5th level HUCs were developed by Alaska Geographic Data Committee (AGDC) in a project managed by BLM. 5th level HUCs were made available by 4th level subbasin. The Copper River basin HUC coverage was created by Ecotrust by merging 5th level HUCs from each of the Copper River's subbasins.
This data was developed in response to a need for hydrologic units of a more manageable size than currently exist. This data set consists of geo-referenced digital map data and associated attributes. The hydrologic unit code attached to each delineated polygon is linked to the attribute data, which can contain information on area in acres, non-contributing area, state(s) the HU falls within, name for 5th and 6th level HU, 5th and 6th level code for downstream hydrologic unit, and hydrologic unit modifications.
This data set is intended as a tool for water-resource management and planning activities, particularly for site-specific and localized studies, which require the amount of detail provided by a large-scale map.
In the NHD, generally streams longer than one mile (approximately 1.6 kilometers) were collected. Most streams that flow from a lake were collected regardless of their length. Lake/ponds having an area greater than 6 acres approximately 2.4 hectares) were collected. Swamp/marsh features were not collected. Note, however, that these general rules were applied unevenly among maps during compilation. Some map quadrangles have a much sparser pattern of hydrography than do adjoining maps and these differences continue in the digital rendition of these features. Near the international boundary with Canada, only the parts of features within the United States are delineated.
The watershed shapefile was georeferenced to the 1:63360 DRG as required by federal guidelines.The differences in positional accuracy between the hydrologic unit boundaries and their digitized map locations is unknown. Hydrologic unit boundaries generally were digitized within 0.01 inches of their locations on the digitizing source.