When the northern section of the Lancaster Canal in Kendal began to lose 12M litres of water a day, some 40% of peak flow, it was 'an emergency that had to be solved in the shortest possible time', according to Les Clarke, senior project engineer in the Technical Services Department of British Waterways.
The problem occurred in the early part of 1998 and it was essential that the flow was restored in time for summer traffic on the canal. The northern section of the canal, which is cut off from the rest of the network by the M6, feeds the navigable southern section, maintaining water levels throughout the system.
The section that was losing water was known as the Millness cutting. Built around 200 years ago, its trapezoidal profile had originally been lined with puddled clay, but wear and tear over the years had eroded the lining in places and shrinkage and cracking during periods of drought had created seepage points.
'The solution was to drain the canal over this section, dig out the old clay lining and replace it with a new one,' says Clarke. 'In the normal course of events British Waterways would probably have opted for a medium density polyethylene or PVC liner, but on this occasion a product new to the UK market was chosen. This was a bituminous geomembrane called Coletanche which had been used successfully in France for more than 25 years.
Following removal of the clay a layer of sub-drainage layer material was placed, topped by a 100mm layer of compacted Type 1 material. The 5m wide, 4mm thick liner was then rolled out across the width of the canal, allowing a 200mm overlap between sections. After the seams had been hot torched and welded they were rolled and then ultrasonically tested.
A final 100mm layer of mass concrete was then placed, because this section of the Lancaster Canal may be made navigable at some future date. Clarke says that since the relined section was opened in July there have been no reports of leakage.