Staircase locks - differing chamber depths

[magpie patrick]

Whilst writing a report on the river Boyne yesterday I penned the following regarding one of the locks

 

a double lock will normally have approximately the same fall for each chamber, indeed the lower chamber must not be deeper than the upper chamber as it is filled from the upper chamber. The [surveyed height of the] copings on the upper and lower chamber allow us to estimate the fall of the upper chamber, and thus the fall of the lower one.

 

A double lock is a staircase - in Ireland it counts as one lock, and I'm confident that Rosnaree Double does have two chambers of equal depth - I've seen it. But I wondered if my premise was correct, I know of staircases where the lower chamber is shallower, in some instances because it was added as an afterthought (Snakeholme on the Driffield) or later modification (the bottom chamber at Fonserranes) but is my statement in bold actually true? If one follows the Midi practice of filling the entire straircase from the top then chambers could vary in depth without any problem*. But are there/were there any staircases that had a lower chamber deeper than the top one?

*although going down might be more of an issue

[1st ade]

No way an expert on canal's (or much else for that matter!) but from an engineers perspective, the lower chamber(s) must have a volume less than or equal to the upper or everything becomes a bit of a faff.

 

Obviously (I think) there is no point in having chambers of hugely unequal length since the maximum length boat which can pass is the shortest of all chambers but if the two chambers were (say) 69 and 72 feet, that's nearly five percent difference and the bottom chamber could have a 5% bigger fall without running short of water to fill?

 

To a certain extent the same is true of width.

[magpie patrick]

55 minutes ago, 1st ade said:

To a certain extent the same is true of width.

There is one on the Grand Canal of Ireland (lock 12 I think?) where the upper chamber is larger by virtue of width rather than length. The first attempt to build the canal saw wider and longer locks, and some, including this upper chamber, got repurposed by narrowing them at the gates.

[Tacet]

I was tempted to suggest the narrow staircase at Stourport - but it is the upper chamber that has the side weir, presumably to regulate the basin.

 

The first lock on the Wey, with the additional gates sometimes used to lift boats over the cill is an example - but not a conventional one

 

Putting aside 1st Ade point about differing lengths/widths, the use of a staircase will tend to move the two rises towards each other.  I.e. if the top lock has an ostensibly greater rise, when its contents are discharged into the lower chamber it will leave the level higher than the bottom of the coping stones - and the top chamber will not be as low as otherwise.   There shouldn't be an issue on draft over the lower cill.  But if the masonry is insufficient to accept half the total rise, it will be overtopped.

 

So the hydraulic rise will always be the same for each chamber (assuming other factors remain constant) - and the masonry etc needs to allow for it, and a little bit more for canal level changes etc.

 

Incidentally the same applies to a canal which, in concept is one long staircase until the summit/sump is reached.  But there are a lot more factors in play in the longer pounds - with weirs, inlets, boats changing defections, pairing up etc.  The effect is more obvious on short pounds which rise and fall as adjacent locks are drawn

[andy3196]

3 hours ago, magpie patrick said:

But are there/were there any staircases that had a lower chamber deeper than the top one?

 

Could the middle chamber of Grindley Brook be a candidate? When descending you need to have it partly filled to the line on the lock wall.

 

cant find a decent photo of the sign giving instructions, or a copy of the leaflet that was available when I did them some years back, but these are probably out there somewhere.

[Jen-in-Wellies]

You'd  need extra water to cope with normal gate leakage, so extra volume on the upper chambers, going down a bit for each one would be a good idea. This extra volume could be in lock length, width, depth, or even a small side store. Doesn't work with lack of maintenance leakage, but a staircase in good condition will still leak a bit during the course of operation.

Jen

Edited February 3, 2021 by Jen-in-Wellies

[magpie patrick]

1 hour ago, andy3196 said:

 

Could the middle chamber of Grindley Brook be a candidate? When descending you need to have it partly filled to the line on the lock wall.

 

cant find a decent photo of the sign giving instructions, or a copy of the leaflet that was available when I did them some years back, but these are probably out there somewhere.

