Safety concerns have forced Powys County Council to impose traffic restrictions on a section of the A4077 between Gilwern and Crickhowell.

The move was taken after a crack was discovered in the road and slippage in the embankment below during a routine highways inspection.

Traffic lights are now restricting use of a 50-metre section of the eastbound lane while the council and the Canal and River Trust carry out investigations to establish the cause of the problem.

And it could be months before it’s resolved - which is not good news for motorists already coping with road closures and diversions in the area connected to the A465 Heads of the Valleys dualing project.

Councillor John Brunt, Cabinet Member for Highways, said, “We would like to apologise for the inconvenience this will cause but the lights are needed in the interest of road safety.

“In the meantime, remedial drainage work will be carried out to reduce the stress on this section of the road while we wait for the results of our joint investigation.”

The council says it is too early to speculate on the cause of the problem but a topographical survey is already underway to see if there is any further instability in the embankment.

Work on providing remedial drainage will start in the next two to three weeks but, as there is no existing drainage at the site, it will be necessary to create drainage channels which can be connected to the nearest drainage infrastructure - and that could mean extending the traffic restrictions.

Monmouthshire County Councillor Simon Howarth, represents many local residents who use the A4077 every day.

He said safety was always the first priority but, with the area already ‘awash’ with extra traffic due to the A465 scheme, he hoped the investigations wouldn’t take longer than necessary - given that traffic lights had previously been in operation on the A40 at Glangwyrney for 18 months!

The work is certainly going to take some time as the Canal and River Trust is unable to even start its own investigations until October.

“We don’t believe there’s any significant risk to the canal or anyone using it, but we’re going to drain the canal anyway, to help us with the investigation process,” said a spokesperson.

“Although it has been suggested there may be a minor leak in the canal, the cause could be something else, such as groundwater run-off.

“The council will be investigating whether there’s a problem within their section of the embankment, or whether it’s an issue with highway runoff.”

The task for specialists from the Canal and River Trust will be to drain the canal from bridge 103 Gilwern main road to bridge 109 Gilwern woods.

A stop-plank dam will be installed at both locations and the canal will be drained through a sluice valve into the River Clydach - a system that has been used for the past 200 years.

“When 75 per cent of the water is removed we will enlist specialist contractors who will carry out a fish rescue by Electro fishing,” she explained.

This involves passing a current through the canal water, stunning the fish which float to the surface.

The fish, which are unharmed by the procedure, are then transported in plastic drums to sections of the canal where works are not required.

Once the remainder of the water is removed, engineers will inspect the canal bed to determine if any repairs are needed.

Afterwards the canal will be refilled by closing the sluice/drain valve and removing the top plank of the dam, which allows water to flow over the top and refill the area.

When tested, if successful, the remaining planks are removed and the fish swim back to their original locations.