Floods at Great Falls

Floods at Great Falls. Great Falls Park. , The high-water marks seem hard to believe, but powerful Potomac River waters sometimes cover this area. How can that happen? High water occurs at least once a year when all the rocks in the falls are covered. Floods occur about every 10 years after extremely heavy rainfall or a series of storms upstream in the Potomac River watershed. When the deluge reaches Mather Gorge, where the riverbed narrows from nearly 1,000 feet into a rocky, mile-long funnel 60 to 100 feet wide, the waters have no place to rise but upward. As high waters recede, they deposit organic matter, minerals, and seeds that help make this one of the nation's most biologically diverse areas.,

Major Floods , 1936 March 18-19: Highest Recorded flood after rapid melting of snow and ice and torrential rains , 1937 April 26-27: Heavy rainfall , 1942 October 15-17: After 10-19 inches of rain in parts of watershed , 1972 June 24: Hurricane Agnes , 1985 November 4-7: Tropical Storm Juan , 1996 January 19-22: Blizzard followed by warming temperatures and rain , 1996 September 6-8: Tropical Storm Fran floodwaters came up to the pole's base, unmarked.

, [Captions - clockwise from top:] , The Potomac splits into two sections at Olmsted Island. Great Falls also can be viewed via a trail and bridge at the Chesapeake and Ohio Canal National Historical Park in Maryland., Viewed from upstream, the river flows into Great Falls toward Mather Gorge., In 1966 a severe drought exposed the jagged rocks of the Great Falls of the Potomac., Occasionally the Potomac River rises above its banks and floods park facilities as this 1996 photo shows., This January 1996 flood crested in 48 hours, then receded over the next 24 hours. High wet marks on the post are splashes. The red tape shows the highest water level.