Background

The Afon Brennig, located in Tregaron in mid Wales, is an upland tributary of the River Teifi, which flows into Cardigan Bay. The river lies within the Afon Teifi Special Area of Conservation (SAC) and Site of Special Scientific Interest (SSSI), designated for the high quality habitats it supports, including important fish, mammal and vegetation communities.

Historically, the town of Tregaron had suffered frequent flooding, with up to 133 residential and commercial properties at risk. Existing flood defences largely consisted of informal walls that formed part of buildings or property boundaries, rather than purpose designed flood protection assets.

The Environment Agency initiated a scheme to strengthen and formalise the existing riverbank defences, improving flood protection while enhancing the ecological value of the river corridor.

The challenge

The project needed to address several overlapping challenges:

  • Reducing flood risk to the town centre and surrounding properties
  • Strengthening ageing riverbank defences that were not purpose built
  • Working within a protected SAC and SSSI environment
  • Minimising disruption to river flows and sediment transport during construction
  • Delivering a solution that blended visually with the natural river setting
  • Enhancing, rather than compromising, river ecology

A highly sensitive, carefully engineered approach was required to balance flood protection, ecological enhancement and constructability.

The solution

As part of the flood alleviation scheme, the Environment Agency formalised the flood defences through the town by installing a bespoke Redi Rock™ retaining wall solution along the riverbanks.

Key elements of the solution included:

  • Installation of Redi Rock retaining blocks on a geotextile scour apron, protecting foundations from erosion
  • Construction of new Redi Rock walls to infilling and raising sections of the existing vulnerable flood defences
  • Temporary diversion of approximately 200 metres of the river through flume pipes, allowing safe construction within a dry riverbed and minimising sediment release
  • Use of Redi Rock blocks to help secure the flume pipes prior to their integration into the permanent walls
  • Raising of an existing footbridge by 1.5 metres to provide access for construction plant

To support biodiversity, the riverbanks were finished with ready grown river vegetation turf installed above the Redi Rock blocks. In addition, the riverbed was regraded and deepened to create a sequence of pools, riffles and lateral gravel bars, improving habitat diversity for fish and aquatic wildlife.

The outcome

The completed scheme now provides effective flood protection for 133 properties and buildings in Tregaron, while delivering significant environmental benefits.

  • Increased flood resilience through purpose designed riverbank structures
  • Reduced erosion and improved stability of riverbanks
  • Enhanced river morphology supporting fish migration and wildlife habitats
  • Creation of riparian habitats where previously artificial banks existed
  • A visually sympathetic solution that blends into the natural landscape

Tim Hopkins, Project Manager at the Environment Agency, commented:

“Redi Rock™ is an ideal solution for this location, particularly in view of the speed with which flood walls can be constructed.”

The River Teifi scheme demonstrates how bespoke modular retaining systems can deliver flood protection and ecological enhancement in highly sensitive river environments.