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The Watershed Boundary Dataset (WBD) from The National Map (TNM) defines the perimeter of drainage areas formed by the terrain and other landscape characteristics. The drainage areas are nested within each other so that a large drainage area, such as the Sacramento River, will be composed of multiple smaller drainage areas, such as the Feather River. Each of these smaller areas can further be subdivided into smaller and smaller drainage areas. The WBD uses six different levels in this hierarchy, with the smallest averaging about 30,000 acres. The WBD is made up of polygons nested into six levels of data respectively defined by Regions, Subregions, Basins, Subbasins, Watersheds, and Subwatersheds. For additional information on the WBD, go to https://www.usgs.gov/core-science-systems/ngp/national-hydrography/watershed-boundary-dataset. DWR is the steward for NHD and WBD in California. We work with other organizations to edit and improve NHD and WBD, using the business rules for California. California's WBD improvements are sent to USGS for certification and incorporation to the national geodatabase. The certified WBD is included within the National Hydrography Dataset downloadable file geodatabase, and is also available in shapefile format and as web map services accessible from the USGS website. (https://www.usgs.gov/core-science-systems/ngp/national-hydrography/access-national-hydrography-products)

Drainage areas (or watersheds) were calculated for each stream segment in the National Hydrography Dataset High Resolution Plus Beta (NHD HR Plus Beta) using non-end junction points and the provided hydrologically enforced Digital Elevation Model (DEM). The DEM was used to create a flow direction raster. The pour points used were determined from junction points at each stream intersection excluding stream ends (i.e. channel heads are not included). Watershed calculations were automated using the ArcGIS "watershed" tool and then edited manually for accuracy. In western San Diego County (non-desert) there were 39,980 drainage areas calculated. The percent impervious in each watershed was calculated using the National Land Cover Dataset 2019 Impervious surface.

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Areas for state water resource planning and administration.