Open Water Habitat

• For the Delta, we measured the net downstream flow through the Delta, which is affected by both inflows and water diversion rates at the Delta water export facilities. We used QWEST, which is the estimated net flow in the San Joaquin River at Jersey Point, located in the western Delta.
• In the Bay, we measured the occurrence and extent of low-salinity habitat in Suisun and San Pablo Bays. We used X2 data, which represents the linear distance in kilometers upstream from the Golden Gate of the 2 ppt isohaline, and it is calculated as a function of Delta outflow (or Bay inflow) from equations published in Jassby et al. (1995).

For each indicator, we assessed metrics for frequency, magnitude, and duration of the relevant variable flow. We scored the values numerically on a scale from 0-4 relative to benchmark values that we established based on review and analysis of five types of data:

• Actual and unimpaired flow data (see the Freshwater Flow Indicator).
• Biological information on the relationship between low-salinity habitat and the population abundance of fish and invertebrates.
• Contra Costa Water District (CCWD) Flow Index for Old and Middle Rivers.
• Measured and modeled fish entrainment rates of the water export facilities (CCWD 2012).
• State Water Resource Control Board (SWRCB) regulatory flow criteria for San Joaquin River inflows (SWRCB 2006).

We calculated the Bay and Delta Open Water Habitat indices as the average of the numeric scores for each of their three metric components. Status scores were based on a five-point scale from 0-4, with scores under 2 considered Poor; under 3 as Fair; and 3-4 as Good. Trend scores were determined by simple regression on the decadal average Open Water Habitat index scores.