A new study from the North Carolina State University suggests that repeated flooding has a cumulative impact on flood defences, damaging them in ways that may not be picked up by current inspection techniques.
Earth embankments, or levees, are widely used for flood protection in the US, and are typically more than fifty years old. The study, in Engineering Geology, looked at the local Princeville levee and the effect of recent hurricanes Matthew and Floyd.
Repeated storm cycles of high and low water meant that the levee experienced a huge difference in forces from the weight of the water. These forces shift the levee fractionally each time, and the rate of shifting increases with the number of storm cycles. The cumulative damage may not be noticed by visual inspections, but is still significant. “With increasing flood cycles, the risk [of the levee failing] changes from ‘acceptable’ to ‘unacceptable,’” says Professor Mohammed Gabr.
Gabr says they are now developing a way to monitor and track the minute movement of levees via satellite imaging so the level of distress can be accurately estimated. This will help planners ensure that levees at risk are rebuilt before disaster strikes. This type of analysis may become more urgent as climate change makes floods more frequent and levees suffer a steady battering.
• This article was amended on 1 February 2020 to correct the name of the Princeville levee. An earlier version referred to the Princetown levee.
