NEWS NOTES ON SUSTAINABLE WATER RESOURCESHydrologic Unit Codeshttps://en.wikipedia.org/wiki/Hydrological_code“A hydrological code or hydro...

NEWS NOTES ON SUSTAINABLE WATER RESOURCESHydrologic Unit Codeshttps://en.wikipedia.org/wiki/Hydrological_code“A hydrological code or hydrologic unit code is a sequence of numbers or letters that identify a hydrological feature like a river, river reach, lake, or area like a drainage basin (also called watershed (in North America)) or catchment. One system, developed by Strahler, known as the Strahler stream order, ranks streams based on a hierarchy of tributaries. Each segment of a stream or river within a river network is treated as a node in a tree, with the next segment downstream as its parent. When two first-order streams come together, they form a second-order stream. When two second-order streams come together, they form a third-order stream, and so on.” A comprehensive coding system is in use in Europe. This system codes from the ocean to the so-called primary catchment. The system determines a set of oceans or endorheic systems identified by a letter. These systems are subdivided into a maximum of 9 seas. The seas are numbered 1 to 9. Seas lying far from the ocean, for example the Black Sea receive a higher number. The seas are delimited using the so-called definitions made by the International Hydrographic Organization in 1953. The coasts of these seas are defined clockwise from north west to south east from the strait where the sea connects to the ocean or the other seas.”The United States Geological Survey created a hierarchical system of hydrologic units originally called regions, sub-regions, accounting units, and cataloging units. Each unit was assigned a unique Hydrologic Unit Code (HUC). As first implemented the system had 21 regions, 221 subregions, 378 accounting units, and 2,264 cataloging units. Over time the system was changed and expanded.  As of 2010 there are six levels in the hierarchy, represented by hydrologic unit codes from 2 to 12 digits long, called regions, subregions, basins, subbasins, watersheds, and subwatersheds.”Details of the USGS system can be found here: https://water.usgs.gov/GIS/huc.html“The United States is divided and sub-divided into successively smaller hydrologic units which are classified into four levels: regions, sub-regions, accounting units, and cataloging units. The hydrologic units are arranged or nested within each other, from the largest geographic area (regions) to the smallest geographic area (cataloging units). Each hydrologic unit is identified by a unique hydrologic unit code (HUC) consisting of two to eight digits based on the four levels of classification in the hydrologic unit system.The outdated text-formatted list of hydrologic units names and numbers are still available from the 1987 USGS Water-Supply Paper 2294. in either the old original format or in the old tab-delimited format. or old pdf format. The most current and newest list of Hydrologic Units are located and accessible at the bottom of this page under "Newest List of Hydrologic Units Are The Watershed Boundary Dataset (WBD).”“Newest List of Hydrologic Units Are The Watershed Boundary Dataset (WBD)The newest and most recent HUC delineation efforts have been completed. This dataset named the Watershed Boundary Dataset further divides the huc levels to (5th and 6th levels) .see the Watershed Boundary Dataset WBD . The WBD contains the most current 8-digit, 10-digit and 12-digit hucs and are available below. A pdf file which lists the 2-digit, 4-digit, 6-digit and 8-digit hucs for the WBD and their naming convention is available at wbd_huc8.pdf. ( This pdf file is no longer accurate )”The Watershed Boundary Dataset (WBD) - is a nationally consistent watershed dataset that is subdivided into 6 levels (12-digit hucs) and is available from the USGS and USDA-NRCS-National Cartographic and Geospatial Center's (NCGC).”