| Predicted Areas of Wetlands in Loudoun County, VA (2009) | |
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Data format: SDE Feature Class File or table name: GISDBB.GISBROW.WETLANDS_MODEL_POLY Coordinate system: Lambert Conformal Conic Theme keywords: environment, geoscientificInformation, biota, wetland, predictive model, NWI, watershed |
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Abstract:
The Predictive Wetlands Model layer identifies areas that are predicted to be wetlands in Loudoun County. This is a weighted estimation of actual wetland presence based on wetland characteristics. This model predicts pre-development wetlands only and does not take into account changes either permitted by the U.S. Army Corps of Engineers (USACE) or the Virginia Department of Environmental Quality (DEQ). Post development wetlands will be evaluated in the future. |
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Metadata elements shown with blue text are defined in the Federal Geographic Data Committee's (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM). Elements shown with green text are defined in the ESRI Profile of the CSDGM. Elements shown with a green asterisk (*) will be automatically updated by ArcCatalog. ArcCatalog adds hints indicating which FGDC elements are mandatory; these are shown with gray text.
The Predictive Wetlands Model layer identifies areas that are predicted to be wetlands in Loudoun County. This is a weighted estimation of actual wetland presence based on wetland characteristics. This model predicts pre-development wetlands only and does not take into account changes either permitted by the U.S. Army Corps of Engineers (USACE) or the Virginia Department of Environmental Quality (DEQ). Post development wetlands will be evaluated in the future.
The Predictive Wetlands Model Data assists in identifying potential areas of wetlands, in support of the Loudoun County Revised General Plan (Policy 23 on page 5-11), which states "The County will support the federal goal of no net loss to wetlands in the County and will identify optimum receiving sites with priority to each geographic Policy Area within the RSCOD for the construction of new wetlands in association with adjacent stormwater management best management practices or required as part of federal wetland mitigation programs."
The predictive wetlands model was developed by Loudoun County Staff with technical assistance provided by the United States Environmental Protection Agency (EPA), and the United States Army Corps of Engineers (ACE). The project was partially funded through the "Loudoun County, Virginia Wetlands Inventory and Mapping Project" (WetIMP) Grant, provided by the EPA. The predictive wetlands model data are derived from the County's Corporate data and the United States Fish and Wildlife Service data. It has a currentness reference of June 2007, and is currently considered a static layer with no planned updates. Data are stored in the corporate ArcSDE Geodatabase as a line feature class. The coordinate system is Virginia State Plane (North), Zone 4501, datum NAD83 HARN (vertical datum, if applicable, NAVD88), US Survey foot units.
ground condition
The predictive wetlands model data were derived through a modeling process. Currently no national standard for this type of process exists. The predictive wetlands model data were generated using the best available data for Loudoun County and should only be used as a reference.
Every reasonable effort has been made to assure the accuracy of these data. Loudoun County, Virginia does not assume any liability arising from the use of these data. These data are provided without warranty of any kind, expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular service. Reliance on these data is at the risk of the user.
These data were generated for use by Loudoun County and are available to the public. These data are intended for use at 1:2400 scale or smaller. Acknowledgement of Loudoun County would be appreciated in products derived from this data.
1 Harrison Street SE, 2nd floor
MS 60
Topologically clean
To assist Loudoun County, Virginia in the maintenance of the data, please provide any information concerning discovered errors, omissions, or other discrepancies found in the data.
Soil coverage, H_drains coverage, Spoints coverage, and the National Wetlands Inventory (NWI) coverage used to generate the predicitive wetlands model data
The Predictive Wetlands Model Data is derived from Loudoun County corporate data (soils, soil drains, soil points, drains, and waterbodies) and United States Fish and Wildlife Service data (National Wetlands Inventory). The model utilizes ESRI geoprocessing and produces a weighted estimation of the presence of actual wetlands. This estimation is the result of points being assigned based on features typical of wetlands. Due to different physiographic characteristics of Eastern Loudoun and Western Loudoun, different parameters were used accordingly. (The dividing line between Eastern Loudoun, the Triassic Basin, and Western Loudoun, the Blue Ridge Providence, is the Bull Run Fault, which runs approximately coincident with U.S. Highway 15.) These points are then totaled to give a value, representing a relative scale of the likelihood of wetlands. Through data collection, model modifications, and field verification visits, the value of 20 or greater was categorized as areas predicted to be wetlands.
Eastern Parameters and Point Values: Hydric Soils = 10 points, Soils with Hydric Inclusions = 5 points, 50 foot Perennial Stream Buffer = 20 points, 25 foot Intermittant Stream Buffer = 5 points, Water body = 20 points, Double line stream = 20 points, National Wetland Inventory polygons = 5 points, Soils with slope (0 - 5%) = 5 points, 50 foot lakes/ponds buffer = 5 points, 50 foot Spring/Marsh/Wetspot buffer = 5 points
Western Parameters and Point Values:
Hydric Soils (Mapping Unit 4A) = 15 points, Hydric Soils (other than Mapping Unit 4A) = 10 points, Soils with Hydric Inclusions = 5 points, 50 foot Perennial Stream Buffer = 20 points, 50 foot Intermittant Stream Buffer = 5 points, Water body = 20 points, Double line stream = 20 points, National Wetland Inventory polygons = 5 points, Soils with slope (0 - 2%), (0 - 5%), or (0 - 7%)* = 5 points, 50 foot lakes/ponds buffer = 5 points, 50 foot Spring/Marsh/Wetspot buffer = 5 points
*the slope ranges depict the lowest ranges for each mapping unit
Additional processing steps were performed to combine the results from the Western Model and the Eastern Model into one countywide dataset. The model results were dissolved, to reduce the number of features, and then clipped to the model areas, to remove overlapping polygons. Sliver polygons and minimal area polygons, resulting from geoprocessing and varying input data, were then removed from the dataset to improve aesthetic quality and increase confidence levels. The datasets were then loaded into a personal geodatabase and then into SDE.
Source that created or modified feature class
Loudoun County
Not for public distribution. Internal User ID of editor creating or modifying feature class.
Loudoun County
Date feature class created or modified
Loudoun County
Wetland type predicted through model
Loudoun County
Predicted wetland through model
Loudoun County
Internal feature number.
ESRI
Feature geometry.
ESRI
Area of Loudoun County where predicted wetland is located
Loudoun County
WE_SOURCE: Source that created or modified feature class
Source Definition 0 Undetermined 10 Legacy 20 County 30 Contract 40 Model
WE_AREA: Area of Loudoun County where predicted wetland is located
Area Description EAST Eastern Loudoun County WEST Western Loudoun County
1 Harrison Street S.E., 2nd floor
MS 65
Every reasonable effort has been made to assure the accuracy of these data. Loudoun County, Virginia does not assume any liability arising from the use of these data. These data are provided without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular service. Reliance on these data is at the risk of the user.
ESRI Personal Geodatabase Feature Class
ESRI Shapefile
AutoCAD Digital Exhange file
Size limit: 4.5 GB. Visit our website at: http://www.loudoun.gov/omagi, click on "Loudoun County Mapping Documents & Order Forms." The "Forms" directory will lead you to custom & standard (countywide) data order forms. Hardcopy maps may also be available; please contact the Mapping Office Public Information Counter for more information regarding all data requests.
1 Harrison Street SE, 2nd Floor
MS 65