Friday, September 07, 2012

A bit odd…

That’s the Selby Canal.
Unusual features – the navigable channel is quite narrow and shallow, the banks are high and sloping, leaving the towpath maybe 10 feet above water level and 15 feet away. And there are these unusual circular or semi circular stone “ponds” either side of the waterway.

High BanksSAM_2974

So, no canal engineer worthy of the name would have cut the channel far deeper than necessary. And this one was William Jessop, who had a very good reputation.
Also the canal, built in 1778, connected two river navigations, The Aire and The Ouse. These carried large barges, larger than could easily be accommodated on the current canal. The locks are 78 feet x 16½ feet, designed to take Humber Keels, around 62 feet x 16 feet beam.

The only thing I can think of is that the canal in it’s current form was not as originally conceived. I reckon the cut channel would have been a lot fuller, making the navigation deeper, wider, and with a towpath that is a lot closer to the water. The channel would easily take another 4 foot of water.

So why not now? Well, a look at the Aire gives me a clue.

The Aire at West Haddlesey
SAM_2980 R Aire
Although at summer levels, the river is a lot lower than the banks. Ah, I hear you say. Raised flood banks. But they don’t seem to be, not much higher than the fields either side.
So has the river level been deliberately lowered as part of a flood defence scheme?  If it has, this would account for the lower water in the canal, too. As it’s fed from the Aire, it couldn’t possibly be higher.

There’s just one fly in what would have been a convincing theory. The beautiful stone bridges are built to fit the current levels. If they were at this height over what I surmise would have been the initial water level, nothing with more than three feet or so of air draught would have got through!

Paperhouse Bridge and one of the pond-like stone structuresSAM_2972

That brings us to the last riddle. What are these stone built ponds for?
They are positioned in pairs, pinching the canal between them. Relics of long removed swing bridges? Goole Maps shows clearly what I mean.

This is Paperhouse Bridge again…

View Larger Map

On the other hand, an interpretation  board near the flood lock tells of improvements made during the 1830s. Maybe that’s when the navigation was widened and deepened, and it has since reverted back to it’s original size.

Post Script...
Just been doing a bit of research. It seems that these round structures are “drainage knuckles”, running under the canal are large pipes to carry flood water from one side of the navigation to the other. Neat, huh.
And in the 1830s, the volume of traffic prompted the widening and deepening of the channel. But the flood management system prevented digging the bottom out. So the banks were raised instead. Now the canal is back near it’s initial level.

I walked back to West Haddlesey taking these pictures this morning. Moored there above the lock was NB Rose of Arden, so I knocked and was rewarded with mug of very welcome coffee. We spent the best part of an hour chatting before I set off back.

Mike, Abbey and Poppy on NB Rose of ArdenSAM_2981 Mick, Rose of Arden
They’ll be in Selby now, having passed us at lunchtime. We may catch up in York…

Oh, and thanks for the warning, Alf. But I guess they’ve all moved on. Not a stripy jumper to be seen!

Locks 0, miles 0

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