CARMEL VALLEY, Monterey County — The glassy, cold Carmel River surged through a little valley in the Santa Lucia Mountains, cascading in front of a half-dozen workers and observers one day last week down a series of rock outcroppings, as if its sinuous path had been designed by nature.

Nature, of course, had nothing to do with it. The half-mile section of river, with steppingstones, pools and a tableau of freshly planted trees and bushes along the bank, flows through what was once the flooded plain of the San Clemente Dam, a Monterey County landmark for 94 years until it was removed last year.

The Carmel was diverted around the dam site into a channel fashioned out of a historic creek bed. The $83 million dam removal and river restoration project was the most ambitious in California history — and could now provide lessons in a state beset by aging infrastructure and reliant on balancing environmental needs with a thirst for water.

The channeling of the Carmel through a carefully engineered basin was needed to bypass tons of sludge trapped behind the 106-foot-tall San Clemente dam. With the river diverted, workers could take down the structure without worrying about a catastrophic mudslide.

Results studied

Agencies in California and throughout the country are studying the design and results, including government and nonprofit groups working on a plan to tear down the Matilija Dam, north of Ojai in Ventura County.

“We are going to learn so much about fish migration, the forces of the river, how it changes and what happens in the lower river,” said Trish Chapman, the Central Coast program manager for the California Coastal Conservancy, as she peered into a resting pool designed for steelhead trout along the river.

But she added, “Honestly, it’s the places that don’t work where we will learn the most. It will indicate a gap in the knowledge that we had when we created the design. That’s where the learning will come and where we can help future projects.”

200 aging dams

What’s happening in Carmel Valley is important because there are 200 dams in California that are at least partially filled with mud and are approaching the end of their working lives.

The Matilija Dam may be next to come down. One proposal is to divert the river through a tunnel into a creekbed while the dam is removed. The ecosystem would also be restored in an attempt to aid steelhead, similar to what engineers did in the Carmel River.

Environmentalists are also pushing for the removal of the silted-up, 65-foot Searsville Dam on Stanford University property, but many questions remain, including who would foot the humongous bill.

The biggest project contemplated is the removal of four hydroelectric dams on the Klamath River. Federal and state officials in California and Oregon agreed last month to bypass Congress and take down the dams, a plan that would also include restoration of 300 miles of spawning habitat for salmon.

The project would require California, Oregon, dam owner PacifiCorp, and the American Indian tribes along the Klamath to work with federal energy regulators to decommission the dams. The cost could be as high as $500 million, half of which has already been set aside by Gov. Jerry Brown’s administration.

Tom Gibson, chief council for the California Natural Resources Agency, said the coalition working on the Klamath mirrors the San Clemente partnership, which included the federal government, four state agencies led by the Coastal Conservancy and California American Water, the utility that owned the dam.

River diversion won’t be possible on the Klamath or in many other dam removal projects, even though accumulated sediment is always a problem. It is crucial, experts say, that innovative ways be found to remove the silt behind dams.

Dam posed danger

The San Clemente Reservoir was 95 percent full of mud, with the state declaring a seismic hazard as far back as 1992. It had been out of commission since 2002. Left alone, it was a disaster waiting to happen, with 1,500 homes and numerous businesses downstream in danger if a collapse released a cascade of water and mud.

The Carmel, which flows 36 miles to the Pacific Ocean, had an estimated 12,000 to 20,000 steelhead in 1771, when a Spanish mission was built on the river. The first dam was built in 1883, and it was replaced in 1921 by the San Clemente, which sat atop an earthquake fault in a remote forest 18 miles from the ocean.

The dam did have a fish ladder, but it was the country’s steepest, and very few fish made it upstream to spawn. The Carmel averaged about 700 spawning steelhead a year, but in many years no fish returned, said Catherine Stedman of California American Water. A fish counter attached to the dam documented only seven adult steelhead over the two years prior to the removal.

The utility, which serves 100,000 residents on the Monterey Peninsula, decided that removing the equivalent of 125,000 dump-truck loads worth of sediment would cost too much. Instead, they built a half-mile channel and allowed the Carmel to join San Clemente Creek, leaving all the accumulated sediment in place.

Financing channel

The three-year project cost the utility $49 million, which is being passed on to customers through a $2.94-per-month rate increase. It was possible largely because the utility is planning to build a desalination plant, which will supply 40 percent of the district’s water.

The rest of the cost is coming from the California Coastal Conservancy, National Marine Fisheries Service, The Nature Conservancy and other conservationist groups.

The engineered river channel, which includes 56 carefully arranged rock step pools that act like flights of stairs for fish, is already doing what it was designed to do. Biologists counted 14 egg nests in the river two weeks ago, eight above the old dam site. They also counted 10 adult steelhead in and around the channel — and last week, several were spotted in the step pools.

“It means fish are already getting up there, and that they can get by the step pools,” said Joyce Ambrosius, supervisor for the West Coast region of the NOAA Fisheries Service, the lead federal agency on the project. “It’s really exciting that they are making it through.”

More fish anticipated

Fish experts predict steelhead numbers will double next year and continue to rise. Chapman said the restoration will help other species, including endangered red-legged frogs, which are being lured by seasonal ponds designed for them along the river bank.

“The whole system will function more naturally than it did with a dam, so we’ll see a lot of species,” she said, “but it is the steelhead and red-legged frogs that are critical because they are on the endangered species list.”

Stedman said the San Clemente project’s innovation is destined to inspire water agencies and dam operators throughout California and the country.

“While what we did may not apply directly to other projects,” Stedman said as she stood by the river admiring a flock of geese, “we’ve shown others not to be constrained by limitations and to keep searching for what is possible.”