Saturday, 18 July 2015

I've got that sinking feeling.....

Subsidence in Walsall Wood
July 2015

Before you leap to the wrong conclusions - neither of our boats is in imminent danger of sinking.... I hope! True, I have replaced the packing in the stuffing box today so a tragedy could follow but overheating from over tightening is a more likely outcome.

No, today's post is about subsidence of the Daw End Canal as it passes through Walsall Wood, less than a mile from our home.

The Daw End Branch canal ran over a very good coal measure so naturally enough them mined the stuff out and in time the surrounding land settles several feet as the workings collapsed. The mines were last worked over 100 years ago and the general view is that if subsidence is to occur it will stop after 40 years.

The canal neat our house therefore suffered severe subsidence and had to have its banks built up repeatedly and even today the channel, with its silt, is over 6 feet deep. Raising the banks is ok, but it bridges are a problem. In areas prone to subsidence the old hump backed bridges were replaced with flat topped ones, which could be jacked up as an when necessary.

There is one bridge which particularly catches my eye every time I pass under it - Black Cock Bridge.

This venerable old iron span has been lifted on at least one occasion and its walls have built in jacking points to cater for any future movement. If you look closely al the walls lower down you can see a row of old jacking holes which have been bricked up and who knows if there and now underground / under water.

The other tell tale evidence of subsidence are the rope rollers which should go from ground level to the bridge span. Instead they are half buried which indicated that the last lifting was after horse drawn traffic switched to diesel in the 1930's.

Finally, if looked at from a distance you can see the pipe which accompanies the road has been cranked up to give headroom and shows just how much lifting was needed.

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