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What is a Watershed?

In which watershed do you live?

Every point on dry land falls within a watershed. The EPA’s Surf Your Watershed website allows you to determine the major watershed of any location in the U.S. and Puerto Rico.

Hydrologic Unit (HUC) Codes

Watersheds within the United States are cataloged by Hydrologic Unit Codes (HUC ’s) by the U.S. Geological Survey (USGS). These 8-digit codes represent four levels of classification, each becoming progressively more specific. The first two digits represent the region code; the next two digits refer to the sub-region; the 5 th and 6 th digits refer to the accounting unit; and the final two digits specify the cataloging unit. A double 00 in the two-digit accounting unit field indicates that the accounting unit and the sub-region are the same. Likewise, if the cataloging unit field is 00, it is the same as the accounting unit.

For example, the HUC for the Upper Verde watershed in central Arizona is 15060202. The Upper Verde watershed is located in region 15, sub-region 06, and accounting unit 02, and is cataloging unit 02.

As stated by the Federal Standard for Delineation of Hydrologic Unit Boundaries,

"A hydrologic unit is a drainage area delineated to nest in a multi-level, hierarchical drainage system. Its boundaries are defined by hydrographic and topographic criteria that delineate an area of land upstream from a specific point on a river, stream or similar surface waters. A hydrologic unit can accept surface water directly from upstream drainage areas, and indirectly from associated surface areas such as remnant, non-contributing, and diversions to form a drainage area with single or multiple outlet points. Hydrologic units are only synonymous with classic watersheds when their boundaries include all the source area contributing surface water to a single defined outlet point."


All contents copyright 2007. Arizona Board of Regents.