Although not posted to for awhile, I thought I'd add this little tidbit about Niagara Falls.
I also watched a History Channel's show about the Niagara Falls. One thing mentioned in that show is the fact that the four upper lakes water level will drop by up to the height of the falls 52 meters (167 feet). Of course, this won't happen for about another 12,000 years, and the water won't empty all at once but occur over several years to a couple of decades. That increase of water flow will do a heck of a gouging job.
rmfr