Thank you - I'm not sufficiently familiar with Grindley Brook to know why the line is there - but at least you got my question the right way round! 

 

Has anyone ever tried the upper chamber being shallower than the lower one? I realise for a variety of reasons it doesn't work if the staircase is operated the way we normally operate them, but other countries do things differently, some canal companies did things differently and sometimes downright daft things happen 

 

Edited to add - there is yet another way of working staircases on the Caledonian Canal I think, where there is just a constant stream of water through the locks: the paddles are opened in front of the boat and closed behind it. 

 

1 hour ago, Jen-in-Wellies said:

You'd  need extra water to cope with normal gate leakage, so extra volume on the upper chambers, going down a bit for each one would be a good idea. This extra volume could be in lock length, width, depth, or even a small side store. Doesn't work with lack of maintenance leakage, but a staircase in good condition will still leak a bit during the course of operation.

Jen

I get that, if I'd designed Bingley 5 Rise then the locks would gradually get shallower as one went down, 14 foot or so at the top reducing to about 10 foot at the bottom.

Edited February 3, 2021 by magpie patrick

[Nick G]

Going up Grindley Brook with a deep draughted boat last year, the volunteer lock keeper was careful to run a bit of extra water down to fill the middle lock so we could get over the cill into the top lock. Simply emptying the top lock into the middle lock does not fill the middle chamber sufficiently.

[Tacet]

3 hours ago, magpie patrick said:

I get that, if I'd designed Bingley 5 Rise then the locks would gradually get shallower as one went down, 14 foot or so at the top reducing to about 10 foot at the bottom.

You would be making a soggy mess,  Anything that leaks through an intermediate gate will end up, for a while at least in the lock below.  So if you are following a boat up a Bingley-style staircase after a mid-reasonable interval the top lock will be a bit down and the intermediate locks full as leaks-in will largely equally leaks out.  So draining the second from bottom lock into the bottom lock will over fill it.  Assuming it is not overtopped, the level between the two will be on the high-side and increasingly so as you ascend.  If the top lock was well down from full, you might get away with it at the final point but the chances are you would have wet feet before then 

 

A fast way to ascend a Bingley-style staircase (when no-one important is watching) and all chambers are at the low level (i.e. the previous boat has descended) is to draw all the intermediate and the top paddles at then drop each set (working uphill) when the relevant chamber has made the correct level.  It's very easy to become confused at to the correct level or not be in the right place at the right time

 

When filling a drained pound, Mrs Tacet's conscience is such that he will not draw paddles at both ends on the next lock; water has to be let down, one lockful at a time.

[Pluto]

At the design stage, it depends upon whether you expect each upper lock chamber to be drained fully, as happens on the Canal du Midi, or whether you expect every chamber to be left with sufficient water to float a boat when empty, as tends to happen in this country. In the former case, the central chambers can be shallower by the water needed to float a boat, while in the second case all chambers have the same fall.

There will almost certainly be a slight variation in depth between riser lock chambers as 18th century canals were not built to the exacting standards of today, particularly as their method of operation does not really need that exactitude. Boatmen and lockkeepers would know these slight variations, and would allow for them. For example, on Bingley 5-rise there are overflows which return excess water into the by-wash. If you kept your boat against the overflow to restrict the water flowing out of the chamber, you could carry down a little more water into the next lock if it was a little deeper. However, I suspect this was more wishful thinking than of any great benefit.

[andy3196]

4 hours ago, magpie patrick said:

Thank you - I'm not sufficiently familiar with Grindley Brook to know why the line is there

 

I'm not too familiar with them either, have only done them twice, (it was close to being only once as I really didn't want to come back over Pontythingywotsit), but i remembered that the line was there.

 

Went looking for information, which led me to an old BW cruising guide from 1965 at https://www.plaskynastoncanalgroup.org/app/download/5783009099/Llangollen+Canal.pdf which has instuctions for the locks, but no mention of the line. So it would seem to be a modern thing rather than how the locks were originally built.

