If all goes as planned, Gov. Jerry Brown and U.S. Interior Secretary Ken Salazar will gather on the banks of the Sacramento-San Joaquin Delta next month, flanked by an odd mixture of historic enemies – environmentalists, water exporters, fishermen and farmers.

There, Brown and Salazar will announce a breakthrough for the Delta – a deal to reduce conflicts over endangered species, restore habitats and improve the reliability of water deliveries.

It will be a great photo op for both Brown and the Obama administration.

But that's likely all it will be.

The deal they've crafted defers key details – such as how the state and federal governments will operate a planned $14 billion pair of tunnels that would divert water from the Sacramento River to the water pumps in Tracy, 35 miles away.

There are also real questions about whether the water contractors behind this project can afford its price tag.

Can those details be nailed down in timely fashion? If they can't, the Brown-Salazar pact will have as much staying power as the Bay-Delta Accord.

Remember the Bay-Delta Accord?

Crafted by Gov. Pete Wilson and Interior Secretary Bruce Babbit in 1994, that pact was touted with great fanfare as a "peace treaty" that would settle long-standing conflicts in the Delta. But after all the ceremonies were finished, the signatories ended up clashing over critical issues, such as how much water needed to be reserved for fish and how much private interests should pay for new water infrastructure. Nearly two decades later, those issues remain unsettled.

To be fair to Brown and Salazar, they inherited a process called the Bay Delta Conservation Plan that was fraught with problems since it started in 2006. Funded and driven by water contractors south of the Delta, BDCP was far from an open public planning exercise. It enjoyed little legitimacy from other Delta stakeholders, although some came to see it as the only game in town.

Much has been made of the fact that BDCP would result in construction of a peripheral canal or set of tunnels to divert water from the Sacramento River. Critics, including one at a meeting last week, say such a facility would "drain the river dry."

Yet despite such apocalyptic scenarios, more and more environmentalists and fish scientists are coming around to the concept of a canal or tunnel. Many recognize that a diversion point would reduce the "reverse flows" caused by the state and federal water pumps in the south Delta, which misdirect fish and lead to their demise. It also would improve the quality of water consumed by some 16 million people statewide. Marc Reisner, author of "Cadillac Desert," said he could entertain "maybe a medium canal" in 1997. Tom Graff, the late leader of the Environmental Defense Fund in California, told me in 2009 he also would be open to a canal, under certain conditions.

In Graff's view, with or without a canal, there had to be limits on exports of water from the Delta during key periods, such as dry years and times when outflow was essential for the life cycle of salmon and other native fish. All water users, he believed, also needed to recognize the realities of climate change, which could send California into drier periods than it has seen in modern history.

Unfortunately, BDCP was built on a much different premise. The water exporters thought that if they agreed to restore thousands of acres of wetlands in the Delta, they would get permission to export more water from the estuary. In court filings and public relations campaigns, they also attempted to squelch any suggestion that their existing diversions were hurting fish. Instead, they attempted to pin the blame elsewhere – to voracious predators in the Delta, such as sport bass, or to ammonia coming from Sacramento's wastewater treatment plant.

To date, science hasn't yet backed up their premise. The State Water Resources Control Board and the National Academy of Sciences have made clear that Delta flows, at certain times of the year, are crucial for threatened smelt, salmon and other fish. Federal fish agencies have also issued "red flag" memos, warning that increased exports and reduced flows, even with better wetlands habitat, will further imperil threatened species.

Knowing that it was hitting a wall, the Brown administration started pursuing Plan B in May. Last week, administration officials announced they would seek to get permits for a tunnel project that would be 40 percent smaller in size yet still be capable of diverting a huge quantity of water – 9,000 cubic feet per second.

They also signaled that they would defer decisions on how the facility would be operated – leaving open how water would be diverted in a given year and during different flow conditions – until after the project was already under construction.

"We are going to put aside hard commitment on water supply," said Mark Cowin, director of the Department of Water Resources, in a recent interview. Instead, he said, the state is going to set up a "structured approach" on Delta restoration and a scientific process for determining flow issues as it pushes forward on the tunnels.

From a political standpoint, I can understand the rationale. State officials could spend the next 10 years trying to better understand the life cycles of Delta fish and the link to flows. At the end of the day, they still might be convinced a tunnel or canal would be preferable to the status quo. So why not build it now?

The problem is the economics. So far, the water contractors have vowed to pay for new "conveyance" in the Delta, even as the price tag has steadily risen. If the canal gets built, and science says they can only divert 4 million acre-feet per year instead of 5.3 million acre-feet, will they go along with it? Would that be the most expensive 4 million acre-feet of water in California history?

The reality is, water contractors would never allow such a limitation on exports after spending $14 billion. Once the facility is built, they'd unleash enormous political pressure to maximize the amount of water they could divert, which is why Brown and Salazar need to negotiate firm limits now.

Every politician wants to be part of a win-win deal, but sometimes, that is impossible. The Delta may be that type of situation. There may be no way to reverse the decline of this estuary while water contractors get the water they want or think they need. If that is the case, state and federal officials should figure that out now, not after a $14 billion investment is made.

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