LORRIES carrying thousands of tonnes of soil could increase congestion on the A34 for three years during the construction of a £120m flood channel, council transport bosses have warned.

Environment Agency (EA) officials are working on a solution but admitted excavated material for the four-mile channel – from Seacourt Park and Ride to Sandford Lock – would be removed using the A34.

But Oxfordshire County Council transport bosses said a 'comprehensive' mitigation strategy was needed as the project was taking place on a 'very busy and constrained' part of the city's road network.

The county council's principal transport planner, Chanika Farmer, said: "Impacts will not just be related to the number of construction vehicles on the network but will also be brought about by construction enabling works, such as road closures and diversion of traffic, buses and other road users.

"It is likely that mitigation strategy will have to be comprehensive, particularly as works are taking place on parts of the transport network that are very busy and constrained."

The channel has been designed to protect thousands of homes by taking water away from the city centre to prevent the severe flooding which hit the city in 2007, 2012 and again in 2014.

The three-year project, which could begin in 2018, would see 400,000m3 of soil, gravel, sand, clay and silt excavated and transported away.

It comes after new figures revealed an estimated 80,818 vehicles – including more than 8,000 HGVs, pass Oxford every day last year, 15 per cent higher than five years earlier.

Documents seen by The Oxford Times revealed the main access for construction vehicles would be at the South Hinksey junction to the A34, a move the EA said would reduce the number of lorries using the city's arterial roads.

A contingency plan is being investigated – to build a storage site south of Hinksey Heights golf course with lorries using an access overbridge to avoid the road.

A 'conveyor' could also be built to transport materials over the A34 instead.

But the plan hinges on ongoing discussions with landowners, while Highways England, in charge of the A34, said it would object to a future planning application for the flood alleviation channel unless it included the contingency plan.

Such an application is due to be submitted in February, provided it is signed off by central government.

Dr Kate Prendergast, from the Sustainable Flood Plan Group, said the channel was a 'done deal' but cheaper, less disruptive options should have been explored.

She said: "The last thing we want is more traffic coming off the A34.

"I'm sure there are cheaper and less disruptive solutions than the flood channel – I'm concerned what the real drivers of the channel are.

"We are digging up historic flood plain land with habitats we should be preserving.

"I'm not sure where the channel fits in with the plans to build thousands more homes in Oxford, we certainly need to start thinking about more environmentally-friendly answers."

Oxford Preservation Trust, which owns 25 per cent of the land used for the channel, said it remained 'unconvinced' the benefit of the scheme would outweigh the harm to Oxford's green setting.

Director Debbie Dance said: "There remain a number of unanswered questions on how it will work technically and the extent to which any improvements to the flooding situation can be achieved.

"We cannot see any references to plans showing how public access to might be improved or any details as to how environmental improvements to land between North Hinksey and South Hinksey would be incorporated into the scheme."

Sally Freeman, from the EA's Oxford Flood Alleviation Scheme, said: "We will produce a traffic management plan and submit this as part of our planning application.

"This will include using the A34 to remove excavated material from site.

"We are investigating using the field south of Hinksey Heights to permanently store some of our excavated material.

"This material would be transported by lorry across an access bridge to South Hinksey."

The project is still £4.4m short of its funding target, which it needs to reach by November, but the EA said it was confident the remaining investment would be found.