California Interagency Watershed Mapping Committee

Federal Naming and Numbering System - WBD

The US Geological Survey (USGS) and the Natural Resources Conservation Service (NRCS) are sponsoring a National update of watershed maps for the United States. NRCS is the lead agency on updating and certifying the watershed boundaries to 5th and 6th level (10 and 12 digit numbers).

NRCS has agreed to change the numbering system to match the FIPS sequence, so that what were the 11 and 14 digit watershed codes, will now be 10 and 12 digit watershed codes.

The NRCS guidelines (NI 170-304) were updated into new interagency FGDC (Federal Geographic Data Committee) Watershed Boundary Dataset standards, and are available from the NRCS.

New names and numbers

Level	Name	Number	Area (approx.)	California State Codes Description	California Approx. Area
Level 1	Region	2 digit	180,000 sq miles 115,193,577 acres
Level 2	Sub-region	4 digit	16,844 sq miles 10,779,559 acres	Hydrologic Region	12,735 sq miles 8,150,000 acres
Level 3	Basin	6 digit (used to be "accounting unit")	10,600 sq miles 6,783,622 acres	Hydrologic Units	672 sq miles 430,000 acres
Level 4	Sub-basin	8 digit (used to be "cataloging unit")	703-1,735 sq miles 449,895 – 1,110,338 acres	Hydrologic Areas	244 sq miles 156,000 acres
Level 5	Watershed	10 digit (used to be 11 digit in NRCS)	63-391 sq miles 40,000 to 250,000 acres	Hydrologic Sub-areas	195 sq miles 125,000 acres
Level 6	Sub-watershed	12 digit (used to 14 digit in NRCS)	16-63 sq miles 10,000 to 40,000 acres	Super Planning Watershed	78 sq miles 50,000 acres
Level 7	Drainage	14 digit	15 sq miles 10,000 acres	Planning Watersheds	5-16 sq miles 3,000-10,000
Level 8	Site	16 digit	1 sq mile 650 acres

California acknowledges the need for local watersheds to delineate in more detail than planned for by the National Guidelines. We propose that Drainage and Site levels be added to California's guidelines to allow for this local detail.

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