The two giant water diversion tunnels Gov. Jerry Brown proposes building in the Delta would be large enough to meet annual water needs for a city such as Newport Beach in a single day's gulp from the Sacramento River.
That gulp, however, would also prevent a lot of fresh water from flowing through the Sacramento-San Joaquin Delta. This would likely make water saltier for farms near Isleton and cities such as Antioch, which draws some of its drinking water from the Delta.
This marks just one of the complex trade-offs sprinkled through the Bay Delta Conservation Plan, the massive proposal to re-engineer California's primary water delivery system that includes the two tunnels.
The plan is intended to resolve decades of conflict between human demand for river water in counties south of the Delta, which are eager to secure water supplies in the face of earthquakes and climate change, and the harmful consequences for the estuary's imperiled wildlife, including native fish such as chinook salmon and Delta smelt.
Whether the project ultimately benefits these species, and the people of Northern California, depends largely on how the tunnels change various aspects of water flow in the Delta how much water is flowing through and from what mix of sources.
The engineering described in the Bay Delta plan would result in the biggest water flow changes in the Delta in 50 years, and they are the most complicated aspect of the project. Even proponents, after seven years of study, can't explain all the potential consequences.
A draft environmental impact study is expected to be released for public review by Oct. 1, and a decision is planned by April 2014. In the meantime, the California Department of Water Resources has released thousands of pages of planning documents, including an "interim" draft of a required environmental impact study.
These documents describe many of the likely water flow changes. They also illuminate a lot of uncertainties.
For example, officials have no specific solution to prevent farms and cities in the Delta from losing access to fresh water if the tunnels make the estuary saltier. They merely propose to consult with the affected entities to provide compensation or alternate water supplies after the fact.
Another example: Diverting the Sacramento River means the San Joaquin River would compose a larger share of the water in the estuary. The San Joaquin is poorer quality water, laden with salt, pesticides and selenium, a naturally occurring mineral that can deform wildlife in excessive concentrations.
Some of the effects of these water quality changes are deemed "unquantifiable" in the planning documents due to scientific uncertainties. Officials intend to manage selenium, for example, by planting vegetation in restoration areas in hopes plants would absorb it.
The project would be approved as part of a habitat conservation plan, which would receive a 50-year-operating permit from state and federal wildlife agencies. By agreeing to sweeping habitat improvements, DWR would qualify for a permit that would exempt the agency and its contractors from routine water delivery cutbacks, which occur now under laws that protect endangered species such as Delta smelt and spring-run salmon.
The tunnel proposal has sharply divided the state's elected officials between north and south. Southern California politicians generally support the project because it would help secure water deliveries for their constituents.
North state officials generally oppose the project, saying it would harm water supplies in the Delta and their constituents who depend on those supplies for crop irrigation and drinking water. About a week ago, five members of Congress gathered on the Sacramento waterfront to condemn the plan.
"The Bay Delta Conservation Plan is designed in such a way that the Delta will be destroyed," said Rep. John Garamendi, D-Walnut Grove, who offered a warning to the Brown administration. "If there be a fight, let it be this one. Let it be about maintaining the extraordinary agricultural and economic viability of Northern California. If you continue on this path, you will lose this fight."
Sen. Dianne Feinstein and 12 Southern California politicians recently issued their own letter supporting the project. They say the new tunnels are essential to secure a water delivery system crucial to 25 million Californians against wild swings in supply and the threat of natural disasters.
"We are operating today's economy with 1960s technology," said Jeffrey Kightlinger, general manager of the Metropolitan Water District of Southern California, at a recent water conference in Sacramento. "This is absolutely going to be a technological improvement."
Flow mechanics change
The Bay Delta Conservation Plan calls for building two huge tunnels, 40 feet in diameter and 35 miles long, to divert a portion of the Sacramento River's flow. They would draw from three intakes, with a combined capacity of 9,000 cubic feet per second, located near Courtland.
That volume is sufficient to meet the annual needs of a city of 38,000 households such as Newport Beach, which is served by Metropolitan in a single day's pumping.
This diversion capacity is no different from the present state and federal systems, which rely on pumps near Tracy. But it would divert the fresh water before it reaches the estuary, changing many of the mechanics of flow and water quality in the Delta's 1,100 miles of sloughs and channels.
The plumbing hardware alone is estimated to cost $14.5 billion. This is to be funded by bonds issued by DWR, the project's lead agency, under existing legal authorities. No public vote is planned.
