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The Carmel River Gets a Boost

Matt Kondolf, Lori Pottinger August 18, 2015
SanClementeDam

The Carmel River is a shadow of its former self these days, due to overuse of its waters, drought, and dams. But an ambitious project to remove one of its two large dams will bring some life back to the overtaxed river.

The removal of the 106-foot-high San Clemente Dam, now filled with sediment, will be the largest in the state. It will open miles of spawning and rearing habitat for threatened steelhead trout and restore some of the river’s natural flow of sediments. The restoration of sediment flows will support the riparian ecosystem downstream, create gravel beds used by spawning fish, and help replenish sands at Carmel Beach.

The 1920s design of the dam does not meet modern safety standards. Removal of the dam involves many complex challenges, but the biggest by far is managing the 2.5 million cubic yards of sand, silt, gravel, and cobble behind the dam that have displaced all of its water storage capacity. The dam’s remote site precludes removing these sediments mechanically; instead, the project will create a permanent sediment storage area by rerouting the river for half a mile.

Removing San Clemente Dam will help improve habitat, but it isn’t a panacea for all of the river’s problems. Upstream of San Clemente Dam, Los Padres Dam blocks the best spawning and rearing habitat, which is in the Ventana Wilderness Area. Questions still remain about the fate of this dam and fish passage around it. However, removal of San Clemente Dam sets the stage for addressing other aging dams that are ripe for removal around the state.

California has more than 120 reservoirs—most of them small—that have lost at least 75% of their storage capacity to sedimentation. At least three dams in the Coast Ranges are prime candidates for removal: Matilija Dam on the Ventura River, Searsville Dam on San Francisquito Creek on Stanford University property, and Rindge Dam on Malibu Creek. While removing these dams would open up habitat for migratory fish, a key issue hindering their removal is what to do with the decades of sediment accumulated behind them.

Dams are often the principal factor causing degradation of the river ecology. Removing them can often be the single action with the greatest restoration benefits. But other factors affect river health, too, from land use to water abstractions. The Carmel River is not just constrained by dams, it also has been subject to excessive diversions of its waters. Starting in 2017, the river will get increased flows in response to an order by the State Water Resources Control Board to significantly reduce water diversions. Thanks to these efforts, the Carmel River is looking to be a rare success story for the state’s troubled rivers and native fish—and one that is even more important given the huge setbacks the environment has suffered during the drought.

Watch the removal of the dam via webcam.

Learn more about reducing the negative impacts of dams in chapter 5 of Managing California’s Water: From Conflict to Resolution (pp. 228-238).

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