Hydrological code: Difference between revisions

Revision as of 22:41, 5 September 2018

Revision as of 08:59, 29 September 2018

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==United States==

The [[United States Geological Survey]] created a hierarchical system of hydrologic units originally called [[Water Resource Region|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.<ref name="USGS HUCs">{{cite journal|last=Seaber, Paul R., F. Paul Kapanos, and George L. Knapp|title=Hydrologic Unit Maps|journal=United States Geological Survey Water-supply Papers|year=1987|volume=No. 2294|pages=i-iii, 1–63}}</ref><ref name=usgs>{{cite web|title=Hydrologic Unit Maps - What are Hydrologic Units?|url=http://water.usgs.gov/GIS/huc.html|publisher=[[USGS]]|accessdate=2010-10-27}} {{PD-notice}}</ref> Over time the system was changed and expanded.<ref>{{cite web |title= Overview and History of Hydrologic Units and the Watershed Boundary Dataset (WBD) |publisher= [[Natural Resources Conservation Service]] |url= http://www.ncgc.nrcs.usda.gov/products/datasets/watershed/history.html}} {{PD-notice}}</ref> As of 2010 there are six levels in the hierarchy, represented by hydrologic unit codes from 2 to 12 digits long, called [[Water Resource Region|regions]], subregions, basins, subbasins, watersheds, and subwatersheds. The table below describes the system's hydrologic unit levels and their characteristics, along with example names and codes.<ref>{{cite web |title= Watershed Boundary Dataset (WBD) Facts |publisher= [[Natural Resources Conservation Service]] |url= http://www.ncgc.nrcs.usda.gov/products/datasets/watershed/facts.html}} {{PD-notice}}</ref>

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The original delineation of units, down to subbasins (cataloging units), was done using 1:250,000 [[Scale (map)|scale]] maps and data. The newer delineation work on watersheds and subwatersheds was done using 1:24,000 scale maps and data.{{Contradiction inline|This page says below that the newer delineation work on watersheds was done at a "higher resolution" but 1:24,000 is a lower resolution than 1:250,000.|date=October 2015}} As a result, the subbasin boundaries were changed and adjusted in order to conform to the higher resolution watersheds within them. Changes to subbasin boundaries resulted in changes in area sizes. Therefore, older data using "cataloging units" may differ from newer, higher resolution data using "subbasins".<ref name="WBDstandard">{{cite web|url=https://pubs.usgs.gov/tm/11/a3/pdf/tm11-a3.pdf|title=Federal guidelines, requirements, and procedures for the national Watershed Boundary Dataset: U.S. Geological Survey Techniques and Methods 11–A3|last=|first=|date=|year=2009|website=|publisher=[[Natural Resources Conservation Service]] and [[United States Geological Survey]]|accessdate=4 November 2010}}</ref>

[[Image:Huc region-edit.png|thumb|right|The 21 top-level 2-digit "region" hydrologic unit boundaries. The names are as follows: 01 New England, 02 Mid-Atlantic, 03 South Atlantic-Gulf, 04 Great Lakes, 05 Ohio, 06 Tennessee, 07 Upper Mississippi, 08 Lower Mississippi, 09 Souris-Red-Rainy, 10 Missouri, 11 Arkansas-White-Red, 12 Texas-Gulf, 13 Rio Grande, 14 Upper Colorado, 15 Lower Colorado, 16 Great Basin, 17 Pacific Northwest, 18 California, 19 Alaska, 20 Hawaii, 21 Caribbean.]]