Introduction
The purpose of Calwater 2.2.1 is to standardize the boundary delineation, coding, and naming of California watersheds by government agencies. Calwater also cross-references watershed codes implemented by the California Department of Water Resources (DWR), the California State Water Resources Control Board (SWRCB) and Regional Water Quality Control Boards (RWQCB), as well as Hydrologic Unit Codes (HUC) published by the U.S. Geological Survey (USGS) for California and the nation.
Standardized watershed delineations, codes, and names from both State and federal systems are used primarily to map, analyze, and document water resources and water quality information and regulations. Examples include water quality reporting to the U.S. Environmental Protection Agency by SWRCB and Timber Harvest Plan tracking by the California Department of Forestry and Fire Protection (CDF). Applications also include regional planning, environmental analysis, hydrology, wildlands research, soils, agriculture, and fish and wildlife habitat management. Calwater is also useful in geographic information systems (GIS) and for online data retrieval. Calwater 2.2.1 and versions to follow are intended to provide a comprehensive geographic frame of reference for the California landscape.
Previous Calwater versions (1.2 and 2.2) described California watersheds, beginning with the division of the State's 101 million acres into ten Hydrologic Regions (HR). Each HR is progressively subdivided into six smaller, nested levels: the Hydrologic Unit (HU, major rivers), Hydrologic Area (HA, major tributaries), Hydrologic Sub-Area (HSA), Super Planning Watershed (SPWS), and Planning Watershed (PWS). At the Planning Watershed (the most detailed level), where implemented, polygons range in size from approximately 3,000 to 10,000 acres. At all levels, a total of 7035 polygons represent the State's watersheds. The present version, Calwater 2.2.1, refines the watershed coding structure and documentation (database fields were added and some were renamed). There are significant watershed boundary, code, and name differences between Calwater versions 1.2 (1995), 2.0 (1998), and 2.2 (1999). The differences between versions 2.2 (1999) and 2.2.1 (2004) are attribute field names and some inserted lines that identify differences between State and federal watersheds.
Calwater 2.2.1 most accurately delineates true watersheds in mountainous terrain. However, neither Calwater 2.2.1 nor any of its predecessors is a "pure" watershed map because administrative boundaries such as the State border were used to delineate watershed areas. Some of the boundaries, particularly in developed valley areas, also have legal and administrative purposes other than the representation of actual drainage divides. Examples include the so-called "Legal Delta" (California Water Code, Chapter 2, the Delta, Sec. 12220) and other district boundaries. Neither is Calwater a legal map document, as it does not represent State of California Regional Water Quality Control Board (RWQCB) jurisdictions, officiated by the State Water Resources Control Board (SWRCB) under California Water Code Section 13200. Calwater is a hybrid, a spatial cross-reference for use in local, State, and federal information communities.