Fairfax County RPA Maps are Changing



Fairfax County deferred the originally scheduled public hearings regarding the addition of 7.7 miles of perennial streams and removal of 2.2 miles of perennial streams that form the core of a Resource Protection Area (RPA) to:

Planning Commission ~ June 16, 2005 at 8:15 pm
Board of Supervisors ~ July 11, 2005 at 4:00 pm

Property owners directly affected by these map changes were sent notices last week requesting public comments.

Because of the numerous questions being revised, the Planning Commission will likely defer their decision until June 23, 2005 at 8:15 pm and hold an informational meeting on Thursday, June 23, 2005 at 7:30 pm in the Fairfax County Government Center conference rooms 9 and 10.

The proposed map changes are the result of a reassessment of a mixture of randomly selected sites and targeted sites using the same protocol originally used. Actual physical observation of flow regime during low flow periods of a non-drought year, as required by the current Public Facilities Manual (PFM) for landowner requested changes, was not employed by this study. Thus it appears that the traditional QA/QC approach of comparing predictive models to actual observed conditions was not employed and gives hope to citizens, who already believe some changes are in error, that physical facts may still govern.

More information on the proposed changes is available in the Staff Report (disregard the old dates for hearings); while specific map changes can be found for every tax map on the county GIS map viewer (under step 1 – map type, look for the Chesapeake Bay Map 2005 Proposed selection).

The 9.9 miles of RPA changes represent just 1.2 percent of the 850 miles of perennial streams. However, 45 sites out of 154 studied changed; almost 1/3 of all sites. The average change was an increase of ± 1,040 lf per site and a reduction of ± 1,900 lf per site. If only randomly selected sites were used in this analysis, 30 sites out of 124 sites, or 24 percent, were found to be in error.

Thus the interesting question is which conclusion is accurate, and therefore, a prime topic for public hearings:

  1. Fairfax County’s staff report statement, which says that “This net change of 5.5 miles… represents 0.6 percent of the 850 miles… The result of the field surveys for the randomly selected sites indicate the level of quality and dependability of the 2003 sites.”1

  2. The fact that 1 out of 4 randomly selected sites, and 1/3 of all studied sites, were found to be mapped in error on average by ± 1,000 lf suggests that the public still should be granted a reasonable and affordable means of correcting these maps because they are not as precise as originally expected in 2003.
For further information contact: Mike Rolband, Mark Headly, Frank Graziano, Laura Giese or Craig Tumer.

 1 Oddly enough these end points were never actually surveyed, so we are finding discrepancies between where we have survey-located actual features, such as springs or headcuts that clearly mark the end of perenniality and the county RPA maps – so take these lengths with a grain of salt.