Kent and East Sussex Canal Restoration Group

KESCRG and London WRG at Dauntsey, August 2011

In August KESCRG and London WRG joined forces for a weekend dig at Dauntsey Lock on the Wilts and Berks canal, staying at the ever popular Foxham Reading Rooms. Dauntsey Lock is on the section of canal just to the west of the 7 locks, which have been the focus of a lot of work on the Wilts and Berks for the last couple of years.

Dauntsey lock itself was restored some years ago but the pound above the lock has recently been suffering from leaks. It was some of these that we were tasked with resolving.

The first suspect was a culvert not far above the lock, so a team and a large excavator set off to try and locate the exact position of the culvert so it could be investigated…

Unfortunately despite a lot of looking, the culvert proved elusive!

The next target was a spill weir a little further up the canal. The brickwork on the weir crest has cracked, and water had been leaking both through the face of the weir and the base. The solution was to use Bentomat – a reinforced geosynthetic clay liner. This is effectively a thick carpet impregnated with sodium bentonite, which has been used on several restoration projects to provide an effective alternative to several feet of puddling clay where leakage has proved a problem.

The first task (after setting up and testing the tea station) was to level out the existing base of the weir to get an even profile on which to lay the matting.

The carpet was then unrolled in strips to cover the base and front wall up to the crest. The strips were sealed together with a special sticky bentonite clay gel, and attached to the brick work, after some experimentation with the nail gun, by a combination of nails and plastic strips. The Bentomat thus formed a (hopefully) watertight bowl in the spill weir.

When Bentomat gets wet, the bentonite expands. This has the very useful property of making the Bentomat ‘self-healing’ – if it is damaged, the clay expands and plugs the hole. However this also means that when it is used as canal liner, it must be covered in a heavy protective layer, otherwise when it gets wet the whole carpet will expand and eventually disintegrate. So the next step was to lay bricks on the Bentomat to weigh it down and finally apply a layer of puddling clay over the bricks, which as well as adding weight will also help to seal the edges of the mat to the brickwork.

A third team carried out a bit of a scrub-bash, clearing saplings from the canal bed and tidying the towpath and hedge. All in all a great mid-summer weekend, well attended despite being in the middle of a busy camp season.

Report: Stephen Davis
All photos Alan Lines.

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