Natural defences can reduce flood height in towns by up to 20%, and should be used alongside conventional defences, say scientists
In a study led by the Universities of Birmingham and Southampton, scientists found that planting trees could reduce the height of flooding in towns by up to 20%.
They found strategic planting on flood plains could help towns downstream reduce the “peak height” of floods.
But the scientists warned that natural flood defences would need to be combined with conventional prevention techniques. The researchers studied a 100km river catchment in the New Forest, upstream of the town of Brockenhurst.
In a bid to better understand natural flood defences such as tree planting, river restoration and logjams – man-made dams – the researchers used a digital model of the terrain.
Planting trees on the flood plain and increasing the number of logjams across just 10-5% of the total river length was found to be able to reduce the peak height of a potential flood in the town by 6% once the trees had grown for 25 years. More extensive river restoration, for example in 20-25% of the total river length, resulted in a reduction in flood peak height of up to 20%.
Dr Simon Dixon, the study’s lead author from the University of Birmingham’s Institute of Forest Research, said: “We believe that tree planting can make a big contribution to reducing flood risk, and should be part of a wider flood risk management approach, including conventional flood defences.
“Tree planting would represent an extra element that helps to slow down the arrival of rain water to vulnerable locations.”
The research, funded by the Environment Agency, is published in the journal Earth Surface Processes and Landforms.
Ben Lukey, flood risk manager at the Environment Agency, said natural flood defences also improved water quality but was not suitable everywhere. He said: “The Environment Agency is already working with partners to use natural flood management measures – such as tree planting – in our flood defence work and have found that they can make an effective contribution when used alongside other, more traditional, flood defences.”
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