A series of drastic measures - including a flood barrier across the river at Great Yarmouth - are needed to protect the Broads from the effects of climate change, an influential group has warned.

Paul Rice, chairman of the Broads Society, said a major new network of Dutch-style drainage dykes should also be considered, to protect the waterways from the impact of rising sea levels.

The Society, which was set up to secure the future of the Broads, declared a 'climate emergency' for the river network at its recent AGM.

Mr Rice said there was no time for delay and that specific actions were urgently required. He said water levels had been rising in the region over recent years and that this was likely to continue.

Without swift action, he said the Broads would become increasingly vulnerable to flooding, as a result of seawater moving up the network from the sea at Yarmouth, and that this would threaten homes and businesses and the future of the area as a cherished landscape.

A flood barrier at Yarmouth could prevent water from coming in from the sea, while more drainage dykes could help by taking excess water away from the main rivers, reducing their levels.

Such large and expensive infrastructure projects would take several years to deliver and need the support of organisations like the Broads Authority and the Environment Agency.

The Environment Agency said it was an option currently being considered as part of its strategy for managing flood risk.

But Mr Rice, who is also a flood warden, said now was the time to move the idea up the agenda.

“We are not talking one in 100-year events, we are not even talking one in 50-year events, we are talking about now," he added.

“In the last three years, since I became a flood warden, we have had extended periods where the water levels don’t go down the way they did 10 years ago. Climate change is definitely having an impact.

“If we don’t start working with nature, we’re going to have a major problem in the next 10 years."

He said current measures were not enough to deal with the issue. “The difficulty is what do we do about the flood alleviation schemes at the moment. They are not fit for purpose.

“We are expecting more floods over the Christmas period, we need to do something now, we can’t wait. If we don’t do something now, we are going to lose a lot of things."

Some experts predict a sea-level rise of between half a metre (19in) and a metre (39in) over the next 100 years. A one-metre rise would put much of the Broads underwater.

Mr Rice's comments follow a recent interview in which John Packman, chief executive of the Broads Authority, spoke about the impact of climate change. He accepted that the area would see major changes as a result of sea-level rises.

Dr Packman said the Broads landscape of the future would be more like how the waterways had appeared in Roman times than now.

The effects of rising water levels are already being felt on the Broads with, for instance, less clearance for boats to pass under small bridges like at Potter Heigham than in the past. This closes off some areas of the waterways to larger craft. And many riverside areas are already more prone to flooding.

James May, director of Maycraft, a family-run boatyard near Potter Heigham, said rising water levels were becoming an increasing problem.

"We are flooded out every year now. It happens quite often. It comes in through the slipways and out the door completely flooding our access path. It's not just a problem for us, it's every boatyard on the Broads."

Mr May said events like this used to happen every three or four years but now it happened regularly and he expected the floodwater would be back in a few weeks.

He said the flooding means they are unable to bring boats in and that electric tools cannot be used, meaning works and repairs are delayed.

He welcomed the suggestion of a flood barrier put forward as an idea by the Broads Society.

"The Thames doesn't flood, Holland doesn't flood, they have a barrier. Why don't we have one? A barrier at Yarmouth would be a positive step, it would help no end," Mr May added.

Mr Rice said the Broads Society was determined to secure a sustainable future for the waterways.

He said a flood barrier across the river at Yarmouth would be "helpful", and outlined how a Dutch-style system of ditches would also assist, as they could be filled with water in the winter - when levels are highest - for use by farmers in the summer, with reeds stopping them from drying out. He described this as a “win-win”.

The issue of rising water levels on the Broads and their vulnerability to climate change has been on the agenda for some time.

In 2008, there was anger after draft proposals from Natural England suggested surrendering a large area of Broadland, including several villages, to rising water levels.

While Mr Rice said Norfolk had a “stay of execution” at the time, he worried in the future it could become policy again, or happen by accident.

The Roman Broads

Experts suggest that as a result of climate change, the Broads of the future will look more how they were in the Roman period than they do now.

Back then, the rivers entered the sea via a vast saltwater estuary called Gariensis, near where Great Yarmouth now stands.

The Romans built defensive forts on either side, at Caister in the north and Burgh Castle in the south. Burgh was also the site of a huge harbour for ships which traded with Rome and throughout the empire. The estuary gradually silted up and became Breydon Water.

The area further inland now covered by the Broads would have been a damp place of marsh, fen, reeds, and water-logged peat soil, with large areas underwater.

The peat was later dugout during the medieval period, creating the 'Broads' - the areas of open water - themselves.

One theory is that during the Roman period one of the local rivers actually flowed the opposite way to its current course.

The River Thurne now flows in a rough south westerly direction, joining the River Bure and then continuing to the sea at Yarmouth.

But some have suggested it previously followed a channel from west to east, eventually reaching the North Sea between Somerton and Horsey. Roman finds near to Martham have supported this theory.

The river created the Isle of Flegg, a vast area of land hemmed in by the Thurne, to the north and the Bure to the south.