Bonnie Creek Watershed Data Review
5.1 Existing Data Review
The following data sources were reviewed for model selection and analysis:
t opography data
existing water quality data
dairy and animal confinement locations
5.1.1 Mapping Data
USGS quadrangle maps (scale 1:24,000) were collected for the watershed in paper and
electronic form. These were utilized for base mapping.
5.1.2 Topography Data
A Digital Elevation Model (DEM) was used to delineate watersheds in a geographic
information system (GIS) for impaired segments NCD03, NCD05, NCDB, and
NCDC01. A DEM is a digital representation of the landscape as a GIS-compatible grid
in which each grid cell is assigned an elevation. DEMs of 90-meter resolution were
downloaded from the BASINS database (USEPA 2002a) for watershed delineation.
GIS watershed delineation defines the boundaries of a watershed by computing flow
directions from elevations and locating elevation peaks on the DEM. The GIS-delineated
watershed was checked against USGS 7.5-minute topographic maps to
ensure agreement between the watershed boundaries and natural topographic
boundaries. Figure 5-1 at the end of this section shows the location of historic water
quality gages for the Bonnie Creek Watershed and the subwatershed boundaries for
each impaired segment in the watershed. The subwatershed boundaries define the area
investigated for causes of impairments in each segment. Purple areas in Figure 5-1
represent features of the topographic maps that have been updated through aerial
photography, but have not been field verified.
Surface mining activities in the Bonnie Creek Watershed have significantly altered the
natural landscape through changes in topography and the creation of inclined lakes and
final cut lakes. Figure 5-2 shows an aerial photograph of the area surrounding the
confluence of Bonnie Creek and Galum Creek and the GIS-delineated watersheds. The
inclined and final cut lakes are visible in Figure 5-2. These lakes were originally strip-mined
areas and roads dug to the mine floor that were left to become impoundments
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