Protecting the River and the Land During Rosina Weir Removal

Executive summary

West Wales Rivers Trust appointed Enviroculture to support the partial removal of Rosina Weir on the Afon Loughor at Pantyfynnon, Ammanford. The concrete structure restricted fish movement and affected natural river processes, so the project needed practical delivery that improved the river while protecting the surrounding environment.

The work involved precise demolition of the central section of the weir, careful handling of concrete waste, protection of private land and strict sediment and biosecurity controls. When stormwater and high flows began affecting the original sediment protection, the team adapted by trialling a Frog Environmental Bubble Curtain alongside ground protection, tracked dumpers and controlled machinery movements.

About the client

West Wales Rivers Trust works to improve rivers across the West Wales catchment. On this project, the Trust was working with Natural Resources Wales to deliver fish passage and river habitat improvements as part of a wider programme of river restoration activity.

The Trust had already secured the necessary permissions, including regulatory consents, landowner access and liaison with the angling club. Enviroculture was appointed to deliver the practical works on site while maintaining environmental protection, safety and landowner confidence.

The challenge

Rosina Weir was a concrete structure on the Afon Loughor. The centre section needed to be removed to bed level, while the raised side sections were to remain in place at the request of the angling club. This required controlled breaking and lifting from the bank, with minimal disturbance to the riverbed and surrounding habitat.

Access formed one of the main project risks. The working area sat across private land, with soft ground, livestock considerations, a locked field gate, overhead services and a gas main to manage. The landowner needed confidence that the access route would not be damaged, which made ground protection, controlled traffic routes and the use of tracked plant essential.

Sediment control was another critical issue. Breaking out concrete in a live river environment can disturb silt and fine material, and stormwater conditions were knocking out sections of the initial sediment protection. The project needed a quick, practical and environmentally responsible adjustment to reduce the risk of sediment travelling downstream.

Biosecurity also had to be managed carefully. Himalayan balsam had been present on the site, so plant, tracks, attachments, boots and equipment needed to be cleaned and controlled to reduce the risk of spreading invasive non-native species.

The solution

Enviroculture developed a low-impact delivery method built around bank-side working, careful access planning and environmental protection. A long-reach excavator was used with breaker and grab attachments so the weir could be broken into manageable sections and lifted out without unnecessary entry into the watercourse.

Ground protection mats were installed across the private land to spread plant loadings, reduce rutting and protect the landowner’s grassed access routes. Tracked dumpers were then used to move concrete waste from the river corridor to the disposal area, keeping wheeled traffic and heavy loads away from vulnerable ground wherever possible.

Sediment protection was installed within the working area, but stormwater and high flows created a practical challenge. After contract award, West Wales Rivers Trust and the project team agreed to trial a Frog Environmental Bubble Curtain. The bubble curtain added a further layer of in-channel mitigation by creating a curtain of microbubbles designed to limit downstream movement of disturbed silt and sediment while also supporting oxygenation of the water column.

The approach combined traditional site controls with adaptive environmental management. Instead of relying on one method, Enviroculture used a layered system: physical sediment protection, controlled demolition, bank-side working, bubble curtain trial, ground protection, tracked material handling and biosecurity cleaning before plant left the site.

·         Long-reach excavator used from the bank to reduce unnecessary in-channel access.

·         Breaker and grab attachments used to control demolition and remove concrete pieces.

·         Tracked dumpers used to transport waste off site via protected access routes.

·         Ground protection installed across private land to reduce compaction and rutting.

·         Sediment protection adapted in response to stormwater and high river flows.

·         Frog Environmental Bubble Curtain trialled to strengthen silt management.

·         Plant and equipment cleaned under biosecurity controls due to Himalayan balsam risk.

The implementation

The project began with access planning and a site set-up focused on safety, utilities and protection of private land. Working zones were controlled using fencing and barriers, with plant movements managed along agreed routes. Ground protection mats were placed to create a stable access corridor and protect sensitive grassed areas from rutting, compaction and unnecessary reinstatement work.

Once the working area was established, Enviroculture positioned sediment controls downstream and around the work zone. The long-reach excavator then broke the central section of the weir in a controlled sequence. Broken concrete was lifted using the grab attachment and transferred to tracked dumpers for removal from the river corridor.

When high-flow conditions and stormwater affected the original sediment protection, the team adapted the method by assisting with the Frog Environmental Bubble Curtain trial. The system was positioned across the river to create a bubble barrier, helping to reduce the downstream spread of disturbed sediment during the weir removal works.

After the demolition and waste movement were complete, the site was tidied, remaining materials were removed, and plant was cleaned before leaving site. Biosecurity measures were treated as a core part of the demobilisation process, not as an afterthought, because of the Himalayan balsam risk and the sensitivity of moving machinery between watercourse environments.

Additional project challenge: Bubble Curtain trial

The Bubble Curtain trial became an important addition to the project because stormwater was reducing the effectiveness of the initial sediment protection. Frog Environmental provided the system for use on the River Loughor project, giving the team a practical opportunity to test a more resilient mitigation method in challenging river conditions.

Frog Environmental’s public case study notes that the curtain was trialled during Storm Agnes, when the river was full and flows were challenging. Although the high flows made it difficult to achieve two straight lines of bubble tubing, the microbubble barrier still helped limit the downstream movement of disturbed silt and sediment during the weir removal works. Frog also identified the added benefit of increasing dissolved oxygen levels, which can support fish and other aquatic organisms during construction activity.