www.lapal.org
The Lapal Tunnel
3,795 yards 1798 - 1917

 

Lapal Heroes : Tunnels and Tunnellers

The initial surveys for the entire Dudley No. 2 Canal and its two tunnels at Gorsty and Lappal, were made by Josiah Clowes (1735-1794). First commissioned at the height of Canal Mania (1789-1796), between the eras of James Brindley (1716-1772) and Thomas Telford (1757-1834), Clowes was a prolific consultanting tunnel engineer whose many credits include the nearby Brandwood Tunnel (352 yds) on the Stratford Canal, the Sapperton Tunnel (3,817 yds) on the Thames & Severn and the distant Foulridge summit tunnel (1,640 yds) on the Leeds & Liverpool.
For a while, Clowes was married to Jane Henshall whose younger sister, Anne, subsequently married James Brindley.
On the death of Josiah Clowes in December 1794 at the age of 59 - his death was probably due to overwork! - the two tunnels on the Dudley No. 2 were completed under the supervision of the appropriately-named William Underhill.

 

The Lapal Tunnel : a boating drain-pipe ?


At 3,795 yards, [3,470 metres] the Lapal Tunnel enjoyed the distinction of having been 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 the Sapperton (3,817 yards) on the Thames & Severn are longer.

The Lapal Tunnel was built for 'legging' being the then traditional means of transit. It had only a small bore of dimensions: 9 feet wide and 9 feet high above the water line [9' = 3m] sufficient for one-way working at a time. Subsidence, however, reduced this to a mere 7' 6" wide and 6' high in places [2.3m x 2m] and was to prove troublesome throughout its operational life. Indeed, although it had only opened in 1798 the tunnel was closed for repairs for 2 months in 1801 and 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.

This photo of a partial collapse inside the Sapperton Tunnel is by kind permission of the Cotswold Canals Trust. The Lapal Tunnel, though totally sealed for safety's sake, is believed to have several similar localised collapses. However, at 14' 4" wide and 15' 4" high [4.5m x 5.4m] the Sapperton does not impart the same sensations of tunnel claustrophobia as the Lapal!

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 capping bricks in the ceiling arch allowing soft sand to pour in and plug the tunnel (over a short length).


Construction :
30 shafts and a horse-drawn rope

Construction of the tunnel proved to be quite difficult, primarily because of mistakes made with levels and the soft running sand. It involved the boring of 30 shafts, just one of which survived to serve the tunnel as a midway vent. Spoil mounds from the excavations can still be seen at several locations on the Woodgate Valley country park and a now-collapsed shaft can be located at the rear of the Visitor Centre.

The technique for positioning the shafts correctly had been to draw a hefty rope, by horse, overland from the required position of one portal to the required position of the other.  Then, excess slack in the rope would be taken up as it was 'flipped' to make it find its most natural, straight and taught lie along the ground.

The shafts were then sunk to approximately correct depths so that small horizontal tunnels could be  dug away in the direction of each neighbouring shaft. Then, when two such small tunnels met, the navvies (the workforce) dug out and constructed the masonry to full tunnel dimensions, heading back towards 'their' original construction shaft. This ensured that the ground around the base of each vertical shaft was left undisturbed until the last activity of that section. Where roof sections were formed from two layers of brickwork, small boys were employed to install the outer (eventually hidden) course above the main roof arch. In many cases, the base of the construction shaft was lined with timbers to support the infill. With time, these will have rotted and contributed to recent collapses.


Brewin's Pump :
the world's first log-flume ride?

In 1841, an innovative and unusual system was set up by Thomas Brewin to reduce boat passage time. Since there was no towpath, passage by laborious legging took up to 4 hours. So, to speed things up, Brewin installed a steam pumping engine, near to the western or Lapal portal, together with a narrows and stop-lock, 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 flush 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 that 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 likely that boats were still legged through the tunnel to add to the momentum created by the current.

This simple but very effective expedient, halved the typical transit time from 4 hours to 2 hours!

However, there is some evidence that the flushing water may have also contributed additional wear and tear to the masonry and mortar, and so hastened the early demise of this, the most precarious feature of the Dudley No. 2 Canal.


Going "OTT" :
 our realistic restoration strategy

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; the south portal and early section of which still have dimensions which closely approximate those of the Lapal 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. Similar arguments are echoed in the proposed restoration strategy for the Lapal canal.

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 the Manor Way dual-carriageway was used to infill that section so that it is now difficult to discern the exact 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 brickworks 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 may not be 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.

However, taking all factors into consideration, ATKINS, acting as Civil Engineering Consultants to the Lapal Canal Trust in 2007, have recommended an alternative route. This will pass Over The Top ("OTT") of the Woodgate Valley parkland in a series of staged restoration projects, rarther than require the single expense of a major rebuild of the Lapal Tunnel to modern dimesnions which would permit bi-directional passge of modern, powered vessels.  The full rationale for this decision  is given elsewhere in the Lapal Canal Trust literature an web site.

However, a modest scheme has also been proposed to recognise the former significance of the Lapal Tunnel.

© David R. Carson with additional material by Ged Pakes and Peter Best - 1999, 2006, 2008-OTT