Thousands of acres of Norfolk farmland could suffer catastrophic flooding unless rivers are dredged.

The warning came as drainage board representatives met MPs, Environment Agency managers and one of the government's top flood defence officials at Downham Market Town Hall today, to discuss proposals to raise the road across Welney Washes, to stop it flooding.

Officers from Norfolk County Council, which has proposed the £1.1m scheme, said it was at its early stages and £700,000 in extra funding would need to be found to raise the lowest parts of the A1101 Welney Causeway.

A feasibility study would also need to be carried out, to check whether the work would cut the number of the days each winter the road is closed, leaving villagers and through traffic facing long detours.

But the meeting heard drainage boards fear siltation in the tidal Ouse, which has occurred since Denver Sluice was damaged by last December's tidal surge, has left tens of thousands of acres at risk of flooding.

Ken Goodger, of the Upwell Internal Drainage Board, which pumps water off the Fens into the Ouse via the Old Bedford River, said: 'This year we only pumped 50pc of what we pumped last year. Had we pumped as much as we did last winter, those rivers would have been far fuller and there would have been an incident.

'There will be a serious issue. There will be a Somerset here, if it's not dredged.'

Tens of thousands of acres of farmland were flooded and villages cut off for weeks last winter after rivers on the Somerset Levels burst their banks. The EA was criticised for failing to dredge watercourses, which drain an area similar to the West Norfolk Fens.

Mr Goodger said the Hundred Foot reach of the tidal Ouse was half the width it was when he was a boy.

Gerald Allison, manager of the Downham Market group of drainage boards, said its members were seeking assurances that Denver Sluice would continue to be maintained and that the Environment Agency would have a programme of de-silting, dredging and weed cutting to ensure the river system was 'fit for purpose'.

He added: 'The boards pump water from the Fens via their pumping stations into the EA-maintained river system and if these EA systems are not maintained and kept free of debris, the boards would have nowhere to evacuate their water to.'

Mr Allison said agricultural land should be regarded as being of high value when drainage boards applied for funding to protect it.

He also asked whether the boards could be given more say over how the levies they collect from farmers were spent.

Julie Foley, area manager for the EA, said the secretary of state had committed £270m to flood defences. She said repairs to Denver Sluice were in the pipeline, adding bed levels in the tidal river were at their lowest for 30 years.

But West Norfolk councillor Brian Long, who sits on the King's Lynn Conservancy Board, which maintains navigation to and from the port of Lynn, said: 'Over the last few months, we have seen deposition start again, when before that's been pushed seaward by the water washing out.'

Roger Sexton, chair of the East Anglian Waterways Association, said: 'The tidal river badly needs dredging in places, the banks are barely up to the job.'

Mrs Foley said the EA did what it had been asked to do by central government. She said it would have an 'open dialogue' with the drainage boards.

David Lees, head of emergency preparedness and response co-ordination at Defra, said he would be taking comments from the meeting to Environment Secretary Owen Paterson, who had asked him to report back.

South West Norfolk MP Elizabeth Truss said the meeting had cleared up a number of issues. She said it was clear drainage boards could take on extra work in return for keeping more of their precepts.

She added work needed to be done on the Welney proposal, to find out how many more days the road might remain open if the money were spent.