“After Pardee studied the canyon of the Flathead River, he estimated that flood waters in excess of 45 miles per hour (72 km/h) would be required to roll the largest of the boulders moved by the flood. He estimated the water flow was 9 cubic miles per hour (38 km3/h), more than the combined flow of every river in the world. Estimates place the flow rate at ten times the flow of all current rivers combined.”
https://en.wikipedia.org/wiki/Missoula_floods
“After Pardee studied the canyon of the Flathead River, he estimated that flood waters in excess of 45 miles per hour (72 km/h) would be required to roll the largest of the boulders moved by the flood. He estimated the water flow was 9 cubic miles per hour (38 km3/h), more than the combined flow of every river in the world. Estimates place the flow rate at ten times the flow of all current rivers combined.”