The document describes Fairfax County, Virginia's process for developing land use and land cover data layers for watershed management plans. It involved grouping existing land use codes into 11 categories, assigning categories to tax and parcel data, and using aerial imagery to estimate impervious surfaces. The resulting data provided information on existing and future land use and imperviousness at the sub-basin level to support water quality and hydrologic modeling.

1. Watershed Management Plans
A Fairfax County, Virginia Publication, February 2014

2. 
Develop countywide land use/land cover GIS
data layers useful for plan development
◦ Watershed characterization (i.e. maps, data analysis)
◦ Pollution and hydrologic modeling

Key requirements
◦ A layer containing a land use mix for existing and
future conditions
 Key parameter for modeling water quality
◦ A layer containing impervious values (connected and
disconnected) for both conditions
 Key parameter for modeling water quantity

3. 
Tax Administration Dept. real estate records
◦ Each record contained a unique code for each parcel
 Existing land use
Codes > 200 types
 Zoned land use

Adopted land use comprehensive plan
◦ Polygons containing planned land use information
◦ Twenty-two planned land use categories

Parcel data
◦ Polygons contained a unique ID for each parcel
◦ Included vacant and underutilized parcels

Planimetric data (1997 aerial photography)

4. 
The need to simplify (i.e. group) land use types
through consolidation was evident
◦ 200 codes (included embedded towns)
◦ Code numbering convention facilitated consolidation

5. 

Grouped existing, zoned and planned land
use types into 11 categories
Miscellaneous:
 OS - Open Space
 GC - Golf Course
 INT - Institutional:
 Government/Universities
 IND - Industrial
 Airports
 Railways
Transportation:
 TRANS - Road rights-of-way

6. Existing conditions
 Each real estate record was assigned a
category for existing, zoned and planned
land use
 Joined the tabular tax record data to the
parcel layer polygons
 Included category: TRANS landuse
◦ Areas outside of the parcel boundaries = ROW

Included category: WATER land cover
◦ Planimetric data of the stream network, lakes

7. Future conditions
 Intersected comprehensive plan coverage
with the parcel layer
◦ Most parcels were already built-out

Vacant and underutilized parcels
◦ Compared zoned vs. planned land use
◦ Where different, chose classification that yielded
the greatest density

8. Existing conditions - Tysons Corner

9. Future conditions - Tysons Corner
future

10. 
Used planimetric data
◦ Features were assigned a corresponding percent
imperviousness
 Buildings, roads, parking lots and sidewalks/trails – 100
percent
 Parking lots, unpaved – 50 percent
 Areas outside planimetric features – 0 percent

Feature types sampled to estimate the typical
DCIA/NDCIA split
◦ Roads, parking lots – 100 percent DCIA
◦ Sidewalks/trails – 85 percent DCIA, 15 percent NDCIA
◦ Buildings – DCIA varied by type
 Commercial – 100 percent
 Industrial – 95 percent
 Multi-Family Residential – 90 percent
 Single Family Residential – 50 percent

11. Planimetrics - Tysons Corner

12. 
Estimating existing and future condition
imperviousness values by land use
◦ Sampled planimetric data in areas representative for
each land use category
◦ Average percent imperviousness was calculated for
each land use category
◦ Assigned percent DCIA/NDCIA to each category based
on appropriate feature types

DCIA and NDCIA values were aggregated to a
“sub-basin” level
◦ Polygons were created for modeling purposes
◦ Typically 300 to 500 acres in size
◦ More than 1800 polygons

13. Existing percent imperviousness by land use - Tysons Corner

14. Future percent Imperviousness by land use - Tysons Corner

15. 

The LU/LC methodology Fairfax County
implemented for its watershed planning effort
worked well at the local scale and could be a
method used to help standardize urbanized LU/LC
categories across the bay watershed.
Many smaller jurisdictions have less readily
available data. However, many larger urban areas
maintain data similar to Fairfax (i.e. comprehensive
plan, tax/parcel information and planimetrics)
which could be used with this methodology.

16. Questions?
For more information or to request this document in an
alternate format call 703-324-5500, TTY 711 or email
SWPDmail@fairfaxcounty.gov
Fairfax County Department of Public
Works and Environmental Services
Stormwater Planning Division
12000 Government Center Parkway
Fairfax, VA 22035
www.fairfaxcounty.gov/dpwes/stormrwater
Thank you.