The USDA-Natural Resources Conservation Service, Raleigh Office in cooperation with the NC Center for Geographic Information & Analysis, and the NC Dept. of Environment, Health and Natural Resources, Division of Water Quality developed the Hydrologic Units-North Carolina digital data to track resource and conservation activities in the state's river basins and subbasins. Using the 14-digit hyrologic unit code the regional, subregional, accounting, cataloging, NRCS sub-unit, and NRCS reporting unit boundaries id's are recorded. The area attributes allow the user to see hydrologic unit, river basin and subbasin levels of geography. This River Basins file was produced from the Hydrologic Units data and identifies the major NC river basins.
This data was created to assist governmental agencies and others in making resource management decisions through use of a Geographic Information System (GIS).
Data from the protected and critical watersheds layer for the state was used during the development of the HU boundaries. This coverage supersedes data on past versions, particularly the cama24.hu coverage, which was completed as a preliminary to this statewide version. Some boundaries may have changed between the two versions. There are two additional coverages which were generated from this data, the huncrb-river basins; and huncsb-subbasins files. See the cross references section for details. The following is an excerpt from the "North Carolina Hydrologic Unit River Basin Study," USDA, Natural Resources Conservation Service, November 1995. Under the sponsorship of the Water Resources Council, a nationally uniform hydrologic unit system was developed in 1974 by the US Geological Survey's Office of Water Data Coordination. This system divides the country into 21 regions, 222 subregions, 352 accounting units, and 2,149 cataloging units, based on surface hydrologic features. A hierarchical code consisting of two digits for each of the above four levels combine to form an eight-digit hydrologic unit. The hydrologic unit system is used to identify any hydrologic area of interest. An eight-digit hydrologic unit generally covers 700 or more square miles. In 1978, the USDA-Natural Resources Conservation Service (NRCS) issued a policy that all resource inventories and surveys were to be coded with and capable of being retrieved by hydrologic unit codes (HUCs). At about the same time, NRCS initiated a national program to further subdivide HUCs into watershed-sized areas (nominally 250,000 acres, or 390 square miles) for use in water resource planning. An extension of three digits was added to the eight-digit HUC to designate sub-watersheds, thus forming elevin-digit HUCs. This 1995 Hydrologic Unit (HU) Study divides the state river basins and subbasins into smaller fourteen-digit hydrologic units that will be useful in targeting project activities, resource inventories, and reporting conservation activities. These fourteen-digit hydrologic units of approximately 4,000 acres (6 sqare miles) to 50,000 acres (78 square miles) are small enough in size to be useful as a planning and reporting tool for the USDA-Natural Resources Conservation Service (NRCS) and other government and state agencies. This 1995 fourteen-digit HU map will replace the 1974 eight- digit HU map [U.S. Water Resource Council (WRC)] and the 1978 NRCS eleven-digit HU map as the locating tool for planning in NRCS. The 1995 HU map were produced using 7.5 minute USGS quadrangle base maps (1:24,000 scale). >14-digit number breakdown: >Assigned by US Water Subunit Reporting Unit (established >Resource Council (1978 NRCS) during this study) >|---------------------|----------|--------| >0 3 0 6 0 1 0 1 0 1 0 0 1 0 >|----|----|-----|-----| >| | | | >| | | Cataloging Unit Boundary >| | Accounting Unit Boundary >| Subregional Boundary >Regional Boundary NOTE: The subbasin 6-digit code (SUBBASIN#) was developed independently from the hydrologic unit codes, from an entirely different numbering system. (Example of code: 03-03-01.) The first two numbers identify the river basin designations adopted by the Environmental Protection Agency. (Date of source: 1974.) Subbasin boundaries were added within individual river basin boundaries (by the office that is now known as the Division of Water Quality, Water Quality Planning Section). Sequential numbers (example -01) were added by DWQ to the first four-digit EPA code to give each subbasin a unique six-digit identifier. (Each subbasin incorporates three or more hydrologic units. The subbasin boundaries have been modified to be