Data and Documentation
MSDI Hydrologic Units Data – Watershed Boundary Dataset (WBD)
The Watershed Boundary Dataset is provided in two different formats: a file geodatabase (version 10.2) which includes the 8-digit, 10-digit and 12-digit HUCS for Montana, and separate ESRI shapefiles for each of these HUC levels. For all products the data is provided in NAD 1983 Montana State Plane (FIPS 2500) coordinates.
Watershed Boundary Dataset Documentation
The WBD for the United States has been developed by the USDA – NRCS and the USGS using a consistent set of standards and procedures. The document Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD) can be found here. Additional information fully documenting the history and development of the WBD can be found at: http://nhd.usgs.gov/wbd.html
The Watershed Boundary Dataset (WBD) provides a uniquely identified and uniform method of subdividing large drainage areas. The data is intended to be used as a tool for water-resource management and planning activities, particularly for site-specific and localized studies requiring a level of detail provided by large-scale map information.
The WBD defines the areal extent of surface water drainage to a point, accounting for all land and surface areas which establish a baseline drainage boundary framework and define Hydrologic Units (HU). Watershed Boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. The hydrologic units represent drainage areas delineated to nest in a multi-level, hierarchical drainage system.
At a minimum, the WBD is delineated and georeferenced to the USGS 1:24,000 scale topographic base map meeting National Map Accuracy Standards (NMAS). Hydrologic units are given a Hydrologic Unit Code (HUC). For example, a hydrologic region has a 2-digit HUC. A HUC describes where the unit is in the country and the level of the unit. HUC boundaries are defined by hydrographic and topographic criteria that delineate an area of land upstream from a specific point on a river, stream or similar surface waters. A hydrologic unit can accept surface water directly from upstream drainage areas, and indirectly from associated surface areas such as remnant, non-contributing, and diversions to form a drainage area with single or multiple outlet points. Hydrologic units are only synonymous with classic watersheds when their boundaries include all the source area contributing surface water to a single defined outlet point.