Canal Levels

[Heartland]

Whenever the heights of canals are mentioned it is now based on the ordnance datum at Victoria Dock, or was from 1844. Bradshaws map (1832) was based on a depth that was 6ft 10 inchws below the "sill" Old Dock at Liverpool and this has led to discrepancies in heights between the Bradshaw map and the later data quoting heights. For example Tring Summit according to Bradshaw was 405ft 6in where is now regarded as 395 od. Such a fact raises the question of determining height at the time of canal building and how measurements changed with the ordnance survey.  

[David Mack]

More information on the difference between Liverpool and Newlyn (Ordnance Survey) datums is available at https://www.ordnancesurvey.co.uk/gps/legacy-control-information/liverpool-to-newlyn

[Pluto]

The file DP175 in Lancashire Record Office includes a file on canal water levels in Liverpool, taken when they were considering using the canal as a water supply in the 1830s. The datum used was the curb stone at the SE corner of Canning Dock. Did the specific height really matter for a canal, as long as they knew the variations in level. Sea level was only important if the canal emptied directly into the tideway, and most fed into a dock which would give the necessary datum.

[Heartland]

I suppose canal heights matter mainly for the historian, Bradshaw 1832 records a host of different levels for canals and early railways. The canal from Wigan to Whittle is given  as 307 ft 4in above the datum at Liverpool as Lancaster Canal property.. The rise of the Leominster Canal from Stourport to Sousnet Tunnel (recorded as not yet executed) was to be 207 ft and 22 locks whilst the Andover Canal was 184 ft and 10 inches above the Liverpool datum at Andover and only  5ft 10 in at Redbridge Lock, so the must have been a valid reason to include such data.  

Edited June 27, 2018 by Heartland

[Scholar Gypsy]

And Fenny Stratford lock on the GU, allegedly, shows what can happen if you get your levels wrong ....

[David Mack]

2 minutes ago, Scholar Gypsy said:

And Fenny Stratford lock on the GU, allegedly, shows what can happen if you get your levels wrong ....

Although the Grand Junction long precedes any national datum. It's just a consequence of the inaccuracies of surveying at the time.

Or perhaps the lack of wisdom in starting the construction of a long pound from both ends!

[Pluto]

1 hour ago, David Mack said:

Although the Grand Junction long precedes any national datum. It's just a consequence of the inaccuracies of surveying at the time.

Or perhaps the lack of wisdom in starting the construction of a long pound from both ends!

The following gives the history and reason for the lock: http://www.bucksas.org.uk/rob/rob_19_1_67.pdf

[Scholar Gypsy]

12 hours ago, Pluto said:

The following gives the history and reason for the lock: http://www.bucksas.org.uk/rob/rob_19_1_67.pdf

Thank you for that.  Demonstrates that the myth in many books (that the lock was a result of an arithmetic surveying error) is incorrect.  

[Heartland]

Myths reproduced in print and passed down from author to author has been one of the objects, members of the Railway & Canal Historical Society aim to redress through their Waterways History Group as the last RCHS president, will no doubt agree to.

 

Construction factors are often forgotten, or ignored, by those looking for reasons as to why canals are the way they were.

[Scholar Gypsy]

I will need to annotate my copy of Priestley's navigable rivers and canals (1831)... apols for the lack of rotation. 

 

[Heartland]

Priestley is not the best source for totally accurate histories, but it is good for following the statutes

 

The wording definitely makes the statement that the lock was a mistake of levels, and perhaps this is where the myth came from....

 

 

[Pluto]

Just came across this section for the canal route from London to the NW. It is from an 1837 French book, De la dépense et du produit des canaux et des chemins de fer, comparing canals to railways. The number of locks and summits does suggest why long distance canal traffic did not survive in this country.

[TheBiscuits]

2 hours ago, Pluto said:

Just came across this section for the canal route from London to the NW. It is from an 1837 French book, De la dépense et du produit des canaux et des chemins de fer, comparing canals to railways. The number of locks and summits does suggest why long distance canal traffic did not survive in this country.

That's an excellent argument for building the Grand Contour Canal.  Thanks for sharing, Mike.

 

Edit to add:

 

The other rationale of sending all the spare water from the Pennines down to London is a little tenuous this year!

Edited July 24, 2018 by TheBiscuits

[Pluto]

12 hours ago, TheBiscuits said:

That's an excellent argument for building the Grand Contour Canal.  Thanks for sharing, Mike.

 

Edit to add:

 

The other rationale of sending all the spare water from the Pennines down to London is a little tenuous this year!

A good engineering argument, but I am still looking for a good economic one....

[Heartland]

That is indeed a useful map, and one that shows the journey flyboat from Preston Brook was required to take to reach London at the time both the Grand Junction Railway and the London and Birmingham Railway were nearing completion. It should be noted that these rival railway schemes were laid for considerable lengths on stone blocks and iron rails, which was a certain handicap until engineering of these routes were improved. 

 

Lock flights and tunnels were inevitable delay points for fly boat operation, yet it continued into the railway era and much later. 

 

Looking at the map in closer detail the steepest climb was the Trent & Mersey from Middlewich to Harecastle

 

 

With the Grand Junction having two major summits with climbs and descent of a more gradual nature:

 

It should be born in mind that canal carriers did have alternate routes to choose from, by 1837, where climbs and descents proved easier

[MoominPapa]

On 24/07/2018 at 19:04, Pluto said:

Just came across this section for the canal route from London to the NW. It is from an 1837 French book, De la dépense et du produit des canaux et des chemins de fer, comparing canals to railways. The number of locks and summits does suggest why long distance canal traffic did not survive in this country.

That's fabulous. The familiar canal names sound, somehow, more exotic in french.  I particularly like "Canal de Wyrley a Essington". What's the tunnel (Souterrain) between Fradley and Haywood? I don't remember any tunnels along that bit.

[pete harrison]

4 minutes ago, MoominPapa said:

I particularly like "Canal de Wyrley a Essington". What's the tunnel (Souterrain) between Fradley and Haywood? I don't remember any tunnels along that bit.

Was there not a tunnel at / near Armitage ?

[MoominPapa]

9 minutes ago, pete harrison said:

Was there not a tunnel at / near Armitage ?

I believe there was. That would explain it.

 

MP.

 

[David Mack]

14 minutes ago, pete harrison said:

Was there not a tunnel at / near Armitage ?

 

Yes. Opened out in 1971.

[Heartland]

Looking at the tunnels, there is one missing on the French Map it would be Barnton or Saltisford.