Thursday, 13 September 2012

Lock Theory

I have had a few interesting conversations about locks. There are certain misconceptions that people have. Especially where there are more than a couple of locks forming a flight. Often people think that you need a lock full of water for each lock. Not only that but the water is then lost. So if you go down 21 locks such as the Wigan Flight you will be using 21 locks worth of water.

In theory, the water out of one lock is used to fill the next lock further down. In a perfect world of locks without leaks, this might just have a bit of truth. The real problem is that its just a theory.

The old canal engineers came up with a number of solutions to the problem of saving water. For the engineer canal water was a jealously guarded commodity to be used carefully. Obtaining sufficient water was always a problem on certain canals.

One solution was to have a side pound. When a boat came to a lock, when the gates were closed the water in the side pound was run into the lock and the paddle closed. The lock was then topped up by water from above the top gates. The next boat going down would first drain water back into the side pound and close the paddle between the lock and side pound. The remaining was drained down to the lower level.  Quite a bit of water could be saved and reused in this way.

Time as well as water was also a valuable commodity. A solution to the problem of saving time was to have two narrow locks side by side.  A boat could use the narrow lock in either direction at the same time. Water being transferred from one lock to another via side gates between the locks.

In other places a broad lock would be placed at points where there was congestion. Where a boat and boat and butty would use the wide lock side by side. This saved time and  where combined with the use of side pounds quite a bit of savings could be made. 

In the real world, as you release water out of one lock you should be running it in to the next lock down the flight. On a full pound water released before the lock below is ready will go down a bywash. Then when you get to the next lock and draw water out of the pound. You have used two locks full - one into the lock and one over the pound bywash. 

On the Wigan Flight however the major problem is leakage over time through the various lock gates. And when more boats are going up than are coming down the flight. 


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