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Lido’s new lease of life

3 Nov 21 In the World Heritage city of Bath, contractors are working on the restoration of Britain’s oldest outdoor swimming pool and lido. Paul Thompson reports

The City of Bath, with all its Georgian architecture, Regency splendour and spa-town grandeur, is well loved by locals and tourists alike.

In pre-pandemic 2019 more than six million visitors spent time marvelling at its Roman Baths, Royal Crescent and Pulteney Bridge, many of them doubtless lured by the romantic vision of the city depicted in the novels of Jane Austen.

In fact, Austen did rather a good job of glossing over the true state of the city at the time she lived there. By the early 1800s its position at the height of fashionable society had been trumped by other resort towns such as Cheltenham, Leamington Spa and Brighton. It still boasted a thriving middle class but slums and red-light districts had sprung up alongside the River Avon in the centre of the city and developers were eyeing land to its east.

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Here, the Duke of Cleveland agreed to lease an area of marl pits alongside the river at Bathwick for speculative residential development but the economic slump caused by the Napoleonic wars forced a rethink of the housing strategy.

In 1815, partly in response to the prohibition of nude bathing in the River Avon, the development of a swimming pool on this land - formed by diverting the river’s flow - was funded by public subscription.

The resulting Cleveland Pools, with its Georgian lido and crescent of caretaker’s cottage and changing rooms, was well loved and well used for the next 150 years. By the mid-1980s however, fashions had changed and the swimmers had left for purpose-built leisure centres.

Slowly the buildings started to fall into disrepair and in 2003 owner Bath & North East Somerset Council put the site up for sale.

That sparked the creation of the Cleveland Pools Trust, a band of like-minded locals focused on saving the pools and returning the site to its primary purpose. And now, almost 20 years after its formation, the trust has fought to the point where Swindon-based contractor Beard Construction is working on a £6.1m contract that will deliver its vision.

It’s a difficult task for the Beard team, led by project manager Mark Tregelles. Hemmed in between the Avon and the terrace of Regency cottages on Hampton Row above, the steeply sloping site falls 14m from kerbside to poolside. The only access is the unassuming 1.2m-wide pedestrian alleyway between two of the cottages and the river itself.

“It makes life very difficult,” admits Tregelles. “We are only permitted to use Hampton Row when placing concrete or blacktop. Ninety-five per cent of plant and materials have to be brought on and off the site using the river.”

That movement is by no means a small task. Plant, machinery, fill and muck-away is all moved using a spider crane that sits alongside the riverbank. It loads as much as 30 tonnes of material onto a twin boat and pontoon barge that ferries everything to and from a small temporary wharf and depot the team has set up at Avon Rugby Club, just a mile or so upstream (see Avon calling).

Since the team started work on site in April it has been busy clearing the debris and silt that has accumulated in the years since it last opened as a functional swimming pool. Concreting work has seen the team pump up to 45 m3 of blinding material down to the poolside level from Hampton Row using a pipeline fixed along its length, with the slab itself providing a key focus for the scheme’s engineer Hydrock (see Floating pool puzzle for Hydrock).

Work has also started on the clean-up of the cottage and changing rooms that form the crescent alongside the main pool. Blasting paint from the faces of the Bath stone buildings is currently underway. The team is using high-pressure water jetting techniques but will consider additional chemicals or treatments if required.

 “The whole site – buildings and pool – is Grade II* listed and we have to respect that. We need to blast away the paint from the changing rooms and cottage. We’re using water-only jetting because it is easier to handle any run-off but we will look at other techniques if we need to,” says Tregelles.

The crescent buildings are facing a ‘light touch’ restoration – walls are brought back to stone, benches and roofs are replaced while the cottage gets spruced up at poolside level – although there will be the addition of an access bridge at the rear into the new caretaker’s apartment at first floor level and wider disability access.

The steeply sloping nature of the land has required the Beard team to temporarily cut the bank away behind the cottage in a series of batters, installing geomesh tied back into anchors screwed into the ground. This temporary work will be reinstated once the new retaining wall and access bridge are installed.

To the east of the buildings the team is painstakingly excavating and underpinning the walls of the former children’s pool, which is included in the Grade II* listing. The space will become the plant room and house the heat exchangers for the water-sourced heat pump (see River water pumps out the heat) with a roof slab cast and covered to become a refreshment kiosk, seating area and performance space.

With around 12 months to go before the Cleveland Pools Trust’s vision for the site is realised, its project director Anna Baker is looking forward to taking a swim in its waters and welcoming crowds back to its lido areas.

“The business case is based on seasonal opening and we are hoping to be able to offer some level of off-season swimming throughout the cooler months. We still need to raise funds though. We welcome any financial help. We want the pools to be a true community asset – open and accessible for all, not just swimmers,” she says.

