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View Full Version : Really dumb question about the Panama Canal


Zsofia
01-01-2012, 09:20 PM
Okay, seriously, I know I'm supposed to be smarter than this, but I don't get it. So one side is higher than the other, which is why you need all those locks to take a ship from one end of the canal to the other. Why, once they built the canal, didn't the taller ocean equalize with the shorter one? And why did it never happen in the past? Frankly, how can one ocean be higher than another considering that they all communicate one way or another?

silenus
01-01-2012, 09:26 PM
Actually, the locks are there because the middle of the canal is higher than the ends. Gatun Lake is 85 ft. above sea level.

Colibri
01-01-2012, 09:26 PM
You need the locks, not because of any difference in level between the oceans, but because the middle part of the canal is made up of an artificial lake, Lake Gatun, which is 85 feet or so above sea levels. Ships enter one end of the canal; are lifted to lake level via locks; pass through Lake Gatun; and then are lowered back down to sea level with the other set of locks.

obfusciatrist
01-01-2012, 09:34 PM
A Cecil column (https://academicpursuits.us/columns/read/1091/if-the-locks-on-the-panama-canal-were-blown-would-one-ocean-pour-into-the-other) on the underlying misconception in this question.

Colibri
01-01-2012, 09:40 PM
At Panama, the Pacific is slightly higher than the Caribbean. (http://psmsl.org/train_and_info/faqs/#3)

Sea level is about 20 cm higher on the Pacific side than the Atlantic due to the water being less dense on average on the Pacific side and due to the prevailing weather and ocean conditions.

The Pacific is less salty (and hence less dense) than the Atlantic because water evaporates in the tropical Atlantic, leaving the salt, and then the water-vapor-laden air passes over the isthmus driven by the trade winds. The vapor condenses over the Pacific and falls as rain, freshening the water.

As the link indicates, because of this even if a sea-level canal were built locks would still be necessary. Also, Pacific tides are much higher and out of sync with those on the Atlantic side.

Exapno Mapcase
01-01-2012, 09:53 PM
The question works for many, if not most canal systems, like the Erie Canal, which is basically downhill all the way from Buffalo to Albany.

The simplest answer is that the water is flat up until the lock, where it hits a wall. When the lock opens, the water spills out, but only when the lock is open. The canal is an artificial basin along each step that is built to retain a given height of water.

standingwave
01-01-2012, 09:54 PM
Actually, the locks are there because the middle of the canal is higher than the ends. Gatun Lake is 85 ft. above sea level.

Here's a nice profile picture (http://czbrats.com/CuPA/bfall/ProfilePC.jpg) for the OP. The vertical scale is exaggerated but one gets the idea.

friedo
01-01-2012, 09:59 PM
Here (http://youtube.com/watch?v=fA-pnN54uPw) is a cool timelapse of a ship traversing the canal. You can see how the locks operate.

Xema
01-01-2012, 10:12 PM
When the lock opens, the water spills out, but only when the lock is open.
Well, not really.

A lock has two gates arranged so that the water level difference tends to close them, preventing - or at least greatly restricting - water flow. The area between the gates can be filled from the higher water and drained to the lower water, but this is done with pipes and valves, not by opening the gates. One of the gates is opened when the water level between them equalizes to one of the two levels.

Pixel_Dent
01-02-2012, 12:37 AM
Unrelated to this question, but my favorite fact about the canal is that the Atlantic end is West of the Pacific end.

Xema
01-02-2012, 08:58 AM
... my favorite fact about the canal is that the Atlantic end is West of the Pacific end.
Another good one is the fact that the canal is actually east of Miami FL.

Of course, it's pretty much due south - but in terms of longitude, about 15 miles east.

Son of a Rich
01-02-2012, 09:16 AM
Unrelated to this question, but my favorite fact about the canal is that the Atlantic end is West of the Pacific end.

My favorite fact* is that, before they controlled them, mosquitoes were thick enough to, at times, put out a candle. :eek:

*according to David McCullough

Joey P
01-02-2012, 09:31 AM
Here's a nice profile picture (http://czbrats.com/CuPA/bfall/ProfilePC.jpg) for the OP. The vertical scale is exaggerated but one gets the idea.

Ahhh, that makes sense now. I too always wondered about this. So it's not that the locks are there because the two oceans are at different heights, it's there so the canal didn't have to be dug nearly as deep.

John DiFool
01-02-2012, 09:40 AM
Note that the Suez Canal has no locks and water does flow freely from the Med to the Indian Ocean.

Mk VII
01-02-2012, 10:48 AM
Assuming for a moment that they had built it to be level, there would probably be a tidal current from one end to another, which would change with the tides, and you might get a buildup of silt near the entrances

guizot
01-02-2012, 11:33 AM
Assuming for a moment that they had built it to be level, there would probably be a tidal current from one end to another, which would change with the tides, and you might get a buildup of silt near the entrancesAnd if all the locks were all just suddenly removed somehow, the lake would drain, and wouldn't be navigable, correct?

Xema
01-02-2012, 11:44 AM
... wouldn't be navigable, correct?
Correct - the bottom of Lake Gatun is definitely not below sea level.

Elendil's Heir
01-02-2012, 03:17 PM
Here (http://youtube.com/watch?v=fA-pnN54uPw) is a cool timelapse of a ship traversing the canal. You can see how the locks operate.

That is VERY cool - thanks!

Senegoid
01-02-2012, 04:55 PM
And if all the locks were all just suddenly removed somehow, the lake would drain, and wouldn't be navigable, correct?

You would have to use prairie schooners (http://carriageassociation.files.wordpress.com/2010/09/prairie-schooner-1.jpg) :p

tellyworth
01-02-2012, 05:12 PM
You would have to use prairie schooners (http://carriageassociation.files.wordpress.com/2010/09/prairie-schooner-1.jpg) :p

Or call in the Aussies (http://en.wikipedia.org/wiki/Henley-on-Todd_Regatta).

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