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Watershed Boundary Dataset (WBD)
Watershed boundaries define the areal extent of surface water drainage to a
point. The intent of defining hydrologic units (HU) for the
Watershed Boundary Dataset is to establish a base-line drainage boundary
framework, accounting for all land and surface areas. The selection and
delineation of hydrologic boundaries are determined solely upon science-based
hydrologic principles, not favoring any administrative or special projects nor
particular program or agency. At a minimum, they are being delineated and georeferenced to the USGS 1:24,000 scale topographic base map meeting National
Map Accuracy Standards (NMAS). A hydrologic unit has a single flow outlet
except in coastal or lakefront areas. 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.”
The Watershed Boundary Dataset is being developed under the
leadership of the
Subcommittee on Spatial Water Data, which is part of the
Advisory Committee on Water Information
(ACWI) and the Federal Geographic Data Committee
(FGDC). The USDA Natural Resources Conservation Service (NRCS), along with
many other federal agencies and national associations, have representatives on
the Subcommittee on Spatial Water Data.
As watershed boundary geographic information systems (GIS)
coverages are completed, statewide and national data layers will be made
available via the
Geospatial
Data Gateway to everyone, including federal, state, local
government agencies, researchers, private companies, utilities, environmental
groups, and concerned citizens. The database will assist in planning and
describing water use and related land use activities.
Watershed Boundary Dataset Resources
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