Editorial: If we can’t build two tunnels to bring Sacramento Delta water to SoCal, will one suffice?

If two massive, 40-mile long, 40-foot-diameter tunnels that would direct Sacramento River water around the fragile Sacramento-San Joaquin River Delta to Central and Southern California are too big, too expensive and too scary to contemplate, how about splitting the difference and going with a single tunnel?

That’s been the response of some officials and observers after actions by a number of the water agencies that were slated to participate in the $17-billion California WaterFix put the fate of the twin tunnels in doubt.

The Southern California Metropolitan Water District — the wholesaler serving cities and agencies that supply water to about half of of the state’s population — approved its own $4-billion stake in the project, and a majority of other participants voted yes as well. But several districts called for limits on their investment and one opted out altogether, leaving WaterFix short of the funding it needs to move forward with the full-size project, at least as things stand now.

The Natural Resources Defense Council and other environmental groups proposed a “portfolio alternative” years ago that featured a variety of water sources, including a single tunnel with a maximum flow capacity of 3,000 cubic feet per second — a third of the WaterFix’s capacity. They argue that the smaller project would allow more water to flow though the delta and out to sea to sustain migrating fish and stem the ecological collapse of the estuary. Los Angeles Mayor Eric Garcetti has expressed support for a single tunnel. Even the Metropolitan Water District has a single-tunnel backup plan — with up to two-thirds the capacity of the WaterFix — in case financing for the full project fails to materialize. The question now is whether Gov. Jerry Brown, the WaterFix’s champion, is prepared to pivot to a smaller, single-tunnel project — and if he does, whether it looks more like the environmentalists’ alternative or the Met’s.

On paper, the value of the full-size twin tunnels is that they would be big enough to divert large pulses of stormwater that come during the handful of winter storms that provide about half of the state’s supply within the space of a couple weeks. Capturing water from those few deluges will presumably become increasingly important as a warmer climate delivers less snow and more rain. Warmer winters will mean smaller snowcaps and more volatile runoff that will rapidly, but only briefly, fill rivers.

In theory, the two large tunnels would capture enough water to significantly reduce pumping at the south end of the delta — pumping that currently is so powerful, it reverses the direction of the lower San Joaquin River and sucks migrating fish into either the screens that protect the pumps or the mouths of waiting predators.

A single tunnel would fail to fully capture the storm pulses and would not reduce reliance on the south delta pumps. Construction costs would be lower, but with proportionately less water per dollar spent.

Granted, the project’s critics dispute the WaterFix numbers and contend that the plan is to keep up south delta pumping one way or the other. The infrastructure alone doesn’t dictate how it will be used. Only the operating rules can do that — and the proposed rules are subject to interpretation.

The important issue is what California gets out of the project and what will be the trade-offs — and there necessarily will be trade-offs. Enough water must be allowed to continue flowing through the delta to sustain not just the migrating salmon but also the human-made structures that hold back the salty bay water, keep levees intact and direct mountain runoff to Californians in the Bay Area, Los Angeles and nearly everyplace in between. There must be enough water to sustain the world’s most productive agricultural region (although at some point we just have to ask how much almond milk, almond crackers and almond soap we really need). There must be enough to back up Southern California’s supply while it develops its local stormwater-capture and recycling abilities (and it’s fair for all those almond growers to ask just how many lush green lawns we need).

And of course there will not be enough for anybody. The already-crippled delta needs more. Whether it’s to be one tunnel or two, the rest of us will have to learn to make do with less. The Times supports the full two-tunnel project as best able to provide the state what it needs, but if it can’t get built we need something that can. It’s now up to Brown — with his unparalleled political capital, but entering the final year of his uniquely long tenure as California’s leader — to decide how much less is still enough.

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