Missouri Hydrologic Unit Mapping

The Natural Resources Conservation Service (NRCS) and the Missouri Department of Conservation (MDC) have completed a draft revision of Missouri’s hydrologic unit map.  The revision is based on the 8-digit Hydrologic Unit Code (HUC) system developed by the U. S. Geological Survey (USGS) in the mid-1970’s and the 14-digit system compiled by the Missouri NRCS in the mid-1990’s.  The data set is a complete digital hydrologic unit boundary layer compiled to the Subwatershed (12-digit) 6^th level for the State of Missouri. The data set consists of geo-referenced digital boundary lines and associated attributes for two thousand 12-digit subwatersheds  created in accordance with the “FGDC Proposal, Version 1.0 – Federal Standards For Delineation of Hydrologic Unit Boundaries”.  Upon certification, the Missouri data set will be appended to the national Watershed Boundary Dataset (WBD).

The 10-digit watershed and 12-digit subwatershed hydrologic unit boundaries provide a uniquely identified and uniformed subdivision of the state’s 66 large 8-digit subbasin drainage areas.  Compiled at a scale of 1:24,000, the statewide revision features enhanced watershed segmentation and sequential coding.  Each polygon is attributed with codes for its’ 8, 10, and 12-digit levels, name, size, type, and modifications.  Each arc is attributed with the highest level hydrologic unit it represents, the base map source the arc was delineated on and the metadata ID code that identifies which metadata file applies to the arc.

The data set will be subjected to a national certification process conducted by the NRCS through its’ National Cartography and Geospatial Center (NCG) prior to official release.  The certification process will consist of two phases.  Phase I will be a provisional verification conducted by the NCGC staff and an interagency review team.  A successful provisional review will initiate a Phase II final verification conducted by the FGDC Subcommittee on Spatial Water Data.  Upon approval by the FGDC, the Chairman of the Subcommittee on Spatial Water Data will send a letter to the Missouri NRCS State Conservationist specifying the HU data set is approved and meets the national guidelines.

For more information on NRCS 12-digit hydrologic unit mapping and the national Watershed Boundary Data set: http://www.ftw.nrcs.usda.gov/huc_data.html

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