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The
data sets required for this model included:
1.
linear hydrography (to locate
permanent water sources)
2.
hypsography (to identify topographic
variation)
3.
flood plains
The
above data were acquired for the 111 Digital
Orthophotographic Quadrangles (DOQ’s) from
various sources. Linear hydrography data
sets were downloaded by county from USC’s Geographic Information Center (USC GIS,
2001).
Hypsographic data were downloaded by
DOQ from the South Carolina Deptartment
of Natural Resources (SCDNR) GIS Data
Clearinghouse system (SCDNR, 2001).
Flood
plain data were not readily available.
The original intent was to use Soil
Survey Geographic (SSURGO) data to
approximate flood plains – this is done by
selecting ‘frequently flooded’ polygons
only. Of the study area, however, soil data were available for 33
DOQ’s – these were primarily in the
lower lying (i.e., Coastal Plain) regions of
the state.
Floodplain approximations were thus
required for the remaining 78 DOQ’s,
requiring some ‘bootstrap’ techniques.
To obtain floodplain approximation,
therefore, ESRI-USC, after some consultation
with SCIAA, decided to use the following
method:
1.
Convert hypsography to 50m x 50m
Digital Elevation Model (DEM) format
2.
Calculate slope and select slopes of
less than 2 percent
for conversion to vector polygon
format (named lt2pctslop)
3.
Intersect lt2pctslop with linear
hydrography to differentiate flat upland
areas from floodplains
Processing
power to do the above exercise once for all
78 DOQs was not available, while the process
would have taken excessive manpower input on
a individual DOQ basis.
ESRI-USC chose a compromise route by
dividing the 78 DOQs into four contiguous
areas (of 17-21 DOQs each) and then
proceeding with the bootstrap approach.
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