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Sediment Necessitates & Complicates San Clemente Dam Removal

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There are two big dams on the Carmel River. One of them, the San Clemente, is about to be demolished to restore fish habitat. But with a reservoir full of sediment behind it, that’s a delicate process. KUSP’s Wes Sims reports.

San Clemente Dam. Photoby Wes Sims.

San Clemente Dam. Photoby Wes Sims.

With the threat of winter storms mostly faded, California American Water is continuing its $83 million project to remove the San Clemente Dam and restore the river to its original state. The work, located 18-miles up the Carmel River from the Pacific Ocean, involves capturing 2.5 million yards of mud and rerouting the river.

A Dam That Has Outlived Its Usefulness

A stairway leads to a narrow concrete walkway, separating the top of the reservoir from the spill-way, one-hundred-ten feet below. Built in 1921, the San Clemente Dam is set to be torn down because of diminished functionality, seismic vulnerability, and threatened fish habitat on the Carmel River. The dam hasn’t been used for water supply since the mid 1990s, because 95% of its storage capacity is silted up with sediment. CalAm Engineer, Aman Gonzales is manager of the San Clemente Dam Removal Project.

“The challenge was what do we do with the sediment?” he says. “There’s about two and a half million cubic yards of sediment here. At a ten-yard dump truck, you’re talking 250,000 truck loads to get that sediment out of here.”

So instead, the sediment is being left in place. Loren Letendre president of the Carmel River Watershed Conservancy explains the process.

“They’re going to drain the sediment field that’s behind the dam so that it basically will stay in place,” Letendre says. “Remove the dam and leave a small amount of concrete in place to keep the sediment from moving anywhere, take all the concrete from the dam and put it up above the gap to make sure the river never migrates back and pushes all this sediment, this 3-million tons of sediment, downstream. The end benefit is to restore the river back to its original functioning and to allow another eight miles of steelhead passage for rearing.”

Future Uncertain for The Other Dam

There is one other dam on the Carmel River. Located 7-miles further upstream, the Los Padres Dam serves what CalAm spokesperson Catherine Stedman refers to as an environmental function.
“Because during the summer when the Carmel River dries up, we are able to make releases from Los Padres Dam to have water flow down the river which helps keep it running and which is good for the habitat” Stedman says.

It seems there’s no clear agreement on the future of the Los Padres Dam. Dave Stoldt is the general manager of the Monterey Peninsula Water Management District. The agency that manages water service provided by CalAm.

“There are some fisheries biologists who would like to see the Los Padres Dam eventually removed,” he says, “and there are others who think that a regulated river benefits the fishery far more than removal of the dam would. California American Water is starting to look at options to remove the dam in the long term. We’re starting to look at options to keep the dam or some other form of regulation on the river.”

In the meantime, contractors on site at the San Clemente Dam continue their prep work for demolition to begin this summer, with the entire dam removal project wrapping up in late 2016 or early 2017.

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