I knew we'd come out an easy winner. Niagara Falls, at peak time, has a flow rate of 2,832 cubic meters per second - a huge amount of water. That would give the Black Sea waterfall a flow rate of 56,640 cubic meters/second. Surely nothing could top that. Well, at the site I checked, Victoria Falls, at peak flood season, has a flow rate of about 9,100 cubic meters/second. Gads, considering a cubic meter has 35.3147 cubic feet in it, and a cubic foot has 7.48 gallons, that means the Black Sea falls had about 15 million gallons going over each second. Incidently....the Guaira falls in Brazil/Paraguay is the waterfall in the present world with the most volume with 13,300 cubic meters per second, but I suspect that not even our waterfall at the Bosporus would hold a candle to the falls at the Pillars of Hercules, when the Atlantic broke through to refill the Mediterranean.