£4.2 million scheme to extend life of Dunball Sluice

25th August 2022
SRA

Work has begun on a £4.2 million refurbishment of Dunball Sluice north of Bridgwater, one of the Environment Agency’s most important tidal defence assets.

Dunball Sluice (pictured above) controls flows between King’s Sedgemoor Drain (KSD) and the tidal River Parrett.

Dunball sluice became operational in 1971.

Many of the sluice’s components are now close to the end of their working life.

They are being repaired or replaced so that the sluice can continue to help protect Bridgwater and villages in the Somerset Levels and Moors for another 25 years.

In this old photo of Dunball, water from King’s Sedgemoor Drain (bottom right) flows into the much broader expanse of the tidal River Parrett. Because there is no controlling structure in between them, water from the Parrett also flows into King’s Sedgemoor Drain. On the left bank, where the two meet, you can see a circular coffer dam in place for work on the construction of Dunball Sluice. Since 1971, the Sluice has been used to control the intersection of the two rivers.

Work on the refurbishment of Dunball Sluice is due to be completed by 2024. It is largely being funded by the Department for Environment, Food and Rural Affairs (Defra), with Somerset Rivers Authority (SRA) contributing an additional £650,000 as part of its mission to give Somerset greater flood protection.

Rachel Burden, Somerset Flood and Coastal Risk Manager with the Environment Agency, said: “The project will extend the life of Dunball Sluice, reducing the potential for failure, and mitigate the risk of flooding to properties and internationally and nationally important freshwater habitats.”

Cllr Mike Stanton, Chair of Somerset Rivers Authority (SRA), said: “I’m delighted that the SRA is helping to make this work possible. Dunball Sluice is a crucial facility. Refurbishing it boosts the SRA’s own major scheme to increase the floodwater-carrying capacity of the River Sowy and King’s Sedgemoor Drain.

“Sowy-KSD works are being delivered for the SRA by the Environment Agency up until the end of October. As partners we’re working together to reduce flood risks across a large part of the Somerset Levels and Moors.”

Dunball Sluice

Dunball Sluice is a critical structure in the defence of the Somerset Levels and Moors. It sits where King’s Sedgemoor Drain (KSD) meets the tidal River Parrett. It helps to control flows of floodwater through the King’s Sedgemoor Drain and the River Sowy. The River Sowy is also known as the River Parrett Flood Relief Channel. It was created between 1969 and 1972, when work on Dunball Sluice was also carried out. Water flows into the Sowy from the Parrett downstream of Langport, and then into the KSD, before rejoining the Parrett through Dunball Sluice.

Map showing course of River Sowy and King's Sedgemoor Drain. — A simplified map showing where Dunball Sluice sits in relation to the River Parrett and River Sowy-King’s Sedgemoor Drain system, and Bridgwater and the floodplains of the Somerset Levels and Moors.

At the Sluice, four gated culverts control water levels by releasing water into the Parrett when the tide permits while preventing the tide from bringing saltwater into the KSD. Saltwater would have an undesirable impact on Somerset Levels and Moors freshwater habitats which are nationally and internationally designated for their ecological importance.

The Sluice refurbishment scheme will also see environmental improvements made to encourage the migration of eels and to improve access for otters between the KSD and the River Parrett.

There will also be health and safety improvements for agency staff and contractors who operate and maintain the sluice.

The work will not affect the continuing operation of the Sluice and all refurbishment works will be undertaken within the compound area.

If there is a need to move water out of the system into the Parrett but the tidal gates cannot be used due to the state of the tide, temporary pumps can be set up at the Sluice to pump water over the structure and into the river. This was last done in 2014 and upgrades have been made since to better accommodate temporary pumps deployed from the Environment Agency’s nearby depot at Bradney.