Water Body Agriculture in Margin

The National Hydrography Dataset forms the basis of the water body margin dataset.

The National Land Cover Dataset was compiled from Landsat satellite TM imagery (circa 1992) with a spatial resolution of 30 meters and supplemented by various ancillary data (where available). The analysis and interpretation of the satellite imagery was conducted using very large, sometimes multi-state image mosaics (i.e. up to 18 Landsat scenes). Using a relatively small number of aerial photographs for 'ground truth', the thematic interpretations were necessarily conducted from a spatially-broad perspective. Furthermore, the accuracy assessments (see below) correspond to 'federal regions' which are groupings of contiguous States. Thus, the reliability of the data is greatest at the State or multi-State level. The statistical accuracy of the data is known only for the region.

The following NLCD categories compose the agriculture class:
82. Row Crops - Areas used for the production of crops, such as corn, soybeans, vegetables, tobacco, and cotton.
83. Small Grains - Areas used for the production of graminoid crops such as wheat, barley, oats, and rice
84. Fallow - Areas used for the production of crops that are temporarily barren or with sparse vegetative cover as a result of being tilled in a management practice that incorporates prescribed alternation between cropping and tillage.

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.  An example for one margin distance and one water body class follows:
gp.EucDistance_sa(static_sm, EucD_wbwb, "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", Eucwb_rc, "DATA")

(6) Combine NLCD land cover with NHD margin grid

The 30m NLCD binary agricultural file (created from a mosaic of rowcrop, fallow, and small grain categories) was combined with the euclidean margin grid to create ag in margin grids.
gp.Combine_sa(Eucsm_rc + ";" + us_ag, Comb_wb)

(7) Create individual subregion grids for water body class margin distances

The subregion combined grids were then extracted by margin distance into single binary grids for summarization.  An example for one margin distance and one water body class follows:
# Process: Conditional Margin distance...
gp.Con_sa(wb_ag, Input_true_raster_or_constant_value__2_, con_wb120a, "", "Z_z_z2c1 < 3")
# Process: Conditional for NLCD Agriculture in Margin...
gp.Con_sa(wb_ag, Input_true_raster_or_constant_value, con_wb120, con_wb120a, "Z_z_z2c1 < 3 AND Z_z_z2c2 = 1")

Metadata imported.

Metadata imported.

Internal feature number.

ESRI