More on Delta tunnels impacts

A schematic by the state Department of Water Resources shows what one of the three intakes to the Delta tunnels might look like.

Wildlife agencies are still writing the permits that would be required to build Gov. Jerry Brown’s Delta tunnels, but bits and pieces of the draft documents have been posted online, along with a report from a independent peer-review panel of scientists.

While the scientists’ job wasn’t to directly weigh the merits of the tunnels, they did examine the methods that the wildlife agencies are using to measure the project’s impact in a wide range of areas.

And they concluded that the agencies “have provided evidence that some aspects of the (project) will have significant adverse effects on listed species and critical habitat.”

This non-scientist finally went through the panel’s findings. They are complex and nuanced. Some of the details, as best I understand them:

• There are “numerous” construction impacts. The estimated 15,000 barge trips needed to bring construction materials into the Delta could cloud up the water and increase the risk of chemical spills. The docks built to accommodate those barges could turn into hiding places for hungry predatory fish which will chow down on the natives. And if they’re not eaten, the native fish may be stressed by all of the construction noise.

• Habitat for threatened Delta smelt may be diminished if cofferdams are used in the Sacramento River during construction. Those dams would be built within the river to drain the water from the area where the intakes to the tunnels will be built. A natural consequence of those dams is that the river itself will have less room to handle downstream flows, which means water will travel through the area at a faster velocity.

Those faster flows may effectively prevent smelt from accessing habitat farther upstream. On the other hand, the dams could help to keep construction impacts away from sensitive areas inhabited by fish.

• Once the tunnels are operational, and the dams are removed, loss of habitat might still be a problem because smelt won’t be strong enough to swim past the three very powerful intakes, which will each be more than 1,000 feet long. The probability of any fish successfully passing all three of the screens is “almost certainly less than 0.04 percent,” the panel found.

Hundreds of acres of new fish habitat would be created elsewhere to offset the loss above the intakes, but it could take years or even decades for habitat restoration to reach maximum benefit.

Still, on the south side of the Delta, if the tunnels allow for fewer smelt to be killed at the existing pumps, then it’s possible the fish may become better established on the San Joaquin River, which would be good news. Overall, the project should result in a net reduction in the “entrainment” of smelt, the panel found.

• Another habitat impact: During the summertime, with the tunnels in place, saltwater will move farther upstream in the Delta, potentially prohibiting smelt from accessing downstream, open-water habitat in the Suisun Bay area.

• For salmon, the three screened intakes collectively are expected to kill 5 percent to 10 percent of the migrating juveniles. But that may be an underestimate. “Realistically, fish successfully navigating past any one screen may be weakened by the effort, and hence their loss/injury rates are likely to increase for the next screen, and again for the next,” the panel found.

Overall, they found the operation of the tunnels may cause a “significant reduction” in the survival of endangered winter-run Chinook salmon. And even small changes in survival rates “could lead to significant population-level impacts.”

• On algae: If the tunnels are in place and the south Delta pumps are used less often, higher flows in that area could reduce harmful algae blooms. But that problem may instead occur at the Sacramento River near the intakes, where algae hasn’t historically been an issue.

• Many uncertainties remain about the impacts of the tunnels. While “adaptive management” is a tool officials can use to change the way the project is operated as scientists learn more about those impacts, the success of adaptive management will depend on how robustly those plans are executed, and who is in a position to make decisions about how the tunnels are operated.

• The draft permits consider climate change only through 2030, not a long enough window of time.

More to come on this, of course, once the permits themselves are published.

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  • Blog Author

    Alex Breitler

    A native of Benicia, he lives in Stockton with his wife, Ann, who forces him to go backpacking in the Sierra Nevada or Trinity Alps at every opportunity. He has been writing mostly about natural resources since 2003, first in Redding and now in ... Read Full
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