Mapping the history beneath Preston Brook Tunnel

For the next few hours, they’ll make their way slowly through the murky passage, deep beneath the Cheshire countryside, carefully checking for any cracks, loose bricks or subtle changes to the structure. It’s all part of a rigorous, six-yearly inspection to ensure this historic tunnel remains safe, open and navigable, work that is only possible thanks to the continued support of people who care about the future of our waterways. 

Designed by renowned canal pioneer James Brindley, Preston Tunnel was part of his wider vision for the Trent & Mersey Canal – an ambitious project to connect two of England’s great rivers and speed up the flow of goods across the country. Work began on the tunnel in 1766, but sadly, Brindley wouldn’t live to see it. Following his untimely death in 1772, his brother-in-law, Hugh Henshall, took up the mantle, and Preston Brook Tunnel finally opened to boat traffic three years later.

At the time, it was one of the longest and most ambitious tunnels ever constructed, a vital link on a trade route that carried pottery, salt and clay from the burgeoning industries of the North West to the Irish Sea and beyond. Today, the Grade II-listed tunnel is recognised as a marvel of the age; but caring for such an old structure is no easy task.  

Like all our tunnels, Preston Brook is inspected regularly, so we can assess its condition and plan for any repairs. And here, that degree of care is particularly important.  

In 1982, following some minor repairs the year before, a 30-metre section of the tunnel collapsed, taking part of the Post Office above with it. Thankfully, no one was hurt, but it’s a stark reminder of how important it is to understand exactly what’s going on, unseen, beneath our feet.

To improve this understanding, our engineers are combining traditional methods with remarkable new technology. Earlier this year, as part of its six-yearly principal inspection, we carried out a comprehensive survey to create a digital twin of the tunnel – a highly accurate three-dimensional model that allows us to study the structure in extraordinary detail. 

A specially equipped boat, bristling with sensors, travelled through the darkness, using laser scanning, photography and sonar to record everything above and below the waterline. The result is one of the largest and most detailed digital models the Trust has ever produced. 

“It allows us to re‑examine the tunnel without having to return to the site,” principal engineer Peter Simpson explains. “If we miss a measurement or want to examine a particular feature, we can simply refer to the model.” 

And the benefits aren’t just practical; they’re financial too. By investing in better data now, we can reduce uncertainty and avoid costly surprises later on. 

“Potentially, we could save tens of thousands of pounds on future repair projects,” says Peter. “It means fewer assumptions, more accurate calculations, and more confidence that we’re choosing the right solution first time.” 

For all the benefits of modern technology, a digital model can never tell the whole story. Our engineers still have to go into the tunnel and put their hands – and ears – to the bricks. 

“We do what’s called a tactile inspection,” says Peter. “We go in, and we tap the tunnel walls. We're listening for changes in sound to detect voids between the brickwork, finding loose masonry, looking for cracks, and monitoring any changes. The technology is a great tool to have, but it can't replace what an engineer can physically see, hear and feel on site.”  

Thanks to your support, we’re able to ensure we have experts like Peter and his team to continue monitoring and maintaining extraordinary structures like Preston Brook Tunnel, preserving the history beneath our feet and keeping our canals alive for generations to come.