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# If the Atlantic and Pacific Oceans are at sea level, why are locks needed in the Panama Canal?

Question #121742. Asked by mehaul. (Jun 05 11 8:57 AM)

Because it has to overcome a height difference. The ground is higher than sea level at the middle of the canal. So instead of digging the canal to an impossible depth the locks are used to lower and raise the ships instead.

http://en.wikipedia.org/wiki/Panama_Canal_Locks

 Jun 05 11, 8:59 AM
Mugaboo

Sea Level is about eight inches higher at the Pacific end than the Atlantic end. Tidal variation is greater on the Pacific side as well, so it would be a good idea to have locks even if the canal was level. In addition it's a bad idea to have marine wildlife from the two oceans mix.

 Jun 05 11, 3:19 PM
mehaul

A closely related question was asked before here. That question explained that the level difference is an "urban myth". See:

There is no difference in sea level in the Pacific or the Atlantic Oceans. They merge surface heights above and below (North and South) of the Americas and N & S again of the Eurasian land mass and Africa. If there were a difference as you say let's do some math. 8 inches is 20cms or 0.2M. The entrance to the canals at the locks are around 400 meters across giving a face of the Pacific on the lock 80 sq M above the Atlantic times the square meterage of the Pacific above the Atlantic to get a volume figure multiply times 165 million square kilometers or 13,200,000,000 cubic meters of water above the Atlantic. At 1000 pounds per cubic meter of water, that's 13,200,000,000,000 pounds per square meter of force being exerted on the lock face.
The locks are solely to act as a lifting mechanism to hoist the sea lanes up and over the elevation of the Isthmus of Panama and then to lower them back down. If either side were to be higher, it should be the Atlantic side. The Carribean acts as a tidal basin and as the earth rotates to the East, the water should build up towards the West on the Atlantic side and withdraw from the Pacific side. But the tides of both Oceans are noted to rise and fall the same amount due to the gravitational pull ot the moon.

 Jun 05 11, 6:20 PM
star_gazer

A good photo of a Panama canal lock:

 Jun 05 11, 6:56 PM
Watchkeeper

A cubic metre of water is actually 1,000kg or 1 tonne, not 1,000 pounds as stated.

And there WILL be a difference in level at each end, simply because of the tides. High tide occurs at different times in different places. Also, there is a difference in tidal range - low to high tide is about 1ft in the Atlantic but 20ft in the Pacific.

"In 1883 it was realised there was a tidal range of 20 feet at the Pacific, whereas, the Atlantic range was only about 1 foot. It was concluded that this difference in levels would be a danger to navigation. It was proposed that a tidal lock should be constructed at Panama to preserve the level from there to Colon. This plan would save about 10 million cubic metres of excavation."

http://www.eclipse.co.uk/~sl5763/panama.htm#The Locks

-----------------
Further to above, this site

http://www.tides4fishing.com/pa/canal-panama

gives tide details for Cristobal and Balboa, at either end of the Panama Canal. You can see the differences in time and height. Today for example:

"In the high tide and low tide chart, we can see that the high tide was at 2:20 am and the low tide was at 10:46 am.

The tidal coefficient today is 71, a high value and therefore the range of tides and currents will also be high. The tide heights today are 0.3 m and -0.1 m. We can compare these levels with the maximum high tide recorded in the tide tables for Cristobal which is of 0.5 m and a minimum height of -0.2 m.

In the high tide and low tide chart, we can see that the first high tide was at 6:06 am and the next high tide at 6:16 pm. The only low tide of the day was at 12:13 pm.

The tidal coefficient today is 71, a high value and therefore the range of tides and currents will also be high. The tide heights today are 4.7 m, 0.5 m and 4.7 m. We can compare these levels with the maximum high tide recorded in the tide tables for Balboa which is of 5.7 m and a minimum height of -0.9 m."

In brief:
Cristobal: high tide 02:20, 0.3m
Balboa: high tide 06:06, 4.7m

Also, the 0.5m low tide at Balboa is higher than the 0.3m high tide at Cristobal!

 Jun 05 11, 6:59 PM
gtho4

This web page at the BBC has a map of Panama and the canal, and a cross section to the same scale, showing the height differential of the land; referred to in the first post by AdamM7

http://news.bbc.co.uk/2/hi/americas/4941126.stm

 Jun 05 11, 7:44 PM
davejacobs

The weight of any amount of water acts downwards, on the sea bed, not horizontally against the lock face as suggested by mehaul. Basic physics.

 Jun 06 11, 12:36 AM
mehaul

Then why do aboveground pools keep blowing through their sides? The Pacific end of the canal is 50 km East of the Atlantic end therefore tide charts for the Pacific should precede those of the Atlantic.

Perhaps this matter of Heights of the two Oceans should be in a different question. My question is answered: The locks are to allow lifting and lowering vessels using the shortcut.

 Jun 06 11, 2:46 AM
Baloo55th

Any above ground pool or waterway can burst its banks if they are not strong enough to retain the water. If one pours water on a table, one merely gets a wet table (and floor and feet...). If one pours water into a glass, it stays there. If one runs water into a metal tank, it will likewise stay there - unless there is a rust problem, in which case when the patch becomes thin enough the water will exit increasingly rapidly. The force of the weight of the water is directed downwards from the point of supporting it, but there is sideways force to be taken into consideration. If there weren't, then ink wouldn't make such a mess, and balloons wouldn't inflate so neatly. Gases exert force in all directions, liquids downwards and sideways, solids downwards only.

 Jun 06 11, 12:11 PM
davejacobs

The sideways force is called 'water pressure' and is directly proportional to the depth only. It has nothing to do with the amount of water being contained - or failing to be so!
http://en.wikipedia.org/wiki/Pressure

 Jun 07 11, 12:40 AM

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