Restoring fish passage and river habitat while protecting sensitive woodland access and managing changing river levels

Executive Summary

West Wales Rivers Trust appointed Enviroculture to deliver the removal of three concrete weir structures on the Afon Llan, a tributary of the Afon Loughor, as part of wider fish passage and river habitat improvement works. The project required careful in-river delivery, public safety management, biosecurity controls for Himalayan balsam, protection of woodland access routes, and adaptive programming around river levels that rose quickly during periods of heavy rainfall.

Enviroculture completed the weir removal works using long-reach excavator methods, tracked dumpers, temporary ground protection and downstream sediment controls. Additional vegetation clearance was undertaken to allow safe machine access, and patch repair works were completed where the removal left concrete ends and exposed areas untidy, leaving the river corridor safe, tidy and better connected for fish movement and natural river processes.

About the Client

West Wales Rivers Trust is a river conservation charity working to improve the rivers of the West Wales catchment. For this project, WWRT worked with Natural Resources Wales to deliver fisheries habitat improvements on the Afon Llan through Penllergaer Woods, where three historic concrete weirs were identified as barriers to fish movement and natural river function.

The project formed part of a wider programme to improve fish passage, reduce artificial impoundment, and restore more natural geomorphological and hydrological processes within the watercourse.

The Challenge

The Afon Llan structures were positioned within a sensitive woodland setting with constrained access and live public use nearby. The concrete weirs were approximately 7 metres wide and around 0.5 metres high, with two structures requiring full-width removal and one requiring partial removal due to an existing breach. The side pillars were to be retained where required to reduce the risk of adjacent bank erosion.

·    The river could rise rapidly, meaning works had to be planned around safe river levels and paused when conditions changed.

·    The site included Himalayan balsam, requiring strong biosecurity controls, cleaning and disinfection of plant, tyres, tools and PPE.

·    The access route crossed sensitive land and woodland routes where damage had to be avoided to protect the landowner and public amenity.

·    Vegetation clearance was required to create safe access for the excavator to reach the working area.

·    Sediment release had to be controlled during concrete breaking and removal, with in-river protection monitored during changing flows.

·    The removal works left some exposed concrete ends and untidy edges, requiring additional patch repair works to leave a better finished result.

The Solution

Enviroculture developed a practical delivery approach focused on safe access, controlled demolition, sediment management and minimal disturbance to the surrounding woodland. Works were planned to begin at the upstream structure and progress downstream, helping manage the risk of moving disturbed sediment through the working area.

A long-reach excavator was used to work from the bankside wherever possible, reducing the need for plant to enter the river channel. Tracked dumpers were used to remove arisings from the workface to the designated disposal route, while ground protection mats were installed across vulnerable access areas to prevent rutting, compaction or damage to the landowner’s ground.

Vegetation clearance was carried out where needed to create a safe working envelope for the excavator and to allow the machine to position close enough to the weirs. Biosecurity controls were built into the work process, with plant and equipment cleaned to manage the risk of spreading Himalayan balsam or transferring invasive non-native species between locations.

Implementation

·    Set up the working areas with safe access controls, exclusion zones and public safety management around the woodland route.

·    Installed ground protection to protect sensitive land and keep access routes in acceptable condition for the landowner.

·    Cleared vegetation required for safe machine positioning and visibility at the workface.

·    Monitored river levels daily and adjusted the programme around high-water events, including standing down and returning once levels dropped.

·    Removed concrete structures using bankside excavator techniques, retaining side walls where specified to protect the banks.

·    Loaded removed material into tracked dumpers and transported it off site for appropriate disposal.

·    Maintained sediment protection and reviewed its performance during stormwater events and increased flow.

·    Completed additional patch repair works to tidy exposed ends and improve the final finish following the main removal works.

Additional Works and Challenges

1. Patch repair after weir removal

Following the removal works, some of the remaining ends and exposed areas of the former structures were left looking untidy. Enviroculture identified that leaving the edges in this condition would not reflect the quality of the wider project and could create a poor finish for the client and landowner. Additional patch repair works were therefore undertaken to neaten the retained areas and provide a more acceptable final appearance.

2. Vegetation clearance for machine access

Although some access preparation had been considered before the works, further vegetation clearance was required on site to safely position the excavator next to the working areas. This was carried out carefully to support the works while limiting unnecessary disturbance to the surrounding woodland habitat.

3. River-level monitoring and stop-start programming

A key practical challenge was the behaviour of the river during wet weather. High water made in-river works unsafe and increased the risk of disturbing sediment protection. Enviroculture monitored river levels throughout the project and, on several occasions, stood down the works when conditions were unsuitable. The team then returned once levels had dropped, allowing the project to be completed safely rather than forcing works through poor conditions.

4. Biosecurity and Himalayan balsam control

The woodland was known to contain Himalayan balsam. Enviroculture implemented strong biosecurity controls, including cleaning plant, removing mud and debris from equipment, and managing movements to reduce the risk of spreading invasive material from the site.

The Results

·    Three concrete weir structures were removed or partially removed in line with the client’s specification.

·    Fish passage and river connectivity were improved by reducing artificial barriers within the Afon Llan.

·    Concrete arisings and waste materials were removed from site rather than left in-channel or on adjacent land.

·    Sensitive access routes and landowner ground were protected through temporary ground protection and tracked plant logistics.

·    Works were adapted around river levels, helping maintain safety and reduce unnecessary environmental risk.

·    Additional patch repairs improved the final presentation of retained structure ends and exposed areas.

·    Biosecurity controls were followed to reduce the risk of spreading Himalayan balsam and other invasive species.

The project demonstrated Enviroculture’s ability to combine practical construction delivery with ecological awareness, public safety, landowner care and adaptive environmental management.

Lessons Learned

This project reinforced the importance of flexible programming on river works. Although the contract allowed for extension due to river levels, the day-to-day reality required active monitoring, good judgement and a willingness to pause rather than push ahead during unsafe or environmentally sensitive conditions.

The additional patch repair also highlighted the value of reviewing the finish after the main removal works. In river restoration, technical completion is only part of the outcome; the final appearance, retained edges and stakeholder confidence all matter.