California Water Plan 2013: Sacramento-San Joaquin Delta Regional Report

Some areas of the state with common water issues or interests cross the boundaries from one hydrologic region to another. To acknowledge this, the California Department of Water Resources (DWR) developed the concept of “overlay areas” and first described overlay areas in California Water Plan Update 2005. The purpose of the overlay areas is to collect and provide information that will better enable planners and decision-makers to address issues in areas of special interest where both of the following criteria apply: (1) the area is of statewide significance — meaning that water management strategies and actions taken in one area affect much of the remainder of the state — and (2) common water management conditions exist in the area — meaning that issues and integrated planning opportunities span more than one of the 10 hydrologic regions.

The two overlay areas of special interest are the Sacramento-San Joaquin Delta (Delta) and Mountain Counties.  For Update 2005, the Delta and Suisun Marsh were included as an overlay area because of its common characteristics, environmental significance, and the important role it has in the State’s water systems. The Delta and Suisun Marsh encompasses about 840,000 acres of tidal influenced land near the confluence of the Sacramento and San Joaquin rivers; and occupies portions of the Sacramento, San Joaquin, and San Francisco hydrologic regions.

The geographic extent of the Delta overlay coincides with the statutory Delta boundary that defines the Legal Delta (California Water Code [CWC] Section 12220) and the Suisun Marsh as defined in California Public Resources Code Section 29101.