coincident with the hydrologic unit boundaries.) Contact Alan Clark at DWQ for more information on the subbasin# code (733-5083, extension 570). >system filename: huncrb file size = 0.8 mb >(huncrb and huncsb need to be updated whenever hunc is >updated). > >Revisions and updates to this layer include: >3.) filename: huncrb1298 The December 1998 update to this layer >consisted of projecting the data from NAD27 datum, State Plane >projection, units of measure feet TO: NAD83 DATUM, State Plane >PROJECTION, UNITS OF MEASURE METERS. This was done to comply with >the NC Geographic Information Coordinating Council's "Statement of >Direction for North Carolina Corporate Geographic Database >Horizontal Reference, Datum and Unit of Measure". This reprojecting >was done in various ways depending on the data type and content. >Vector data was projected using the 'project' command in ESRI's Arc >software and topology was cleaned and built based on coverage needs. >Raster data was projected using ESRI's Grid module and various steps >as applicable. > >2.) filename: huncrb496 The April 15, 1996 update replaced >the old nc.rivbasin file which was a general reference layer only. >It is archived under the nc.rivbasin name. The huncrb496 was >created in late 1996, but backdated to reflect the data currency >date of the Hydologic Units file. > >1.) filename: rivbasin89 (previously called nc.rivbasin) >This file was created in the late 80s to assist in >identifying the major river basins in North Carolina. This >data was for display purposes only, ie. locator maps, since >its scale is 1:1,000,000. This file contains ABRV (CHO) >river basin name abbreviation; and, NAME (CHOWAN) attributes >in the PAT. The AAT contains system default attributes only. >This file was replaced with the huncrb river basins file >from the hydrologic (hunc) units file boundaries at 1:24,000-scale.
Hydrologic Units file currency date
Acknowledgement of products derived from this data set should cite the following: The source of the Hydrologic Units - North Carolina data is the North Carolina Corporate Geographic Database. Earlier versions of this data set may exist. The user must be sure to use the appropriate data set for the time period of interest. While efforts have been made to ensure that these data are accurate and reliable within the state of the art, CGIA cannot assume liability for any damages or misrepresentation caused by any inaccuracies in the data or as a result of changes to the data caused by system transfers.
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>USDA Natural Resources Conservation Service Director, Richard A. Gallo >USDA Natural Resources Conservation Staff, Sherman Biggerstaff >4405 Bland Road >Raleigh, NC 27609 > >DENR-Div. of Water Quality - Water Quality Planning Section Director, >Steve Tedder >DENR-Water Quality Section-Water Quality Planning Staff, Alan Clark >512 N. Salisbury Street >Raleigh, NC 27611 > >North Carolina Center for Geographic Information & Analysis >301 North Wilmington Street, Suite 700 >Raleigh, NC 27601-2825
The USDA-Natural Resources Conservation Service delineated the hydrologic units for North Carolina on 24k USGS topographic maps. These boundaries were attributed with USDA-NRCS classification information, acres per polygon, and square miles per polygon. The digital files were plotted and overlayed to the originals and linework and label corrections were made. Once complete and under the direction of DENR-DWQ, the digital file was further defined by subbasins derived from HUs and the river basins derived by subbasins. Appropiate ids were added to the attribute files. Attribute accuracy is considered high. There are no lookup tables, annotation or cartosets for this data.
Using ESRI's ARC/INFO GIS software, the data set was built for arc and polygon topology using the "build" command. The data set was then cleaned with a fuzzy tolerance of 1 foot. Topology has not been edited since the last build or clean.
These data depict the boundaries and unit numbers from the USDA-NRCS Hydrologic Unit River Basin Study, 1995. The study divides the state river basins into subbasins used to track resource and conservation activities.
Hydrologic Units for North Carolina were delineated on 7.5 Minute USGS paper topographic maps which meet National Map Accuracy Standards, using a best estimate with reference to surrounding features. Boundaries drawn were digitized and check plots used to ensure correct boundary location, within a line-width. map units: meters, precision: single, fuzzy: 1.0, dangle: 10.0.
