A series of willow ‘hydro-hedges’ being built in the basin of a former Kendal reservoir could hold back up to 5,000 cubic metres of water during a storm event like Storm Desmond. Once the hedges are completed, any stored water will release slowly after the flood peak, reducing the impact on properties during a storm event. The reservoir is no longer in use and is owned by United Utilities.

Volunteers from Kendal Conservation Volunteers, a group that works to protect and enhance the natural environment around Kendal and the South Lakes, has started the work at Birds Park, which will continue for some weeks.

Stephen Lockwood from Kendal Conservation Volunteers said: “This is the first natural flood management scheme we have been involved in, so it’s wonderful to be learning skills on the job as we’ve never done anything like this before. Most of the projects we carry out are for the benefit of nature and the landscape. We’re pleased to be involved with a project that will directly help people in Kendal. We go home covered in mud but its great fun!”

Woody dams have been widely used in natural flood management research pilots across the UK which rot over time. However, the dams created at Birds Park will incorporate the use of living willow in the construction. This is a new technique that creates a living structure because the willow thrives in really wet conditions and will create a living semi-permeable structure drawing in water as well as holding the dams together.

Peter Bullard, who is heading up the construction of the hydro-hedges for Cumbria Wildlife Trust, explains the detail: “The methodology for creating the living willow structures is to use nearby trees to create the base of the structure. Branches from willow and sallow trees are then pushed into the ground along both sides of the logs which will quickly root in the wet soil on their own creating posts to provide stability. Flexible willow and sallow branches are then woven between these posts in a manner similar to basket making. The structures will vary in length from 50 to 100 metres and be no more than 1 metre high.

“Any water stored would all discharge in fewer than ten hours, so the storage is available for future flood events. To monitor and understand what actually happens a water flow gauge will be monitored by staff from Lancaster University who will collect and analyse the data.”

During Storm Desmond in 2015, significant rainfall in the small catchment where Birds Park lies caused flooding to over 600 properties in eastern Kendal. This small catchment, which starts above Birds Park on the slopes of Benson Knott, feeds water into the three arms of Stock Beck. Stock Beck flows through culverts in Sandylands, occasionally appearing as open concrete channels. The culverts are too small to cope with the high volumes of water during extreme storm events, which leads to the flooding of properties. Slowing the flow of water in the Stock Beck catchment is an important option as holding back large volumes for short periods of time could reduce the height of flood peaks.

Stewart Mounsey, Flood Risk Manager (Cumbria) at the Environment Agency says: “The Environment Agency is pleased to be able to support this project through £2.5m of Defra funding allocated to Cumbria for natural flood management pilots.  The work at Birds Park is part of the much wider programme of work to reduce flood risk and improve the environment in for the River Kent catchment that the Environment Agency and partners are delivering.”

John Gorst, Catchment Partnership Officer at United Utilities says: “United Utilities is delighted to be working in partnership with Cumbria Wildlife Trust and the Environment Agency on this innovative and exciting natural flood management project. The site at Birds Park has not been used for water supply since the 1970s and it has since developed into a fantastic local wildlife site.  With the addition of these hydro hedges it will also provide an important addition to the wider programme of flood mitigation for Kendal. We look forward to seeing the results of this work and the monitoring work that Lancaster University are delivering.”

Nick Chappell, of Lancaster University, who is helping assess the effectiveness of schemes such as these, says: “The Defra research pilots on natural flood management in Cumbria and elsewhere are essential to demonstrate that local nature-based interventions can be installed, and how much they can reduce flood peaks. We need very intensive deployment of such interventions to be effective to reduce risks for flood-affected communities. This demands a diverse range of methods for removing water from flood peaks to permit both farming and environmental gain. Cumbria Wildlife Trust’s multiple hydro-hedge installation is one such novel approach deserving of research”.

Cumbria Wildlife Trust is working in partnership with the Environment Agency, which has funded the project, to deliver a programme of natural flood management research in the Stock Beck Catchment. The partnership is looking to work with land owners in the catchment to hold significant volumes of water on a temporary basis in numerous locations. Land owned by United Utilities around Birds Park is one of the first locations identified to do this.