This document establishes interagency guidelines for creating the Watershed Boundary Dataset (WBD) as seamless and hierarchical hydrologic unit data, based on topographic and hydrologic features across the United States. This document provides guidelines, requirements, and procedures for expanding and revising the previous U.S. Geological Survey (USGS)-Natural Resources Conservation Service (NRCS) national data published in 1994. Expansion is accomplished by creating two additional levels of detailed hydrologic unit boundaries nested within the 1:250,000-scale hydrologic units, and revision occurs through increasing the data resolution to 1:24,000-scale in the conterminous United States.

This publication has been updated and clarified from the previous NRCS guidance document "Federal Standard for Delineation of Hydrologic Unit Boundaries, Version 2.0, October 1, 2004," through contributions of the WBD Technical Support Team, as requested by the Subcommittee on Spatial Water Data. The USGS online publication is available on the Web at http://pubs.usgs.gov/tm/tm11a3/.

A standardized hydrologic unit system, referred to as the Hydrologic Unit Code (HUC) system, was developed in the mid-1970's by the U.S. Geological Survey (USGS).  This system divided the country into 21 Regions, 222 Sub-regions, 352 Basins and 2,149 Sub-basins based on surface topography.  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 unit code.  The underlying concept is a topographically defined set of drainage areas organized in a nested hierarchy by size and number of divisions per nested level. The standardized 8-digit USGS hydrologic units (Levels 1, 2, 3 and 4) are broadly used; however, the geographical area of units is too large to adequately serve many water resource investigations, resource analysis and management needs. 

In January 2009, certification of the WBD in Texas was completed.  This new product was developed through a coordinated effort between various state and federal entities both within Texas and in neighboring states.  The WBD subdivides 8-digit hydrologic units into 10- and 12-digit units.  Each 8-digit unit was subdivided into multiple 10-digit units, each comprising 40,000 to 250,000 acres.  Each 10-digit unit was subdivided into multiple 12-digit units, each comprising 10,000 to 40,000 acres.

Data can be downloaded from the USDA National Resources Geospatial Data Gateway via http://datagateway.nrcs.usda.gov.

TNRIS has completed the latest round of data enhancments to the 1:24,000-scale NHD. The focus of this effort was to complete population of the Value Added Attributes (VAAs) table from the NHD geodatabase schema.  The VAAs include 20 new attributes computed from the NHD flow table and assigned to each feature in the stream network.  The VAAs are designed to enhance the capabilities of NHD in three areas: 1) Navigation/Traversal; 2) Analysis; and 3) Display. 

Here is how it works: The geometry of the NHD forms a giant network in which lines flow into other lines.  To figure out where the water has come from and where it is going is simply a matter of following those lines.  But following those lines takes computer processing power and that can eat up a lot of time.  By processing much of the networking ahead of time and storing the calculations, scientists can speed up their analysis and work more productively. The Value Added Attributes are a table of pointers generated by pre-processing the NHD geometry. This is known as the VAA table, or NHDFlowLineVAA, a database table that is included in the NHD. 

To find out more about the NHD VAA table, go to http://www.epa.gov/waters/ and click on NHDPlus.

The Texas Statewide Aerial Imagery project is beginning to receive data from Northwest Geomatics, the vendor selected by the USDA Farm Services Agency Aerial Photography Field Office.  Clear weather in South Texas has allowed for optimum flying and data acquistion conditions for the Texas NAIP project.

Northwest Geomatics has begun the delivery of compressed county mosaics (CCM's) as per their agreement with USDA-FSA. 16 counties have been received by TNRIS and are undergoing data quality checks and metatdata verification. These are provisional products subject to final acceptance by USDA-FSA and are comprised of four spectral bands processed to one meter ground pixel resolution.

The Texas funding partners include Texas Commission on Environmental Quality ( Air and Facilities Divisions), The General Land Office, Commission on State Emergency Communications, and the Texas Water Development Board (TNRIS and the National Flood Insurance Program - Mapping Services.

This project is supported by a number of techincal partners including:

• Texas Height Modernization Program - Texas A&M Corpus Christi, Ground Control
• The University of Texas Center for Space Research, Ground Control and image quality checks
• Brazos Valley

The participation by local field partners has provided invaluable assistance to the project.

Several state agencies are establishing a series of agreements to partner with the U.S. Department of Agriculture Farm Services Agency (FSA) to acquire statewide digital ortho quadrangle (DOQ) imagery for Texas. TNRIS is working with FSA to establish project parameters and specifications to serve the needs of partners and support the FSA priorities for their National Agricultural Imagery Program (NAIP). 

FSA will be engaging pre-qualified providers in the next two months and is planning to begin imagery acquisition in April. 

The project is described in more detail here: PartnerBriefing011508