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The one, the only, Dalmuir drop lock!


ronnietucker
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Having bought myself a new bike (electric no less!) for Chrimbo. I decided to cycle down to my boat to try it out.

As I passed Dalmuir drop lock I thought I'd take some photos for you guys as it's the only one of its kind (apparently). From Wikipedia (so it must be true!):

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the only example in the world of a drop lock that has actually been constructed is at Dalmuir on the Forth and Clyde Canal in Scotland. This lock, of the single chamber type, was incorporated during the restoration of the canal, to allow the replacement of a swing bridge (on a busy A road) by a fixed bridge, and so answer criticisms that the restoration of the canal would cause frequent interruptions of the heavy road traffic. It can be emptied by pumping – but as this uses a lot of electricity the method used when water supplies are adequate is to drain the lock to a nearby burn.

This is just one side of the bridge. It's the same on the other side.

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It is slow, because the water is pumped out, rather than run through a paddle. Also, it is now operated by lowering it all the way, whereas initially boats could pass through as soon as the level was low enough to get under the bridge. Weed across the pump inlet is also a major problem !

With the benefit of hindsight, an improvement in design might be the provision of a sump pond at lower level, into which the lock could be emptied via sluices, with the sump pond being back pumped to the canal by a much smaller pump than that currently used. Much faster operation, and not quite so dependent on electricity and electronic control systems! :ninja:

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Very interesting, I did not know one existed.  A drop Lock is I believe one of the option of Bradley locks ever get restored.  The design of the Dalmuir one seems rather over engineered, and surprised there is no gate between the two sides so the you would only need to fill one side to let the boat exit, I guess there must be no shortage of water.

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13 minutes ago, john6767 said:

I guess there must be no shortage of water.

 

It would certainly seem that way. I always wondered why there was no link between Scottish and English canals. From what I read it's so that (in short) we don't give all our water to England. Every now and again there seems to be a resurgence of the idea to link the canals in some way.

This is from 2014: https://www.scotsman.com/news/environment/14bn-plan-to-share-scots-water-with-england-1-3613430

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A bold proposal to tackle water shortages in Britain’s southern counties by building a vast “super canal” between the two countries is being considered by both the UK and Scottish governments.

The plans, devised by one of the world’s biggest architectural and engineering design firms, envisage a new £14 billion waterway running from the Scottish Borders down through Newcastle and Leeds, winding its way along the west coast of England and taking in extra water on its way.

Known as the Natural Grid, it would eventually branch off as it reached the Home Counties, with routes running down into Hertfordshire and Hampshire to supply homes, businesses and utilities.

 

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45 minutes ago, ronnietucker said:

It would certainly seem that way. I always wondered why there was no link between Scottish and English canals. From what I read it's so that (in short) we don't give all our water to England. Every now and again there seems to be a resurgence of the idea to link the canals in some way.

This is from 2014: https://www.scotsman.com/news/environment/14bn-plan-to-share-scots-water-with-england-1-3613430

 

Don't know why as you are hardly short of the stuff.

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It seems the whole water shortage thing isn't new at all. A 'Grand Contour Canal' was proposed in the 1940's.

From a Guardian article published in 2013:

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in 1942 JF Pownall proposed a Grand Contour Canal that would use gravity to transport water from one end of the country to the other, avoiding the need to use expensive and energy-intensive pumping equipment.

Transporting water without the need for pumping is one of the key features of Weight's scheme, and he claims the canal would be more efficient and more resilient than smaller-scale, piecemeal water transfer projects.

 

 

... and here's a good article from the 1960's on said Grand Contour Canal:

gcc.jpg

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17 hours ago, john6767 said:

Very interesting, I did not know one existed.  A drop Lock is I believe one of the option of Bradley locks ever get restored.  The design of the Dalmuir one seems rather over engineered, and surprised there is no gate between the two sides so the you would only need to fill one side to let the boat exit, I guess there must be no shortage of water.

There is a bit of over-design, IMO. Not sure why the gates need the additional booms, which could have been incorporated into the gate. I suppose it's some protection against being hit by boats!  The lock doesn't actually use any water, as it is pumped (up) from the lock chamber into the canal.

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1 hour ago, Iain_S said:

There is a bit of over-design, IMO. Not sure why the gates need the additional booms, which could have been incorporated into the gate. I suppose it's some protection against being hit by boats!  The lock doesn't actually use any water, as it is pumped (up) from the lock chamber into the canal.

