Engineers have questioned the cost of building the £175M Thames Garden Bridge, which is due before planners at Westminster Council in early December.
Independent consultant Simon Bourne insisted a bridge with the same look, feel and functionality could be created for less than a third of the cost.
And bridge consultant Flint & Neill’s chief operating officer Ian Firth has said that the proposed scheme fails to satisfy either artistic or practical criteria.
The proposed Thames Garden Bridge has been masterminded by London 2012 opening ceremony cauldron designer Thomas Heatherwick with support from engineering firm Arup. Actress and campaigner Joanna Lumley has given it celebrity endorsement.
The project received a major boost recently when it secured planning permission from Lambeth Council. Plans will go before London mayor Boris Johnson if approved by Westminster next month.
If Johnson gives it the final go ahead, the ambitious scheme to create a garden walkway across the Thames from London’s South Bank could be underway by the spring.
The project’s promoter, registered charity the Garden Bridge Trust, has received pledges worth £110M towards the total cost of the scheme, including £30M from Transport for London, the same amount from theTreasury and, most recently, £3M from banking firm Citigroup.
But Bourne questioned the need for the money to be raised at all.“By my sums, this structure works out at £25,000/m2,” he told NCE. This is up to 10 times what a beautifully designed bridge should cost.
“At the same time, for £175M you could get up to 40ha of fabulous new garden - but the Garden Bridge Trust wants to deliver less than 1ha.”
Bourne said the use of copper cladding on the bridge was unnecessary and ramped up the cost for no reason.
“We don’t clad bridges,” he said. “Not since the Victorian era. The structure is the purest element and should be exhibited as the artistic form.
“It smacks of using Victorian technology rather than 21st Century methods. With the precision finishes available now, you could have copper-coloured concrete that would give the same effect at a fraction of the cost.”
Bourne estimated that a “beautiful” bridge could be created for less than £50M but that a crossing at that point of the river - between Westminster and Blackfriars Bridges - was not the best use of taxpayers’ money.
“I don’t think it is needed as infrastructure, so there is an argument that it should be entirely privately funded,” he said.
“There are adjacent bridges close by so it’s not needed as a pedestrian link. It’s a garden space, which I am keen on, but you could have the whole of Hyde Park turned into a garden for £175M.”
Firth said that the scheme could not be justified as an artistic venture when it would, he claimed, damage existing views along the Thames.
“It might be a fantastic scheme down the river at Bermondsey,” he said. “But not on that location, by some of the most special buildings in London.”
Maintaining the structure would be expensive, as well as building it, Firth added.
“No steel bridge wants lots of wet soil on it - it’s a nightmare,” he said. “No self-respecting highways authority has plants on its bridges.
“I foresee problems maintaining the bridge; lots of painting and repair work. There are issues to be addressed with the design.”
A spokesman for the Garden Bridge Trust defended the cost of the project, saying the structure was “unique”.
“As well as a transport link, it will also be a new public garden, which adds to the load the bridge must hold,” said the spokesman.
“The size and scale of this project, as well as providing a host of benefits, requires considerable funding. The Garden Bridge Trust expects to be able to deliver the bridge for a cost of £175M.
“With a project of this scale, the Trust needs to allow for a prudent level of risk and contingency, which is included within the £175M.” Arup declined to comment.
Why you wouldn’t be able to cycle on the bridge - or walk on it after midnight
The Garden Bridge Trust this week admitted that cyclists would have to dismount to use the £175M crossing – and that it would be closed from midnight.
The organisation also conceded that a proposal existed to ensure groups of nine people or more would have to inform the Trust in advance of using the bridge.
Trust executive director Bee Emmott wrote an open letter in response to criticism of the proposed garden bridge in the media.
“Cyclists would be able to push their bikes over the bridge. However the Trust needs to ensure the bridge be a safe and pedestrian friendly environment,” said the letter.
It added that the maximum number of guests allowed to visit without informing the Trust was not yet set.
“Once this number is confirmed, groups of greater than that size visiting the bridge will be requested to inform the Trust of their visit,” it said.
The Garden Bridge will be open between 6am and midnight.
“The timing structure has been put in place to mitigate concerns about noise carrying to residential areas, and is a condition of the planning application,” said the letter.
The Trust admitted it was exploring the possibility of holding private events on the bridge.
“Every effort would be made to ensure the bridge remains open to the general public during these events, but there may be occasions where the bridge is closed,” said Emmott.
“The Trust reiterates that the Garden Bridge is fully intended for public use. It will be an open space to be used by everyone. People will be encouraged to meet and spend time there. It will provide a crossing to link the cultural centres and tourist attractions on the North and South Banks.”