Graffiti artists have editorialized on the obsolete Matilija Dam in Ventura County | Photo: Patrick Maloney, some rights reserved When Interior Secretary Donald Hodel suggested in 1987 that California might tear down OShaughnessy Dam in Yosemite National Park, few took him seriously. The powers that be in San Fransisco were outraged: the Hetch Hetchy Reservoir supplies San Francisco with its drinking water. Even the radical environmentalists who sometimes talked about removing dams like Glen Canyon mistrusted Hodel, saying that he was likely trying to manipulate greens into supporting the controversial Auburn Dam as an alternative to Hetch Hetchy. The era of building big dams was just ending, and the thought of removing them was so far off the radar that Hodel just wasnt taken seriously.
Flash forward 30 years, and dams are starting to fall across the west. Two huge dams on the Elwha River in Washington State came down in 2011. The San Clemente Dam in Monterey County is coming down from the Carmel River. Four dams on the Klamath River are so ripe for removal that their owner intends to take them out even if the state and federal governments arent on board. In Southern California, the handwriting is on the wall for the Rindge Dam on Malibu Creek and the Matilija Dam on the Ventura River.
It may seem counterintuitive. California and the rest of the west are held in a crippling drought that this current El Ni o season is doing little to alleviate. And from the 1850s through the 1980s, dams went up in California in part to ensure a secure supply of water for homes, farms, and factories. But dam removal is still often a good idea even as the state looks at yet another year of drought. Here are five reasons why.
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1: Safety
Eighty-eight years ago this month, the poorly engineered St. Francis Dam failed just a few years after it was completed near Santa Clarita. It sent a wall of water down San Francisquito Canyon and the Santa Clara River to the sea, killing at least 431 people; perhaps more than 600 actually died in the flood, some swept all the way out to the ocean.
The St. Francis Dam failed mainly because its construction was unequal to Californias geology. Unbeknownst to engineers of the day, the dam site sat on ancient, unstable landslides. We know a lot more about Californias geology these days, and what weve learned about the locations of many existing dams is unsettling. One example of many: when the Anderson Dam was built near the Northern California city of Morgan Hill in 1950, geologists thought the nearby Calaveras Fault was inactive. Weve since learned the Calaveras Fault is anything but. A sizable quake on the Calaveras could cause the 240-foot earthen dam to fail, devastating Morgan Hill and dumping eight feet of water into downtown San Jose. (The Santa Clara Valley Water District is in the process of retrofitting the dam to be more seismically sound.)
One of the states most prominent dam removal projects stemmed in part from new awareness of earthquake risks. The San Clemente Dam, removed from the Carmel River in 2015, was identified as seismically unsafe as early as 1991. The 106-foot concrete arch dam, built in 1921, was also determined to be at risk of failure in a large flood, in part due to its reservoir having silted up almost entirely - more than 95 percent of the reservoir had been filled with sediment by the time it was removed. If the San Clemente Dam had failed, a wall of mud would have devastated communities downstream.
All dams fail eventually. Flowing water is one of the most inexorable forces on the planet. One of the biggest dams ever built in western North America, the 2,300-foot-tall lava flow in the Grand Canyon that geologists call Prospect Dam, was worn away to almost nothing over just a few millennia by nothing more than the flow of water and river-borne silt. Come back to visit planet Earth in 500 years, and its unlikely any of our present-day dams will be both unmodified and in working order.
Thats especially true in earthquake-prone California, where many of the best sites for dams - deep river canyons cut into rising mountain ranges - are found near earthquake faults. A 5.7 quake near Oroville Dam in 1975 surprised engineers, who reexamined the site of the then-proposed Auburn Dam on the North Fork of the American River and found a major fault system beneath the site capable of unleashing a 7.0-magnitude quake. Thats much of the reason Auburn is yet unbuilt.
But before the advent of modern seismology, we did build a whole lot of dams, large and small, in earthquake hazard zones. And even if a quake never damages those dams, watersheds in seismically active California carry a lot of eroded sediment. That sediment silts up reservoirs, reducing dam operators ability to manage seasonal flood. Sediment can also speed erosion of dams, as we saw when the silty Colorado River nearly took out Glen Canyon Dam in 1983.
Sometimes, a dam just isnt a safe answer for water management in Californias unstable watersheds. And dams built before we knew what we were doing, such as the completely silted-up Rindge Dam on Malibu Creek, just need to come out for public safety.
Shasta Dam being built, circa 1939 | Public domain photo via Library of Congress
2: Dams are bad for fish
Its no secret that dams hurt fish populations. Some of Californias once-thriving salmon runs have been wiped out, or nearly so, by huge 20th Century dams. Take the Shasta Dam, for instance. When that 600-foot dam closed its gates in 1943, it closed off access to almost all of the Sacramento River winter-run chinook salmons historic spawning habitat. Before 1943 there had been hundreds of miles of winter-run habitat on the Upper Sacramento, the Pit, and McCloud rivers, which flowed together to form the Sacramento River just above the site of Shasta Dam. After 1943, there was 1
