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How much is a "lock"


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Recent discussions on this forum have mentioned fires put out by the fire brigade and water used from the canals nearby. Another thread talks about water shortages and canal pounds becoming dry with boats stranded beside the banks.

 

In the past canals such as the Birmingham Canal Navigations would mention their reservoirs as holding a certain amount of "locks" to describe volume of the water stored there. Similar mentions were made of the amount of water supplied from the mine pumping and South Staffordshire Mines Drainage establishments. Yet a lock on a canal was not of a standard dimension even on the BCN where depth varied. On other canals the locks might be barge width. For the engineers the tern lock as a form of measurement would have been a standard amount, but in modern terms what would that amount be in litres for example.

 

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Though the locks vary in depth, water usage on a flight is largely set by its deepest lock. For the BCN, you'd need to compare the size of the deepest locks in each flight off each of the levels, both now and historically, when there were more flights than now. If it turns out the deepest on each flight is a similar depth, then the concept of locks worth of water available becomes valid. I've no idea if this is actually the case on the BCN. Evaporation and leakage are a constant, or dependent on weather conditions, but every time a boat goes up, or down a flight uses one deepest lock full.

Edited by Jen-in-Wellies
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8 minutes ago, Jen-in-Wellies said:

Though the locks vary in depth, water usage on a flight is largely set by its deepest lock. For the BCN, you'd need to compare the size of the deepest locks in each flight off each of the levels, both now and historically, when there were more flights than now. If it turns out the deepest on each flight is a similar depth, then the concept of locks worth of water available becomes valid. I've no idea if this is actually the case on the BCN. Evaporation and leakage are a constant, or dependent on weather conditions, but every time a boat goes up, or down a flight uses one deepest lock full.

 

reminds me of the Deep Lock in Bath.   each time it is used the upstream lock needs to be emptied a couple of times to keep boats in the short pound from being stranded.

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On the L&LC a standard lock full was 80,000 gallons. The average rise of a lock on the canal is around 9 or 10 feet, which I suspect is slightly more than on most narrow canals, so for them I would suggest 35,000 gallons. I did suggest to BW's water engineers that they returned to such measurements, rather than cubic metres, as it would remind them that they were dealing with canals used by boats.

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My favourite unit of volume is the acre-foot, which is used in the United States for water management, for example recent media coverage of the shortages on the Colorado River system. ! acre-foot is about 270,000 Imperial gallons. 

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Just now, Tracy D'arth said:

I work on 180 to 200 tonnes for a narrow lock of "average depth", 7 to 9 feet.

Which seems crazy to lift a 20 tonne boat!


A lock will use more water to move boats uphill compared to downhill.  Imagine a canal where each lock has to be left empty after use, and boats are very infrequent (ie operate independently of each other), Then, assuming the capacity of the lock is indeed 180 tonnes, when a 20 tonne boat goes uphill a total of 200 tonnes (180+20) would move from the upper pound to the lower pound. When it goes downhill 160 tonnes (180-20) would move from the upper pound to the lower pound. This makes sense in terms of conservation of energy, thinking about the potential energy of the water and the p.e. of the boat. (Note, this result requires you to think about water movement when the boat moves into and out of the lock, not just the boat going up and down in the lock). You are of course right that a lock is not very efficient (20/180 = 11% in this example). Inclined planes, boat lifts etc use much less energy.

 

If you then add back pumps, or a reservoir, then to replenish the water level in the upper pound a total of 180 tonnes would need to be pumped. This is independent of the displacement of the boat, and whether it is going up or downhill.   

 

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9 hours ago, IanD said:

40000 gallons (or 180000 litres in 21st-century-speak) is what I've usually seen quoted for a typical narrow canal lock.


that would be a very deep lock. I use the  figures of 28,000 gallons for the water used transiting s narrow lock and 56,000 for a wide lock

 

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I would agree with Tim. Most quotes I have heard are of 56,000 gallons for wide locks (Grand Union size) and around 26,000 for narrow locks. Depths will of course vary therefore the amount in volume.

 

Heartland's original question can be answered only in theory, as lock depths vary. The volume of water in a 'lockfull' therefore also varies, and can only be used as a rule of thumb.

 

The alleged American measurement of acre x foot (depth presumably) is neither here nor there. It may well be 270,000 gallons, but is that Imperial or Elizabethan gallons? As to how much water is used going uphill against downhill being different, and displacement of a vessel in the same calculation (was water over bywashes considered?), it's about as much use as fog on a dark night (apologies for being blunt).

The fact is - it varies. Volumes used will also be affected by the difference between a shallow draught short narrow boat in a wide lock, compared to a heavily laden wide boat in a wide lock. Then there's evaporation and leakage to consider.

