What if the Panama Canal locks weren't there?

Answer 1

then there would be a flood?

No. The Canal has locks to raise ships to the level of Gatun Lake. This lake sit considerably higher than sea level where the ships begin transiting though the Panama Canal. Gatun Lake and it's connecting rivers are used as the main portion of the "canal" to transport ships (close to 30 miles).

If you took the locks out, Gatun Lake would drain out. Aside from the environmental impact, that entire portion of the canal would need to be re-dug deeper so that ships can pass through the entire way at seal level.