The area (margin) around surface water was generated at 60m, 120m, 360m, and 480m from National Hydrography Dataset (NHD) NHDinArc in February 2004 for subregions of the contiguous US. The margin dataset represents a grid of 30 m pixel buffer zones around the NHD hydrology. The NHD was divided into (1) ponds/reservoirs less than or equal to 5 acres in size [sm], (2) lakes/reservoirs greater than 5 acres in size [lg], (3) river/canal perennial polygon water bodies [fl], and (4) stream/canal perennial linear water bodies [dr]. This margin file can be combined with land cover information to extract coincident pixels (i.e., 30m NLCD land cover pixels can be summarized by the margin grid).

The main objective of this project was to generate a generalized and nationally consistent water body margin data layer for the entire conterminous United States. These data can be used as a layer in a geographic information system (GIS) for any number of purposes such assessing stream habitat, water quality and pesticide runoff, etc. For use with the GEOSTAC database, this data set has been compiled in order to simplify pesticide risk assessment and provide a common data set for vested interests.

Users are cautioned to carefully scrutinize the data to see if they are of sufficient reliability before attempting to use the dataset for larger-scale or local analyses. The NHDinArc was obtained in February 2004, and updates to localized hydrology may not be reflected by the use of these margin files.

Process_Description:

Lineage/Process Step:

(1) Create subregion NHD geodatabases

USGS NHD Append 2.25 AMLs were used to aggregate Huc-08 NHDinArc hydrology to the Huc-04 subregion level.

(2) Project NHD

The resulting coverages were then projected from decimal degrees to Albers Conical Equal Area using ArcInfo:

Standard Parallel: 29.500000
Standard Parallel: 45.500000
Longitude of Central Meridian: -96.000000
Latitude of Projection Origin: 23.000000
False Easting: 0.000000
False Northing: 0.000000

Planar Coordinate Information
Planar Distance Units: meters
Coordinate Encoding Method: coordinate pair
Coordinate Representation
Abscissa Resolution: 0.000095
Ordinate Resolution: 0.000095
Geodetic Model
Horizontal Datum Name: North American Datum of 1983
Ellipsoid Name: Geodetic Reference System 80
Semi-major Axis: 6378137.000000
Denominator of Flattening Ratio: 298.257222

(3) Create subregion water body classes from NHD

In ArcGIS 9.0 python script, the subregion static water body class was defined using the coverage FCODE field:
gp.Select_analysis(nhd_alb83_wb, WBstatic, "(FCODE = 39000 OR FCODE = 39002 OR FCODE = 39004 OR FCODE = 43600 OR FCODE = 43601 OR FCODE = 43614 OR FCODE = 43615 OR FCODE = 43616 OR FCODE = 43617 OR FCODE = 43618 OR FCODE = 43619 OR FCODE = 43620) ")

Small water bodies were extracted using the area field corresponding to equal or less than 5 acres (20,234.3 square meters) in size:
gp.Select_analysis(WBstatic,static_sm,"AREA <= 20234.3")
Large water bodies were extracted using the area field corresponding to more than 5 acres (20,234.3 square meters) in size:
gp.Select_analysis(WBstatic,static_sm,"AREA > 20234.3")
Polygon water bodies that are flowing water bodies were extracted from the water body  feature class and classified accordingly:
gp.Select_analysis(nhd_alb83_wb, WBflowing, "(FCODE = 46000 OR FCODE = 46004 OR FCODE = 46005 OR FCODE = 46006) ")
Linear flowing waterbodies were extracted from the nhd drain feature class and classified accordingly:
gp.Select_analysis(nhd_alb83_drain, drain_flow, "(FCODE = 46000 OR FCODE = 46004 OR FCODE = 46005 OR FCODE = 46006) ")

(4) Create subregion NHD margin grid

The resulting water body class was then exported to a corresponding subregion ArcGIS 9.0 personal geodatabase.  The geodatabase water body class was then buffered in a raster environment using the Euclidean Distance tool:
gp.EucDistance_sa(wb, EucD_wb, "480", "30", Output_direction_raster)

(5) Reclassify subregion NHD margin grid

The subregion euclidean distance raster was reclassified into four distance categories: 60m, 120m, 360m, and 480m.
gp.Reclassify_sa(EucD_wb, "Value", "0 60 1;60 120 2;120 360 3;360 480 4", Euc_rc, "DATA")

Water Body Margin

Metadata: