In Thursday’s Classic Column – http://www.straightdope.com/classics/a5_046.html – Cecil ignores the most ruinous scenario that may arise from mingling the oceans: weather. I recall that long ago a professor of mine argued that such a project would spur huge and destructive air movements.
Sorry to go off-topic, but the column mentioned the Pacific has 20 foot tides and the atlantic 1 foot?
That’s huge! How will the currents only reach 6 MPH? This is exactly the picture of one ocean pouring into another that I had in mind (except, of course, that it’d pour back).
The hypothetical channel would be about 50 miles long. The speed of the water would depend largely on the depth of the channel, but we’re talking a big lag from one end of the channel to the other. It wouldn’t be like opening the floodgates of a dam.
Um, think about it. A 20 foot hight difference over the entire length of the canal? Hell, fast flowing rivers have much greater elevation changes than that. 
Why would it have this effect?
I can’t answer that (perhaps Nametag can), but I do recall reading scenarios of massive changes due to intermingling of the 2 oceans ; interaction with the Gulf Stream and differences in temperature and salinity were at least part of the picture, IIRC.
FWIW There was a book book by Clive Cussler wherein some “doctor evil” type was going to force a similar situation using nuclear weapons or something. Somehow he was going to financially benefit from it.
Also, IIRC, if you were going to do this it might not be at Panama ; Nicaragua was an alternate site for the canal and had some advantages but lost out politically.
Isn’t the Panama Canal higher in the middle than on either side?
I always thought that was the case, because the things I’ve read talk about how there’s enough rainfall at Gatun Lake & Miraflores Lake to keep the thing operational, despite losing water when moving ships up and down in the locks.
So blowing the locks would probably just drain out the water from those two lakes and eliminate the canal as a navigable waterway.
You’d have to tunnel it out at sea-level to see anything really interesting, I’d think.