Raising a busy Fenland road in order to reduce the length of time it is shut by winter floods could cost almost five times as much as previously thought.
The stark warning about the scale of the works needed to keep the A1101 Welney Wash Road open for longer was set out during a flood summit held in Downham Market on Friday.
But environment secretary and South West Norfolk MP Elizabeth Truss, who chaired the meeting, insisted that a solution must be found.
She said: “It’s an A road. It’s not acceptable for it to be closed for so long. I think the costs of that are growing for local residents and businesses.”
The road is regularly flooded in the winter because it runs across the Ouse Washes flood storage reservoir, which is part of a national flood management network and is regularly left submerged in bad weather.
When necessary, water is released from the River Great Ouse in the Bedford area so that it can be discharged into the sea at The Wash.
But that forces drivers who would normally use the A1101 to cross the county boundary between Norfolk and Cambridgeshire to take detours of up to 20 miles via Wisbech or Downham Market.
In the summer of 2014, funding was secured to carry out a feasibility study into whether the height of the road could be increased in order to cut the length of the closures.
The meeting heard that closures caused by flooding would be reduced by more than 50 per cent if the minimum height of the road was raised by one metre.
Initial estimates put forward when the study funding was first announced suggested the work would cost around £1 million to complete.
But Dave Stephens, Norfolk County Council’s network management team manager, said he feared achieving the full metre height increase would cost around £5 million, because of the need for more extensive works.
He added that such a height increase could not be achieved using conventional maintenance techniques.
Lower cost alternatives are also being examined, including raising the road by half a metre, which Mr Stephens said could be delivered for around £1.1 million, and achieve a 38 per cent reduction in closure times. Studies into them are set to continue.
Local representatives said such a rise would mean the road could still be open to traffic now.
But North East Cambridgeshire MP Stephen Barclay questioned why raising the road by a metre would cost so much more than half a metre.
Mr Stephens explained that, in order to achieve the level of closure reduction sought, almost 1,000 metres of the road, around two-thirds of a mile, would have to be raised by an average of 73 centimetres.
But he admitted the council could not afford to fund the scheme alone, adding: “It would need a significant contribution from other sources.”
The meeting, which was attended by a number of parish and district council representatives from around the area as well as members of several local drainage boards, also heard concerns that a dam could be created if culverts were not installed to allow the water to drain away in times of flooding.
And Mr Stephens admitted that modelling of the environmental impact of the project still needed to be carried out.
However, Environment Agency officials told the meeting that money was available in its current investment programme, which covers the period up until 2021, to go towards the project.
And Ms Truss indicated talks should also be held with both Cambridgeshire County Council and the area’s two local enterprise partnerships to encourage them to contribute, because of the benefits they would also generate from the works.
But she added: “I’m keen to see the project progress as soon as possible. It does seem to be taking quite some time.”
The meeting was also told of concerns about the signs warning drivers about the depth of flood water on the road either not recording the maximum depth or sometimes not working at all, due to lack of signal coverage.
A driver had to be rescued by fire crews on Thursday after becoming stranded in the waters.