The Lapal Tunnel : a boating drain-pipe ?
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At 3,795 yards, the Lapal Tunnel on the Dudley No.2
canal enjoys the distinction of being the fourth longest canal
tunnel in Britain. Only the Standedge (5,698 yards) on the
Huddersfield Narrow Canal , which was reopened on May 1, 2001
after may years of dormancy, the Strood (3,946 yards) on the
Thames & Medway (which is now a railway tunnel!), and
Sapperton (3,817 yards) on the Thames & Severn, are
longer.
The Lapal Tunnel was built to be a 'legging' tunnel with a
small bore of dimensions: 9 feet wide and 9 feet high above the
water line. Subsidence, however, reduced this to a mere 7' 6"
wide and 6 feet high in places, and was to prove troublesome
throughout its operational history. Indeed, although it had only
opened in 1798 the tunnel was closed for repairs for 2 months in
1801, and then again for 4 months in 1805. It is known that there
were several further temporary closures during its 120 years
service, until it was finally closed to navigation in 1917.
The original cross-section profile of the Lapal Tunnel
resembled an inverted horse-shoe or n-shape
with a flat bottom. This resulted in non-uniform pressures from
the rock and marl strata, particularly at the two base right-angles and
the vertical sides at about the water-line. The latter bowed
inwards in several places to give the tunnel an almost egg-timer
or figure-8 profile. This action sometimes
dislodged bricks in the ceiling arch allowing soft sand to pour
in and plug the tunnel (over a short length).
Construction of the tunnel proved quite difficult, primarily
because of mistakes with levels and the soft running sand, and
involved the boring of 30 shafts, just one of which survived to serve
the tunnel as a vent shaft. Spoil mounds from the excavation
process can still be seen at several locations on the Woodgate
Valley country park.
Brewin's Pump : the world's
first log-flume ride?
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In 1841, an innovative and unusual system was set up by
Thomas Brewin in order to reduce boat passage time. Since
there was no towpath, passage took up to 4 hours and was achieved
by boats being 'legged'
through the tunnel; the tunnel having been designed just for this
type of transit.
To speed things up, a pump engine was installed near to the
Western portal together with a Narrows and Stop Lock at that end,
approximately 200 yards before the tunnel mouth.
Boats heading east towards Selly Oak would queue between the
gate and the tunnel mouth until departure time. A notice fixed on
the wall of the keeper's cottage near to the portal displayed
these times together with other information concerning passage
through the tunnel. Then, the gate was closed and pumping began
thereby creating a current which served to push the boats through
the tunnel.
Although there was no gate at the other end of the tunnel, the
stop lock at Selly Oak (located at the narrows adjacent to the
Birmingham Battery & Metal Company) was closed so that the
pumped water accumulated in the pound (i.e. from Halesowen pump
to Selly Oak - almost 4 miles in length). Such was the magnitude of the current created by
the pump that the level in that pound could reach 6 inches above
the normal water level.
Of course the stop lock could still be used during this time
so boats could enter or leave the pound at Selly Oak
junction.
Boats would by now be starting to accumulate at the California
end of the tunnel waiting for east-bound boats to clear, and at
the appropriate time they would enter the tunnel. Now, with Selly
Oak stop-lock still closed, the paddles were drawn at the
Halesowen stop gate and the boats were both drawn and pushed
through the tunnel by the reversed water flow. It is probable
that boats were still legged through the tunnel to add to the
momentum created by the current.
This simple but effective expedient, halved the typical
transit time from 4 hours to 2 hours.
A New Tube : our restoration strategy
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Throughout the tunnel's operational life, it is known that
several repairs were carried out and so it is a distinct
possibility that new sections were constructed at more ample
heights than the original bore. Certainly, this was the case with
the nearby Gosty Hill tunnel.
Much has been made of the roof fall which resulted in the
closure of 1917. However, it should be noted that the decision to
close the tunnel was brought about by economic factors, most
notably that a modern alternative route to Birmingham was
available to traffic and that the limited amounts of money
available for maintenance were more prudently spent
elsewhere.
The section of the canal between Manor Way and the eastern
portal was severed from the system when the bridge over Manor
Lane (as it was known at the time) was dismantled during the
early 1960s. Spoil from the construction of Manor Way was used to
infill that section so that it is now difficult to discern the
line that the canal took through the fields to the tunnel mouth.
The foundations of the pump house, however, can still be seen
close to Lapal Lane South.
At the California portal, the cutting approach to the tunnel
and the site of the adjacent brick works was filled with
household refuse during the 1970s, and is now a grassed area
situated at right angles to Barnes Hill road.
Only an educated guess can be made of the condition of Lapal
Tunnel at the present time. It is thought that damage is largely
localised and that it is not in as poor a state as was originally
feared. The Department of Transport has confirmed that there is
no truth in the rumours that the tunnel was pumped with liquid
cement during construction of the M5. Some quite recent (1999) but minor movements suggest that one of the long-filled bore holes, may
have dropped.
But, taking all factors into consideration, it is currently
envisaged that an eventual restoration of the Lapal Tunnel to a
safe working feature of the Lapal Canal which allows for the
bi-directional passage of today's motor-powered boats, will
require a complete re-bore to modern dimensions using modern
materials and construction methods. This can be achieved by
'drilling' along the former tunnel and sp treating it as the
'pilot-hole' for its long-anticipated replacement.
David R. Carson (with additional
material by Peter Best and Ged Pakes) - 1999
