ECS installs penstock system to support environment and migrating fish
The installation of a replacement penstock system in a Site of Special Scientific Interest (SSSI) will ease the passage of fish and ensure that the ecology of the area is upheld. ECS Engineering Services completed the project at Ballsgate Sluice on the River Lugg, near Aymestrey, Herefordshire to maintain the water level, vital for the river’s environmental stability, and to continue the operation of a downstream water mill.
Just upstream of the village of Aymestrey, the River Lugg splits, with the branch-off creating an island and feeding a water mill before re-joining the river’s main course. The flow of the branch-off is managed by the Ballsgate Sluice, which comprises penstocks and stoplogs. The penstocks’ gates can be controlled to manage the upstream and downstream water level of the branch-off, while the stoplogs provide additional control for more extreme water levels or to halt flow when downstream maintenance is required.
Flow management is vital to protect the river’s ecology. This area of the Lugg, managed by the Environment Agency, forms part of an SSSI, mainly on account of its fish species that include brown trout and salmon. The Lugg’s main course at Ballsgate includes a weir, which has recently been installed with a fish pass that also promotes new upstream salmon spawning areas. Some fish still cannot navigate the fish pass, meaning that the water level of the small branch-off, exiting the Lugg’s main course just upstream of the weir, must be maintained. The branch-off also feeds a water mill that drives a hydroelectric generator, which also requires a consistent, regulated river flow.
Ballsgate Sluice’s penstocks were rotten and the structure’s stonework was crumbling. Failure of the structure would impede flow, upstream and downstream, with harmful ecological consequences impacting the mill as well. The Environment Agency turned to ECS to manage the installation that demanded continued flow throughout the project, including harm-free fish passage. As a sensitive environmental area, it was also imperative that the installation works minimised any ecological impact.
The first challenge was to divert and control the water flow to enable the installation to take place. One option was to use an over pumping system, involving temporary pipework and two pumps. However, this approach would have increased cost and emissions as the pumps would have had to run constantly for 24 hours a day throughout the duration of the project. Despite using fish-friendly pumps, they could also cause a potentially harmful ecological impact. As a result, ECS identified an improved solution.
“Instead, we planned to dig a trench around the work that would divert the water course,” says ECS’s Project Manager, Mick Smith. “Blocking off upstream and downstream of the structure using concrete blocks and sandbags, we could then open the trench and bypass the flow.”
This provided the Environment Agency with a significant cost saving and improved the environmental outcome with a much lower carbon footprint over the seven-week project. As the bypass channel enabled effective working conditions for maintenance on the sluice, most significantly it avoided the risk of concrete spillage into the water course that would otherwise cause disastrous ecological consequences.
The two 450 mm penstocks would be positioned within a concrete structure, approximately 1.9 m wide and 1.8 m high. The penstocks were prefabricated with a cast iron frame and door, as well as stainless steel spindles and pedestals – durable materials that would ensure long-term operational reliability. The majority of the project’s construction work included the concrete’s formwork, and while some sections were prefabricated, the majority was assembled onsite. Wooden shuttering formed the external mould surrounding the formwork that the concrete mix was poured into.
The concrete structure also features a headwall secured with a chemical resin. After drilling a hole, resin was inserted, acting as a glue against the penstock’s threaded support rod that was then inserted.
“The resin acts as a chemical anchor that sets harder than concrete and is used in place of expansion bolts that can work loose over time in water applications,” explains Mick.
The original wall was also repointed with mortar in all the joints where it had previously fallen away. While providing a heavy-duty industrial structure, the stonework blends in with the environmental setting. Across the top of the structure, a footway with hand-railing was installed to access the island. On the far side, the sluice’s existing stoplogs were retained, providing a bypass should the penstocks become blocked or need to be closed for any maintenance requirement.
Before the watercourse was opened, a fish rescue took place, plus the removal of signal crayfish, the invasive species that harm native crayfish numbers.
“With the penstocks opened and the Lugg’s branch-off rediverted, the flow and water level can now be easily maintained,” says Mick. “The penstocks can be opened or closed, dependent on the time of year and water levels, to maintain and regulate downstream flow.”
The diverted channel was removed and returned to its natural state, and the project completed within the seven-week schedule. Installation of the new penstocks will help the Environment Agency maintain the SSSI and ensure salmon can continue to spawn on the Lugg’s upper reaches. The robust structure will provide decades of flow regulation to the benefit of the environment as well as the mill owner.