 

The 'lock full' of water as a precise measurement is a useful estimate at best, but does give an 'indication' of how many lock emptyings/fillings that a reservoir is capable of supplying - roughly. Then there's the displacement in a reservoir caused by gradual silting from the banks; detritus thrown in; and fish displacement. It can get quite silly when an attempt at precise volumes are spoken of..

 

Edited by Derek R.
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12 hours ago, Tacet said:

When a boat goes uphill in a lock, water is drained from the upper pound to fill the lock but none immediately moves to the lower pound.

 

May I point out, that if the boat going uphill presents itself to a bottom lock (in a flight or single) that is full, then immediately it has moved a lockfull into the lower pound which will have to be replaced ultimately by water from the upper pound. Only if the lock is empty upon approach can the above statement be true.

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The engineers of the day had to have an accurate measure of some form, perhaps, or was it more guesswork

Philip Weaver in 1986 talked about the Ocker Hill pumping engines being capable of lifting 1062 locks in 24 hours approximately 26.5 million gallons and stated that the six engines were installed side by side in the same time in the engine house. Philip also suggested that it was one of the largest indoor installations of beam engines in the country.
 

 

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1 hour ago, Derek R. said:

 

May I point out, that if the boat going uphill presents itself to a bottom lock (in a flight or single) that is full, then immediately it has moved a lockfull into the lower pound which will have to be replaced ultimately by water from the upper pound. Only if the lock is empty upon approach can the above statement be true.

True - depending on semantics.   And not (I think) in the case which Scholar Gypsy is making.

 

If the lock is full, you draw nothing off the top pound when it is emptied unless you consider the lock itself to form part of that pound.

 

The lock is sometimes part of the upper and sometimes part of the lower pound and sometimes a separate pound, depending on levels and, perhaps, whether the gates are open or closed.

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1 hour ago, Heartland said:

The engineers of the day had to have an accurate measure of some form, perhaps, or was it more guesswork

Philip Weaver in 1986 talked about the Ocker Hill pumping engines being capable of lifting 1062 locks in 24 hours approximately 26.5 million gallons and stated that the six engines were installed side by side in the same time in the engine house. Philip also suggested that it was one of the largest indoor installations of beam engines in the country.
 

 

A bit like today when the media says an off shore wind farm will supply X number of homes with all their electricity 

 

An example

This is enough clean energy to power almost 280,000 British homes. Compared to fossil fuels that is a reduction of around 500,000 tonnes of CO² emissions every year.

Edited by ditchcrawler
I did it again
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Whichever way you look at it, water is needed from a summit supply and will ultimately end up at a lower level.

 

39 minutes ago, Tacet said:

(snipped)

If the lock is full, you draw nothing off the top pound when it is emptied unless you consider the lock itself to form part of that pound.

 

The lock is sometimes part of the upper and sometimes part of the lower pound and sometimes a separate pound, depending on levels and, perhaps, whether the gates are open or closed.

 A lock is a lock. The area of water between locks is a pound.

If a lock is full (going uphill) you have emptied a lockfull into the lower pound in order to enter the lock. You then have to draw a lockfull of water off the upper pound to rise in the lock, thereby replacing the lockfull you emptied to enter. Therefore, you have taken a lockfull of water off the upper pound to proceed uphill (or conversley downhill). Water is needed to move a boat uphill or down. It gets used by moving water from a higher level to a lower level. This is basic stuff.

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You are correct, except that on the L&LC, the water between two locks is a pool, not a pound. The standard lock full will vary from canal to canal as it will depend upon what is considered the average fall of a lock on that canal. Some canals, such as the L&LC, tend to have falls around 10 feet, whilst on many narrow canals it will be more like 8 feet. The result being that a standard lock on the L&LC is 80,000 gallons, whilst on narrow canals the figure could be more like 30,000 gallons, though this would vary from canal to canal. One of the more interesting books on water supply for canals is John Sutcliffe's from 1816 where he uses tons of water, though not all the time. 

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A standard lock for the L&LC would include those between Liverpool and Leigh. Also, from the lock dimensions produced by the L&LC, many locks had considerable clearance at either end, with widths of over 15 feet. Narrow canal locks seem to be much closer to the 72 by 7 dimensions. The term 'lock full', when used by a canal company, was a very general term and would probably be on the generous size, as in terms of water usage that passing through locks was usually considered around one third of the total amount of water required. All that was needed was a standard which allowed comparison between years, and a rough idea of how much water was in store, and how it was varying over time. There are too many variables and unknowns to make water supply an exact science, the problem today is that we have too few people who understand the art.

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"The term 'lock full', when used by a canal company, was a very general term and would probably be on the generous size, as in terms of water usage that passing through locks was usually considered around one third of the total amount of water required. "

 

The actual amount of water used when a boat uses a lock will depend on the boat's displacement and  whether or not the lock is set for the boat's passage.  

