Leaky river barriers can reduce flooding. Do we thank beavers?

New research has found that leaky river barriers made up of natural materials like trees, branches, logs, and leaves can reduce flooding in at-risk communities by storing water upstream.

New research has found that leaky river barriers made up of natural materials like trees, branches, logs, and leaves can reduce flooding in at-risk communities by storing water upstream.

The study, led by scientists from Cardiff University and the University of Worcester, assessed the impact of leaky barriers at a natural flood management site on a small Shropshire river over two years.

Human-made leaky barriers, designed to imitate beaver dams, work in units of 50–100, deliberately raising water levels upstream to slow down river flow through storage and diversion, providing ecological benefits to the river corridor and on nearby farmland.

Until now, scientists have used numerical modelling based on multiple assumptions to measure their impact. However, the Cardiff and Worcester team gathered real data from 105 leaky barriers over three miles to understand how they operate when overtopped by flood waters.

Their study, published in the Journal of Hydrology, found the site’s leaky barriers could store enough water to fill at least four Olympic-sized swimming pools during significant weather events such as Storm Dennis.

The team recorded raised water levels up to 0.8 meters at each barrier, which they say slowed the river’s flow during these storm events, taking seven to nine days to return to normal and protecting communities from flooding downstream.

Flood risk potentially alleviated by leaky river barriers

Dr Catherine Wilson is a Reader at Cardiff University’s School of Engineering and one of the study’s authors. She said, “In recent years, we’ve seen a significant increase in flood risk across the U.K. and internationally due to greater storm intensity and other climate change-related factors.

“Where flooding does occur, we often see extreme human and socio-economic costs. And so, it’s vital that we better understand how to combat these events in the most effective way possible.”

The team placed monitoring equipment on three channel-spanning leaky barriers to measure their effects on water levels upstream and downstream over time.

Further data was extracted from drone images of the site using a technique known as photogrammetry, which enabled the team to make highly accurate measurements of the land elevation in areas of the river covered by trees and other flora.

“For the first time, our study provides quantifiable in-depth evidence of the effectiveness of nature-based solutions in tackling these flood events. We show that leaky barriers effectively slow down the river’s flow during rainfall, storing up vast quantities of water which would otherwise rush through, causing damage to communities downstream. Instead, this force is slowly released over a week to 10 days,” says Wilson.

“Leaky barriers are most effective in narrow channels with steep banks and better at reducing flooding during smaller storm events than larger ones. This tells us they are valuable to existing flood management strategies.

“Not only that, leaky barriers offer a low-cost solution of between £50 and £500 and are a sustainable flood defence which increases biodiversity in our rivers and on nearby land.”

Further research needed

The team continues to monitor the effectiveness of leaky barriers at the Shropshire site, one of sixty identified by the Department for Environment, Food and Rural Affairs, to evaluate natural flood management.

They say their findings can be used by government and industry to develop flood defences for smaller, more frequent storms and help create an approach to modelling leaky barriers for larger storms as well.

Professor Ian Maddock, Professor of River Science at the University of Worcester and one of the study’s co-authors, said, “The results of the study have helped inform our work with local authorities to identify new sites for natural flood management. It’s enabled us to target sites where installing leaky barriers will have the greatest impact in reducing flood risk to communities and landowners downstream.”

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