Geoscience Reference
In-Depth Information
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30 m digital elevation data, including slope and contours
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Digital orthophoto quarter quadrangles
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Digital soils data
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National Wetlands Inventory data
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Land ownership data
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Land cover and land use data
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Drainage structures
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Sediment sources
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Public Land Survey System data
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Historical aerial photography for selected wetland areas
Wherever feasible, geospatial data were obtained and/or developed at a scale
of 1:24,000 (nominal spatial resolution of 30 m). All data were geo-referenced to
the Universal Transverse Mercator Projection (UTM), zone 14, using the NAD83
datum and GRS 1980 spheroid. Data processing was accomplished using ArcGIS
and ERDAS Imagine software.
7.3.1.1 Wetland Basin Boundaries
Wetland basin boundaries were identified by RWBJV staff, delineated on U.S.
Geological Survey (USGS) 1:24,000 topographic quadrangle maps and subse-
quently digitized. The resulting vector coverages were buffered by 1 km and all
associated data layers (see below) were clipped or generated to the 1 km boundary.
7.3.1.2 Digital Elevation Data
Digital elevation data were accessed from the USGS National Elevation Dataset
(NED), a raster product having a resolution of one arc-second (approximately 30 m).
The digital elevation data were subsequently used to calculate percent slope for
the study area. Both the raw elevation data (in feet and meters), and the derived
slope dataset were clipped to the RWB study area, the wetland basins and associated
county boundaries.
7.3.1.3 Elevation Contours
Ten-foot elevation contours were obtained from the Nebraska Department of Natural
Resources (NDNR) which produced them as a by-product of a cooperative USGS-
NDNR project to develop digital orthophotos for Nebraska. The contour data were
mosaicked into a seamless coverage of the entire RWB. Elevation contours were
subset for the wetland basins and for individual counties.
7.3.1.4 Digital Raster Graphics
Digital Raster Graphics (DRGs) representing the USGS 1:24,000-scale topographic
maps were obtained from USGS, clipped to remove overlapping areas and map
