According to new research, river barriers built of natural materials like trees, branches, logs, and leaves can prevent flooding in towns at risk of it by storing water upstream.
Researchers from Cardiff University and the University of Worcester conducted a two-year study to evaluate the effects of leaky barriers at a natural flood management site on a minor river in Shropshire.
Designed to mimic beaver dams, human-made leaky barriers function in groups of 50–100, purposefully boosting water levels upstream to reduce river flow through storage and diversion, offering ecological advantages to the river corridor and on neighboring farmland.
The Cardiff and Worcester team collected actual data from 105 leaky barriers across a distance of three miles to understand how they function when they are overtopped by flood waters, whereas scientists have previously measured their impact using numerical models based on several assumptions.
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 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 the installation of leaky barriers will have the greatest impact in reducing flood risk to communities and landowners downstream.
Professor Ian Maddock
The researchers noticed elevated water levels of up to 0.8 meters at each barrier, which they claim caused the river’s flow to slow down during these storm events, taking seven to nine days to return to normal and preventing communities upstream from flooding.
Dr. Catherine Wilson, a Reader at Cardiff University’s School of Engineering and one of the study’s authors, 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 cost. And so, it’s vital that we better understand how to combat these events in the most effective way possible.”
To track the effects of three channel-spanning leaky barriers on water levels upstream and downstream over time, the team installed monitoring equipment on them.
The team was able to produce incredibly precise measurements of the land elevation in portions of the river covered by trees and other flora thanks to additional data that was retrieved from drone photographs of the site using a method called photogrammetry.
“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 are effective in slowing down the flow of the river during periods of 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 period of 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 during larger ones. This tells us that they are a valuable addition 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 defense which increases biodiversity in our rivers and on nearby land.”
The team are continuing to monitor the effectiveness of leaky barriers at the Shropshire site, which is one of sixty identified by the Department for Environment, Food and Rural Affairs, to evaluate natural flood management.
Government and business can utilize their findings, they claim, to construct flood defenses for smaller, more frequent storms as well as to establish a method for simulating leaky barriers for larger storms.
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 the installation of leaky barriers will have the greatest impact in reducing flood risk to communities and landowners downstream.”
