Natural Flood Management (NFM) aims to reduce community flood risk by protecting, restoring and mimicking the natural functions of a catchment, improving the ability of the landscape to slow and store water, reducing peak flows which cause flooding. The NFM approach fits well with community forestry, as it provides benefits for local communities by improving water quality, creating habitat, storing carbon, and increasing biodiversity alongside the reduction in flood risk.
The Mersey Forest has been working with partners on two sites in St Helens – Colliers Moss North and Griffin Wood – to explore the possibilities for NFM on these sites.
Over autumn/winter 22/23 plans and designs for a series of NFM interventions on both sites were prepared, with funding being provided by the Green Recovery Fund, a project aiming to boost nature recovery and connect more people with nature across the area.
Specialist contractors were appointed, and work began at Colliers Moss in February 2023 before moving on to Griffin Wood in March 2023.
At Colliers Moss, 21 living leaky dams were installed in two groups to slow the flow of water and temporarily store peak flows. It is hoped that these interventions will reduce the flood risk for a community at risk of flooding downstream at Moss Nook.
The two groups of leaky dams have been constructed using freshly cut willow stems, which should re-establish as new trees making the dams living structures. Creating them in this way will mean that living timber should last much longer than deadwood logs and they’ll provide all the other benefits trees bring to a site.
At Griffin Wood, a previously underground land drain has been brought to the surface, diverting a 100m stretch of underground watercourse into approximately 150m of meandered open-air watercourse. As well as slowing the flow and increasing channel storage capacity by creating a longer, meandering channel (instead of a straight land drain), this also creates an entirely new section of woodland stream, creating new habitat that is much more valuable for a range of wildlife than the previous underground drain provided.
With construction now over, Mersey Forest are looking forward to spring’s new growth, providing some vegetation over the work area, allowing the new structures to blend into the landscape.
Plans are in place to start a program of monitoring at both sites to gather evidence on how the interventions work during storm events, allowing Mersey Forest to learn more about them and potentially refine and improve their approach and designs in the future, both on these sites and elsewhere. Mersey Forest will keep you posted on how they are working throughout the year via their social media channels.
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