Implementing 27 leaky dams on the Ridgemoor Brook at Croft Castle has improved the water quality in the pools further downstream by reducing the silt feeding into them, and by preventing dams from overtopping and reducing soil runoff.

The Challenge

Leaky dams are built using locally sourced bankside materials such as timber to create natural dams. They come in varying sizes and designs, and can be built using several different techniques, for example pleaching, using live trees as wedges and pinning using natural materials.

During high flow events, the leaky dams are designed to slow down the flow of water and help push flows onto the floodplain during flood events. By temporarily attenuating small volumes of water they help to reduce the flood peak and flood risk to downstream communities. Leaky dams are also designed to allow the normal flow of water to pass beneath them and where appropriate are designed to allow the safe passage of fish.

Fishpool Valley at Croft Castle and the woodland area upstream of it (Lady Wood) is the source of the Ridgemoor Brook, which during normal times is a small trickling brook. However during periods of heavy rain, large volumes of water begin to flow down the brook, over the tracks and through the valley.

The Solution

In an effort to slow the flow of water, in January 2020, staff from the National Trust, Forestry England, Environment Agency, Wye and Usk Foundation and Herefordshire Council worked collaboratively to install 27 leaky dams on the Ridgemoor Brook at Croft Castle.

Starting with a training day, which was led by experienced staff at the Wye and Usk Foundation and Environment Agency, everyone developed their knowledge on the different techniques available to build and install leaky dams, for example, pleaching and pinning logs using natural materials. All staff involved were trained to use chainsaws and winches.

On the second day, using their shared experiences and skills, everyone worked collectively to build the remaining leaky dams. National Trust volunteers also helped out for the day, building the four leaky dams which are installed in Fishpool Valley SSSI.


Since implementing the Natural Flood Management, water quality has improved in the pools in Fishpool Valley, with less silt feeding into them. In addition, better-manage water through the valley has resulted in no dams overtopping in storms, as the dams are holding back the water even during heavy rainfall events.

Key Learnings

  • lots of small interventions can result in a big difference.
  • The use of NFM techniques has increased local interest in the dams and their construction and function.
  • NFM techniques and concepts can be easily embedded into everyday working practices.

Further Developments

None reported at this time.

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