Hydrologic units delineations for North Carolina
Paper maps used to delineate the hydrologic units
Paper maps used to delineate the hydrologic units
Hydrologic Units were delineated on USGS 1:24,000 paper topographic maps by following contour lines. HU codes were written onto the topo maps for later attribute coding. All topo maps within the Coastal Area Management Act (CAMA) area were given to CGIA for digitization. All other topos across the state were given to Westinghouse-Landmark GIS, Inc. for digitization. The USDA-Natural Resources Conservation Service delineated the hydrologic units for North Carolina on 24k USGS topographic maps. The digital files were plotted by CGIA and overlayed to the originals and reviewed by staff at NRCS and DENR-DWQ. Needed corrections were made. Once an agreed upon, digital file was created. DWQ assisted NRCS in modifying certain boundaries which were not at the time coincident with the subbasins that DWQ manages. After that was completed, NRCS met with officials from neighboring states (Virginia, South Carolina, Georgia, and Tennessee) to edgematch the Hydrologic Unit boundaries across the state line. This was done to the 11-digit boundary, not the 14-digit. Once this file was complete, DWQ assisted CGIA in establishing new subbasin boundaries derived from HU boundaries, and then established new river basin boundaries derived from subbasin boundaries. This digital file is updated as changes occur.
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Hydrologic units were digitized from hand delineated boundaries on USGS 7.5 Minute series paper base maps. The digital files were attributed and checkplots were created for review by the Natural Resources Conservation Service and the NC Division of Water Quality. Necessary corrections were made and new plots were run. Post processing involved edgematching and mapjoining of USGS 7.5 Minute series maps used to create the digitized data. This process generated one statewide polygon coverage. CGIA updates the digital file as needed. The River basin boundaries were selected out of the hydrologic units file, subboundaries dissolved, and attributes checked.
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Delineated hydrologic unit boudaries on 24k topographic maps were given to Westinghouse-Landmark GIS, Inc. by the NRCS. The HU boundaries were hand-digitized and combined into on file. After some review by NRCS and DWQ, this file was given to NCCGIA where it was joined to the existing 24 counties of coastal HU data. This file was then checked by NRCS and DWQ staff. Corrections were made.
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Internal feature number.
ESRI
Internal feature number.
ESRI
Total perimeter in coverage units
Software computed
Feature geometry.
ESRI
Feature geometry.
ESRI
From-node identifier of linear feature
Software computed
To-node identifier of linear feature
Software computed
Internal number of poly to left of arc
Software computed
Internal number of poly to right of arc
Software computed
Length of arc in coverage units
Software computed
Internal feature number
Software computed
Internal ID number
User defined
A polygon coverage with areas depicting the boundaries of the state's river basins. The polygon attribute table (PAT) has attribute data including total area in coverage units, total perimeter, polygon internal identification number, polygon user identification number, and the name and abbreviated name of the river basin. >HUNCRB.PAT Polygon Attribute Table >COLUMN ITEM NAME WIDTH OUTPUT TYPE DEC DESCRIPTION >1 AREA 4 12 F 3 Total area in square meters >5 PERIMETER 4 12 F 3 Total perimeter in linear >meters >9 HUNCRB# 4 5 B - Polygon internal ID number >13 HUNCRB-ID 4 5 B - Polygon user ID number >88 RIVBASIN-ABRV 8 8 C - River basin abbreviation >96 RIVBASIN-NAME 20 20 C - River basin name >HUNCRB.AAT Arc Attribute Table >COLUMN ITEM NAME WIDTH OUTPUT TYPE DEC DESCRIPTION >1 FNODE# 4 5 B - From-node id of linear >feature >5 TNODE# 4 5 B - To-node id of linear >feature >9 LPOLY# 4 5 B - Left-side polygon id of >linear feature >13 RPOLY# 4 5 B - Right-side polygon id of >linear feature >17 LENGTH 4 12 F 3 Length of linear feature >in meters >21 HUNCRB# 4 5 B - Internal id number >25 HUNCRB-ID 4 5 B - Internal id number
See Cross_Reference item.
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NCCGIA is charged with the development and maintenance of the State's corporate geographic database and, in cooperation with other mapping organizations, is committed to offering its users accurate, useful, and current information about the state. Although every effort has been made to ensure the accuracy of information, errors and conditions originating from physical sources used to develop the corporate database may be reflected in the data supplied. The client must be aware of data conditions and bear responsibility for the appropriate use of the information with respect to possible errors, original map scale, collection methodology, currency of data, and other conditions specific to certain data. NCCGIA does not support secondary distribution of this data. The use of trade names or commercial products does not constitute their endorsement by the NCCGIA or North Carolina State Government.
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