Specialist divers are pouring underwater concrete to protect two major railway viaducts carrying the West Coast main line in Carlisle.

Detailed laser surveys carried out by Network Rail showed fast flowing water on the River Eden has caused parts of the riverbed to wash away posing a risk to the viaduct foundations.

Because of the deteriorating riverbed condition, trains have been running at reduced speeds of 20mph over the Victorian and 1940s-built structures.

Approximately 900 tonnes of special setting concrete is now being poured by the diving teams to provide a stable platform for the viaducts’ columns or piers.

The immediate repairs are being made to the structures as part of a £1.3m Great North Rail Project investment.

Once this first phase of work is complete in the next few weeks, trains will be able to run at full speed of 100mph over the viaducts, meaning faster, more reliable journeys for passengers and freight.

Chris Pye, Network Rail infrastructure director for the north-west, said: “It’s not every day you call in diving teams to help improve railway lines, but this work is essential to keep passenger and freight trains moving on the West Coast main line over the River Eden in Carlisle.

“After using the latest laser mapping technology to give detailed scans of the riverbed we brought this work forward so we could secure this crucial rail link between England and Scotland for the winter ready for the second phase of work next summer.”

The professional divers from Scour Protection Ltd work in challenging conditions to shore up underwater structures like bridges and viaducts around the UK and beyond. Water visibility in the River Eden is particularly poor, with a lot of the work done by touch alone.

More than 2,200 tonnes of rock has also temporarily been put into the river to calm the waters and divert its flow so the divers can work under the surface.

Network Rail’s ecology teams have been working closely with the Environment Agency and Natural England to monitor the river and make sure this work has the least impact possible. The concrete is made from a mix with ‘zero leach’ meaning it’s wildlife friendly and safe for the environment.

The second phase of viaduct strengthening work will take place in Summer 2022 as a permanent fix to the riverbed erosion.