Flood Tracking for the Potomac River Basin
By Edward J. Doheny, Timothy W. Auer and Andrew LaMotte
The "Flood Tracking Chart for the Potomac River Basin" can be used by local citizens and emergency-response personnel to track and record the latest river stage and predicted flood-crest information during a flood event. By comparing the most current river stage (water-surface elevation above mean sea level) and predicted flood crest to the recorded peak stages of previous floods, emergency-response personnel and residents can make informed decisions concerning the threat to life and property. The flood-tracking chart shows a map of the Potomac River Basin, the location of major streamflow-gaging stations in the basin, and graphs of historical recorded peak stages at the gaging stations. Each graph represents a gaging station and has a scaled axis on which to record the most recently reported river stage from the U.S. Geological Survey (USGS). The predicted flood-crest information from the National Weather Service (NWS) can also be recorded on each graph.
During a flood, the USGS provides current river-stage information to the public through news releases and, more directly, through the USGS "Home Page" on the Internet. The Maryland-Delaware-District of Columbia District of the USGS displays available real-time river-stage data on the World Wide Web at the following address: http://md.waterdata.usgs.gov/nwis/rt.
The NWS has direct access to all information collected by the USGS for use in its forecasting models, and routinely broadcasts the forecast information to the news media and on shortwave radio. The radio frequencies are 162.400 MHz (megahertz) in Moorefield, W. Va., and Baltimore, Md.; 162.475 MHz in Hagerstown, Md., Salisbury, Md., and Philadelphia, Pa.; and 162.550 MHz in Manassas, Va., and Lewes, Del.
To use the flood-tracking chart for a particular property, determine the approximate elevation of the threatened property and record the elevation in the box at the lower left corner of the map along with the elevation of the "key gaging station." The "key gaging station" is the gaging station closest to the threatened property. For example, people living in Washington, D.C., would use the Potomac River near Washington, D.C. as their "key gaging station." Using the news media, Internet, or shortwave radio, obtain the latest river-stage information on a regular basis. Record the information for each station, especially the "key gaging station," and convert the river stage to sea level (see the example in the lower left corner of the map). A sea level conversion (SLC) factor is shown on the corresponding graph for each station and can be added to the current river stage and also to the historical recorded peak stages to relate the information to sea-level elevation. Compare the information to the elevation of the property to determine if the property has an impending threat of flooding. It is important to remember that the surface of flowing water is not flat, but rather, has a slope. Therefore, the water-surface elevation near a threatened property may not be exactly the same as the river stages at the gaging stations.
The network of streamflow-gaging stations in the Potomac River Basin is funded and operated by the USGS Maryland-Delaware-District of Columbia and West Virginia Districts in cooperation with the U.S. Army Corps of Engineers, the Maryland Geological Survey, the District of Columbia Department of Public Works, the Upper Potomac River Commission, the West Virginia Department of Natural Resources, and the West Virginia Consolidated Federal Power Commission. For more information about USGS programs in Maryland, Delaware, or the District of Columbia., contact the State Representative, U.S. Geological Survey, at (410) 238-4200. For more information about USGS programs in West Virginia, contact the State Representative, U.S. Geological Survey, at (304) 347-5130.
For more information about USGS activities in Maryland, Delaware and the District of Columbia:
MD-DE-DC Water Science Center
U.S. Geological Survey
5522 Research Park Drive
Baltimore, MD 21228
Telephone: (410) 238-4200
Fax: (410) 238-4210
or access the USGS Water Resources of Maryland, Delaware, and District of Columbia home page at: http://md.water.usgs.gov/.