Watershed Boundary Dataset

 

The Watershed Boundary Dataset (WBD) provides Hydrologic Units that define drainage areas for surface water. Most Hydrologic units have one outflow point where water exits and flows into a neighboring unit, or, in coastal areas, into the ocean. Hydrologic Units are subdivided progressively smaller units and each unit of measurement has a Hydrologic Unit Code (HUC) which describes the level of subdivision and the geographic location of the Hydrologic Unit. Hydrologic Units are nested within one another; for example HU-4's are nested with HU-2's.

 

See a description of the methodology used to define WBD Boundaries (WBD Standards).

 

Breakdown of the WBD

Name Level Digit Number of HUCs Alias
Two-Digit Hydrologic Unit

1

2

22

Region

Four-Digit Hydrologic Unit

2

4

219

Subregion

Six-Digit Hydrologic Unit

3

6

378 Basin
Eight-Digit Hydrologic Unit

4

8

2,283 Subbasin
Ten-Digit Hydrologic Unit

5

10

17,828 Watershed
Twelve-Digit Hydrologic Unit

6

12

97,442 Subwatershed

 

 

 

The attributes associated with the WBD are as follows:

Field Name

Definition

Applies to

Comments

Gaz_ID

Unique identifier assigned by GNIS, length 10.

All feature classes

 

Area_Acres

 

All feature classes

 

Area_SqKm

 

All feature classes

 

States

 

All feature classes

 

LoadDate

 

All feature classes

 

HUC_X

Numeric identifier for each level (2,4,6,8,10, and 12) of hydrologic units

All feature classes

 

HU_X_Name

Name assigned to each level (2,4,6,8,10, and 12) of hydrologic unit

All feature classes

 

HU_X_Type

Geomorphic and other considerations used to  develop the hydrologic unit.

 

HU10, HU12, HU14, HU16

See

ftp://ftp-fc.sc.egov.usda.gov/

NCGC/products/watershed/hu-standards.pdf

for domain of values

HU_X_Mod

A collection of two-character, uppercase abbreviation(s) for either (1) the type of modification to natural overland flow that alters the location of a Watershed boundary or (2) the special conditions GF-ground-water flow, GL-glacier, IF-ice field, OF-overbank flow, KA-karst, NC-noncontributing area, and IT-interbasin transfer.

HU10, HU12, HU14, HU16

See

ftp://ftp-fc.sc.egov.usda.gov/

NCGC/products/watershed/hu-standards.pdf

for domain of values

NContrib_Acres

Area that does not flow toward the outlet of a hydrologic unit.

HU12, HU14, HU16

 

NContrib_SqKm

Area that does not flow toward the outlet of a hydrologic unit.

HU12, HU14, HU16

 

HU_2s are not included with the data

HU_14 and HU_16 are included only where created by local stewards.