A new study reveals data from 105 manmade “leaky barriers” that mimic the logs-and-branches-style engineering of beaver dams. Researchers want to understand how effectively the barriers operate when overtopped by flood waters, and whether communities could benefit from them.
Led by scientists from Cardiff University in Wales, and the University of Worcester in England, the study analyzed the effectiveness of the nature-inspired barriers, which greatly slows but does not completely stop streamflow.
Previously, scientists have only used numerical modelling based on multiple assumptions to measure the impact of these barriers. Now, researchers were able to monitor the barriers over a distance of about five kilometres with pressure transducers, rain gauges, flowmeters, and drone-based photogrammetry.
The engineered leaky barriers, which sometimes had logs secured to the banks with wooden pegs or rebar, controlled flooding behind the barriers and created temporary pools of water, says the study recently published in the Journal of Hydrology. The barriers were able to store enough water to fill at least four Olympic-sized swimming pools during some 15 storms, prompting researchers to want to further understand the feasibility of communities implementing such low-cost, soft-engineering solutions.
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During the study, researchers recorded raised water levels up to 0.8 metres at each barrier. These areas took between seven to nine days to return to normal, and could protect communities from flooding downstream.
The spacing between barriers varied from 11 to 50 metres, while the vertical gap below the barriers varied between zero to 0.75 m.
“Leaky barriers are most effective in narrow channels with steep banks and better at reducing flooding during smaller storm events than during larger ones,” said Catherine Wilson, Cardiff University environmental scientist and study co-author, in a statement about the study. “This tells us that they are a valuable addition to existing flood management strategies. Not only that, but leaky barriers also 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.”
Wilson added that the study’s findings can be used by government and industry to develop flood defences for smaller, more frequent storms, and help create an approach for modelling leaky barriers for large storms.
Ian Maddock, professor of river science at the University of Worcester, and one of the study’s co-authors, said that the results of the study have helped to inform work with local authorities who want 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,” Maddock said in a statement.
In particular, the study’s findings indicate that to maximize the magnitude of backwater rise, leaky barriers should have a large vertical extent and be located in deeper, confined cross-sections along a stream reach.
The U.K. Department for Environment, Food, and Rural Affairs (DEFRA) has been funding the investigation of similar flood protection research. It has implemented some 4,500 green infrastructure measures nationwide, providing approximately 1.6 million m3 of additional stormwater storage space.
In September, the U.K. Environment Agency and DEFRA announced £25 million (CDN $41.7 million) for flood resilience through a new Natural Flood Management program.
In the spring, The Canadian Standards Association released a report designed to help governments shift from traditional grey or engineered infrastructure, such as walls and dikes, to nature-based solutions like restoring forests and wetlands, to manage flooding and erosion.
One of the largest beaver dams in the world is located in northeastern Alberta’s Wood Buffalo National Park. The front of the dam runs approximately 775 metres in length and the entire perimeter is close to 2,000 metres.