Trench across the Isthmus?

Your reasoning is perfect, proving that the original answer was WRONG.

A sea-level canal with no locks would have water running along it in alternate directions twice a day because of the differences in the times of high and low tide, and the heights of high and low tide, between one end and the other. The amount would be minuscule compared with the contents of the Gulf of Mexico.

Apparently there is, indeed, a fairly steady current from the Pacific to the Atlantic around the southern tip of South America.

I did not see the earlier answer you speak of, but I guarantee you it was total BS....

If the Panama Canal was dug out to be free flowing , there would be absolutly no flooding of any kind.... What there would be is a tital change current through out the whole canal lenght so strong that ships probably would be able to navigate through it...

Why ?

Because the canal is only 50 miles long and the tides on the Pacific side average 20 feet and the average tide on the Atlantic side is about 2-3 feet....

Ah, now you ask, how come the Suez canal is ocean level and there is no tidal force ? Well, it because the Suez is so long ( acouple,three hundred miles ?) that any tide change between the two entrances has no effect...

what