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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.

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National Watershed Boundary Dataset

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  1. National Watershed Boundary Dataset THE WEST VIRGINIA SUBSET

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Started with the original 11-digit (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.

  11. As a result of defining the subwatersheds (6th level) the watersheds (5th level) were also redefined.

  12. 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 • ??

  13. Subwatersheds

  14. Watersheds

  15. Sub-basin

  16. 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 Sub-basin 8-digit (4th Level) or Subwatershed 12-digit (6th level).

  17. Questions

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