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Hurricane Isabel September 2003: Flood Magnitude
  This map provides links to basin maps showing the magnitude of flooding caused by Hurricane Isabel.  Only minor flooding or no flooding occurred in the gray-shaded basins.
  chowan roanoke potomac rappahannock and york james shenandoah shenandoah shenandoah Virginia river basins
  Scientists map the areal extents of floods and assign recurrence intervals using streamflow data collected by the USGS and the Virginia Department of Environmental Quality since the late 1800s. Recurrence intervals express the likelihood that an event, such as a flood, will occur in any given year. For example, a 100-year-flood has a 1% chance of occurring in any year, and a 25-year flood has a 4% chance of occurring in any year.



USGS--Water Resources of Virginia                                                

U.S. Department of Interior, U.S. Geological Survey
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