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Rail lines can only be reopened once the bridge has been inspected and confirmed as being safe, and Network Rail is charged “delay minutes” while the bridge is closed. The charges vary depending on the type of line and rail service that is affected but can be substantial and quickly mount up.

What’s more, post-flood inspections are usually done by divers, who can only enter the water when conditions allow and rely on touch to establish whether damage has occurred.

If the bridge is confirmed as high risk, we put a board up and when the water level hits a predetermined level, the bridge is closed. If we can prove the bridge is not high risk, that closure board can be removed and the impact on travellers is massive as we’re no longer closing structures unnecessarily

But some Network Rail regions are now using a custom-built data gathering system from specialist Ultrabeam to make inspections more efficient and even to reopen bridges more quickly after floods.

In November 2024, the company was called out to inspect Evesham Viaduct on the River Avon during a flood event. Arriving on site within 24 hours, the team carried out a survey and processed the data within four hours, showing that the bridge condition allowed for it to be reopened the same day. It was a further seven days before divers were able to enter the water to inspect the bridge, meaning the use of the new system represented an estimated £3.5M saving in delay fees.

As Network Rail senior design engineer for drainage and scour management Iain Fox explains, there is nothing radical about the technology involved. But combined with equipment that is custom-built for the sector, it offers a big step change in how scour risk is assessed.

Historically, surveyors use manual methods – ‘a person with a stick’ – to take depth measurements at predetermined cross-sections both at the structure and at set locations upstream and downstream.

“We create what’s called a ‘1-D model’ which interpolates those points – it basically joins the dots,” says Fox. “Where the new system comes in is that we get a full, detailed bathymetric survey so we know exactly what’s happening, and we use 3D computational fluid dynamics (CFD) to make hydraulic models. It gives us absolute precision rather than guessing what’s going on between cross-sections spaced 30m apart.”

The system was first used by Network Rail at Reddish Vale Viaduct near Stockport, explains Mark Brundle – programme engineering manager in works delivery for North West & Central Region.

“We were looking to put scour protection on the viaduct and someone suggested the Ultrabeam technology might be useful to survey the bed for the design of the scheme. Within about nine months of putting the protection in place, there was a massive storm and it washed out the bed right down to the foundation level of the piers,” Brundle recalls.

“We got Ultrabeam back to do a scan to check the damage, as it was difficult to see with all the turbidity and debris in the water. They also had the ability to overlay the as-built drawings of the viaduct on the underwater scan so that we could pinpoint where the foundations were. It gave us a really good plan of how to attack the repair works,” Brundle says.

Once the repair had been carried out, two subsequent surveys were commissioned to establish whether the changes were having any impact on the river environment. “We’d used rock armour to replace the embankment, and the surveys enabled us to demonstrate to the Environment Agency that the repair was not having a detrimental impact downstream. It would have been impossible using divers or manual surveys.”

Equipment and data collection

Ultrabeam’s custom-built equipment carries out a full sonar scan of the riverbed over the appropriate length of river and the below-water parts of the structure, as well as above-water laser scans of the bridge itself. These can be combined to provide engineers with a comprehensive picture of how they interface.

Data collection is carried out by a compact, modular survey platform dubbed Black Swan. It is built around a lightweight, carbon fibre chassis on inflatable buoyancy chambers, and has flexible mounting configurations for multibeam echosounders, Lidar sensors, acquisition pods, cameras and control systems.

“We’ve enhanced equipment that was primarily developed for use in the offshore oil and gas industry to get the best data we can acquire,” says Ultrabeam technical director Gabriel Walton.

“Its light weight means it can be lifted over fences and stiles and doesn’t need a slipway to launch. It carries a lot of tech and has four thrusters, so it can move in any direction and hold its position really tightly. It is really useful to be able to collect data both above and below water. If we just collected underwater data, it would leave us with a big gap in comparable data when water levels rise due to flooding,” he adds.

“We have precise control of the movement and orientation of the vehicles that the sensors are attached to. Then we fuse the underwater data with above-water data to build a digital 3D twin of the asset, enabling us to see the structure, any undercutting or deformation on the brickwork and so on.”

Ultrabeam’s system is a different beast to sensor-reliant set-ups that promise real-time detection of scour. These use fixed sensors that are positioned to monitor the locations where scour is expected to occur.

“If flooding causes debris to become wedged on the structure, it can completely change the hydraulics,” explains Fox. “You might build a really detailed CFD model and have your sensors placed to monitor where you expect scour to start, but if you’ve got something that changes the hydraulics, the scour hole is likely to start somewhere else completely.

“The benefit of the Ultrabeam solution is that it scans the entire structure, upstream and downstream. To put fixed sensors everywhere would be very expensive; even a two span bridge would be £100,000- £150,000.”

We have precise control of the movement and orientation of the vehicles that the sensors are attached to. Then we fuse the underwater data with above-water data to build a digital 3D twin of the asset, enabling us to see the structure, any undercutting or deformation on the brickwork and so on

Detailed assessments

While the system has proved effective in emergency situations, it is in the wider assessment of scour risk that Fox sees its greatest potential.

All bridges over waterways are classified according to scour risk and assessed in a two-stage process.

The initial, high-level assessment includes a lot of assumptions and no inspections or modelling are involved. Structures identified as high risk then go to the more detailed stage two assessment.

“We check the foundation depth in relation to current bed levels and get a hydraulic survey – conventionally this is a standard survey with interpolated levels, but now we get a detailed bathymetric survey. If it’s still showing as high risk, we can do a 3D CFD model that gives us more details about where a scour hole might be along with information such as flow conditions. Having the data from the bathymetric survey makes the model very accurate,” Fox says.

“If the bridge is confirmed as high risk, we put a board up and when the water level hits a predetermined level, the bridge is closed. If we can prove the bridge is not high risk, that closure board can be removed and the impact on travellers is massive as we’re no longer closing structures unnecessarily.”

Fox confirms that Network Rail currently has 508 bridges on the high-risk register, 368 of which have been confirmed.

North West & Central region is already using the system to carry out more detailed assessments, as Brundle explains.

“We engaged Ultrabeam to start looking at our high-risk scour structures, eliminating the person with the stick process and getting in there with more accuracy so we have a better idea of the situation.

“The empirical process throws out a number that relates to channel width, abutment sizes, fluid dynamics and depth of foundations among other things, but what we were seeing was that some bridges weren’t as high risk as predicted. It’s a refinement tool that we are using to understand where to direct our resources.”

The equipment is useful on coastal and estuarial structures, where tidal conditions would normally dictate access, Brundle says.

Ultrabeam has also developed a new vehicle that his team is using to inspect culverts.

“Normally you have to dewater them which can cost a lot of money. Ultrabeam came up with a pipe scanner that we could send in so we don’t have to dewater and we can get a profile and video of what is going on inside it. We trialled it and it works very well,” says Brundle.

He hopes that adoption by other asset owners will drive the system’s cost down so it can be used more widely.

“It is an expensive process and we are quite frugal with it at the moment. But we aren’t the only organisation with assets over rivers – local authorities, National Highways and so on also have a need for it.”

Ultrabeam’s latest development is an augmented reality asset inspection system known as Echo Vision that gives clients the means to view the 3D data that is collected via a wearable headset.

This is particularly useful on site when engineers need to rapidly assess flood conditions.

“We do a survey, collect 3D data, then hand over the headset to the Network Rail engineer who can look towards the structure and ‘see’ what’s happening below the water. We still provide the usual engineering deliverables, cross-sections and so on – this is just a way to aid interpretation of what’s happening on the bridge,” Walton says.

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