Barhale has secured a £14.8M package with Thames Water to carry out rehabilitation works on New River, one of London’s oldest water infrastructure assets.
The New River was opened in 1613 to carry water from Hertfordshire into central London, drawing water from springs along its path and later on taking water supply from the River Lea and other water courses.
Barhale is now refurbishing the aqueduct at two locations in Hornsey, north London, and Waltham Cross in Hertfordshire, north of London, to prevent leakage and extend the asset’s life.
Thames Water senior project manager Rachel Whiteman confirmed that the aqueduct is leaking in the Hornsey area of the New River, entailing water loss and resulting in the gradual erosion of the embankment. Small-scale repairs have been carried out to date and previous drainage works have diverted leaked water into the sewer network to prevent flooding.
Whiteman said: “Over the years, we’ve been carrying out several smaller leak repairs and have put in place different solutions to manage leakage in ways that minimises disruption locally. However, our annual inspections have identified further areas of leakage and we have decided that a large-scale upgrade is now necessary.”
Barhale is addressing the root cause of the issue by strengthening the northern side of the waterway with sheet piling. This entails a revision of a previous design, which was to build a concrete channel, with the Barhale team selecting sheet piling as a more cost-effective solution. Gradual weathering of the sheet piling will also ensure the riverside blends into the natural environment.
Barhale will use the Giken system developed by the Japanese equipment specialist of the same name to install the sheet piling. Unlike conventional methods whereby prefabricated sheet piles are hammered or vibrated into the ground, resulting in high levels of noise and vibration, the Giken method entails a “press-in” technique using a silent piler.
Barhale regional manager John Prendergast said a key challenge for the Barhale team is that New River’s route is tightly constrained as it passes through North London. To address this, Barhale will deploy pontoon barges, initially to carry suction equipment to excavate silt from the river and then subsequently to provide a platform for the lifting crane.
“It’s a bit of a problem getting equipment to the site – hence the decision to use pontoon barges, which we believe is a first for the business,” Prendergast said.
“Additionally, the nearness of residents has been a big consideration. Using the Giken system will minimise noise during construction and the decision to use steel sheet piling will ensure that, over time, the works have almost no visual impact.”
Barhale will also be installing sheet piling along a 1.1km stretch of the New River at Waltham Cross, west of the site of a proposed development for film production company Sunset Studios. The sheet pile will be of varying length to reach the impermeable London Clay formation to prevent water leakage around the base of the existing sheet piles.
When completed, the gap between the new and old piles will be filled with pea gravel to provide additional stability.
Barhale contracts manager Jacques Deneys said that because the existing tow path would not support the weight of the piling rig, Barhale has worked with piling specialist Ivor King and civil and geotechnical engineering specialist OTB Engineering to find a solution.
This entails the Giken Reaction Base System, whereby press-in machines utilise reaction force from installed piles integrated with the earth and carry out piling work while moving along the installed piles.
“Once we have installed the first 10 sheets it [the weight supporting limitations of the towpath] will no longer be a problem,” he said. “Using the Giken Reaction Base System means the entire operation to install the 1.1km of piles will be running on the new sheet pile wall.”
Deneys confirmed Barhale was taking measures to protect the local ecology: “We are working closely with Frog Environmental to specify an innovative bubble curtain to prevent silt debris dispersing through the river and to discourage fauna from approaching the works.”
Work on the two sites along the New River is scheduled to commence immediately and is planned for completion in September 2025.