The spectacular descent of the Caen Hill flight of locks in Devizes is normally one of the most impressive sights along the Kennet and Avon Canal system.
Restoration works have temporarily marred the flight's grandeur however, reducing the clean line of sixteen locks to a muddy construction site. The work is part of the Kennet and Avon Canal Partnership Project, funded by the Heritage Lottery Fund, and accounts for approximately £1M of the total £29.24M allocated for the entire project.
Caen Hill is of particular interest due to its status as a scheduled ancient monument and its position as one of the top three tourist attractions in Wiltshire.
The steep descent of the closely-packed locks and use of side-ponds creates an unusual and beautiful sight, not to mention a haven for plant and wildlife, attracting thousands of canal users and visitors every year.
The side-ponds are not merely an ecological feature however, but an essential component of the engineering of the Caen Hill flight. If a number of boats traverse the flight, large volumes of water naturally move downwards.
This could result in a pronounced rise in downstream water level, potentially overtopping the next lock gate, and creating a danger for inexperienced canal-users.
A long length of free water between locks will minimise this effect. However, if locks are closely spaced the problem is more pronounced. Therefore in cases such as Caen Hill, side ponds are provided specifically for level balancing.
Three of the ponds are currently being re-lined to prevent leakage as part of the restoration works.
Originally lined with a 1m layer of puddle clay up to 1.2m thick, the ponds had been temporarily re-lined with a PVC membrane in the recent past. Unfortunately the membrane quickly became inneffective. Current restoration work is replacing the puddle clay, to a depth of 750mm.
'This return to the historic lining method is part of our endeavours to keep Caen Hill true to its original design, in keeping with the conservation and heritage strategy compiled by the Partnership,' says Kennet & Avon Canal Partnership project manager John Laverick. The strategy was a requirement from the Heritage Lottery Fund to ensure, among other things, 'minimum intervention' at Caen Hill.
This also applies to the locks themselves which, apart from undergoing minimal restoration and safety improvements, will be unaffected by the project.
However, the embankments separating the three ponds are being refurbished to reduce water migration between them, which might upset their separate ecologies.
The embankments will eventually have puddle clay centres like miniature dams.
Naturally, all this work has necessitated draindown of the Caen Hill Flight. As with any canal closure, this has given British Waterways a few 'operational challenges'. It has designed towpath diversions and other temporary arrangements for the many visitors to the Wiltshire landmark. And it has recommended diversions or temporary relocation to users, who include permanent canalboat residents, businesses and holidaymakers.
Some of the plant life on the flight is unique to its particular pond, which meant greater care had to be taken with its removal and eventual relocation. Over 8,000kg of fish also had to be caught and relocated.
An additional complication meant the canal had to be re-filled mid-way though the works in order for the flight to operate over Christmas and New Year. It has now been drained down again and work is continuing. To date, one pond has been successfully re-lined and the work is on schedule.