• Capabilities: Civil Engineering, Water Management

Significantly reducing the flood risk for communities in North Somerset

Wrington, North Somerset - Wrington village, near the Mendip Hills in north Somerset, lies in the valley of the Congresbury Yeo River, about 20km south-west of the Bristol. Rye Brook flows through Wrington and regularly floods. The floodplain intersects a central corridor through the village, with at least 11 residential properties currently at very significant risk and 42 properties at significant risk. Flooding also affects the main roads into the village.

Reducing the flooding risk

to 1 in 50 years
Wrington-Flood-Storage-Area

At some locations there is a 1 in 2 chance of flooding in any year affecting people and property. Between 2007 and 2012, six flood events had caused significant flooding and disruption in Wrington with the most severe in 2012 when there was successive flooding in September, November and December. 

We worked with Jackson Civil Engineering for North Somerset Council (NSC) to prepare detailed designs for a flood storage embankment on the Rye Brook above the village under the Environment Agency’s Water & Environmental Management Framework. In operation, the scheme will protect a total of 79 properties.

The scheme has been developed by NSC, as the lead local flood authority, in partnership with the Environment Agency and Wessex Water. Feedback from consultation on the Scheme options, including numerous public and stakeholder meetings, was positive with support for the preferred option. At the chosen location of the embankment the brook is elevated above the natural valley floor.

We took the original concept design and modified it by changing the position of the spillway so that exceedance flows would re-join the watercourse rather than discharge to the natural valley floor which would have created further flooding problems. The spillway was designed with a permanent turf reinforcement rather than a concrete block system for better aesthetics.

 

 

Wrington-Flood-Storage-Area
The embankment has a 2m clay core which is socketed into the existing ground up to a depth of 3.6m to ensure that leakage is minimised. A compaction method was used to avoid the need for man-entry into a deep excavation, but Skanska eventually elected to install the core using a traditional benched excavation to get to formation level. 

The rear ‘dry’ face uses the excavated arisings from the clay core trench to minimise transport and carbon emissions. The face is founded on 150mm thick coarse sand drainage blanket. The front ‘wet’ face is formed from more granular material to resist the drawdown forces exerted by the rapid drainage of the flood storage embankment after the flood subsides. Both faces are protected with badger-proof mesh and stock-proof fencing to prevent burrowing animals from either forming a path through the dam or causing damage to the faces.

The scheme was successfully completed in autumn 2019 in time to prevent the village from excessive flows experienced early in 2020.

Wrington-Flood-Storage-Area

Nigel Horwell, Associate Technical Director – Water Management & Flood Resilience, said:

“We’re proud to have been involved in a scheme that will make a significant difference to the community in Wrington which has been routinely affected by floods.”


Outcomes

Reducing the flooding risk

to 1 in 50 years

Questions about this project

Nigel Horwell

Associate Technical Director at Arcadis Consulting Ask me a question
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