canalboat.co.uk Canal Boat November 2017 41RESERVOIRS
concerns the Trust, which is spending
£4.3m this year to ensure adequate
protection against the risk of too much
water – and it’s largely driven by those
ten-year reports.
So what’s in the reports? Firstly, general
information such as details of the reservoir
and its catchment area; information about
the ‘draw-down plan’ (for emptying it in an
emergency); construction details and the
local geology. Secondly, the findings of the
inspection (with lots of detail about
leakage and seepage).
Then the conclusions: is the draw-down
plan adequate? Is supervision
satisfactory? Will it survive a ‘once in
10,000 years’ flood event completely
unscathed? Will it deal with the ‘worst
meteorologically possible’ event with only
minor damage? And, finally, there are
recommendations on works needed to
bring it up to scratch.
Killington is a relatively early reservoir
dating from 1819 – and typically for this
era, there are few records of how the dam
was constructed. It’s believed to have a
puddled clay core, but nobody can be
sure without digging down. It’s quite
normal for builders to have simply used
what soil was available (such as sand or
even peat) and not to make any attempt to
dig down to a solid base before building it- often the original topsoil is still there
under the dam.
It’s also been altered several times: the
dam was raised to increase capacity
(early engineers often underestimated
water requirements) and we can still see
where a large block of stonework was
added to raise the height of the overflow
channel – and then a second overflow
channel was added after the 1830 incident.
The draw-off system has been changed
more than once, as a siphon pipe set in
the dam replaced the original culvert, and
was then supplemented by a second siphon.
Unusually, rather than supplying a canal
feeder channel, the water from the
reservoir is fed back into the stream
below the dam. It is then taken out several
miles downstream (metered, to make sure
the same amount is taken out as is put in),
where a feeder carries it to the
unnavigable northern reaches of the
canal, and it eventually runs down the
disused lock flight at Tewitfield to reach
the navigable length, a full 15 miles from
where it left the reservoir.
But the report concludes that the dam
will cope with all that the weather canthrow at it, the overflow is adequate, the
level can be lowered in a hurry if
necessary and, in general, it’s adequately
maintained – but with a few provisos.
There are various recommendations
which are mainly maintenance issues – so
we can see one team at work replacing
sections of the overflow channel’s base in
concrete to deal with erosion, while
another group are using a dye to
investigate leakage in a further section of
the overflow, and in the block of
stonework mentioned above, prior to
grouting work to seal the leaks.
Interestingly, two unrelated projects are
taking advantage of the lowering of the
water levels for this work. Firstly, a local
community hydroelectric scheme is being
set up, taking its feed from the cast iron
draw-off pipe (which has involved some
clever tapping into the pipe while still
under some pressure).
Its turbine is currently working in
parallel with the 1930-built valve house to
control the take-off of water from the
reservoir; in future the entire main flow to
the Lancaster Canal will pass through the
hydro system and generate 30kW for the
local area, with the profits going to the
community. All the work has been done
by local companies, and it’s being
championed as a demonstration of the
capabilities and possibilities of‘The report concludes that the dam will cope with all the
weather can throw at it, the overflow is adequate, the level
can be lowered in a hurry if necessary and, in general, it’s
adequately maintained – but with a few provisos’
Rebuilding sections of Killington’s overflow spillway baseThe Foulridge dam, with concrete crest wallPressure grouting the spillway base