Hydrologic Units

New York State Hydrologic Unit Coverage Documentation

Geographic Data Set:	New York State Hydrologic Unit Coverage
Distribution Constraints:	For internal NYS DEC use. Distribution will be handled by the Natural Resources Conservation Service (NRCS) after final Quality Assurance / Quality Control by their National Cartography and Geospatial Center.
Description:	Hydrologic unit is the area of land upstream from a specific point on a surface waterbody and is defined by a hydrologic boundary that includes the area draining to that point. This data layer is used to identify the boundaries of watersheds that are hydrographic in nature and contribute to the surface waterbodies within New York State.
Available:	Statewide.
Completion or Most Recent Revision Date:	1999.
Type of Data:	ARC/INFO coverage with region subclasses with attribute tables.
Source of Information:	A cooperative effort by USDA Natural Resources Conservation Service, NYS Department of Environmental Conservation - Division of Water, and US Geological Survey - Water Division.
Projection and Map Units:	NYTM in meters, NAD83 horizontal datum.

Attribute Tables:	Items (or Fields) in the Digit11 region subclass Attribute Table Items (or Fields) in the Digit8 region subclass Attribute Table Items (or Fields) in the Digit6 region subclass Attribute Table Items (or Fields) in the Digit4 region subclass Attribute Table Items (or Fields) in the Digit2 region subclass Attribute Table Items (or Fields) in the Arc (line) Attribute Table

Contact:	Internal Use at DEC: Shohreh Karimipour Nonpoint Source Section, DOW NYS Department of Environmental Conservation sxkarimi@gw.dec.state.ny.us 50 Wolf Road Albany, NY 12233-3508 Phone (518)457-9871 FAX (518)485-7786
Documentation Date:

1. Development History: Watershed lines were delineated by USGS WRD from topographic models developed in 1941-1985. These lines were digitized by NRCS and DEC. A seamless coverage was compiled, attributed and reviewed by NYS Department of Environmental Conservation DOW, NRCS and NYS DEC. Development of 14-digit level watersheds is under process now.
2. The Hydrologic Unit Code (HUC) for the smallest watersheds in this data coverage is comprised of 11 digits. The hydrologic unit hierarchy corresponds to codes with 2, 4, 6, 8 and 11 digits. These are presented here as 5 individual Arc/Info Region layers or data sets. In decreasing area (increasing number of digits in the HUC) order each is made up by several of the contiguous watersheds of lower hierarchy:
   Region.digit2 The first two digits of the HUC are the code for the Regional Boundary (e.g. 02, the Mid-Atlantic Region).
   Region.digit4 The next two digits of the HUC are the code for the Subregional Boundary (e.g. 0202, Upper Hudson).
   Region.digit6 The next two digits of the HUC are the code for the Accounting Unit (NRCS 'Basin') Boundary (e.g. 020200, the Upper Hudson again).
   Region.digit8 The next two digits of HUC are the code for the Cataloging Unit (NRCS 'Subbasin') Boundary (e.g. 02020004, Mohawk).
   Region.digit11 The last three digits of HUC are the code for the NRCS Watershed Boundary (e.g. 02020004390, Stony Creek).
3. Following USDA National Cartography and Geospatial Center instructions, when the delineation of watershed boundaries extended to a stream line or crossed a stream, the following criteria were applied:
   A. any land or water body smaller than 3000 acres is ignored and lumped into the adjacent Hydrologic Unit (HU).
   B. Tributary watersheds extending to large rivers (double line streams) stop at the water shoreline.
   C. Lakes with surfaces area > 3000 acres, digitized by NRCS, are excluded in the final delineation of the watershed.
   D. When the boundary of the watershed extends to the edge of a surface waterbody, the watershed lines are replaced with shorelines from the 1:24,000 scale National Hydrography Dataset.
   E. Small lakes are also included as part of the watershed area.
   F. For smaller streams, watershed lines cross the stream. This is necessary to accumulate drainage areas to a point.
   G. A Watershed boundary may cross the stream in some instances, such as in flat areas or tidal marshes. For these areas accuracy checks against Digital Elevation Models were performed.

Attribute Tables

Items (or Fields) in the Digit11 region subclass Attribute Table

HUC:11:	11-digit level Hydrologic Unit Code.
Area:	Area of the 11-digit level Hydrologic Unit, in square meters.
Name:	NRCS Hydrologic Unit, Watershed level, Name.
Last3:	The last three digits of HUC are the code for the NRCS Hydrologic Unit, Watershed level, Boundary.

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Items (or Fields) in the Digit8 region subclass Attribute Table

HUC:8:	8-digit level Hydrologic Unit Code.
Area:	Area of the 8-digit level Hydrologic Unit, in square meters.
Name:	NYS-DEC Watershed Name.
Nrcs_name:	NRCS Hydrologic Unit, Subbasin (EPA's Cataloging Unit) level, Name.

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Items (or Fields) in the Digit6 region subclass Attribute Table

HUC:6:	6-digit level Hydrologic Unit Code.
Area:	Area of the 6-digit level Hydrologic Unit, in square meters.
Name:	NRCS Hydrologic Unit, Basin level (EPA's Accounting Unit), Name.

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Items (or Fields) in the Digit4 region subclass Attribute Table

HUC:4:	4-digit level Hydrologic Unit Code.
Area:	Area of the 4-digit level Hydrologic Unit, in square meters.
Name:	NRCS Hydrologic Unit, Subregion level, as per USGS.

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Items (or Fields) in the Digit2 region subclass Attribute Table

HUC:2:	2-digit level Hydrologic Unit Code.
Area:	Area of the 2-digit level Hydrologic Unit, in square meters.
Name:	NRCS Hydrologic Unit, Region level, as per USGS.

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Items (or Fields) in the Arc (line) Attribute Table

SOURCE:	Code for source of line data (type I, width 2): 09 DEC, WaterGIS developed linework 10 WaterGIS edits (connectors, etc ) 72 USGS-Water Division 76 NRCS
FNODE#, TNODE#, LPOLY#, RPOLY#, LENGTH, HUC11#, HUC11-ID:	ArcInfo internal, for topology/database tracking.

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