Publisher's Synopsis
Excerpt from The Geologic Story of Great Falls and the Potomac River Gorge
The Great Falls of the Potomac River is the most spectacular landscape feature of the Washington metropolitan area. It has influenced the lives and fortunes of man in the Potomac Valley for centuries. Countless generations of Indians used it as a place to gather, to trade, and to fish. For the early settlers it was a barrier to river navigation, an obstacle that canal builders struggled to overcome. The river above the falls has been the principal source of water for the city of Washington for more than 100 years.
In its seaward course, the Potomac River crosses many small rapids and cascades, but these are insignificant in comparison with the foaming fury of Great Falls, where the river drops 12 meters in about 180 meters and is channeled into a narrow rock-walled gorge less than 25 meters wide in places. In the summer the flow may be less than liters a second, but during floods the flow commonly reaches 40 million liters a second. The average flow pouring over the falls is liters of water every second and in a year, more than trillion liters - enough water to flood the entire District of Columbia to a depth of 55 meters, converting the Washington Monument (169 meters high) into a tall lighthouse.
During three periods of recent flooding in 1936, again in 1942, and still again in 1972 - water covered the towpath of the Chesapeake and Ohio (c and 0) Canal on the Maryland side of the river and spread across the area of the Visitor Center and parking lots on the Virginia side. Floods of this size are unusual; but about once every 2 years, floodwaters rise to the brink of the gorge at the falls, reaching to within 4 to 6 meters of the trails and overlooks along the cliffs. There have been 20 such floods since 1930.
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