The bonds would be repaid by water users who benefit from the project, including Kightlinger's agency, which serves about 19 million people in the Los Angeles and San Diego region.
An initial review by The Bee of project documents reveals some of the potential changes in store if the tunnels are built. Among them:
Under certain flow conditions in summer (July to September) the tunnels could divert as much as 60 percent of the Sacramento River's flow. Officials say this would be rare, and that 15 percent to 25 percent would be more common. The current percentage is hard to estimate, because the river mixes with other tributaries before being diverted.
Total freshwater outflow from the Delta to San Francisco Bay would decline, compared with current operating conditions, in every month of the year except June, September and October. Potential effects on the bay have not been studied.
The population of longfin smelt, a threatened species, would decline compared with current operating conditions until near the end of the project's 50-year permit term, when it is estimated to increase by 1 percent. The species is one important indicator of the Delta's health.
There is expected to be zero benefit to winter- and spring-run chinook salmon in the early years of the project. Small population benefits (2 percent and 1 percent, respectively, on average) are predicted after 50 years.
These estimates do not include presumed beneficial effects of 100,000 acres of habitat restoration, which cannot be accurately measured.
How much does water flow matter in the Delta? Proponents of the Bay Delta Conservation Plan say the question is open to debate, particularly on the issues of "when" and "how much."
In particular, the importance of increased spring and fall freshwater outflows is being questioned. Proponents intend to defer decisions on these flow questions, and some other operating rules, to a future "decision tree" process after tunnel construction has begun.
State and federal wildlife agencies, on the other hand, get to decide whether the project gets the permits it needs to move forward, and may demand flow rules be part of the project at the outset.
"We know the more flow there is, the better it is. Biologically, that's true," said Stephen Monismith, a professor of environmental fluid mechanics at Stanford University. He sat on a recent National Research Council panel that examined water management in the estuary.
"I don't think anyone would argue more flow isn't better for biology," Monismith said. "So the question is, how much better can we afford as a state? And that's a political question."
Increased salinity a worry
Jennifer Pierre, a project manager working on water flow questions for ICF International, a DWR consultant, said the Bay Delta Conservation Plan benefits wildlife when all its components are considered together.
"We're getting closer to something that looks like what these species evolved in," she said. "There's definite trade-offs with the new intakes. But we're able to demonstrate with our (modeling) tools that the trade-offs are offset by the benefits."
Wildlife agencies, on the other hand, are not so certain. In early reviews of the documents, they complain that the project's claimed results assume all the habitat restoration succeeds in boosting fish populations, when there is no assurance it will work.
"The total success of habitat restoration efforts remains highly uncertain," National Marine Fisheries Service biologists wrote in an April comment letter.
One reason for the uncertainty, the agency wrote, is that it may be impossible to acquire enough land for restoration. The project proposes to restore 65,000 acres of tidal wetland habitat. But enough land suitable for that purpose simply might not exist.
Another reason is that most of the restoration depends on billions of dollars from future bond measures, which must be approved by voters across the state. Without that approval, restoration would be delayed, perhaps indefinitely.
A basic change that worries Delta residents is increased salinity. Farming on Delta islands is the region's primary economic engine, and it depends on fresh water.
Analysis of water quality changes in the Bay Delta Conservation Plan shows that some locations in the west and central Delta would become saltier.
This is expected for three reasons: less flow in the Sacramento River, more from the San Joaquin River, and sea-level rise.
One location examined in the documents, because it has hosted a water quality monitor for decades, is the southern flank of Brannan Island, south of Isleton in Sacramento County, along the San Joaquin River.
The analysis showed this site would violate state salinity standards, set to protect wildlife and drinking water, about four times more often after the diversion tunnels begin operating. Another site downstream, near Sherman Island, would violate standards as much as 20 times more often.
"It's taking a problem that exists already, and making it a little bit measurably worse," said Ben Giudice, an environmental engineer with Robertson-Bryan Inc., a DWR contractor.
This is troubling for farmers such as Bob Giovannoni, who draws irrigation water at exactly the spot where the Brannan Island water quality monitor sits.
"That's where I make my money, right there," he said. "The water's pretty good over there right now."
Giovannoni grows corn and alfalfa with that water, and salty water does show up occasionally. When that water reaches crops, he said, it turns the ground white and the plants stop growing.
"It just doesn't grow. It just stuns it," Giovannoni said. "It's not a good thing. We'd have to see how bad it really gets, and we might have to grow something else."
Contact The Bee's Matt Weiser at (916) 321-1264. Follow him on Twitter @matt_weiser.