The Cave Dragon of Bowbridge Roars.
by: Buffs
A flurry of emails over the
weekend saw workboat Jasper delivered to Bowbridge lock to support a water
jetting team who were coming on Monday morning to attempt to clear the blocked
spill weir culvert. Unfortunately a competent crew was not properly arranged. Lifejackets were to be provided for the event by the SDC canal team and were
duly delivered to an empty lock site. At the same time a volunteer from Western
Depot arrived to add some modifications to Jasper. These two hapless souls were
sufficiently dedicated to the cause that they did not leave until 17:30 – way
past their bedtime.
The jetting crew from Just
Surveys arrived with their jet pump wagon. The 4000 litre tank was not full,
very not full, so the driver then left in search of a hydrant to fill up. The
enforced interregnum was spent leaning on a fence and looking down a deep hole.
The function of the weir and culvert was explained to the jetset who had not
met such a beast. They were regaled with tales of dragons hiding in the tunnels
waiting to catch the unwary spitting fire and damnation on those too slow to
run away.
When jetting ready to commence
two young men from the jetting team were fitted with lifejackets and joined in
the boat piloted by the WD volunteer. With Jasper held in place at the mouth of
the spill weir by the SDC volunteer the jet hose was inserted into the culvert
and jetting started. Progress was slow with much muddy effluent emerging from
the tunnel mouth. We need a bigger head was the cry from above and the biggest
head was sent down. More jetting and more muddy efflux but still progress was
slow.
Jetting
Nozzles
The tunnel was probed with a
barge pole. It was evident that the silt in the tunnel had become compacted and
hardened over the long period of abandonment. There was also evidence of fine
root growth into the silt from an unidentified source. The nozzle was changed
again, this time for what was called the cutter. This issued a much more
powerful and copious jetting action. It would also waken the dragon in the
pipe. Jetting recommenced with greater penetration and silt removal. It was
evident to those in Jasper that the oldest and most compacted silt was being
removed. The effluent was much darker, almost blue, and came with the
unmistakeable perfume of Canal No 2. Also evident were great clumps of fine
roots, some of which caused the hose to be held in the tunnel.
It had been suspected that the culvert had
been penetrated to a greater or lesser extent by the stand of willows along the
bank of the Frome. These trees have a magnificent coat of green fronds sweeping
down from the high branches to caress the ground below. The coats shine in the
sun having been fed through the dry of this summer by the passing of the waters
of the Frome. It is a sight worth seeing from the East even if willow is no
real friend of ours.
During the second tankerful of
water the hose started to buck and twist. The Dragon was fighting back! More
roots and more foul blue effluent were spat out of the dragon’s lair with a
roar a spray. The dragon had beaten the pump which had to be replaced.
While the pump was away a video
survey of the upper end of the culvert was carried out. It revealed that for
some of the length it was in good order but was fouled by debris. The debris
was much more modern than expected and includes modern house bricks. A recording was made and some stills may be
reproduced here later.
When jetting resumed the
effluent slowly changed colour to a light grey losing its aroma on the way. The
effluent now contained evidence that it was much more recently deposited with
plastic bags and bottles surfacing in the lock.
Jetting was getting very close to the dragon’s lair and with very thrust
and withdrawal of the hose being greeted with a roar which forced spray and
debris into Jasper and onto anyone foolish enough to get close.
The Dragon Roars and Spits
Jetting was brought to a halt
when it was evident that no further progress into the culvert was being made. The total length of hose in the tunnel was measured at 7.6 metres, which is
about the distance from the lock wall to the estimated line of the culvert
parallel with the canal.
There has been some debate about
the shape of the tunnel. Is it a continuous slope from weir bottom to a
radiused turn to the lock wing wall porthole or does follow it a flattish line
to a right angled drop to canal level and a right angle turn to the wall. Plans
are afoot to find out.
