Re: How does the lock to lift boats in a canal work?

Andy,

     Long before there were trains, planes, and semi-trucks, there were 
boats to haul materials, goods, and people.  Canals and waterways were 
(are, actually) an efficient way to move boats to where people needed goods 
and materials to go.  However, sometimes there were waterfalls or elevation 
gains, (even dams), that would prevent boats from continuing upstream.  A 
method for moving boats to or from higher water needed to be found.  Locks 
are what accomplish this, and they work the same way now as they have for 
centuries. (I think they have been around for thousands of years but 
couldn't find a reference for this).

Locks use gravity and water from the higher water elevation to raise and 
lower boats.  First we will start with a boat going upstream.  A lock will 
have two doors or gates at either end.  The gate to the upstream side (the 
higher water) is closed, and ports (or valves) are opened to drain any 
water from the lock itself until the water level inside the lock matches 
the water level of the downstream side (the lower water) where the boat is. 
 The lower gates open and the boat drives into the lock.  The lower gates 
then close as do the ports that drained the water from the lock.  Then 
different ports are opened that allow water from the upstream side to flow 
into the lock.  Since both gates are closed the water has nowhere to go and 
begins filling the lock, much like filling water in your bath tub.  Since 
the water flow is usually gravity fed, the water will continue to raise in 
the lock until it is the exact same level as the higher water on the 
upstream side.  The upper gates are then opened and the boat drives out 
into the upstream side.  Remember, a boat sits the same in water, so as the 
level rises, so does the boat.  As you fill your bathtub, the rubber ducky 
still floats the same, no matter the depth of the water.

To go downstream, the exact opposite happens.  The lower gates are closed 
and the water fills the lock until the level is the same as the upstream 
side.  The upper gates open and the boat drives in.  The upper gates then 
close, and then the water is drained out of the lock through the ports 
until the water level matches the downstream water level.  The lower gates 
open and the boat drives out.  There is a cute animation from the Friends 
of the Delaware Canal web site that shows what I have talked about:
 http://www.fodc.org/info/fodcl
ock.htm

Another good sight to illustrate the historical and commercial significance 
of canals is Syracuse's Erie Canal website:   http://syracuse.com/features
/eriecanal/

I don't have any exact references for the above info, it is mostly from 
what I remember about dams and such as well as what I found from the above 
sites.  Hope this helps and if you have additional questions please e-mail 
me at bradk@jymis.com.  Good luck.
BK