“Flood busting” leaky dams installed on Crompton Moor in Oldham

New natural ‘leaky dams’ have been constructed on Crompton Moor, Oldham

The dams are designed to slow the flow of water before it reaches towns and villages further downstream of the River Beal, including Shaw and Crompton. The latest part of a project which uses natural methods to reduce flood risk in Oldham.

Innovative flood risk management techniques have taken another step forward on Crompton Moor in Oldham with the installation of five “leaky dams”. In a project funded by the Environment Agency and the EU LIFE IP Natural Course programme and delivered by City of Trees in partnership with Oldham Council, The Unity Partnership (LLFA) and the Friends of Crompton Moor, the dams form just one part of the mosaic of measures being trialled on site to test how nature based solutions can reduce risk of flooding.

Leaky dams are natural structures constructed from tree trunks installed across a watercourse to slow the flow of water in a river. They are able to hold back significant volumes of water when it rains and then slowly release the water over a much longer period of time compared to a free flowing river. This has the benefit of reducing the ‘peak’ flow of water thereby reducing flood risk to communities downstream.

David Brown, Flood Risk Senior Adviser for the Environment Agency said:

“Working with natural processes is an important part of managing and reducing flood risk in a sustainable way. This pilot project on Crompton Moor will not only slow the flow of flood water and create habitat for wildlife but will help demonstrate the potential of such schemes for climate mitigation.

Natural flood management can make a vital contribution to the restoration of our green spaces and our flood resilience across Greater Manchester. We continue to be extremely grateful to our partners, volunteers and the local community who are helping to deliver these important schemes. It’s a numbers game though, and we need many, many more of these types of projects to make a real difference to the flood risk downstream.

Pete Stringer, Technical & Green Infrastructure Planning Manager at City of Trees said:

“This project demonstrates that through routine thinning works in woodlands we have a source of material that can be used to reduce the risk of flooding to local communities. This is yet another example of why trees are such a crucial resource in improving our resilience to climate change.”

The Natural Flood Management project forms part of the Environment Agency’s overall vision to develop flood management schemes that will not only reduce the risks to local communities, but also tackle climate change through carbon capture and new habitats for wildlife. More information can be found in the EA’s Flood and Coastal Risk Strategy: https://www.gov.uk/government/publications/national-flood-and-coastal-erosion-risk-management-strategy-for-england–2

Supporting information

On Crompton Moor in Oldham, the woody structures are made up of timber from conifer trees and brash and have been in the Old Brook watercourse and in a tributary that runs through an adjacent plantation woodland. The leaky dams will create new wetland habitats behind the structures which will support a variety of new plants, insects and amphibians.

Encouraging water to back up behind the dams will also help to create the conditions needed for sphagnum moss to grow, which is key to the restoration of the upland peatland bogs, a crucial landscape for locking up carbon and holding onto rainwater. Tree thinning work in the plantation woodlands also has the added benefit of allowing more light to get down to the ground, helping more shrubs and wildflowers to colonise which is good for insects, small mammals and birds.

Other measures carried out at part of the project include planting over 2,000 species of mixed Sphagnum moss which is classed as a super sponge, holding up to 26 times its own weight in water, over 2 hectares on Crompton Moor. Approximately 1,500 other trees are due to be planted in 2021.

The works taking place on Crompton Moor will also act as a pilot to allow teams to monitor and research natural techniques and gather evidence of the benefits they provide for reducing flood risk. The pilot programme will also be used by the Environment Agency to further develop a catchment wide approach to natural flood risk methods across Greater Manchester.


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Images show: Before and after the leaky dam installation on Crompton Moor.

Image showing Crompton Moor before installationsImage showing a leaky dam installation on Crompton Moor