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Avon calling

It was clear from the moment the Beard team first looked at the Cleveland Pools site that it was going to have to be inventive in its approach to the project.

With no opportunity to use Hampton Row, with its terrace of Regency cottages, above the site as a main materials access point for the project, attention turned to the River Avon itself. It is at a reasonably constant depth during normal flow conditions thanks to the influence of weirs up and downstream of the site.

“The river was the only way we could move materials in. Other contractors had suggested a tower crane set above Hampton Row but that was never going to be feasible. We realised straight away that the river would be key,” says Beard project manager Mark Tregelles.

Other than main concrete pours – which will be carried out from pumps on Hampton Row –, everything is being shipped on and off site using a nine-tonne spider crane that sits on a reinforced concrete base set two metres deep into the riverbank.

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Materials are loaded off and onto a small five-tonne-capacity pontoon barge that is then manoeuvred upstream to a temporary stockpile and wharf facility set up at the Avon Rugby Club.

With cargoes limited to five tonnes per boat-load, it is vital the team maximises each trip. Muck-away for the scheme sees mini-excavators load one-tonne dumpy bags which are stacked to ensure water drains from them before they are loaded.

At the Rugby Club wharf, larger, more efficient mobile cranes are able to load and unload the barge more quickly but the constant flow of river traffic has meant the Beard boats need to work closely with local firm Pulteney Cruisers to avoid any potential clash on the river.

“We try and work around the Pulteney Cruisers timetable whenever possible. We will always try and time our runs so that we are following them either up or downstream. That way we avoid having to manoeuvre around one another on the river. It just makes more sense,” says Tregelles.

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Floating pool puzzle for Hydrock

“It is important to understand that the Cleveland Pools is an exceptional project,” says Roger Bareham, technical director at consulting engineer Hydrock. “It is extremely technically challenging in a number of ways but principally you should try and avoid putting a swimming pool in a floodplain.”

The existing pool is 2.7m deep and protected under the listing status. It will remain in place while a new pool lining is cast above it. Although this will make the pool shallower it will make it capable of being heated by the water-source heat pump (see River water pumps out the heat).

Unfortunately, the site is well and truly within the grasp of River Avon floodwaters and a very high water table. Springs feeding in water behind the new pool lining also mean the new pool is potentially very buoyant; and developing a method of resisting this buoyancy proved tricky.

The team couldn’t just beef up the thickness of the new concrete lining as this would increase the deadweight and potentially damage the listed structure. Installing tension piles down through the existing pool and into the water table would similarly damage the integrity of the existing pool and impact the site’s hydrology.

“The piles would have needed to be 6m deep into the water table so were discounted. We needed a system that would ensure the hydrological status quo,” says Bareham.

Therefore the Hydrock team developed a system that will manage the water flowing around the pool, enabling a lightweight construction of the pool lining and mitigating any buoyancy risk.

A system of weepholes through the existing pool lining; coupled with drainage membranes, stone sub-base and SUDS drainage crates beneath the new pool lining, helps manage the water and has allowed the team to design a concrete lining with 250-300mm-thick walls and a 300mm-thick slab.

“The lining will be a Sika waterproof mix concrete with steel reinforcement at 150mm centres,” says Bareham, “The main pours will need a large pump at the top of the site at Hampton Row to pump downhill. That can be more difficult.”

In terms of monetary value this is about as small a project as Hydrock will take on. But the technical challenges prove that even the smallest projects can be daunting.

“We’ve all learnt from this project and I am immensely proud to be part of it. I like that there is an amazing backstory to this scheme. There is more to it than just engineering,” says Bareham.

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River water pumps out the heat

Although the Cleveland Pools were originally little more than a diversion of the River Avon it has been many years since bathers there swam in river water.

But when the lido reopens next year, that historical link with the Avon will be restored thanks to the team using a water-source heat pump located in the river to warm the waters of the swimming pool.

“Using renewable energy systems made sense for the project. There was no space available for ground-source or air-source heat pumps – a water-sourced solution was the obvious answer,” says Bill Gilmour-White, technical consultant at renewable energy engineer Redcotec.

The system will draw in 25 litres of water per second from the Avon across four pumps located in the river. A heat exchanger system, set in the new plant room beneath the old children’s pool, will heat the pool water to a target temperature of 28oC.

The biggest challenge is in keeping the pumps at their optimum position within the river while maintaining the flow of water from the lido pontoon as the river level rises and falls. It is an issue that the Redcotec team is still working on.

“We have to accommodate water level fluctuations of around three metres at the pontoon and that is causing a headache. We want this system to be the best, most efficient and most reliable it can possibly be,” says Gilmour-White.

This article was first published in the September 2021 Top 100 Contractors issue of The Construction Index magazine.  Sign up online

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