Course of Nature

(Left) step pools were engineered in 2015 to last for decades. (Right) the same channel has become barely recognizable in the winter of 2017.

Nature has taken its course on the Carmel River this winter, and the question scientists will have to answer once the flows recede is this: Should we just let it be?

When the San Clemente Dam removal and Carmel River reroute was completed in 2015, the riverbed on the newly engineered channel included a series of 54 “step pools” to provide a gentle climb up the river for migrating steelhead.

The pools were engineered to last for decades, or until the next big flows, but last winter’s El Niño storms – which delivered average rainfall to the region – wiped out 14 of the 54 pools as rocks and debris shifted. Granite Construction, which California American Water hired to design and build the project, restored those pools over the summer.

Yet this winter, all 54 of the pools have been wiped out and made something into new – scientists call it “reshuffling” – and the riverbed on the new channel is barely recognizable from two years ago. That might be a good thing.

“To me, it looks like a natural river,” says David Boughton, a fisheries ecologist with the National Oceanic and Atmospheric Administration. One potential negative aspect of the reconfigured riverbed, Boughton says, is that the channel has grown wider, which might require higher flows for fish to get through.

“We’ll study it this summer to see how it’s going to affect the upstream migration,” he says. “Until then, I can’t say if it’s better or worse.”

Like Boughton, CSU Monterey Bay’s Doug Smith – a fluvial geomorphologist, a scientist who studies the interaction of rivers with the landscape – is not surprised with the river’s transformation, and his preliminary assessment is that the river has changed for the better.

“Some people would call it a premature success, because the river has taken charge and moved the boulders into a more natural formation,” he says. “I think the community will look at this and recognize we should not reconstruct it in the same way, because it will happen again very soon.

“It doesn’t make sense to go back to square one,” he says of the option to rebuild yet again. He later adds by email that when faced with 2 – to 5-ton sandstone boulders, “The river did not care.”

The total price tag of the dam removal and river reroute was $83 million, with $49 million coming from Cal Am and $34 million from the California Coastal Conservancy. In Cal Am’s contract with Granite, Granite a has five-year post-construction obligation to maintain plantings and vegetation in the project site if necessary, but the high flows this winter exceeded the company’s contractual obligation for a stable floodplain.

Cal Am Vice President Rich Svindland says though his company hoped the changes to the river would happen in year five or 10, as opposed to year two, nothing could have been done.

“We knew we could not design a river channel that could handle massive storms,” he says.

Nonetheless, he says, “I think we are good with it. We put all the ingredients in to make this work – boulders, large woody debris, artificial piles of sediment.”

Svindland adds that what regulators ultimately decide to do about the reborn river will have “national implications.”

One key assessment that must be made aside from fish passage suitability is what plants, if any, should be replaced.

Trish Chapman, the regional manager for the Coastal Conservancy and point person for the project, says that assessment will be made after the flow recedes.

“Riparian vegetation comes back pretty fast,” she says, but adds that some species are harder to establish than others. The question, she says, is whether the vegetation will bounce back fast enough naturally to satisfy conditions in the project’s state, federal and county permits.

“The bottom line is: This is what we always expected,” Chapman says, even if it came earlier than anticipated. She expects any changes to the existing pools – if necessary – to be modifications, rather than a complete rebuilding.

Svindland anticipates such modifications would cost in the neighborhood of $200,000. As for who’d pay, he says, “There’d have to be a discussion.”

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