Over Lock, Gloucester - how deep?

[magpie patrick]

See below - sign at the site of Over Lock, where the Hereford and Gloucester Canal joined the Severn. I've visited today for the first time.

 

Simple question, did it really have a fall of thirty feet? I've no evidence to the contrary, and even with the river well up today It was clearly deep, but 30 feet? That would have made it well over twice the fall of the next deepest, and more than the fall of the two rise at Aberfan, (29 feet) which Bradshaw notes as being the deepest in use in 1904 (by which time the H&G had closed)

If it was this deep, I'm surprised I haven't seen any other reference to it. 

[1st ade]

Very tentative investigation and overlaying a modern overhead with the OS six inch of the 1900's; the canal is between the 50 foot contour and the river, there is a range of spot heights around 31 foot to the east of the river --> The canal was no more than 20 foot above the river and possibly less?

Link http://maps.nls.uk/geo/explore/#zoom=17&lat=51.8773&lon=-2.2680&layers=6&b=4

Edited April 9, 2018 by 1st ade

[David Mack]

Do they perhaps mean 30 ft deep from coping to invert, rather than 30 ft fall? Given the tidal range of the Severn the actual fall would vary substantially with the state of the tide.

[john6767]

5 minutes ago, David Mack said:

Do they perhaps mean 30 ft deep from coping to invert, rather than 30 ft fall? Given the tidal range of the Severn the actual fall would vary substantially with the state of the tide.

Would it have only been usable at certaIn states of the tide?

[magpie patrick]

14 hours ago, David Mack said:

Do they perhaps mean 30 ft deep from coping to invert, rather than 30 ft fall? Given the tidal range of the Severn the actual fall would vary substantially with the state of the tide.

That's what I wondered, although the sign says a drop of around 30 feet. The copings were probably 2-3 feet above canal water level.

 

13 hours ago, john6767 said:

Would it have only been usable at certaIn states of the tide?

I suspect so 

Some more background for those who don't know the site

Over Lock dropped into the Severn on the west bank of the west channel - the wrong chnnel for Gloucester Docks. The river is tidal here but about half a mile upstream is Maisemore weir, which had a narrow lock round it to give access to the H&G - the H&G itself was approx narrow beam (7 foot 6 from memory). There was also a lock and weir at Llanthony on tge other channel just downstream from Gloucester Docks, this was designed for the larger vessels that traded on the river and was the same sort of size as Diglis Lock.  

Gloucester Lock falls 12 feet to the river at Summer Levels, which means the the Gloucester Docks are actually higher than the river above Upper Lode Lock 14 miles upstream. I don't know why this level was chosen but In have noted Gloucester Docks are above the highest tides and all except the worst floods, so it may well have been decided to get high enough to avoid trouble with flooding. Gloucester lock has reverse gates to cope with the level in the river being higher than the canal,, I've never seen it more than a couple of feet higher (which give the river is then 14 feet up is bad enough!)

If the H&G took the same logic they'd adopt about the same level, and given that the river is tidal they may often have dropped more than 12 feet. However around one third of tides top the weirs at Llanthony and Maisemore (they hold back the same reach to Upper Lode) so often locking out at high tide would have led to a drop of less than 12 feet. 

Emerging on the west channel was always a pain for the H&G, they tried a canal across Alney Island to gain access to eastern channel, and built an (unauthorised) embankment across the western channel as part of this - the courts told them to take it down again and Maisemore Lock was the permanent, if somewhat unsatisfactory, solution to their problem

I suspect the lock was normally used around high tide and on occasion the fall was greater than 15-16 feet, say an hour or two before neep tides with little or no  fresh in the river, which would fit David Mack's suggestion of a 30 foot chamber from coping to invert

[Jen-in-Wellies]

For the restoration, the H&G Canal Trust plan to restore the Llanthony lock, but not the Maisemore one to reconnect to the rest of the system. The logic is that it is a lot easier to turn off the river in to Over Lock facing in to the stream and coming up from Llanthony lock means that the boat doesn't need to be turned round under most conditions. Having done Keadby and Stockwith locks on the Trent, which are similar with the chamber at right angles to the river I can agree with that. There are several bridges just downstream of the lock just to add to the fun for a boat trying to turn round before going in if it came down from Maisemore. I've only been to Over once, and haven't looked at the nearby Severn lock sites yet, so I don't know how strong the tidal effect is under normal conditions.

My Mum is a member of the trust, so I get to read their magazines. Slow progress, but sure with a lot of work going in to securing the route and arranging a revenue stream to restore and maintain the canal for the long term.

Jen

[Rob-M]

Having been in and out of Gloucester a number of times I don't fancy keeping right and heading for Llanthony weir as there can be quite a pull there. I haven't looked at what it would be like to enter Llanthony lock. I wonder how many boats might miss the lock coming back down from Over lock and end up having to be rescued from further down the Severn.

[Jen-in-Wellies]

3 minutes ago, Rob-M said:

Having been in and out of Gloucester a number of times I don't fancy keeping right and heading for Llanthony weir as there can be quite a pull there. I haven't looked at what it would be like to enter Llanthony lock. I wonder how many boats might miss the lock coming back down from Over lock and end up having to be rescued from further down the Severn.

The chances for wrong turns and being dragged in to trouble by the flow are definitely there. I suspect it will need some control and supervision to prevent this at least in the early days and maybe long term. Perhaps like the Ribble link. It will certainly be like other parts of the system, such as the tidal Trent and Ouse, that require care to traverse safely in a typical ditch crawling narrowboat.

[David Mack]

On 4/10/2018 at 09:51, magpie patrick said:

The river is tidal here but about half a mile upstream is Maisemore weir, which had a narrow lock round it to give access to the H&G - the H&G itself was approx narrow beam (7 foot 6 from memory). There was also a lock and weir at Llanthony on tge other channel just downstream from Gloucester Docks, this was designed for the larger vessels that traded on the river and was the same sort of size as Diglis Lock.  

Interesting that Google Maps satellite view shows both locks very clearly.

https://www.google.co.uk/maps/dir//51.8627958,-2.2595932/@51.8627454,-2.2596718,124m/data=!3m1!1e3!4m2!4m1!3e0

https://www.google.co.uk/maps/dir///@51.8926223,-2.265281,177m/data=!3m1!1e3!4m2!4m1!3e0

[Tim Lewis]

Can't answer your question but this is a photo of the lock site looking from the basin towards the River Severn taken just before the basin reopening:  

[magpie patrick]

23 hours ago, Tim Lewis said:

Can't answer your question but this is a photo of the lock site looking from the basin towards the River Severn taken just before the basin reopening:  

 

It is rather spendid - I walked the restored length (I guess about half a mile) and fancy bringing the canoe out to it - it's a bit short, but then I'd have "done" the Hereford and Gloucester