Floods of January 19-21 Are Among the Highest Ever Recorded in Maryland Area Streams and Rivers

Prepared: Monday, January 22, 1996

Nearly all major streams and rivers in the Maryland area experienced serious flooding this past weekend of January 19-21, according to the U.S. Geological Survey. Many of the streams and rivers approached or exceeded records that were set during major floods in the past.

"The streamflows we measured this past weekend are among the highest January flows we've ever seen in the Maryland area", said Robert W. James, Jr., head of the stream-gaging program for the Maryland-Delaware-D.C. office of the USGS. "Even at streams where we have records back to the 1920's, January flows have never been this high."

The Potomac River at Washington, D.C., which is the second largest tributary to the Chesapeake Bay, recorded its highest flow since Hurricane Agnes in 1972, even surpassing the peak flow recorded during the flood of 1985 in the Potomac Basin. The peak stage of the Potomac River reached 19.31 feet and the peak flow was 347,000 cubic feet per second, or 2.6 million gallons per second. During Hurricane Agnes, the peak stage was 22.03 feet and the peak flow was 359,000 cubic feet per second.

The Susquehanna River at Conowingo Dam, Maryland, the single largest tributary to the Chesapeake Bay, recorded its second highest flow of record with a peak stage of 34.18 feet and a peak flow of just over 900,000 cubic feet per second. In terms of gallons, this translates to a peak flow of nearly 7 million gallons each second. These levels have been exceeded only once before--during Hurricane Agnes in 1972 when the peak stage reached 36.83 feet and the peak flow was 1,130,000 cubic feet per second.

"The floods were the result of an unusual combination of warm temperatures, heavy rainfall, and the associated melting of a thick snowpack from the blizzard of a couple of weeks ago," said James. "Peak flows at several Maryland streams exceeded historical records established during previous major floods, and several other streams were as high as we have seen them since Hurricane Agnes in 1972."

In western Maryland, Wills Creek at Cumberland and Youghiogheny River at Oakland recorded peaks that exceeded the previous highs for those streams. According to James, these flows were the highest ever recorded in more than 50 years at these sites, even exceeding the severe floods of 1972 and 1985. Wills Creek reached a peak stage of 22.53 feet, surpassing the old peak stage record of 20.20 feet recorded in 1936. Youghiogheny River recorded a peak stage of 13.10 feet, surpassing the old peak stage of 12.16 feet recorded in 1954.

Flood conditions were aggravated in many streams and rivers by thick ice that broke up in the rising waters and jammed against bridges and other narrow parts of channels. This caused flood waters in some streams and rivers to temporarily back up behind the ice jams and then surge downstream when the ice jams broke.

"USGS crews will be in the field this week at about 85 Maryland streams, ensuring that the gages are operating properly, verifying flood levels from high-water marks at or near the gages, and documenting damage to the gaging-station structures," said James.

The impact of the floods on the Chesapeake Bay is unknown at this point, although it is likely that large amounts of nutrients--nitrogen and phosphorus--were mobilized and transported by the flood waters. Large amounts of nitrogen were probably deposited with the snow from atmospheric sources during the blizzard of two weeks ago, and as the snowpack melted this past weekend, this nitrogen was released into the flood waters. Large amounts of phosphorus may have been transported along with sediments originating from the erosion of fields and streambanks, and from scour behind dams. The largest water-quality impact on the Chesapeake Bay may result from the large inflows of fresh water into the saltwater environment of the Bay.

The USGS stream-gaging program in Maryland and the District of Columbia is supported by funding from numerous Federal, State, and local agencies, including the U.S. Army Corps of Engineers, Maryland Department of Natural Resources, Maryland Geological Survey, Maryland State Highway Administration, City of Baltimore, and Washington Suburban Sanitary Commission.

During floods, flow data are used chiefly by the Corps of Engineers to manage water projects such as diversions, dams, locks, and levees. The National Weather Service uses the data for flood warning and flood-forecasting purposes and the Federal Emergency Management Agency uses the data as part of its nationwide floodplain mapping and flood-insurance program.

(For additional information on the surface-water resources of Maryland and the District of Columbia and the ongoing flood, please contact Jim Gerhart, District Chief (410 238-4201) or Bob James, Hydrologic Surveillance and Assessment Chief (410 238-4205).

** * USGS * * *

In-depth information about USGS programs may be found on the USGS home page at http://www.usgs.gov and http://chesapeake.usgs.gov/ for Chesapeake Bay activities.

Table listing stage and discharge at selected stream-gaging stations