You are right of course, if pumped back to the canal it does not us any water, I was assuming it was being drained away.

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17 hours ago, ronnietucker said:

Very true.

But why is England seemingly short of water? We're on a tiny island, surrounded by the stuff, and it's not like we're in a tropical climate.

As Boris Johnson said in the article you linked to,

“The rain it raineth on the just and the unjust, says the Bible, but frankly it raineth a lot more in Scotland and Wales than it doth in England.”

But within England, it also rains a lot more in the north and west than it does in the south east, which is densely populated and needs a lot of water for farming, and thus the most vulnerable part of the country in a drought. Over the years a lot of effort has gone into keeping us supplied, for example bore holes down into our chalk hills and a lot of reservoirs fed by the Thames and its tributaries, and most of the time we get by, but being able to bring water down from the north would be a very good option to have. I think I'm right in saying that in the long drought of 1976 for example the north had plenty of water.

So Pownall's Grand Contour Canal idea from the 1940s, discussed at intervals ever since, was to supply London from the north, with a further link to supply from the Scottish border hills as an optional extra. Since the Kielder Water reservoir supplying the north east was built, it's been found to be much more than adequate for its purpose (perhaps due to the decline of heavy industry up there, I don't know?), so the modern thinking is that it would be one of the sources of water.

Given the potential transport benefits, easing the pressure on the roads and railways, my gut feeling is that the government should be taking the idea seriously. I wonder whether it should have been built instead of HS2. It's not a matter of Scotland giving the water away, because the water becomes more valuable when moved to the south east so if the plan is economically viable everyone can potentially benefit, and it just becomes a question of how the money from it is distributed.

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I think the over-designing is just to be uber-safe. I don't think anyone wants their boat squished under the bridge!  :D

This page has a good description of how it works with photos of the tunnel under the road which is used by the lock keepers: http://www.gentles.info/link/Drop_Lock/Drop_Lock.htm. I never saw the tunnel under the bridge (for the lock keepers) as it's apparently on the other side of the canal (to the cycle path I was on).

Another page noted:

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Safety barriers are fitted to protect each set of mitres gates from the impact of a vessel, which could potentially cause the lock to flood rapidly, endangering the lock users.

A major hazard with a lock of this design is that if the lock was to flood whilst vessels are under the bridge, the vessel and occupants would be crushed. To prevent this, further safety barriers adjacent to each side of the road are fitted, which raise and lower with the changing water level in the lock. This prevents vessels from drifting underneath the road and potentially being crushed.

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I'm not sure of their source, but Wikipedia states:

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It can be emptied by pumping – but as this uses a lot of electricity the method used when water supplies are adequate is to drain the lock to a nearby burn.

 

 

Surely thousands of gallons of water rushing by isn't a burn?  :D

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On 12/27/2017 at 14:55, ronnietucker said:

the vessel and occupants would be crushed

"Crushed", "Sunk" or damage the road bridge?

I'm not an engineer (or not that sort anyway) but I'd be marginally surprised if a downward force, applied equally all over the roof* would crush the boat. More likely simply to hold it down until the rising water met some point of entry into the boat?

* - ignoring chimneys, mushroom vents etc

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2 hours ago, 1st ade said:

"Crushed", "Sunk" or damage the road bridge?

I'm not an engineer (or not that sort anyway) but I'd be marginally surprised if a downward force, applied equally all over the roof* would crush the boat. More likely simply to hold it down until the rising water met some point of entry into the boat?

* - ignoring chimneys, mushroom vents etc

I would agree the force from buoyancy is not going the crush the boat it will just sink it.  That issue not one I had thought of with this type of lock, but you can see that from a H&S point of view it's a bit of a deal breaker with the design, being mitigated with these addition features and no doubt electric interlocks the stop the user opening paddles with the boat(s) under the bridge.

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2 hours ago, john6767 said:

I would agree the force from buoyancy is not going the crush the boat it will just sink it.  That issue not one I had thought of with this type of lock, but you can see that from a H&S point of view it's a bit of a deal breaker with the design, being mitigated with these addition features and no doubt electric interlocks the stop the user opening paddles with the boat(s) under the bridge.

