State Water Board Finalizes Delta Flow Criteria

Submits final report to Delta Stewardship Council

Flow criteria for the Sacramento-San Joaquin Delta ecosystem necessary to protect public trust resources-primarily fish and other aquatic organisms-was finalized by the State Water Resources Control Board (SWRCB) in early August and presented at the Delta Stewardship Council during its Aug. 26-27 meeting as required by Senate Bill X7 1.

“This report answers a specific question: ‘What flows are necessary to protect fishery resources in the Delta under current conditions?’” said Les Grober from the SWRCB during the Council meeting. He added that the Legislature did not direct the SWRCB to determine how to best allocate flows among competing resources.

LCombined Sacramento-San Joaquin River average annual unimpaired runoff for water years 1906 to 2006.
Combined Sacramento-San Joaquin River average annual unimpaired runoff for water years 1906 to 2006.
The unimpaired runoff-an estimate of flows without upstream dams or diversions-shows the highly variable
flow conditions from year to year. (Source: California Data Exchange Center 2007)

“The report is serious, substantial and advances our understanding of the ecosystem needs in the Delta,” said Phil Isenberg, Chair of the Delta Stewardship Council. “Did the report answer all the questions that will be needed when the Board adopts its next Delta flow order? No, and the sooner the Board gets to the decision-making stage, the better.”

In March, the SWRCB held a three-day public proceeding to inform its development of flow criteria and identified the key issue for the informational proceeding as “What volume, quality, and timing of Delta outflows are necessary for the Delta ecosystem under different hydrologic conditions?”

Since then, the SWRCB finalized its criteria in August and submitted its report to the Council. According to the report, “The best available science suggests the current flows are insufficient to protect public trust resources.”

The report found that:

  • Recent Delta flows are insufficient to support native Delta fishes for today’s habitats. Flow modification is one of the immediate actions available although the links between flows and fish response are often indirect and are not fully resolved. Flow and physical habitat interact in many ways, but they are not interchangeable.

  • In order to preserve the attributes of a natural variable system to which native fish species are adapted, many of the criteria developed by the State Water Board are crafted as percentages of natural or unimpaired flows. These criteria include:

    • 75 percent of unimpaired Delta outflow from January through June. In comparison, historic flows have been approximately 30 percent in drier years to almost 100 percent of unimpaired flows in wetter years for Delta outflows.

    • 75 percent of unimpaired Sacramento River inflow from November through June. Historic flows have been about 50 percent on average from April through June for Sacramento River inflows.

    • 60 percent of unimpaired San Joaquin River inflow from February through June. Historic flows have been approximately 20 percent in drier years to almost 50 percent in wetter years for San Joaquin River inflows.

Additional criteria are contained in the report. “It is not the State Water Board’s intent that these criteria be interpreted as precise flow requirements for fish under current conditions,” the report stated, “but rather they reflect the general timing and magnitude of flows under the narrow circumstances analyzed in this report.”


“The best available science suggests the current flows are insufficient to protect public trust resources.”

--SWRCB Development of Flow Criteria for the Sacramento-San Joaquin Delta Ecosystem


“The current capacity to export and store additional water during wet years is limited,” said Cliff Dahm, Delta Science Program Lead Scientist. “Therefore, in dry years, when agriculture is most in need of irrigation water, little additional water is available.”

Dahm was a member of the Delta Environmental Flows Group (Flows Group) which provided expert information on flows to the SWRCB. At the August 3rd SWRCB meeting, the Flows Group commented on the draft report. “We especially agree with the general method employed which develops flow criteria around a set of ecosystem function objectives that in turn are constructed around the life stages of desirable fishes and the ecological processes that support them… A functional approach highlights the need to study and coordinate flow modifications with diverse and substantial non-flow actions to allow native fish species to persist and recover in this changing Delta.”

Grober said the SWRCB used a three-step process to arrive at their conclusions:

  • Identify the narrative goals and criteria for protection of aquatic resources (working with the California Department of Fish and Game; what are species and specific life history needs).

  • Identify threshold numeric flow values needed to achieve these goals.

  • Determine flow criteria as a percentage of unimpaired flow that would achieve in the context of an adaptive management program, the numeric flow values and the goals.

“It was challenging to come up with just a single number for a 6-month period,” Grober said. “This isn’t a precise number; it reflects general timing, general magnitude… gives broad strokes of what’s needed.” He listed the limitations of the flow criteria:

  • Are a technical assessment only of best available science on flow needs for fish under existing conditions,

  • Do not address upstream environmental needs, including cold water pool and terrestrial interests, and

  • Have no regulatory and adjudicatory effect and are not pre-decisional to future Board actions.

“There is a conflict between protecting the Delta and providing more flow for it-on whatever magnitude that turns out to be-and meeting our reliable water supply needs,” said Gary Bobker from the Bay Institute after Grober’s presentation. “The strongest scientific evidence for population and ecosystem level effects of any stressor in the Bay-Delta estuary is the alteration of flow… If you’re going to follow the science, the science leads you to flow.”

Dick Poole with the salmon industry concurred. “We’ve felt that way for years and feel flow has to be implemented if we’re going to recover the salmon resources.”

Greg Zlotnik with State and Federal Contractors Water Agency had a different perspective. “While flow is obviously an issue, we are concerned that it has been dealt with for a number of years…,” he said. “Our view is the whole issue of the other stressors that are in the system that the report discussed; that if you dealt with those, you might need less of the flows than they identified to meet some of these goals.”

“Setting flow criteria for rivers and estuaries is an ongoing activity throughout the U.S. and the world,” Lead Scientist Dahm said. “The states of Florida and Texas have state statutes that require setting flow criteria to their major estuaries. Countries like Australia and South Africa have nationally mandated requirements to set flows for their river ecosystems. The science to support these efforts has expanded and improved substantively in the past decade, and these techniques were used in this effort for setting flow criteria for the Sacramento-San Joaquin Delta ecosystem.”