Frazzled by decades of fighting over the Sacramento-San Joaquin Delta, state and federal officials understandably want to sing "Kumbaya" and declare they have forged a breakthrough on balancing the Delta's environmental needs with the state's water demands.

That's what you'll likely hear Wednesday when Gov. Jerry Brown and Interior Secretary Ken Salazar are expected to announce a deal to restore wetlands, recover imperiled fish and restructure the plumbing of this troubled estuary.

Take it with a grain of salt.

Although Brown and Salazar have a deal, it's a deal with crucial details deferred. What they have is a "trust us" framework that keeps the ball rolling but easily could be knocked out of balance by whoever succeeds them in the state Capitol or the White House.

Under the Brown-Salazar plan, California will push ahead over the next year on permits to build a 35-mile-long pair of tunnels that would divert water from the Sacramento River and deliver it to the pumps south of Tracy. That would reduce the need for water contractors to pump water from the estuary, directly killing fish and creating unnatural flow patterns that add to their perils.

The state expects to have a draft environmental report on its plans by the fall of this year and a "record of decision" by mid-2013.

The trouble is, the decision to construct the tunnels would precede a final agreement on how to operate this new form of "conveyance." As the tunnels are under construction, stakeholders would spend the next 15 years nailing down important questions – such as how much water would be diverted in wet years and dry years – and during different seasons of the year – and how much would be dedicated for estuarine flows to help fish with their natural life cycles.

There are two big problems with this plan:

• Water contractors, who could end up spending $14 billion on these tunnels, will want a reasonable rate of return on that mammoth investment. In other words, they will seek to use the tunnels to divert the maximum amount of water, even if the science over the next decade further confirms that more is needed for fish.

What if the science demonstrates the tunnels can only safely divert 4.5 million acre-feet yearly on average, instead of the higher volumes exporters are seeking? Will water contractors accept that? We are dubious.

• Brown and Salazar, and all of their appointees who helped craft this deal, will not be around for its ultimate implementation. Will future governors and interior secretaries have the same commitment to science and a balanced outcome? Again, we are dubious.

It should also be noted there is shaky support for this deal.

Contra Costa and San Joaquin counties strongly oppose it, and Sacramento County may issue its own letter this week. Even some San Joaquin Valley water contractors – particularly the Kern County Water Agency – are questioning if the project will pencil out for them.

The environmental community is similarly split. Many groups oppose the "peripheral tunnels" under any circumstance. Others, such as the Nature Conservancy and American Rivers, see the Bay-Delta plan as the best hope for resolving age-old disputes, restoring wetlands and recovering salmon and other fish.

These groups fear that if the Delta plan tanks, a chance for wetlands restoration will be lost and the water contractors could use their clout to override the Endangered Species Act, increasing water diversions with the existing fish-killing pumps.

That's a legitimate fear, but a bad foundation on which to decide such a monumental project for the state's future. If California is going spend the next 15 years digging tunnels 35 miles through the Delta, its citizens deserve to know how they will be operated, and whether the project will make any financial or ecological sense once the pipes are in the ground.

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