I think the purpose of the two weirs was different.  The Carmyle weir was designed to supply fresh water to the power station and would therefore have been high enough to preclude salt contaminated tidal water from getting into the system.

The GG weir was designed to maintain a reasonably even level of water above it but it could be regularly topped by high tides.  The speed of the water and rate of flow either side of high tides is very low and would pose no danger to banks etc..

The James Watt dock is not a dry dock, it is a wet dock and used to maintain a constant water level by only opening the caisson at high tides.   This makes loading and unloading ships easier and mooring safer - the warps do not need constant attention as the water level rises and falls.

See, you can learn something useful here every day - it never occurred to me that JWD had a wet dock. My past correspondence regarding JWD has always been with regard to service and maintenance of Clyde ferries, and a wet dock would be little use for that.

My closest "hands-on" experience was in the now defunct Govan docks, but they never let is near them, and we were always herded to the jetty where the ships we would be working were berthed.

However, dry or wet, the docks don't really tell us anything about weirs, or locks, which operate quite differently.

Reading the Captain's history lesson, the Carmyle weir predates the power station, and there's no reason to segregate fresh water for cooling duties in a power station, sea water does the job just as well, and would make little difference to the materials used. Fresh water gear would probably be more expensive, since pumping gear at this level of engineering would be built to be corrosion resistant anyway - who want to have to replace parts on such a large scale? There would be two separate water circuits, and the external cooling water would circulate in heat exchangers that had no fluid connection with the working of the station, only heat would pass across the interface, so dirty, or even salty, cooling water never gets anywhere near the workings.

Having worked on similar installations elsewhere on the Clyde, it's probably fair to say the the Carmyle weir had no relevance to the power station. Projects on this scale use massive centrifugal pumps driven by electric motors to draw the water they need from the rive and and pump it to the point of use (and that might be miles away, obviously not at Clyde's Mill though), unlike the old mill, which would have needed some head of water to provide the motive force to get the water into the mill buidlings.

The speed is of a river is changed once a weir is added, a weir is just a specific case of dam design, and the upriver section will slow down. This is because the weir/dam raises the water level behind it, which increases the cross-sectional area of the river - it has no option but to slow down since it's mass flow-rate is effectively constant. This has the effect of reducing bank erosion, but also means the river begins to drop the material it would otherwise carry downriver, so silting can become a problem

Some good thoughts there - and some good links Apollo. Here is the Glasgow Green weir taken from the first O.S. plan, you'll see the banking I was talking about. I was bandying the idea that the lock gates rose above the normal high tide levels and so the bank between the lock and the weir was likewise built high so that spring high tides didn't overflow them and cause damage.





image courtesy of the Trustees of the National Library of Scotland

Great detail, and shows that we have a genuine two gate lock as well.

I'd have to say that the banking is only provided to allow the lock to be constructed and used though, not as any sort of overflow related option.

To operate the lock, people have to be able to walk around the raised area and swing the gates open and closes, and operate the valves. It makes sense to make sure this is built high enough to to keep the operators out of the water.

As I noted earlier, having the lock gear built high keeps it out of the water, but if the tide is high enough to breach the weir, the water will simply flow around or past the lock, and break through elsewhere, where the bank is not as high as the built up lock, and that could be only a couple of feet along from the lock itself, or the opposite bank of the river.

It's interesting to note the direction of the gates, as this shows the designers considered the maximum pressure to be coming from the seaward side. The gates point into the highest incident pressure so that they are held closed naturally. On simple rivers and canals, this is normally into the flow of the water supply.

(Best thread we've had in ages - I'm on the edge of my seat and enjoying all the details that are coming up )

Ah, I think I've been reading the hint at protection as too all-encompassing, and your meaning is protection of the lock and its immediate surrounding if I read your more detailed description correctly, and yes, that would be a most sensible choice. You wouldn't want to be building or repairing the lock every time there was a bit of a swell.

If I read the scale at the bottom correctly, that's 100 and 200 feet shown.

