Depth of Wheaton Aston lock

[magpie patrick]

There's an article in this month's Waterways World on the Shropshire Union Canal, in which it is claimed that Wheaton Aston lock is "the deepest on Telford's canal" (as in, the B&LJ) - the next sentence claims that each lock has a rise greater than the one downstream.  

 

I can see the appealing logic, this should ensure that each lock passed on enough water for the next, but I don't think it's true - and with a 17 mile pound between Wheaton Aston and the next lock I'm not sure it matters anyway. 

 

Does anybody know? I don't have a guide with lock depths to hand. 

[MtB]

38 minutes ago, magpie patrick said:

I can see the appealing logic, this should ensure that each lock passed on enough water for the next, but I don't think it's true - and with a 17 mile pound between Wheaton Aston and the next lock I'm not sure it matters anyway. 

 

 

 

The locks around here seem to have by-washes which cancel out that need. 

 

Do the locks on the shroppie have bywashes? I can't remember! 

 

Edited March 12, 2022 by MtB

[Rob-M]

19 minutes ago, magpie patrick said:

There's an article in this month's Waterways World on the Shropshire Union Canal, in which it is claimed that Wheaton Aston lock is "the deepest on Telford's canal" (as in, the B&LJ) - the next sentence claims that each lock has a rise greater than the one downstream.  

 

I can see the appealing logic, this should ensure that each lock passed on enough water for the next, but I don't think it's true - and with a 17 mile pound between Wheaton Aston and the next lock I'm not sure it matters anyway. 

 

Does anybody know? I don't have a guide with lock depths to hand. 

Nicholson's has Wheaton Aston as 7' 0" and the 5 Tyrley locks as a total of 33' 0".

Edited March 12, 2022 by Rob-M

[Rob-M]

Adderley and Audlem then average slightly less than 7' per lock and the two at Hack Green total 12' 0".

[Tracy D'arth]

All the Shroppie locks have bywashes. I have never been aware that Wheaton Aston is any greater depth than most of the others, if it is its not by much.

[beerbeerbeerbeerbeer]

I thought it was pretty much a given that locks have a bywash?

Some, like on parts of the Staff and Worcester, stand out as lovely bits of architecture.

 

I know there’s a few locks on the Rochdale 9 that don’t have a bywash which helps make them harder work.

[David Mack]

Some canals were built with overflows emptying into the ground paddle culverts, and did not have a bywash round the whole lock. This ensured that any spare water was first used to fill the lock chamber and only then went over the bottom paddle overflow (if bottom ground paddles) or over the bottom gate (if gate paddles). Bywashes have been added later in some cases - the Lapworth flight is a good example.

Edited March 12, 2022 by David Mack

[ditchcrawler]

Just now, David Mack said:

Some canals were built with overflows emptying into the ground paddle culverts, and did not have a bywash round the whole lock. This ensured that any spare water was first used to fill the lock chamber and only then went over the bottom paddle overflow (if bottom ground paddles) or over the bottom gate (if gate paddles). Bywashes have been added later in some cases - the Lapworth flight is a good example.

Isn't that how the K&A one were suppose to work but they got the height wrong, hence emptying them overnight.

 

[magpie patrick]

9 hours ago, Rob-M said:

Adderley and Audlem then average slightly less than 7' per lock and the two at Hack Green total 12' 0".

 Now you mention this I remember this - although I'm not convinced of the reasoning given in WW. At Hack Green the lower level is set by the level of the summit of the Chester Canal. I think more likely is that Telford did sums about cut-fill balance on the long pounds above Tyrley and decided that 7 foot was right for Wheaton Aston - the overall fall (according to Nicholsons is 178 feet which is 6 foot 4 inches a lock - making the 17 mile pound 8 inches higher would have been a big difference in the cut fill balance. There is some benefit in making Tyrley slightly deeper than the locks below as they are then relatively closer together, but the relationship between the fall of Wheaton Aston Lock and the water supply on the long pound is very tenuous, especially with a difference of just 5 inches between Wheaton Aston Lock and the average depth at Tyrley, and I think Telford would have known this. 

In short, I suspect someone has taken a fact and ascribed reasoning to it - reasoning that doesn't bear scrutiny if one has a fuller understanding of canal water supply. 

[Tony Brooks]

11 hours ago, MtB said:

 

 

The locks around here seem to have by-washes which cancel out that need. 

 

Do the locks on the shroppie have bywashes? I can't remember! 

 

 

Yes and always flowing well thanks to the outfall of the sewerage works at the junction with the S&W.

