Edinburgh's Coltbridge Viaduct shows small projects can make a big difference - John Yellowlees

John Yellowlees, Scottish Chair, CILTJohn Yellowlees, Scottish Chair, CILT
John Yellowlees, Scottish Chair, CILT
Talk of transport infrastructure is often dominated by the mega-schemes, which are either strategic investments or vanity projects depending on whether or not you are in favour. Sometimes, however, the smaller schemes repay attention, and one such occurred during the early months of lockdown last year in the leafy Edinburgh suburb of Murrayfield.

The three-arch masonry Coltbridge Viaduct across the Water of Leith had been built by the Caledonian Railway to carry its freight line to Granton. Later there would be a passenger service to Leith North which would be the first to go in 1962, the very last passengers being King Olav of Norway and his entourage on their state visit to Scotland six months after cessation of regular trains. With the demise also of freight in 1967, the tracks were soon lifted, but in due course the route became repurposed as the Roseburn Railway Path for cyclists and walkers.

All seemed well until 2019, when a condition survey for present owner the City of Edinburgh Council found serious deterioration in its condition. Vegetation growth included a mature tree sprouting out of its side. Perhaps surprisingly, the Viaduct had never been waterproofed, and water penetration through the arches had led to freeze-thaw cycles causing deep spalling which, combined with mortar loss, could create a hazard to people using the Water of Leith Walkway and street below.

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With its consultant Mott MacDonald, the City set about a comprehensive repair programme. Under contractor Barhale the surface was stripped back so that a membrane could be installed to direct the rainwater into a new soakaway crate system. Lime mortar was applied and the stonework damaged by the tree was replaced by traditionally-cut new stone. Timber steps which had been provided up from the Water of Leith Walkway were life-expired so were replaced by new ones, and the handrail was taken offsite for reblasting.

The route across the Viaduct had become cluttered by use of old rail to support the sides. That on the upstream side was retained as a feature, but the downstream side had to be removed so as to facilitate sealing of the waterproof membrane at the parapet wall - but sections of the rail were donated to the Institution of Civil Engineers Museum at Heriot-Watt University. At the request of a local antiquarian, the outlet from the tail-lade of the old Coltbridge Mill, one of scores that once lined the banks of the Water of Leith, was restored.

Use of birdcage scaffolding enabled the work to be encapsulated, while a mobile elevating work platform facilitated attention to the arch that crosses the street leading to Coltbridge Gardens. The contractor’s responsible performance which won praise from the local community was recognised by the Considerate Contractor scheme, and it proved possible to keep the Viaduct open to cyclists and pedestrians until the scheme was almost complete in July 2020, when a short closure was necessary to catch up on CoVid-related delays.

So why is all this of more than local interest? Not all cyclists crossing the Viaduct may be aware that they are on National Cycle Network Route No 1, which could take them all the way from Dover to Shetland! If a tragedy of Edinburgh's transport was the loss of the city's entire suburban railway network, a surely Unique Selling Point has been the extent to which the city has gone about repurposing this legacy so that the Roseburn Railway Path across the Viaduct is now linked to a host of well-signposted routes through North Edinburgh and beyond for ease of environmentally-friendly commuting and for the joy of exploration.

All of this has been safeguarded by the Viaduct's refurbishment, and there is now the possibility of shared use by the successor to the suburban railways in the revived proposal for an Edinburgh Trams route from Granton to the city's south-eastern growth areas which has been endorsed in the council's recent Mobility Plan.

John Yellowlees, Scottish chair, CILT



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