Floods at Great Falls

Floods at Great Falls (HM2CLJ)

Location: McLean, VA 22102 Fairfax County
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Country: United States of America
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N 38° 59.682', W 77° 15.204'

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Great Falls Park

—National Park Service, U.S. Department of the Interior —

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.


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.
Placed ByNational Park Service, U.S. Department of the Interior
Marker ConditionNo reports yet
Date Added Monday, October 22nd, 2018 at 11:01pm PDT -07:00
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Locationbig map
UTM (WGS84 Datum)18S E 304849 N 4318603
Decimal Degrees38.99470000, -77.25340000
Degrees and Decimal MinutesN 38° 59.682', W 77° 15.204'
Degrees, Minutes and Seconds38° 59' 40.92" N, 77° 15' 12.24" W
Driving DirectionsGoogle Maps
Area Code(s)540, 703, 571, 202
Which side of the road?Marker is on the right when traveling North
Closest Postal AddressAt or near Old Carriage Rd, McLean VA 22102, US
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