The Grand Union Canal Transfer (Guct) scheme to transport water from the Midlands to the Southeast of England will see a variety of novel and standard civil engineering interventions along its route, ...
The Grand Union Canal Transfer (Guct) scheme to transport water from the Midlands to the Southeast of England will see a variety of novel and standard civil engineering interventions along its route, Affinity Water engineers told NCE.Guct is being delivered by Affinity Water, Severn Trent Water and the Canal & River Trust (CRT). It will transport up to 115M litres of water a day 163km from Severn Trent’s Minworth Advanced Water Treatment Plant in the Midlands to Affinity Water’s service reservoir at Chaul End near Luton.
This will be needed to battle a significant water deficit in Affinity’s catchment in south east England that is projected for the mid 2030s if there are no interventions.
The majority of the water’s journey along the transfer will be made via the Grand Union Canal, a CRT asset.
“Instead of having a pipeline from Birmingham to the south, we’re utilising the canal assets,” said Affinity Water head of strategic resource options (SROs) Natasha Coakley. “It’s very much a partnership between the two water companies and the CRT, bringing us together for a strategic transfer.”
Along the route there will be some new treatment plants and upgrades to the Daventry and Drayton reservoirs, as well as some other new infrastructure to manage the flow.
This will be of benefit to CRT as it will see its infrastructure made “resilient and safeguarded for the future”, according to Coakley.
“The canal experiences droughts and CRT has to close sections of it,” added Clare Carlaw. head of engagement, land and consents, SROs at Affinity Water. “What we’re doing is putting water down at the most vulnerable point from a resilience perspective. So it’s a win-win.”
A statutory public consultation on the scheme is currently open, which will feed into the development consent order (DCO) application.
Map showing sections and assets on Grand Union Canal Transfer
Locks and bank raising
While the works might see the speed of the water flow in the canal increase a little, there is a requirement for it to have a maximum of 3m per second to maintain safe navigation.
“There are some interventions so the water doesn’t just freely zoom down the canal,” Carlaw said. “We have to get it around a number of locks; that’s quite key. Some of them we do that by gravity, sometimes we do it via pumps and the other quite interesting bit is we are proposing a number of ‘transfer’ locks, which are brand new locks.
“The reason for putting these in is to help with the bank raising along the canal; if we didn’t put the transfer locks in we’d have to do a lot more.”
The additional flow would see considerable the water level rise in the pounds (stretches between locks) along the canal – particularly at the top ends. Some of the pounds on the Grand Union Canal are up to 20km long, but the water level rise would still be noticeable, according to Affinity Water head of design and environment for major projects Doug Hunt.
“The transfer locks are an elegant solution,” he continued. “They will be in the middle of the long pounds. You can close them and they act as a normal lock as far as the canal users are concerned – but they contain an intake, an outfall and a pump station.
Water is pumped around the lock when it’s closed. This lowers the water levels upstream and raises them immediately downstream of the lock, reducing the impact of the scheme on water levels in long pounds, and reducing the amount of bank raising required.
“ It essentially halves the water level rise that you get from operating the scheme at high flow,” Hunt said. “So that more than halves the amount of bank raising we have to do.”
Indicative diagram of transfer lock system
There will be three transfer locks along the scheme in three of the canal’s longest pounds.
“They pay for themselves,” Hunt said. “They’re a lower cost solution to bank raising and they also reduce the disruption and cost considerably.”
There will be works within the canal, but they will be done during the closed season.
“It’s essentially putting in a new lock; a restriction with box in it and gates at either side, plus a pump station,” Hunt said.
Visualisation of a transfer lock
Without this solution, embankment raising would have had to have been done “in areas that are difficult to get to – along people’s back gardens in some places”, according to Carlaw.
The innovation of using transfer locks means that there will only be roughly 25km of bank raising split between both sides of the canal along the 120km that is used for the transfer – and it will only be a matter of 200mm to 400mm increase.
“It’ll be in discrete locations where the modelling has identified it is needed,” Coakley said. “And we’ve done a lot of engagement with local groups, particularly the canal user group, to make them aware of the project and the interfaces and to mitigate their concerns about making sure the canals remain open.”
The majority of bank raising will be on the long pounds, where the transfer locks will be, so the engineers will look to carry it out simultaneously with the lock installation during the closed season, where possible.
Where bank raising is required, engineers will seek to install like for like modifications, leaning on the experience of the CRT.
“There’s all sort of different banks [along the route], from sheet piling through to stone brickwork and some of it’s just earth with puddled clay to keep the seals in,” Hunt said. “So it’s like for like, but in most cases it’s literally just putting additional material on top and making sure it’s watertight.”
Reservoirs and water storage
The upgrades to the existing Daventry and Drayton reservoirs will be minimal, but crucial to the scheme.
The reservoirs are already connected to the canal and are used by the CRT for maintaining navigation.
“What we’re doing is putting in an ability to refill them,” Hunt said. “Where the transfer goes over the Braunston Summit there will be a main transfer pipeline that goes around Braunston Tunnel and then a feeder pipeline that allows us to top up the two reservoirs.
