Hydrologic Unit Codes (HUCs)Explained
Hydrologic Unit Codes (HUCs)
Watersheds are delineated by USGS using a nationwide system based on surface
hydrologic features. This system divides the country into 21 regions
(2-digit), 222 subregions
(4-digit), 352 accounting
units (6-digit), and 2,262 cataloguing
units (8-digit). A hierarchical hydrologic unit code (HUC) consisting
of 2 digits for each level in the hydrologic unit system is used to identify
any hydrologic area.
******************************
What the Numbers Mean
Each hydrologic unit is assigned an 8-digit attribute code that
uniquely identifies each of the four levels of classification within four
two-digit
fields. An example is shown below using hydrologic unit code
04030203:
| Level |
Code |
Description |
| Region |
04 |
Great Lakes |
| Subregion |
0403 |
Northwestern Lake Michigan |
| Accounting Unit |
040302 |
Fox River, Wisconsin |
| Cataloging Unit |
04030204
|
Lake Winnebago, Wisconsin |
A complete list of Hydrologic Unit codes, descriptions, names,
and drainage areas can be found in the United States Geological Survey
Water-Supply Paper 2294, entitled "Hydrologic Unit Maps".
*******************************
Below is a list of maps that will show you what the 2,4,6, and
8-digit HUCs look like on a national scale.
HUC
2 map
HUC
4 map
HUC
6 map
HUC 8 map
********************************
More sites with information about
HUCs:
EPA's Surf Your Watershed - A
watershed in Surf Your Watershed is the 8-digit cataloging unit; gives info
about watershed too
Map a watershed
Watershed Information
Network (EPA)
1:2,000,000-Scale
Hydrologic Unit Maps
USGS Water Resources Division
- Hydrologic Unit maps and spatial data
USGS National Hydrography Dataset
USGS GIS Data for Water Resources
EPA Office of Water
USGS
Geographic Names Information System (GNIS) - here you can find the
location of a lake, have it mapped, and through a link to the EPA Surf your
watershed site, find out what HUC it is in. A great tool; we use it all
the time.