[Pluto]

Apart from land drainage, there are two controlled flows of water on a canal, one to replace water lost by evaporation and leakage, and the other to provide water for lock usage. In theory, byewashes supply the former, while the latter comes from water being released as a boat passes through a lock. However, each lock will also have some leakage, so it was considered good theoretical practice to have the locks towards the summit level slightly deeper than those lower down, the excess water being used to compensate for leakage, etc. It does not seem to have happened in practice as the attached graph of lock falls on the L&LC shows. Riser locks were the major problem for water supply, followed by subsidence on the Wigan flight from the mid-19th century onwards, with the falls there being equalised on at least three occasions to reduce water wastage.

[magpie patrick]

Interesting - is it recorded that they did this or is it just an observation based on lock depths? (and as you say, they were a long way off right on the L&L! - even if Bingley weren't a staircase they were the deepest locks on the eastern side at 12 feet each)

 

When looking at new locks on canal restoration, or water supply for restoration, we look at something similar, although in the case of true restoration we can't fiddle with the depths, but the hydrologists I work with would regard the difference between Wheaton Aston and Tyrley, 17 miles away as "lost in the noise" - even on a short pound you'd want, say 20% extra volume to regard it as a "water supply" - it also doesn't make as much difference as you might think - Bath Deep Lock can be worked three or four times a day without ill-effect (other than a temporary reduction after filling it)  even though it's twice the depth of the one 60 yards upstream. 

[Tacet]

I don't buy the increasing depth theory either.  Taking any account of leakage, evaporation and boat not traversing the whole length of the canal, it would be a misplaced counsel of perfection.

 

But on the other hand, the cut-and-fill approach also seems a little flawed.  Over what distance is it more convenient to cart soil rather than dig a hole in one place and create a pile in another?  No doubt it depends on any tramways or even carriage by water used during construction, but in terms of labour alone, you would not want to push a hand barrow more than an additional couple of hundred yards to save the effort of digging up a fresh load of fill. 

[Pluto]

10 hours ago, magpie patrick said:

Interesting - is it recorded that they did this or is it just an observation based on lock depths? (and as you say, they were a long way off right on the L&L! - even if Bingley weren't a staircase they were the deepest locks on the eastern side at 12 feet each)

 

When looking at new locks on canal restoration, or water supply for restoration, we look at something similar, although in the case of true restoration we can't fiddle with the depths, but the hydrologists I work with would regard the difference between Wheaton Aston and Tyrley, 17 miles away as "lost in the noise" - even on a short pound you'd want, say 20% extra volume to regard it as a "water supply" - it also doesn't make as much difference as you might think - Bath Deep Lock can be worked three or four times a day without ill-effect (other than a temporary reduction after filling it)  even though it's twice the depth of the one 60 yards upstream. 

If you look at the graph you will see that Wigan top lock was virtually 16 feet drop in 1887, and that was the problem as a third of that would run to waste. It may be OK for 4 operations a day, but Wigan was one of the most intensively worked flights in the country with at least 70 boats per day, so in a somewhat different league. Long pools, such as the almost 30 mile one from Liverpool to Appley Bridge, have different problems as windage can create a difference in level of several inches between each end. 

[Heartland]

Was Wigan top lock affected by mining subsidence and also were additional locks added.

 

With the BCN the last lock at the junction with the Staffordshire & Worcestershire was a deep lock when that original lock was No 20. With the making of lock 21, the loss of water through the original deep lock was obviously reduced.

 

 

[magpie patrick]

Taking @Plutos point - I'd agree that discrepancies on such a scale are undesirable especially with the level of traffic at Wigan. Bath deep lock was created as part of a 1970s road scheme and it does cause problems too in busier days when water has to be run down the locks above, but @Tacets counsel of perfection is well-made in that Bath Deep lock doesn't cause as many problems as logic suggests it should, and thus a difference of a few inches in fall between locks at opposite ends of a seventeen mile pound will make the square root of beggar all difference.  Indeed @Plutos point about windage comes into play. 

 

In flights regular falls make sense, as they in effect act as a bucket brigade, Icouldn't think of a flight that was built with locks of irregular depth (Widcombe, Tinsley and Wigan all started out with even falls) but @Heartland has reminded me that the bottom lock at Wolverhampton had to be modified to remove a single deep lock 

[David Mack]

34 minutes ago, magpie patrick said:

but @Heartland has reminded me that the bottom lock at Wolverhampton had to be modified to remove a single deep lock 

Is there any explanation for why Brindley put a double depth lock at the bottom of the Wolverhampton flight?