This is Scotland!!! users are not allowed to operate normal locks never mind drop locks . When we first went through the drop lock, the operator could stop the procedure when boats could get under the road but the last few times we have been through they didn't over ride the automatic procedure and we had to wait longer for the booms either side of the bridge to be lifted.

haggis

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1 hour ago, haggis said:

This is Scotland!!! users are not allowed to operate normal locks never mind drop locks . When we first went through the drop lock, the operator could stop the procedure when boats could get under the road but the last few times we have been through they didn't over ride the automatic procedure and we had to wait longer for the booms either side of the bridge to be lifted.

haggis

Yes it get that in Scotland, but the same applies, the operator could still mess up.  I was however more thinking if this design was used for the Bradley restoration on the BCN where it would, one assumes, be user operated.  I don’t know it that puts more onous on the system or not, but it is an interesting design issue.  More likely if the restoration happed would be an electric lift bridge I guess, but this would be different.

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To answer the questions about why the Dalmuir Drop Lock is as it is:

First, yes it is the only one to date, so everything that  went before was theoretical. Many had been proposed, I've worked with groups proposing them including Dalmuir.

The original concept of a drop lock was two back to back locks with a bridge between them, the locks would be conventional and potentially user operated. The process for emptying a lock involved a drain to a reservoir that would be pumped back, or if possible simply a drain to a stream or river.

In principle this is no different to, say, going down Kings Lock and up Wardle Lock in Middlewich, but the problem was in most cases, and certainly in the conceptual model, the canal between the locks is almost entirely under structure. So what? Well, the so what is if a gate bursts then this space will fill up very quickly (unlike below a conventional lock) as there is nowhere for the water to go. Gates do burst, not often, but often enough to mean the risk of a boat being trapped underneath the bridge was unacceptable. At this point the view was that the operation of a "drop lock" had to be supervised and the operation of the two locks coordinated so that a boat would never be waiting under the bridge with a full lock in front of it. 

When Dalmuir was designed the contractors/consultants too the logical decision to do away with intermediate gates, thus the bridge structure would flood every time the lock was filled, which would make sure no one was under it behind a lock gate. Dalmuir is supervised which ensures no one is under the bridge when fillling comences, and booms make sure no one drifts under. The risk of a burst gate was still taken very seriously, and guillotines were considered, but rejected because they can open against a head of water. Not long before the design was commissioned a malfunction at a lock on the Rhone (Bollene?) resulted in the top gates opening instead of the top paddles, so no one was taking chances at Dalmuir. Instead a sort of hybrid double gate was used, that would survive being hit (the usual cause of a burst gate) and couldn't open against a head of water. 

From memory the original plan at Dalmuir involved water draining away rather than being pumped, but continuity of water supply became an issue so pumps it was. I did suggest that this could have been resolved by leaving the lock full with the gates open, but for whatever reason this wasn't followed up.

The only variant I've seen proposed since is for the Shrewsbury and Newport, a proposal that returns to the idea of back to back locks, but with a sealed system, so one lock must be full and the other totally drained, and the total volume of water in the system is enough, and only enough, to float between the locks when they are both at the lower level. A boat would enter one lock, which is then drained, the boat sails to the second lock, which is then filled by pumping the residual water from the first lock leaving it totally dry. This system has never been designed in detail, but potentially is user operable. 

Bet you  wish you hadn't asked now!

6 hours ago, john6767 said:

Yes it get that in Scotland, but the same applies, the operator could still mess up.  I was however more thinking if this design was used for the Bradley restoration on the BCN where it would, one assumes, be user operated.  I don’t know it that puts more onous on the system or not, but it is an interesting design issue.  More likely if the restoration happed would be an electric lift bridge I guess, but this would be different.

And to add - it's only in the Bradley  proposals as an option, and mainly to rule it out. Lift bridge is preferred (Magpie Naylor Young wrote the report)

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1 minute ago, ronnietucker said:

Nope. Fascinating stuff.

Did you have something to do with the drop lock design, or something?

I was involved in the conceptual design of a few drop locks (several had been proposed before Dalmuir) and reviewed* the Dalmuir proposals after another consultant (SWK?) had prepared them

*Jim Saunders, a "retired" engineer (he was in his mid-70's) was the official reviewer, but as was always the case then he and I did it between us over many cups of coffee. Jim passed away over ten years ago, but I recall fondly the many, many conversations we had on this and other schemes. 

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There may be suggestions for drop locks elsewhere. Whether Bradley will happen is yet to be determined. Another BCN where it could apply is on the Balls Hill Branch where the Black Country Road cut off access to the section beyond. A drop lock would put craft back onto the disused section, which have the potential of much needed moorings, residential or other wise.

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