In the summer of 1976, the Department of Water Resources installed an emergency rock barrier in Sutter Slough. (California Department of Water Resources)
In the summer of 1976, the Department of Water Resources installed an emergency rock barrier in Sutter Slough. (California Department of Water Resources)

It’s something they haven’t resorted to since the 1970s.

As California’s monster drought drifts into its fourth year, state water managers are taking a drastic step to keep much of California’s water fit for drinking. The Department of Water Resources says it will have to construct at least one barrier to keep salt water from encroaching deep into the Delta.

This is one of those extreme drought years when there may not be enough natural flow in the rivers to push back the incoming tides. Officials say the “salinity barrier,” northeast of Oakley in Contra Costa County, will help keep that brackish water from mixing with fresh water used for drinking and irrigation.

There will be costs, financial and environmental, and even recreational; the barrier will be a temporary roadblock to boaters.

Officials estimate it will cost $28 million for what is essentially an engineered rock pile, to be constructed in May and then taken down again in the fall. Then again:

“You don’t want salt in your water,” says Randall Baxter, a Stockton-based senior biologist supervisor with the California Department of Fish & Wildlife.

The strategic spot chosen for the barrier is a 750-foot-wide span of the West False River, less than a half-mile from where it meets the oncoming San Joaquin. It’s a kind of gateway to an area known as Frank’s Tract, which in turn leads to the huge pumps that draw freshwater for urban customers and farms. If salt water makes it that far, instead of washing back out with the ebb tide, it can often be trapped there, where it threatens drinking water supplies.

Baxter says there are potential costs to the already teetering Delta ecosystem, particularly for migrating salmon and steelhead.

“There are still fish coming through the system and will be for a while,” he says. “Putting a barrier in False River cuts out one of their emigration routes.” Baxter says it can also make the fish more vulnerable to predators.

The environmental effects could be a mixed bag of good and ill. As Ellen Hanak and Jeff Mount write in a recent post from the Public Policy Institute of California’s new Water Policy Center:

The water savings could also benefit some salmon runs, because more cold water could be saved upstream for release later in the year. But this approach will also involve new trade-offs, because reductions in Delta outflows are likely to harm delta smelt as well as salmon migrating through the Delta. This is yet another example of the tough decisions water managers are having to make during these exceptionally dry times.

Mount and Hanak note that of the roughly four million acre-feet of water that made it through the Delta without being diverted  last year, more than 70 percent of that volume was required just to keep salt water pushed back toward San Francisco Bay.

A Last-Ditch Drought Strategy for the Delta: Rock Barriers 17 April,2015Craig Miller

Author

Craig Miller

Craig is KQED’s science editor, specializing in weather, climate, water & energy issues, with a little seismology thrown in just to shake things up. Prior to his current position, he launched and led the station’s award-winning multimedia project, Climate Watch. Craig is also an accomplished writer/producer of television documentaries, with a focus on natural resource issues.

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