OVERVIEW

This dataset is a digital hydrologic unit boundary layer that is at the Subwatershed (12-digit) level. The layer also includes delineations at the Watershed (10-digit) and Subbasin (8-digit) levels. Each basin is identified by a unique Hydrologic Unit Code (HUC), as well a name, at each level. HUCs are identifiers as assigned to basin polygons by the U.S. Geological Survey (USGS). Data in this layer cover all of Massachusetts and small parts of surrounding states. The names of the statewide datalayers are NRCSHUC_POLY (polygons), NRCSHUC_ARC (arcs), and NRCSHUC_ANNO (annotation). The HUC is a hierarchical, numeric code that uniquely identifies hydrologic units. Hydrologic units are subdivisions of watersheds nested from largest to smallest areas and are used to organize hydrologic data. HUCs are constructed as follows: The first two digits identify the region, the first four digits identify subregions, the first six digits identify accounting units, the first eight digits identify cataloging units, the first ten digits identify watershed units, and the full twelve digits identify subwatershed units. The USGS has developed the first 8-digit HUC for the United States, while the U.S. Department of Agriculture, Natural Resource Conservation Service (USDA-NRCS) within each state is developing the full 12-digit HUC.

The original data set was developed by the USDA-NRCS, by delineating the boundary lines on base USGS 1:24,000 scale topographic quadrangle maps, and digitizing the delineated lines. Digital Raster Graphics (DRG) images were used for edits to the data layer. The dataset produced by the joint NRCS-USGS effort to develop the 12-digit national standard is known as the Watershed Boundary Datalayer (WBD).

The polygon attribute table has the following items:

ITEM NAME		DESCRIPTION
HUC_8		8-digit HUC
HU_8_STATE		HUC 8 State:  CT = Connecticut  MA = Massachusetts  NH = New Hampshire  NY = New York  RI = Rhode Island  VT = Vermont
HU_8_DS		Downstream HUC Subbasin Level 4 (8-digit)
HU_8_NAME		HUC 8 Basin Name
HU_8_MOD		Hydrologic Unit Modifications Subbasin Level 4 (8-digit) (Not coded)
HU_8_TYPE		Hydrologic Unit Type Subbasin Level 4 (8-digit) (Not coded)
HUC_10		10-digit HUC
HU_10_STAT		HUC 10 State (same values as HU_8_STATE)
HU_10_DS		Downstream Hydrologic Unit Code Watershed Level 5 (10-digit)
HU_10_NAME		HUC 10 Basin Name
HU_10_MOD		Hydrologic Unit Modifications WATERSHED Level 5 (10-digit):  BC = Barge Canal  DM = Dam at outlet or HU boundary  IT = Interbasin Transfer  NM = No Modifications  PD = Pipe Diversion
HU_10_TYPE		Hydrologic Unit Type Watershed Level 5 (10-digit):  F = Frontal hydrologic unit  S = Standard hydrologic unit
HUC_12		12-digit HUC
ACRES		Area of polygon in acres
HU_12_STAT		HUC 12 State (same values as HU_8_STATE)
HU_12_NCON
HU_12_DS		Downstream Hydrologic Unit Code Subwatershed Level 6 (12-digit)
HU_12_NAME		HUC 12 Basin Name
HU_12_MOD		Hydrologic Unit Modifications Subwatershed Level 6 (12-digit)  (same values as HU_10_MOD)
HU_12_TYPE		Hydrologic Unit Type Subwatershed Level 6 (12-digit):  F = Frontal hydrologic unit  S = Standard hydrologic unit  W = Water hydrologic unit
FIPS_C		County codes

In the arc attribute table, the item OUTLINE is coded as follows:

ITEM NAME		DESCRIPTION
OUTLINE		Boundary type: 8   8-digit HUC boundary 10 10-digit HUC boundary 12 12-digit HUC boundary 4 Coastline

MassGIS maintains the layer, although no updates are planned.

For other watershed data, see these layers:

• Major Watersheds (similar to 8-digit HUCs)
  
• Major Drainage Basins (similar to 8-digit HUCs)
• Drainage Sub-basins (more delineated than the 12-digit HUCs)
• Mega Basins (4-digit HUC delineations)
  

Last Updated 11/23/2005
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