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
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.