ND Watershed Boundary Dataset
The Watershed Boundary Dataset, or WBD, defines surface water drainage for the nation. Drainages are determined using topography and hydrologic principles, not political or administrative boundaries. Hydrologists use the general term 'hydrologic unit" or HU to refer to any defined drainage area-regardless of size of the area. A hydrologic unit is a drainage area defined or delineated to nest in a multi-level, hierarchical drainage system. At a minimum, the WBD is being delineated and georeferenced to the USGS 1:24,000 scale topographic base map meeting National Map Accuracy Standards (NMAS). These data were created using the same set of mapping standards across the entire country thereby creating a base-line drainage framework for the entire US.
HUCs and the WBD?
Hydrologic units are given a Hydrologic Unit Code (HUC). A HUC describes where the unit is in the country and the level of the unit. For example, a hydrologic region has a 2-digit HUC. The number of digits in the HUC reflect the "level".
The WBD that is distributed on the ND GIS Hub is a subset of the nationwide WBD; it contains only those regions (HUC2), subregions (HUC4), basins (HUC6), subbasins (HUC8), watersheds (HUC10) and subwatersheds (HUC12), and subwatershed lines (HUC12Line) that touch the borders of North Dakota. The data published March 20, 2014 are considered provisional as they have not been approved by the National WBD Technical Review team.