 

I wondered if it's due to a pound being lowered sometime after 1965. I doubt that the pound above the locks would have been just because of it's length. Just below the staircase is a "modern" bridge for the A41, which appears to have fairly low headroom, so I wondered if the pound below the staircase was lowered at that time , but the photo at https://www.geograph.org.uk/photo/1392244 from 1965 seems to be a flat bridge, https://www.geograph.org.uk/photo/5270604 being a more recent photo. Also the falls of the staircase and the three individual locks quoted in both the old BW guide and my more recent Nicholsons are the same.

 

So I'm confused as to whether it is due to one of the lower chambers being deeper, but if it is, I don't think it was by design but a "solution" to a problem that appeared sometime before I was there in about 2005.

[AndrewIC]

3 hours ago, Nick G said:

Going up Grindley Brook with a deep draughted boat last year, the volunteer lock keeper was careful to run a bit of extra water down to fill the middle lock so we could get over the cill into the top lock. Simply emptying the top lock into the middle lock does not fill the middle chamber sufficiently.

Mainly because the gates leak like a sieve, it’s only in recent years that there has been all the faffing around with the top paddles. The line is important though (although I think it’s markers on the upper face of both sets of intermediate gates, rather than the wall, unless they’ve repainted that), in a three or more chamber staircase it’s easier to drain the upper and intermediate chambers too far.

[andy3196]

Thinking about it more, it would be possible to set the locks with the middle chamber empty, rather than at the level of the full bottom chamber, and that is probably the purpose of the line.

 

so best to ignore everything I have said in earlier posts.

[AndrewIC]

1 minute ago, andy3196 said:

Thinking about it more, it would be possible to set the locks with the middle chamber empty, rather than at the level of the full bottom chamber, and that is probably the purpose of the line.

Yes, that’s the usual starting position for coming down, letting water flood over the gates is frowned on.  You  bring a lockfull down with you. 

[Jen-in-Wellies]

I've seen staircases where the lower  chamber has spillways in the sides to safely dump excess water, rather than let it spill over the tops of the gates. I think the lower chamber on the Botterham 2 rise on the Staffs and Worc has them. Relying on my memory though, which is dangerous! Certainly for the these locks when operated according to the instructions there was more water in the top chamber than was required to fill the empty lower one and the excess was spilled away to the side once the correct level was reached.

Jen

Edited February 3, 2021 by Jen-in-Wellies

[David Mack]

15 minutes ago, Jen-in-Wellies said:

I've seen staircases where the lower  chamber has spillways in the sides to safely dump excess water, rather than let it spill over the tops of the gates. I think the lower chamber on the Botterham 2 rise on the Staffs and Worc has them. 

Yes it has. Same at the staircase pairs at Brades on the Gower Branch, Bedford Street on the Caldon and Bunbury on the Shroppie. Probably others too.

Edited February 3, 2021 by David Mack

[ditchcrawler]

1 hour ago, David Mack said:

Yes it has. Same at the staircase pairs at Brades on the Gower Branch, Bedford Street on the Caldon and Bunbury on the Shroppie. Probably others too.

And Bedford Locks on the Caldon 

[Dav and Pen]

In France and also in Ireland the double locks and also the odd triple are worked with middle gates open and water cascaded from the top gates until the level is reached. At a double on the grand canal in Ireland we nearly lost our NB as the water arched  over the cill straight into the front well, luckily the doors were shut. It took a lot of shouting to get the lockies attention.

The earliest staircase locks I know of were built built in France in the 1600’s at a place now named after them Rogny les Sept Ecluses. They are now bypassed by 5 locks.

Edited February 4, 2021 by Dav and Pen
Spell checker

[magpie patrick]

To recap where this started - I'm not saying it is a good idea to have s staircase with a lower chamber deeper than the upper one, I'm just wondering if one was ever built. Odd structures arose in many places although as a general rule the Brits and Irish seem to have been more level headed than those on the continent - I don't think we had any round locks or ones with four or even five entrances for example - there was one with two separate upper entrances on the Arbury Canals but that's it. 

