National Watershed National Watershed Boundary DatasetBoundary Dataset

THE WEST VIRGINIA SUBSETTHE WEST VIRGINIA SUBSET

Why a watershed boundary Why a watershed boundary dataset?dataset?

• The watershed is one of the earliest The watershed is one of the earliest concepts to evolve from American policies concepts to evolve from American policies for planning and managing water resources.for planning and managing water resources.

• The identity of a watershed is directly The identity of a watershed is directly related to the management problems of related to the management problems of concern, from large scale flooding along the concern, from large scale flooding along the Mississippi River to sediment control in small Mississippi River to sediment control in small reservoirs.reservoirs.

• As early as the 1920’s and 1930’s watershed As early as the 1920’s and 1930’s watershed based planning practices were adopted by many based planning practices were adopted by many federal agencies.federal agencies.

• NRCS has the largest national program of NRCS has the largest national program of watershed management originating from the watershed management originating from the national concerns in the 1930’s over wide spread national concerns in the 1930’s over wide spread soil erosion and sedimentation.soil erosion and sedimentation.

• In the mid 1970’s a standardized hydrologic unit In the mid 1970’s a standardized hydrologic unit system, referred to as the Hydrologic Unit Code system, referred to as the Hydrologic Unit Code (HUC) was developed by USGS under the (HUC) was developed by USGS under the sponsorship of the Water Resources Council.sponsorship of the Water Resources Council.

A Brief History of Watershed Management

A Brief History of Watershed Management (cont.)

• The underlying concept of the HUC system is a The underlying concept of the HUC system is a topographically defined set of drainage areas topographically defined set of drainage areas organized in a nested hierarchy based on surface organized in a nested hierarchy based on surface feature size.feature size.

• It divided the country into 21 Regions, 222 Sub-It divided the country into 21 Regions, 222 Sub-regions, 352 Basins (formerly referred to as regions, 352 Basins (formerly referred to as Accounting Units), and 2,149 Sub-basins Accounting Units), and 2,149 Sub-basins (formerly referred to as Cataloging Units).(formerly referred to as Cataloging Units).

• A hierarchical hydrologic unit code containing 2 A hierarchical hydrologic unit code containing 2 digits for each of the four levels was assigned to digits for each of the four levels was assigned to identify the hydrologic units; these four levels are identify the hydrologic units; these four levels are the basis for the 8-digit hydrologic units code.the basis for the 8-digit hydrologic units code.

A Brief History of Watershed Management (cont.)

• Although 8-digit USGS hydrologic units were Although 8-digit USGS hydrologic units were broadly used, the geographic size of the units broadly used, the geographic size of the units were sometimes too large to adequately serve were sometimes too large to adequately serve many water resource investigations, resource many water resource investigations, resource analysis and management needs.analysis and management needs.

• In the late 1980’s NRCS completed mapping of In the late 1980’s NRCS completed mapping of watersheds (Level 5 hydrologic units) for use in watersheds (Level 5 hydrologic units) for use in natural resource planning. natural resource planning.

A Brief History of Watershed Management (cont.)

• In the early 1990’s NRCS began a national In the early 1990’s NRCS began a national initiative to delineate and digitize watersheds initiative to delineate and digitize watersheds (Level 5) and subwatersheds (Level 6) by GIS that (Level 5) and subwatersheds (Level 6) by GIS that meets national map accuracy standards using meets national map accuracy standards using standardized and reviewed criteria.standardized and reviewed criteria.

• In the spring of 2000, the member agencies of the In the spring of 2000, the member agencies of the Subcommittee on Spatial Water Data of the Subcommittee on Spatial Water Data of the Federal Geographic Data Committee agreed that a Federal Geographic Data Committee agreed that a new standard would be written, which supercedes new standard would be written, which supercedes the standard written by NRCS, for hydrologic unit the standard written by NRCS, for hydrologic unit delineation to the 5delineation to the 5thth and 6 and 6thth level delineating level delineating watersheds and subwatersheds. watersheds and subwatersheds.

Federal Standards for Delineation of Federal Standards for Delineation of Hydrologic Unit BoundariesHydrologic Unit Boundaries

• NRCS, USFS, USGS and BLM have worked with NRCS, USFS, USGS and BLM have worked with other federal and state agencies, tribes and the other federal and state agencies, tribes and the FGDC to author this standard.FGDC to author this standard.

• USGS, USFS, BLM and NOAA have assisted NRCS USGS, USFS, BLM and NOAA have assisted NRCS in the review and verification of hydrologic units.in the review and verification of hydrologic units.

Defining the Hydrologic UnitDefining the Hydrologic Unit

• The selection and delineation of HU boundaries The selection and delineation of HU boundaries was determined solely upon science-based was determined solely upon science-based hydrologic principles, not favoring any hydrologic principles, not favoring any administrative or special projects nor a particular administrative or special projects nor a particular program or agency.program or agency.

• An HU is delineated and georeferenced to the An HU is delineated and georeferenced to the USGS 1:24,000 scale topographic base map USGS 1:24,000 scale topographic base map meeting National Map Accuracy Standards.meeting National Map Accuracy Standards.

• HU boundaries are determined solely upon HU boundaries are determined solely upon hydrologic and topographic features. hydrologic and topographic features.

• An HU is generally subdivided into 5 to 15 units.An HU is generally subdivided into 5 to 15 units.

• The typical watershed size is 40,000 to 250,000 The typical watershed size is 40,000 to 250,000 acres. The typical sub watershed is 10,000 to acres. The typical sub watershed is 10,000 to 40,000 acres.40,000 acres.

• Started with the original Started with the original 11-digit (511-digit (5thth level) NRCS level) NRCS watersheds. Some did not watersheds. Some did not meet new definition due to meet new definition due to size.size.

• Then started with 8-digit Then started with 8-digit (4(4thth level) sub-basin with level) sub-basin with 11-digit watersheds 11-digit watersheds outlined and identified outlined and identified possible subwatersheds possible subwatersheds based on size and based on size and identifiable outlets.identifiable outlets.

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

What do we do with the “Old What do we do with the “Old Watersheds”, now that there is a new Watersheds”, now that there is a new dataset available?dataset available?

• Proposal #1Proposal #1– Archive dataset for reference to past Archive dataset for reference to past

watershed sampling and monitoring watershed sampling and monitoring activities.activities.

• Proposal #2Proposal #2– ????

SubwatershedsSubwatersheds

WatershedsWatersheds

Sub-basinSub-basin

• The Watershed Boundary Dataset will be in a The Watershed Boundary Dataset will be in a vector data structure that will be delivered via the vector data structure that will be delivered via the USDA Geospatial Data Gateway (USDA Geospatial Data Gateway (http://datagateway.nrcs.usda.gov/http://datagateway.nrcs.usda.gov/))

• The dataset should be available by July 1, 2004.The dataset should be available by July 1, 2004.

• The dataset will be available for download by The dataset will be available for download by either Sub-basin 8-digit (4either Sub-basin 8-digit (4thth Level) or Level) or Subwatershed 12-digit (6Subwatershed 12-digit (6thth level). level).

QuestionsQuestions