Project Brief

The Afon Brennig is situated in Tregaron in Ceredigion, mid-Wales. The river is an upland tributary of the Afon Teifi, which flows into Cardigan Bay at Cardigan. The Afon Brennig is located within the Afon Teifi SAC and SSSI which is designated due to the vegetation, fish and mammal communities it supports.

Tregaron previously had a long history of flooding, with up to 133 residential and commercial buildings at risk. The flood defences that were in place prior to this scheme formed part of buildings or property boundaries and were not specifically intended to be flood defence assets.

The main purpose of the project was to strengthen the existing walls that bordered the river to provide an increased level of flood protection.

Marshalls Civils and Drainage Solution

As part of the flood alleviation scheme, the defences through the town were formalised. Redi-Rock retaining blocks were placed on a geotextile scour apron along the riverbanks to prevent scouring out of the proposed wall foundations.

On the 14-week project, new Redi-Rock walls were installed to fill in or raise the existing venerable flood defence. The riverbanks were strengthened by installing and fixing a special ready-grown river vegetation turf on top of the Redi-Rock block stones. The riverbed levels were designed to provide pools and riffles that would better support the fish and animal life in the river.

A 200m length of the river was diverted through flume pipes to allow works to the river banks to be carried out. This also minimised the amount of sediment that could have entered the river during construction.

The dry river bed enabled the Redi-Rock block stone natural-looking bank protection to be installed. A footbridge had to be raised 1.5m to afford access for the excavators.

The sections of Redi-Rock concrete blocks helped to secure the flume pipes before being used in the walls.

Although the scheme now provides protection for the 133 properties and buildings in Tregaron, the regrading of the river bed and deepening of the bed levels reaches through the centre of the town has created a series of riffles and pools, with lateral gravel bars at the channel margins. This has created a range of physical conditions that can support a variety of ecological niches.

The installation of rock revetments on either side of the river has successfully narrowed the channel and created riparian habitats in a reach that previously had entirely artificial banks.

The simple Redi-Rock™ big block solution met the needs of the local residents and planners as it blended in with the natural environment with minimal disruption as it is quick to install.
 

Client Comments

Project Manager, Tim Hopkins of the Environment Agency said “Redi-Rock™ is an ideal solution for this location in view, particularly of the speed with which flood walls can be constructed”