 

There seem to be at least three ways to operate staircases - loosely described as follows

 

The "English" way - one lock is filled from the one above

the "French" way - fill the entire thing from the top

The "Caledonian" way - constant stream of water running through, work one lock at a time. 

 

Fonserannes on the Midi has another variant of filling the flight from the next but one lock

 

Everything except the English system could support a deeper chamber lower in the flight - which doesn't make it a good idea. Also, whilst acknowledging the logic of the design in @Pluto post, I don't think I've ever seen a staircase with a deeper upper chamber like this. The ones I know of with obviously shallower lower chambers are:

 

Stamford Bridge

Struncheon Hill

Snakeholme

Dudgrove

 

In all these cases the lower chamber was a fraction of the fall of the upper one, no more than a third, and in the first three it helped deep draighted boats get over the cill of the lock. I'm not sure how the T&S ended up with the oddity at Dudgrove. 

 

30 minutes ago, Dav and Pen said:

In France and also in Ireland the double locks and also the odd triple are worked with middle gates open and water cascaded from the top gates until the level is reached. At a double on the grand canal in Ireland we nearly lost our NB as the water arched  over the cill straight into the front well, luckily the doors were shut. It took a lot of shouting to get the lockies attention.

The earliest staircase locks I know of were built built in France in the 1600’s at a place now named after them Rogny les Sept Ecluses. They are now bypassed by 5 locks.

 

 

 Rogny is in my to-do list, at least to visit by car. Is the lower picture on the new route at Rogny? 

 

15 hours ago, David Mack said:

Yes it has. Same at the staircase pairs at Brades on the Gower Branch, Bedford Street on the Caldon and Bunbury on the Shroppie. Probably others too.

 The one at Brades is big enough to allow emptying the top lock into a full lower one - I think the others are only to mop up a small surplus

 

15 hours ago, Jen-in-Wellies said:

I've seen staircases where the lower  chamber has spillways in the sides to safely dump excess water, rather than let it spill over the tops of the gates. I think the lower chamber on the Botterham 2 rise on the Staffs and Worc has them. Relying on my memory though, which is dangerous! Certainly for the these locks when operated according to the instructions there was more water in the top chamber than was required to fill the empty lower one and the excess was spilled away to the side once the correct level was reached.

Jen

 There are also overflows at Bratch dating from when it was a three rise - about the first twenty (?) years of it's operation before it was modified

[Jen-in-Wellies]

2 minutes ago, magpie patrick said:

The "English" way - one lock is filled from the one above

the "French" way - fill the entire thing from the top

The "Caledonian" way - constant stream of water running through, work one lock at a time. 

What is the relative water wastage of each method? I am guessing that what you call the English way is the least inefficient. Are the French and Caledonian on river fed navigations, where water is plentiful? I don't think running out of water is ever likely to be a problem in Scotland! The English staircases are largely on reservoir fed canals where there is a limited quantity to get through a dry summer.

Jen

[Dav and Pen]

7 minutes ago, magpie patrick said:

 

 

 Rogny is in my to-do list, at least to visit by car. Is the lower picture on the new route at Rogny? 

 

 The one at Brades is big enough to allow emptying the top lock into a full lower one - I think the others are only to mop up a small surplus

 

 There are also overflows at Bratch dating from when it was a three rise - about the first twenty (?) years of it's operation before it was modified

The bottom photo is on the Nivernais canal and this a triple but just below is a double. In July but not the 14 th Rogny has a huge firework display using the old locks as the setting. The village is closed and stands erected along the canal side and hundreds, probably thousands turn up to see it.

[magpie patrick]

38 minutes ago, Jen-in-Wellies said:

What is the relative water wastage of each method? I am guessing that what you call the English way is the least inefficient. Are the French and Caledonian on river fed navigations, where water is plentiful? I don't think running out of water is ever likely to be a problem in Scotland! The English staircases are largely on reservoir fed canals where there is a limited quantity to get through a dry summer.

Jen

 A good choice of words! Staircases are not efficient users of water!

