Perennial Streams


Perennial Stream in Fairfax County

The Perennial Stream Mapping Project was initiated in September 2001 to address concerns that perennial streams were not protected under the county's Chesapeake Bay Preservation Ordinance, Chapter 118 of the Fairfax County Code. At that time, the county's ordinance listed perennial streams as those streams epicted as perennial on U.S. Geological Survey topographical maps. In Fairfax County, a perennial stream is defined as a body of water flowing in a natural or man-made channel year-round, except during periods of drought. Those streams as well as wetlands, tidal wetlands, and tidal shores were included within Resource Protection Areas.

Streams not identified as perennial on U. S. Geological Survey maps did not warrant a Resource Protection Area.

The Chesapeake Bay Local Assistance Department recognized difficulties with the use of the U. S. Geological Survey maps. In December 2001, the Chesapeake Bay Local Assistance Board adopted amendments to the state's Chesapeake Bay Preservation Area Designation and Management Regulations. The revised state regulations became effective on March 1, 2002. The revisions include a requirement to perform site-specific surveys using a scientifically valid method to identify water bodies with perennial flow. The state regulations allow localities some latitude in developing their own definition of perennial streams and protocols for identifying them in the field.

Additional information on the Chesapeake Bay Ordinance may be found on the Chesapeake Bay Preservation Ordinance website.


Perennial Stream Mapping Project

stream mapping project quality control/quality assurance methodology and results report cover

To ensure compliance with the state's revised regulations, the county has completed a Perennial Streams Mapping Project.

Fairfax County staff developed a Perennial Stream Field Identification Protocol and Data Sheet similar to the system used by North Carolina Division of Water Quality. This protocol allowed Fairfax County staff to identify perennial streams based on the combination of hydrological, physical and biological characteristics of the stream. The field work was completed between March 2002 and October 2003 and the new Resource Protection Area maps were generated and approved by the Fairfax County Board of Supervisors.

Report on Quality Control/Quality Assurance Methodology and Results

As part of the Perennial Streams Mapping Project, a Quality Control/Quality Assurance study was conducted throughout 2004 to check the accuracy and precision of the perennial stream determinations.

The following report presents the methodology and results of the study, as well as recommendations and next steps.

For more information on the Perennial Streams Mapping Project, please email the Stormwater Planning Division or call 703-324-5500, TTY 711.


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