2001
Llanelli, Wales
The Millennium Coastal Park
Alfred McApline Ltd
Ove Arup & Partners
Sustainable River Diversion for The Eisteddfod at Millennium Coastal Development
Biomac secured to the new channel bank flood berms
18 months after construction, vegetation has established well
Blockstone & Reno mattresses protecting outside bends
Challenge
As part of the Millennium Coastal development in Wales, a permanent venue for The Eisteddfod required the diversion of the Afon Dulais River. Despite being a relatively small watercourse, the river presented significant engineering challenges due to its high Õ§Õ¶ergy flow conditions, with velocities reaching approximately 2 m/s (6.5 ft/s).
The project demanded a natural river diversion solution that would preserve the original character, appearance, and ecological integrity of the watercourse. This requirement was particularly critical given the cultural importance of the site and the environmental sensitivity of the river system.
The downstream section of the Afon Dulais is a key salmon spawning habitat, making ecological protection a priority. A fish rescue operation conducted prior to construction successfully relocated approximately 1,700 fish from a 300 m (980 ft) stretch, highlighting the biodiversity value of the river.
Further complexity arose from the proposed alignment crossing highly erodible sandy soils, increasing the risk of bank instability and channel degradation. The client specified that sustainable erosion control solutions should be used, replicating natural bed morphology and reinstating native bankside vegetation to ensure long-term environmental compatibility.
Solution
To deliver a sustainable and naturalistic river diversion, a combination of bioengineering techniques and engineered erosion control systems was implemented.
A biodegradable coir erosion control mat, Maccaferri Biomac, was used to stabilise the channel banks. This woven coir matting was secured with steel ‘J’-pins and provided immediate erosion protection while promoting vegetation growth. As a natural fibre solution, Biomac biodegrades within 1–2 years, leaving behind fully established vegetation to provide long-term bank stability.
In higher էնergy zones, particularly along channel bends where shear stress is greatest, more robust solutions were required. Reno mattresses and stone pitching were installed to reinforce these areas. Filled with durable 75–100 mm stone, Reno mattresses offer high-performance erosion protection while maintaining flexibility and permeability.
A Reno mattress structure was also used to construct an overflow weir, enabling controlled water transfer from the river into newly developed fishing lakes. These lakes were carefully designed and excavated within the sandy soils, incorporating submerged shelves and graded slopes to enhance aquatic habitats and promote biodiversity.
A key advantage of Reno mattresses is their ability to support natural re-vegetation. The voids between stones trap sediments, allowing vegetation to establish over time and integrate the structure into the surrounding landscape. This makes them ideal for environmentally sensitive river engineering projects. Where faster vegetation establishment was required, Maccaferri Geomac® could be applied to accelerate ecological restoration.
The completed scheme successfully delivered a stable, sustainable river diversion that balances hydraulic performance with environmental protection. The use of bioengineering techniques and flexible erosion control systems ensured that the new channel replicated the natural morphology and ecological function of the original river.
This project demonstrates best practice in river restoration, erosion control, and sustainable drainage design, providing a resilient solution that supports both infrastructure development and ecological preservation.
Used Products