 

Off the top of my head the "English way" is probably uses the least. The Caledonian is fed by mahoosive great lakes and has parallels rivers that would be carrying the water is it weren't going through the locks. The operation of the locks could be considered to use no water at all compared to no boats going through because of the constant stream through the locks. That said, if you tried to work Bingley Five Rise this way you would very quickly have an empty canal up to Gargrave. 

 

The French system is spectacularly wasteful, it uses even more than a single deep lock, which quite an achievement! They drain Fonserranes every night, the water sloshing everywhere is quite impressive. Edited to add - The Canal du Midi is certainly not river fed, it has a very eleborate water supply from the Montagne Noir in the foothills of the Pyrenees, so they shouldn't be profligate with water - Fonserannes does have "le grand bief" above it - a pound about 35 miles long

Edited February 4, 2021 by magpie patrick

[David Mack]

14 minutes ago, magpie patrick said:

A good choice of words! Staircases are not efficient users of water

 

Unless you have separate water storage ponds at the intermediate levels, as at Foxton, Watford and Bratch. Here the water usage is the same as with conventional separate locks, in terms of a single passage of the flight.

Although the inability to pass boats between locks, means you can't work turns, which will use more water when there are boats moving in both directions.

[Keeping Up]

19 hours ago, AndrewIC said:

Mainly because the gates leak like a sieve, it’s only in recent years that there has been all the faffing around with the top paddles. The line is important though (although I think it’s markers on the upper face of both sets of intermediate gates, rather than the wall, unless they’ve repainted that), in a three or more chamber staircase it’s easier to drain the upper and intermediate chambers too far.

The instruction board there doesn't help, because it tells you to "empty the middle chamber" and a lot of people do exactly that.

1 hour ago, David Mack said:

 

Unless you have separate water storage ponds at the intermediate levels, as at Foxton, Watford and Bratch. Here the water usage is the same as with conventional separate locks, in terms of a single passage of the flight.

Although the inability to pass boats between locks, means you can't work turns, which will use more water when there are boats moving in both directions.

Another one with a misleading notice. It tells you that when the lock-keeper is not present, you should "maximise the use of water by adopting a one-up one-down principle". Indeed it does have exactly that effect, as well as creating delays, but it is the opposite of what you really want to achieve which is to minimise the use of water.

[Pluto]

2 hours ago, magpie patrick said:

Everything except the English system could support a deeper chamber lower in the flight - which doesn't make it a good idea. Also, whilst acknowledging the logic of the design in @Pluto post, I don't think I've ever seen a staircase with a deeper upper chamber like this. The ones I know of with obviously shallower lower chambers are:

 

Stamford Bridge

Struncheon Hill

Snakeholme

Dudgrove

Variation in the depth of individual chambers was for French canals, as far as I know all British riser locks kept water in the chamber after a boat had moved out of that chamber. On Bingley, the lockkeeper would try to ensure all boats passing in the same direction would go through the locks before letting the boats pass in the opposite direction. This did improve water usage, and somewhere I have the figures they kept of water usage at Bingley circa 1900. It is easy to get over-concerned about water supply. Yes, it was a problem in drought years, and improved water resources were needed as traffic increased. However, there was comparatively little traffic through Bingley, with much of the traffic in Yorkshire only going as far as Shipley, with traffic over the summit accounting for less than 10% of trade on the canal. With such conditions, there had to be an almost permanent feed at Bingley to ensure that the canal below was not adversely affected.

 

The Canal du Midi and Canal de Briare were never as successful as English canals in terms of the number of boats, so excessive water usage does not seem to have been a major problem. English canals carried far more traffic than was originally anticipated, with the L&LC probably taking at least 10 times the tonnage originally expected, though it is a bit difficult to decide exactly what was expected originally as prospectuses often used expected income, which can be calculated from ton-miles. They do not state how far an average load was expected to travel, so any calculation today is very much speculation.

 

The photo shows the lower cill of the top chamber of the locks at Rogny. Ground paddles were only fitted on one side, and his lock shows the original situation. The locks were lengthened later, not a problem with the top lock, but the exit from the ground paddle had to be extended more and more as the chambers were extended. The second photo shows a ground paddle tunnel further down the riser flight.