© ROLAND HARRISON/AFP/Getty ImagesA helicopter helps shore up the dam at Toddbrook Reservoir, UK.
Dams are typically designed to cope with a so-called 1-in-100-year flood event. But as the world warms the odds of extreme rainfall are changing, meaning the risk of failure is far greater. Engineers have been warning for years that many old dams around the world are already unsafe and need upgrading or dismantling.
"The 1-in-100-year event is perhaps happening every five years," says Roderick Smith at Imperial College London. "I'm absolutely convinced that it is due to climate change."
What is happening at Toddbrook Reservoir, where 1500 people have had to evacuate, is very similar to what happened at the Oroville Dam in California in February 2017. Both are earthen dams where excess water flows over the top of the dam and down a concrete-lined spillway.
If this concrete is damaged, the water flowing down the spillway can rapidly erode the earth underneath, and there is a risk of the entire dam wall collapsing.
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