Rotating cylinders could be installed on a river in Carmarthenshire to steer debris, like fallen trees, away from bridge supports nearby.

It’s thought it could be the first use of so-called debris sweepers in the UK. The plan is for two of them to be installed in the River Cothi just upstream of the grade two-listed Pontargothi Bridge to help prevent logs and other material jamming up against the bridge.

Flooding has affected the village of Pontargothi in recent years and debris blockages at the bridge has been cited as a key cause, a planning statement submitted to Carmarthenshire Council said.

The document, on behalf of applicant South Wales Trunk Road Agent, said the rotating sweepers would deflect debris away from the bridge supports and through the main arch, reducing the amount of trapped material by 60-70%.

The planning statement said the devices were mainly used in the USA. “The applicant is not aware of other applications of debris sweepers in the UK,” it said.

The River Cothi drains a large catchment area before it joins the River Towy 2km downstream, and residents have reported a rise in flood events since Storm Callum in 2018.

South Wales Trunk Road Agent currently has to clear blocked debris from the bridge itself, resulting in the temporary closure of the A40 trunk road. It considered several options, such as doing nothing, relocating the bridge, installing so-called debris catchers and creating a storage area upstream to slow the flow of floodwater.

The preferred option initially was debris catchers – comprising a boom and piles – and engineers built a scale model of the bridge and section of river to test the proposition at different flow rates. They also built models of trees and observed them floating towards the bridge thousands of times.

Following further assessment the debris sweepers were the preferred option as they would have less impact on the river environment than the catchers and require two piles rather than 22. In both cases some debris would still need to be cleared, as is the case now, but the maintenance regime with the rotating sweepers would be lower. Model simulations with the sweepers also indicated they’d be effective.

The planning statement said consultation has taken place with Cross Hands and District Angling Association, which has fishing rights on the affected stretch of river, environment body Natural Resources Wales, and local residents at meetings in January and February this year.

A CCTV camera is also proposed to monitor the two sweepers, plus new equipment to monitor river flows. South Wales Trunk Road Agent, which works on behalf of the Welsh Government, said the project would taken around 10 weeks, subject to planning permission from the council. A site compound is proposed on the river embankment, and “stop” and “go” boards would be used on the A40 when equipment is delivered.

A member of staff at The Cresselly Arms, just by the bridge, said engineers at the meetings were open and honest about the plans but that the feeling was “the jury was still out”.

Questions were raised, he said, about the noise the rotating devices would make, their visual impact and effectiveness, whether more could be done to prevent trees entering the river upstream, and whether more data could be collected before any work started.

He said flooding affected the pub despite its best efforts and that when debris blocked the bridge the River Cothi could be five to six feet higher upstream than downstream. “The speed of the water is immense,” he said.