One of my relatives recently recommended a new book by David McCullough entitled The Pioneers: The Heroic Story of the Settlers Who Brought the American Ideal. (See the book at Amazon.com.)
On page 136 of the book, the author describes the difficulties of navigating the Ohio River from Pittsburgh to the Mississippi River. The "Falls" or "Rapids" at Louisville, Kentucky, were a dangerous two-mile stretch of whitewater rapids where the water level cascaded downward, ending up 26 feet lower. Experienced pilots were able to routinely guide smaller craft safely through the Falls.