The Environment Agency is warning that rising tides mean that tens of thousands of pounds will have to be spent on flood defences.

It says that high tides on the River Usk could rise by half a metre within the next 50 years. Now Newport council is asking developers working on projects on the east bank of the River Usk to build up their defences by the same level.

The full cost of the schemes is not yet fully known, but the Environment Agency said it will run into tens of millions of pounds.

Richard Owen, project and design manager for Newport council, said: "The east bank of the river is worst affected, and areas around Corporation Road are quite low. Land on the city side is higher."

Currently land on the east side of the river is about eight and a half metres above average sea level.

The Environment Agency predicts global warning could cause the highest tides in 50 years' time to rise half a metre.

Martin Watkins, communications officer with the Environment Agency Wales, said: "This is a theoretical risk but it could happen at any time.

"If all the conditions come together to create a major flood, the defences are not adequate to protect against the worst case scenario."

The highest tide ever recorded on the river had a level of 8.4m.

Mr Owen said: "We are looking for a defence level of just over nine metres, which would defend against what the experts refer to as a '1 in 1000 year flood' in 50 years time."

Mr Owen said current defences are adequate, but the council wants to ensure the city is prepared for the worst.

"The aim is to see a comprehensive set of improved defences in place on the east bank of the River in the length between the railway bridge and the SDR bridge in place in the next two years."

Newport council has applied to raise ground levels between Town Bridge and the railway bridge, but other areas are the responsibility of developers.

The WDA has submitted an application for the development in the Rodney Parade area, set for a £50 million development including 400 waterside homes.

Taylor Woodrow and Persimmon Homes are currently negotiating with the council on their developments close to Corporation Road.

Mr Owen said: "In a number of cases, developers are dealing with sites that have been in industrial use in the past, so they are bringing clean material onto the site in any case.

"Part of the package agreed with developers is that the council will become responsible for the river edge of the sites. This enables us to improve public access to it, and to maintain defences in future."

The low-lying land is causing problems for some householders living in affected wards, with insurance premiums growing.

Lliswerry councillor Allan Morris said: "Insurance companies have got hold of this information from the Environment Agency and as a result people in my ward are having difficulty insuring their properties.

"Premiums for people living in affected areas are going up and it's a big problem. "I think the council's proactive response is an excellent idea. It's a way of safeguarding existing developments and households as well as ensuring new developments are safe." A spokesman for Newport Unlimited said it is not possible to put a figure on how much the work will cost as each developer will use their own methods.

He added: "We do not believe that flood risk is a serious impediment to the regeneration of central Newport."

The city centre side of the river is less affected by the problem, because ground levels are generally higher already.

However the council and Newport Unlimited say they will work with the Environment Agency to improve defences where needed.