[magpie patrick]

11 hours ago, David Mack said:

Is there any explanation for why Brindley put a double depth lock at the bottom of the Wolverhampton flight?

The bottom lock is in a shallow cutting so I guess the original level just followed the lie of the land 

 

Edited to enlarge on this a bit - from memory the locks basically follow the lie of the land, but the S&W at the bottom is in a shallow cutting so if you follow the lie of the land you end up 12 feet above the S&W. For reasons we can now only guess at Brindley (or his sub contractor) decided a single deep lock "would do", possibly using the same logic as I have further up the page but on this occasion getting it wrong - obviously it did prove to be a problem as adding another lock isn't cheap. 

The new lock is obvious as it has a single bottom gate, the bottom lock has double bottom gates but there are subtle clues that it was heavily modified early on in it's life.

Edited March 15, 2022 by magpie patrick

[Pluto]

14 hours ago, Heartland said:

Was Wigan top lock affected by mining subsidence and also were additional locks added.

 

With the BCN the last lock at the junction with the Staffordshire & Worcestershire was a deep lock when that original lock was No 20. With the making of lock 21, the loss of water through the original deep lock was obviously reduced.

 

 

Wigan Top Lock had reached a working depth of 15 ft 10 inches in 1884, suggesting that the land there had subsided around 6 feet. As deep mining developed, there was further subsidence, and the locks were equalised on three occasions over the next thirty years or so. The greatest subsidence was around the Leigh branch, where deeper mines were opened towards the end of the 19th century. I estimate that the land there has subsided by at least 25 feet in places, resulting in the locks at Plank Lane and Dover being moved to Poolstock. On the main flight, I have not seen anything to suggest that any additional locks were added, but reconstruction did end up with lock 13 being comparatively shallow. On many of the locks it is possible to see how they have been rebuilt over the years, with many having additional layer or layers of stone at the top of the chamber.

[Cheshire cat]

Going back to the Shroppie when did Norbury junction come in to play? That would be a drain on the southern Shroppie and is between Wheaton Aston and Tyrley locks 

[Tacet]

12 hours ago, magpie patrick said:

Taking @Plutos point - I'd agree that discrepancies on such a scale are undesirable especially with the level of traffic at Wigan. Bath deep lock was created as part of a 1970s road scheme and it does cause problems too in busier days when water has to be run down the locks above, but @Tacets counsel of perfection is well-made in that Bath Deep lock doesn't cause as many problems as logic suggests it should, and thus a difference of a few inches in fall between locks at opposite ends of a seventeen mile pound will make the square root of beggar all difference. 

At its (unrealistic) simplest with no other losses or additions than lockage and assuming all boats travel the whole length, use of the flight/canal will lead to the fall of every lock being the same.  Which is OK, providing it does not mean insufficient depth over cills or locks/pounds being over topped.

 

 

[mykaskin]

Many canals have other water sources as they drop down from the summit, you can often see when a new water source joins as the locks are suddenly deeper! Some times summit locks can be smaller as there is another source close to the top but not at it, but often a summit lock will be greater in depth to provide enough water for below.

 

Remember when the Shroppie was built it didn't have a water source other than reservoirs - the sewage works coming much later. 

[Heartland]

On page 121 of Silent Highways I show a plan of a sluice installed at Autherley to enable water to be drawn from the Staffordshire & Worcestershire Canal, where the engineer J U Raistrick had designed a machine to measure the water taken so that charges could be made for the water supplied to the slightly lower summit level of the Birminghan & Liverpool Junction Canal as it was first buily as.

 

John Urpeth Raistrick was a capable engineer who was principally associated in railways including early locomotive construction and surveying new railway routes.

Edited March 24, 2022 by Heartland

[mykaskin]

Ah that's interesting. Anything still remain of.it?

[Philip]

From my own observations; Wheaton Aston is definitely deeper than the others - not by a huge amount, but clearly a noticeable difference if you compare; best part of a foot. I'm also convinced that the bottom two Tyrley locks are deeper than the three above and Adderley, Audlem & Hack Green, especially the bottom lock which looks about 7 or 8 inches deeper than all of the locks below and maybe about 4 inches deeper than the top three Tyrley locks. The top Tyrley lock also looks a little bit shallower than the two below; more so the lower two. Audlem, Adderley and Hack Green all look pretty much the same, although Hack Green top lock looks perhaps a couple of inches shallower than the rest.

Edited March 24, 2022 by Philip