November 2005

This layer represents the eight mega-drainage basins for Massachusetts, aggregated from the Major Basins layer.

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This layer represents the eight mega-drainage basins for Massachusetts, aggregated from the Major Basins layer. The delineations were based on the level 2 (4-digit) Hydrologic Unit Codes (HUCs) from the U.S. Geological Survey. Included are delineation of the Narragansett and Thames mega-basins.

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. In the 4-digit HUCs, the first two digits identify the region and the first four digits identify subregions.

The polygon layer is named MEGABASINS_POLY and the line layer MEGABASINS_ARC. Annotation is included in MEGABASINS_ANNO_BASIN.

Attributes

The polygon attribute table has the following items:

ITEM NAME	DESCRIPTION
BASIN_ID	4-digit HUC
NAME	Mega basin name (for informal use only - does not conform to USGS naming)

The mega basins' ID and names are as follows:

BASIN_ID	NAME
0106	PISCATAQUA-SALMON FALLS
0107	MERRIMACK
0108	CONNECTICUT
0109	COASTAL
0109	NARRAGANSETT
0110	HOUSATONIC
0110	THAMES
0202	HUDSON

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

ITEM NAME	DESCRIPTION
OUTLINE	Line type: 0 Internal megabasin boundary 1 State outline

Maintenance

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)
• NRCS HUC (8, 10, 12) Basins (8-, 10-, and 12-digit HUC delineations)

Last Updated 11/23/2005