sdeyrkco.GIS.hyhydb_watershed_hucode11

This coverage contains Hydrologic Unit boundaries and their associated 14-digit
codes for South Carolina watersheds delineated at a scale of 1:24,000.

This data set is intended as a tool for water-resource management and planning
activities, particularly for site-specific and localized studies which require
the amount of detail provided by a large-scale map.

The following procedures were used to produce this data set:

The Natural Resources Conservation Service (NRCS) used 1:24,000-scale topographic
maps to complete the initial delineation of subwatershed boundaries. The U.S.
Geological Survey (USGS) and NRCS worked jointly to delineate additional
subwatersheds and to assign 14-digit codes to these subwatersheds.

The original delineations by the NRCS were checked for accuracy by USGS personnel.
Any discrepancies were resolved between the two agencies.  Of the 568 1:24,000-scale
topographic maps of South Carolina, drainage-basin delineations on 225 (approximately
40 percent) of the maps were reviewed by the Regional Hydrologist, South National
Technical Center (SNTC), NRCS, Fort Worth, Texas, prior to being processed by USGS
personnel.

The data were transferred to new 7.5-minute series topographic maps, then checked and
inked. The basin boundaries were color coded as follows:
Dashed RED, region or sub-region
RED, 6-digit accounting unit or 8-digit cataloging unit
BLACK, 11-digit watershed unit
GREEN, 14-digit subwatershed unit

The delineations on each map were digitized and stored in a GIS file using ARC/INFO*.
The latitude and longitude of the four corners of each map were used to georeference and
join the files for the individual quadrangles, resulting in a seamless, statewide GIS
coverage containing polygon attributes for the basins and arc or line attributes for the
boundaries that define them.

Quality assurance and control procedures were implemented to ensure that the data are of
high quality.  Proper quality assurance procedures are critical when subjective judgment,
such as delineating drainage basins in coastal areas, is required. The delineators and
checkers were trained to make qualitative judgments from similar perspectives.  The
determinations followed set guidelines and were consistent throughout.  Periodic reviews
were made to ensure that delineations were determined consistently and that the basins were
digitized correctly. External reviews of each basin also were made by the SCDHEC and
NRCS personnel.

The quality-assurance procedures used to delineate the 14-digit subwatersheds followed
guidelines set forth in the NRCS memorandum, National Instruction No. 170-304, Guidelines
for Mapping and Digitizing Hydrologic Units (U.S. Department of Agriculture, 1992).  These
procedures were developed from meetings with USGS District and Regional personnel and from
reviews by the South Carolina Department of Health and Environmental Control (SCDHEC) and
NRCS.

In addition to the checks described above, 10 percent of the delineations were reproduced
from the data base and compared to USGS 1:24,000-scale maps.  Moreover, the data for each
basin were compared to USGS 1:100,000-scale maps prior to review by the SCDHEC and NRCS.
In addition, the delineations were compared to 1:24,000-scale digital data, where
available. As a final check, the data set was reviewed and certified by the NRCS National
Cartography and Geospatial Center in Fort Worth, Texas.

The companion map report to this data set (U.S. Geological Survey WRIR 99-4015) contains a
listing of the latitude and longitude coordinates for the outlet points for the basins
included in this dataset. These coordinates were derived by locating the outlet locations
on 1:24,000 and 1:100,000 scale maps and then transferring these location points to the
digital HUC coverage.

*Any use of trade, product, or firm names is for descriptive purposes
only and does not imply endorsement by the U.S. Government.

Although this Federal Geographic Data Committee-compliant metadata
file is intended to document the data set in nonproprietary form,
as well as in ARC/INFO format, this metadata file may include some
ARC/INFO-specific terminology.