Hydrologic Units - North Carolina Subbasins

Title: Hydrologic Units - North Carolina Subbasins

Abstract:

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 file specifically shows the North Carolina subbasins.

Supplemental_Information:

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: huncsb file size = 2.5 mb

(huncrb and huncsb need to be updated whenever hunc is updated).

Revisions and updates to this layer include:

3.) filename: huncsb1298 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.

3.)filename: hunc496 The April 15, 1996 update included

restoring the Arc Attribute Table (AAT) to the coverage. This

was lost while processing the file for riverbasins and subbasins

attributes. It also included names and 6-digit identification

numbers added for subbasins as well as names and abbreviations

added for river basins. Some minor boundary adjustments were made

throughout the coverage to make the Hydrologic Units boundaries

coincident with the Water Supply Watershed boundaries.

1.) filename: subbasin89 (previously called nc.subbasin)

The nc.subbasin file was created back in the late 80s to show

the major river subbasins in North Carolina. This file was

for display purposes only because of its scale of 1:1,000,000.

This file contains a name (ROA7, for Roanoke river basins,

subbasin 7) and Basin# (03-02-07) attributes in the PAT.

The AAT contains system default attributes only. This file

was replaced with the huncsb coverage which shows

the subbassins delineated from the 1:24,000-scale hydrologic

units (hunc) file.

Range of values
Minimum:	0.000
Maximum:	3,159,559,424.000
Units:	meters
Resolution:	.001

Range of values

Minimum:

0.000

Maximum:

3,159,559,424.000

Units:

meters

Resolution:

.001

Range of values
Minimum:	30,247.797
Maximum:	2,156,437.000
Units:	Meters
Resolution:	0.001

Range of values

Minimum:

30,247.797

Maximum:

2,156,437.000

Units:

Meters

Resolution:

0.001

Range of values
Minimum:	1
Maximum:	135

Range of values

Minimum:

Maximum:

135

Range of values
Minimum:	0
Maximum:	134

Range of values

Minimum:

Maximum:

134

Range of values
Minimum:	1
Maximum:	1,379

Range of values

Minimum:

Maximum:

1,379

Range of values
Minimum:	1
Maximum:	1,379

Range of values

Minimum:

Maximum:

1,379

Range of values
Minimum:	1
Maximum:	135

Range of values

Minimum:

Maximum:

135

Range of values
Minimum:	1
Maximum:	135

Range of values

Minimum:

Maximum:

135

Range of values
Minimum:	20.855
Maximum:	86,680.773
Units:	meters
Resolution:	0.001

Range of values

Minimum:

20.855

Maximum:

86,680.773

Units:

meters

Resolution:

0.001

Range of values
Minimum:	1
Maximum:	1,512

Range of values

Minimum:

Maximum:

1,512

Range of values
Minimum:	1
Maximum:	1,512

Range of values

Minimum:

Maximum:

1,512

Hydrologic Units - North Carolina Subbasins

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