“Those two reservoirs are then essentially repurposed; they’re not really used for navigation anymore – they’re used for backup security supply.
“All that really means in terms of works is a pipeline for refilling and some works on the two outlets from the reservoirs. One of them we’re putting an extra syphon to allow more of the water to be taken, the other we’re putting in a new outlet with penstocks. So it’s actually helping the existing reservoir; it’s putting an increased drawdown capacity to help with measures in the interest of safety.”
There will also be a new 575M litre water storage facility constructed at Great Brickhill, just south of Milton Keynes. This new asset is intended to enhance resilience in the case of issues on the canal.
“It’s a storage pond with earth embankments – very standard,” Hunt said. “We’ve located it in an area where there’s a slight natural valley, so that reduces the amount of earthworks. The key things for us were A that it had a good seal – the right geology – and B, that we could get cut and fill balance so we don’t have to import a vast amount of materials to site.
“Most of the embankments will be 1.5-2m high. It’s only on the downstream crescent where it’s up to 7-8m.”
While not a major reservoir, it could still be a nice amenity for the local area. Discussions are still being had with landowners and developers on its final form and whether it will be open to the public.
Pipelines
The overall Guct breaks down into three distinct sections. The transfer along the canal is the middle section, which accounts for the majority of the route – but there are also pipelines at either end.
At the northern end, there is a roughly 15km pipeline to be constructed from the Minworth Advanced Water Treatment Plant to the canal.
While the Minworth pipeline is part of the Guct scheme, the work and funding is being procured under a separate contract.
“That work is on Severn Trent’s existing land, on their existing site and ties into its existing processes, so it will be a design and build tender which Severn Trent will run,” Coakley said.
Severn Trent started market engagement on the estimated £200M delivery contract last year.
This section of the pipeline will be tricky to install. “It’s essentially taking the pipeline out of Birmingham,” Hunt said. “There’s motorways, railways and all those sorts of things it has to bypass.”
The outfall into the Grand Union Canal has been designed to minimise maintenance requirements while bringing benefits to the canal.
“We’re designing a passive system that uses cascades to reoxygenate the water and reduce the flow rate,” Hunt said. “Effectively it’s a load of parallel channels with multiple hydraulic jumps – small weirs – and each of those introduces more oxygen back into the flow.”
At the southern end of Guct, another pipeline of roughly 28km will take water from the canal to the Luton service reservoir. This will cross the Dunstable Downs, an Area of Outstanding Natural Beauty, which is owned by the National Trust.
“We’re having to do a trenchless crossing there and we’re looking at different solutions,” Hunt said. “We’re looking at a directional drill, although it would be getting towards the upper envelope of what you could do [in terms of length] and you’d need to put a landing put in the middle of the downs. Alternatively, we are looking at just tunnelling straight through, but there’s questions over the resilience risk and the depths and geology and all of that.
“We need to look at what’s the best out of the two solutions in terms of deliverability and cost, but also in terms of planning.”
The works along the canal and on the southern pipeline to Luton will be procured by Affinity Water under the direct procurement for customers (DPC) model. An early market engagement notice shared by the company last year put the estimated contract value at £510M.
Placemaking
Along the route of the transfer, the project partners aim to improve amenities while delivering the necessary interventions.
“We’ve got design principles set out in the consultation, including canal-side specific ones,” Carlaw explained. “It’s very much looking at ensuring that whatever building that we put is right for the place. We actually have three canals – the Coventry, Oxford and Grand Union – and because they were built at different times they have different characters, so it’s very much about trying to set any new buildings within that place.”
The project will also look to input any benefits to the wider area too, such as shelters, benches, charging stations, pumps and more.
“There’s so many opportunities – we just want to hear from the communities first and foremost about what some of those things are,” Coakley said. “They might seem small to us but they’ll have huge benefits to communities in terms of canal access or wellness.”
Concerning where the southern pipeline will pass through the Dunstable Downs, Affinity has been speaking to the National Trust about biodiversity net gain opportunities, Carlaw said.
“The scheme is really in the gathering phase at the moment; it’s like ‘tell us the opportunities, tell us what is out there’,” she continued.
“Because it’s a long scheme we have 10 local authorities and 53 parish councils involved on the route. We are trying to unlock who are the organisations that can work collaboratively on some of that stuff.”
Timeline
The current statutory consultation is a key milestone on the path to delivering the DCO and, in turn, the scheme.
“The DCO application will go in around the middle of 2027,” Coakley said. “The back end of 2027 is when we would be looking for our Stage Three approval from Ofwat, which is when we could launch our procurement process.
“You need to have a bit of surety that the DCO process is going smoothly so the market feels it is worth investing time and effort into tendering for our project.”
The project is expected to take two to three years to construct, though many details are still to be finalised. The partnership is aiming to have the transfer online in 2033.Like what you've read? To receive New Civil Engineer's daily and weekly newsletters click here.