.t is moved by natural sedimentary processes.
“This new geological epoch is affecting climate change and placing increased demand on flood defences.”
According to Smith, flood embankments are vulnerable due to their composite structure and many were not the result of engineering design.
“The problem is that they can stand for many years any issues but without being subjected to a design flood,” he said. “There are over 9,000km of flood embankments in England alone and failure only affects a small percentage of this length but the impacts of a small breach can be significant.”
Smith presented an analysis of the impact of flooding over the last 10 years which showed most breaches were due to water flow or uplift rather than conventional slope failure.
“Cooling and Marsland described them as ‘stabs in the back’ in their paper on the failure of flood defences during the 1953 North Sea floods,” he said. “This is still true today but the issue is greater as climate change will increase both the magnitude and frequency of hydraulic loading on flood embankments.
“Engineers must remain vigilant and adaptable to this change.”