Laser Scan of Great Drain, Bath
A laser scan to determine the precise position of a section of the Great Drain below the Roman Baths in Bath City Centre, to facilitate a renewable energy project.
We scanned the site at ground level; in a vault below ground; and finally the Great Drain itself at a 7m depth. The deliverables included an AutoCAD drawing and DWG file with the three tiers overlaid. Equipment included a Faro laser scanner with spherical targets; and Trimble SX10 total station.
Case Study in Detail
Lying beneath one of the UK’s most iconic tourist hot spots, the Great Drain in Bath is an engineering masterpiece. Built some 2,000 years ago, it carries the flow from the famous Roman Baths to the River Avon, 400 metres away. Around 240,000 gallons of hot spring water rise daily and flow along the drain.
The hot water from the spring cools as it passes through the Roman site from 46°C to 35°C, but this is still hot enough to extract useful heat energy from it. An ingenious scheme has been devised to use this hot water to provide underfloor heating for neighbouring Bath Abbey, a huge historic building. Due to its high mineral content , the water itself cannot be used directly; but by placing a heat exchange system in a section of the Drain the heat from the water can be extracted and boosted with heat pumps to warm the Abbey.
A complete survey of the Drain was needed to assess its condition and confirm its exact location, so that the heat exchange installation could be carried out smoothly. Glanville Environmental was engaged by Emery Bros Ltd of Bath to complete a full CCTV walk-through survey of the Drain for the client, Bath & North East Somerset Council. The Glanville Geospatial Services team lent its expertise to provide exact positioning data, to millimetre precision.
Our work was based around Kingston Parade, a busy pedestrian area in the city, close to both the Roman Baths and the Abbey. We completed two traverses of the site using our Faro laser scanner plus spherical targets. The first traverse began above ground, then headed underground through the vaults below Kingston Parade, before returning to the surface. The second traverse then went a layer deeper, down to the Great Drain itself (around 7m below the surface), continuing through the Drain and emerging within the Roman Baths museum. We used our Trimble SX10 total station to geo-reference all the laser scans.
The project presented several challenges. With so many pedestrians in the area, our first challenge was to ensure that the laser scanner could see the targets without interruption, in order to collect data. Below ground, it was hot and steamy work. Although the Great Drain is tall enough to walk through and in excellent condition (the Romans built things to last!), the c.40-degree heat meant we could only work for an hour at a time.
Our survey team of Jake, Sarah and Georgia successfully completed the work over two days in May 2019. We provided the client with a point cloud of the site, the DWG file and AutoCAD drawings which overlaid the three different layers to millimetre accuracy– plus an impressive flythrough video.
