How much is a "lock"

[Heartland]

Ah Patrick how do you measure the water volume ?

 

The main purpose of this text was to discover how the canal engineers interpreted what a lock of water was, be that 80,000 gallons for wide canals or 25-26,000 gallons for narrow canals.  For the BCN the water supply did not only come from reservoirs and the streams that were permitted to flow into their canal. They also received water pumped from the mines which was often paid for. In order to make a payment, and some times it was restrospective, some form of judgement and measurement was required

[magpie patrick]

4 hours ago, Heartland said:

Ah Patrick how do you measure the water volume ?

Worked example

 

The Navan Lateral canal - the only part of the Boyne Navigation not to have a gravity feed from the river. It used to have but the river in Navan above Metge's lock has been lowered and a pumped supply will be needed. Four locks are fed from this level Rowley's and Ruxton at either end of the summit level, and below Rowleys there is Taafes and Thompsons (or Stackallen) descending to the Boyne at Stackallen. The deepest was Thompsons at three metres. All the lock chambers were approximately 14 feet 6 inches wide and 78 feet long to take boats 70 feet by 14 - take the dismensions as an oblong, the mitre of the gates at the bottom is cancelled out by the mitre at the top. Easier to work in metres so this translates as 23.77m by 4.37m, as the lock measurements are approximate and the minimum required for passage of the boats these figures were rounded 4.5m beam by 25m length by 3m drop. This gives a total water requirement of 337.5m3 (74,300 gallons) to fill the deepest lock. 

 

Then's the tricky bit - how often are you actually going to fill it? We tend to work in daily peak-average (as in, what's will be the busiest typical day) and calculate these for the days when it matters, i.e. when water is likely to be scarce, if calculating for a drought peak demand really matters as the canal may have limited storage capacity, so an average daily demand of 4 lockfuls a day may be fine if the variance is between 2 and 6, but not if it's 12 on Saturday and 16 on Sunday with nothing for the rest of the week. 

 

Two points on the number of fillings - first, in almost all examples, over any period of time the same number of boats will go up as go down, indeed not just the same number but the same boats, so displacement, if it has any effect at all will balance itself out, Somewhere like the Coal Canal in it's commercial heyday where virtualy all the loaded traffic was downhill, and thus descending boats had greater displacement than ascending ones, it may have had a measurable impact - second, the real critical factor is how often you are going to fill the lock, get that wrong and semantics about the shape of the cill or the displacement of the boat pale into insignificance.   

Edited August 24, 2022 by magpie patrick

[Pluto]

When canals were first built in England, those authorised prior to 1780, the expected traffic was far almost always less than that which resulted. No one anticipated the success canals would have in encouraging the development of industry, with the result that water supplies had to be extended over the years. As the catchment area for water was restricted, some canals reached the maximum number of boats it was possible to supply with certainty, given that rainfall varied from year to year. One of the main reasons British canals were so successful is the comparatively short distances involved, making it possible to construct them economically using 18th century technology.

 

On displacement, you need to factor in where a boat is loaded or unloaded, as that will raise or lower the height of water, which may or may not run to waste over a byewash. Just looking at one lock in isolation is useless, though the amount of water involved, compared to other factors, makes it pretty much a useless calculation anyway.