 

Let's call the amount of water needed to fill an empty lock x, and the displacement of your boat, y. If going uphill, you find the lock full, then you will obviously need to empty a full lock of water before you enter, and will effectively draw x from the upper pound in order to enter.

 

Once you have entered the lock, The amount if water required from the upper pound to fill the lock will be x -y.  When you leave the lock, y from the upper pound  will enter the lock, which then contains x.  

 

If another boat coming the other way with displacement z enters the lock you have just left,  the lock will now contain x-z of water and z of boat. So when emptying the lock to descend,  that boat will  discharge x - z into the lower pound, not x.

 

So the actual amount if water required to pass a boat through a lock will depend on the boat's displacement. 

Edited by Ronaldo47
typos
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2 hours ago, Ronaldo47 said:

"The term 'lock full', when used by a canal company, was a very general term and would probably be on the generous size, as in terms of water usage that passing through locks was usually considered around one third of the total amount of water required. "

 

The actual amount of water used when a boat uses a lock will depend on the boat's displacement and  whether or not the lock is set for the boat's passage.  

 

Let's call the amount of water needed to fill an empty lock x, and the displacement of your boat, y. If going uphill, you find the lock full, then you will obviously need to empty a full lock of water before you enter, and will effectively draw x from the upper pound in order to enter.

 

Once you have entered the lock, The amount if water required from the upper pound to fill the lock will be x -y.  When you leave the lock, y from the upper pound  will enter the lock, which then contains x.  

 

If another boat coming the other way with displacement z enters the lock you have just left,  the lock will now contain x-z of water and z of boat. So when emptying the lock to descend,  that boat will  discharge x - z into the lower pound, not x.

 

So the actual amount if water required to pass a boat through a lock will depend on the boat's displacement. 


This isn't quite right. When a boat goes into a lock then y of water is pushed out of the lock into the pound; and vice versa when you leave the lock. Once the boat is in the lock the amount of water that moves when the lock is filled or emptied is x. To see this, you need to think about the volume z of water that is in the lock and below the lower pound level.  When the lock is empty, the amount of water in the chamber is z-y; and when the lock is full the amount of water in the chamber is z+x-y.  The difference between the two is x, independent of y (and z).  

This is one of those situations where the question needs to be very precisely posed .... 

The maths of side ponds is quite interesting.....

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3 hours ago, Ronaldo47 said:

"The term 'lock full', when used by a canal company, was a very general term and would probably be on the generous size, as in terms of water usage that passing through locks was usually considered around one third of the total amount of water required. "

 

The actual amount of water used when a boat uses a lock will depend on the boat's displacement and  whether or not the lock is set for the boat's passage.  

 

Let's call the amount of water needed to fill an empty lock x, and the displacement of your boat, y. If going uphill, you find the lock full, then you will obviously need to empty a full lock of water before you enter, and will effectively draw x from the upper pound in order to enter.

 

Once you have entered the lock, The amount if water required from the upper pound to fill the lock will be x -y.  When you leave the lock, y from the upper pound  will enter the lock, which then contains x.  

 

If another boat coming the other way with displacement z enters the lock you have just left,  the lock will now contain x-z of water and z of boat. So when emptying the lock to descend,  that boat will  discharge x - z into the lower pound, not x.

 

So the actual amount if water required to pass a boat through a lock will depend on the boat's displacement. 

Not quite. The quantity of water required to fill a lock is the surface area of the lock multiplied by the rise of the lock. This is independent of the displacement of a boat, whether it is in the lock or not.

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If you want to address the displacement of a boat, you have to look at the relative levels of water in the pound/pool above and below a lock, and this will depend upon whether water is running over a byewash, or not, and if that overflow is caused by an empty boat being loaded, or by a boat entering from a lock. Anyone designing a canal in the 18th century would ignore the effects of displacement as insignificant when compared to the water required for locks, leakage and evaporation.

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3 hours ago, Iain_S said:

Not quite. The quantity of water required to fill a lock is the surface area of the lock multiplied by the rise of the lock. This is independent of the displacement of a boat, whether it is in the lock or not.

 

Not by the rise of the lock exactly, as it needs to take into account the displacement into the lock structure of any cill.

These xyz mathematical calculations may be necessary when designing and constructing, but do not take into account water lost through leakages at gates. Reality has an unerring way of messing with figures, do they not? Water in real life, is fluid - it escapes, in differing amounts.

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Amongst the services my company offers is a forecast of water demand on restored navigations (along with likely supply if its part of the brief) - believe me we don't muck about with the displacement of boats or how far the cill sticks into the locks! It's all lost in the noise given the volume needed and the uncertainty of the variables involved.

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