Transcript National Watershed Boundary Dataset

National Watershed
Boundary Dataset
THE WEST VIRGINIA SUBSET
Why a watershed boundary dataset?
• The watershed is one of the earliest concepts to
evolve from American policies for planning and
managing water resources.
• The identity of a watershed is directly related to
the management problems of concern, from
large scale flooding along the Mississippi River to
sediment control in small reservoirs.
A Brief History of Watershed Management
• As early as the 1920’s and 1930’s watershed based
planning practices were adopted by many federal
agencies.
• NRCS has the largest national program of watershed
management originating from the national concerns in
the 1930’s over wide spread soil erosion and
sedimentation.
• In the mid 1970’s a standardized hydrologic unit system,
referred to as the Hydrologic Unit Code (HUC) was
developed by USGS under the sponsorship of the Water
Resources Council.
A Brief History of Watershed Management (cont.)
• The underlying concept of the HUC system is a
topographically defined set of drainage areas organized
in a nested hierarchy based on surface feature size.
• It divided the country into 21 Regions, 222 Sub-regions,
352 Basins (formerly referred to as Accounting Units),
and 2,149 Sub-basins (formerly referred to as Cataloging
Units).
• A hierarchical hydrologic unit code containing 2 digits for
each of the four levels was assigned to identify the
hydrologic units; these four levels are the basis for the
8-digit hydrologic units code.
A Brief History of Watershed Management (cont.)
• Although 8-digit USGS hydrologic units were broadly
used, the geographic size of the units were sometimes
too large to adequately serve many water resource
investigations, resource analysis and management
needs.
• In the late 1980’s NRCS completed mapping of
watersheds (Level 5 hydrologic units) for use in natural
resource planning.
A Brief History of Watershed Management (cont.)
• In the early 1990’s NRCS began a national initiative to
delineate and digitize watersheds (Level 5) and
subwatersheds (Level 6) by GIS that meets national map
accuracy standards using standardized and reviewed
criteria.
• In the spring of 2000, the member agencies of the
Subcommittee on Spatial Water Data of the Federal
Geographic Data Committee agreed that a new standard
would be written, which supercedes the standard written
by NRCS, for hydrologic unit delineation to the 5th and
6th level delineating watersheds and subwatersheds.
Federal Standards for Delineation of Hydrologic
Unit Boundaries
• NRCS, USFS, USGS and BLM have worked with other
federal and state agencies, tribes and the FGDC to
author this standard.
• USGS, USFS, BLM and NOAA have assisted NRCS in the
review and verification of hydrologic units.
Defining the Hydrologic Unit
• The selection and delineation of HU boundaries was
determined solely upon science-based hydrologic
principles, not favoring any administrative or special
projects nor a particular program or agency.
• An HU is delineated and georeferenced to the USGS
1:24,000 scale topographic base map meeting National
Map Accuracy Standards.
• HU boundaries are determined solely upon hydrologic
and topographic features.
• An HU is generally subdivided into 5 to 15 units.
• The typical watershed size is 40,000 to 250,000 acres.
The typical sub watershed is 10,000 to 40,000 acres.
• Started with the original 11digit (5th level) NRCS
watersheds. Some did not
meet new definition due to
size.
• Then started with 8-digit (4th
level) sub-basin with 11-digit
watersheds outlined and
identified possible
subwatersheds based on size
and identifiable outlets.
•As a result of defining
the subwatersheds (6th
level) the watersheds
(5th level) were also
redefined.
What do we do with the “Old Watersheds”,
now that there is a new dataset available?
• Proposal #1
– Archive dataset for reference to past
watershed sampling and monitoring activities.
• Proposal #2
– ??
Subwatersheds
Watersheds
Sub-basin
• The Watershed Boundary Dataset will be in a vector data
structure that will be delivered via the USDA Geospatial
Data Gateway (http://datagateway.nrcs.usda.gov/)
• The dataset should be available by July 1, 2004.
• The dataset will be available for download by either Subbasin 8-digit (4th Level) or Subwatershed 12-digit (6th
level).
Questions