A quick fiddle on the screen shows the lock to be 27 feet wide, and 75 feet long.

Tidal charts from the time would be needed to determine the probable depth, as the depth and width of the river have been engineered somewhat since those days, so modern figures don't mean much, or would have to be fiddled about and values assumed otherwise.

I was looking up some lock designs, and the culverts (which I am assuming to be depicted on the map by the slightly widened section to the west) are on the wrong gates compared to the diagrams. These allows the lock to be flooded, and are usually shown around the gate pointing upriver, into the water supply.

I know it's making an assumption about something shown in very little detail, but it echoes the first oddity I noticed as what I would have taken to be the upriver gate is pointing seaward. I doubt the mapmakers got such a detail wrong and wonder if there was a reason, if it was a mistake, or the nature of the installation made this apparent departure from the norm "a good idea"?

I am puzzled by the gate alignment too as they should open against the main flow as when closed it is the pressure of the water on the high side of the lock that keeps the gates shut and sealed.  This is standard canal operation practice.

Afraid the stated scale is no use unless you're looking at a life-size 1:1 copy of the map, and the scan/pic/screen variables render it meaningless. The only thing we can do with the image is assume the scale line shows 100 foot steps (and the tenths, or 10 foot steps to the left).

The Rutherglen boatyard build vessels much much bigger than the lock, but they were built in sections, then floated downstream for assembly at other, larger, Clyde yards.

(Maybe we're using the same words differently. I'll waffle a bit more.)
Both lock gates are shown pointing from west to east on the map above, depicting the lock. This means the gates can only swing to the east to open.The normal direction for lock gates is given as pointing into the flow of the water supply. I'm guessing this makes them "fail-safe" in so far as the upriver side will have a higher water level than the downriver side, which means the gates are held shut by the imposed water pressure. Manual intervention is needed to open them.

I'm just wondering why they would depict the opposite on the lock on the Clyde. The upriver level will (normally) always be above the level on the downriver side of the weir.

The only thing that occurs to me is that the idea is that the lock can be used to bypass and relieve the weir, by just leaving the gates open. When the tide is dominant, simply pushing the gates shut will lead to the tidal water pressure holding them closed with no further action needed, and the gates would then open themselves when the tide reversed and the river became dominant again.

Oh well. There you are... answered my own question again

Yup. Ok.

I see the problem after a nap, now I have to work out why!

And why it wasn't obvious before.

Well, somone must be having a good laugh at this one

As to why this map is inverted, we'll have to hope the provider will put us out of our misery.

As for myself, I'm happy to admit that I'm a dumpling and fell into the trap of seeing what I expected - my usual view of the weir is from the north bank. looking across to the spot where the lock would have been on the opposite bank, and with the river flowing from left to right. Seeing the map presented with the same orientation, I put the two together and saw the flow from left to right as the usual west to east orientation that would be expected on a normal map, and never twigged to the inversion.

I rattled the following together to teach myself to be more careful in future, and explain the gate logic since the foregoing drivel will confuse late arrival to the thread:

Last dying attempt at trying to retain some sort of credibility by a drowning man - inverting the map was supposed to be a sign of despair (meant to signal not serious, a sign of desperation, and better than jumping in the Clyde).

I'm seriously flummoxed by the gate's direction.

What we may be looking at is the County River Engineer's (or whatever he was called) expertise coming into play...

Namely that the theory says the gates should be places one way for sound reasons, but in practice, the better way is actually contrary to theory.

Perhaps allowing the flapping operation to be dictated by tidal forces is potentially less damaging, and relieves excess pressure on the weir and acts as a safety measure?

I don't know. Unfortunately when you encounter these kinds of anomaly, where the experiences engineer and accepted practice fly in the face of the logical theory, you can go and concoct any number of crazy ideas to explain them, any of which might even work, but are not based on actually building and operating the thing, and finding out what it does in reality.

We need a lock builder with river and weir experience!