A new UK Environment Agency publication has captured the latest research about natural flood management to help understand what works best where.
The new Working with Natural Processes Evidence Directory indicates that nature can play a major role in improving the nation’s resilience to flooding and coastal erosion.
Informed by significant scientific research, including more than 700 papers, the directory summarises the latest evidence for 17 natural flood management (NFM) measures relating to river and floodplain, woodland, run-off, and coast and estuary management.
NFM protects, restores and emulates the natural functions of rivers, floodplains, catchments and the coast to reduce flooding and coastal erosion. It takes many different forms and can be implemented in urban and rural areas, rivers, estuaries, and coasts.
Which methods of natural flood management are working best?
Among the findings, catchment woodland is shown not only to help reduce flood risk but also to provide benefits for soil, biodiversity and water quality, alongside access to nature.
The review showed that catchment woodland can reduce the height of flood water, with the greatest reductions occurring during smaller events. One study in Cumbria suggested the flow of flood water was slowed by 14-50% in woodland compared to pasture.
The latest science also showcases the significant wider benefits of saltmarsh and mudflat restoration, including their ability to store large amounts of carbon, helping to mitigate climate change. They can also filter sediments and nutrients, improving water quality.
Managed realignment at Steart Marshes in Somerset, created 250 hectares of saltmarsh. A recent study showed that the marsh stored 36.6 tonnes of carbon per hectare per year following restoration, a number which is compared favourably with that of woodland.
New measures for flood risk reduction
For the first time, the updated directory includes emerging evidence for three new methods of natural flood management.
It highlights the potential flood risk reduction and wider benefits of coastal reefs, submerged aquatic vegetation, and beavers.
There is still more to learn about these measures, including understanding what the best depth is for oysters to grow and develop while also effectively reducing wave energy.
The new Working with Natural Processes directory demonstrates that the evidence for NFM has grown significantly, building confidence in flood risk reduction and wider benefits.
Julie Foley, Environment Agency Director of Flood Risk Strategy and National Adaptation, stated: “With climate change increasing the threats of flooding and coastal erosion, we must work together with nature to boost resilience across the country.
“Our £25m Natural Flood Management programme was shaped by the Working with Natural Processes Evidence Directory to test our approaches to future investment and the delivery of natural flood management.”
A combination of NFM techniques has the best results
New evidence also demonstrates the benefits of combining multiple natural flood management measures.
The five-year Littlestock Brook trial on the River Evenlode in Oxfordshire tested several measures at the same time, including putting in woody dams, creating 230m of new water courses, and planting 14.4 hectares of new woodland. Results from the trial show reductions in the height of flood waters of up to 55.2% across all the storms analysed.
Additionally, the Salmons Brook NFM project in Enfield, north London, combined planting 200 hectares of woodland with reducing the width of the channel by 75% and installing 46 bunds in a rural catchment.
Modelling found that, during a once-in-a-25-year storm, the combination could reduce flood flows by half and peak water levels by 10-30cm in the urban areas downstream, with the effectiveness expected to increase with the woodland’s maturity.
Kathryn Brown, The Wildlife Trusts Director of Climate Change and Evidence, concluded: “I’m delighted to see the latest science on natural flood management coming together in one place through the Environment Agency’s Evidence Directory, with a focus on co-benefits – and to see new recognition of the role beavers can play in natural flood management.”
