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Earthquake Flood Risk Prompts Fed Order To Drain Northern California Dam

MORGAN HILL (AP) - Officials worried that an earthquake could collapse a big dam south of San Francisco have ordered its reservoir to be completely drained by October to reduce the risk of the dam failing and sending floodwaters into communities.

The 240-foot (73-meter) high earthen Anderson Dam, built in 1950 and located between San Jose and the community of Morgan Hill, poses too great of a risk of collapse and it must be fully drained by Oct. 1, said the Federal Energy Regulatory Commission, which regulates dams, the Mercury News reported.

"It is unacceptable to maintain the reservoir at an elevation higher than necessary when it can be reduced, thereby decreasing the risk to public safety and the large population downstream of Anderson Dam," wrote David Capka, director of FERC's Division of Dam Safety and Inspections, in a letter to the Santa Clara Valley Water District on Thursday.

Anderson Reservoir is owned by the Santa Clara Valley Water District, a county government agency based in San Jose. When full, it holds more water than all other nine dams operated by agency combined.

In a collapse, runoff could damage cities and rural areas from the San Francisco Bay to the north through Monterey Bay to the south, including much of Silicon Valley, the Santa Clara Valley Water District said in a statement Monday.

The agency since 2009 has kept the dam's water level at a maximum of 74 percent capacity after learning the dam could fail in a 7.2 quake. The reservoir is built along the Calaveras Fault.

Norma Camacho, the water district's CEO, said in a statement Monday that draining the largest reservoir will likely kill wildlife downstream in Coyote Creek, including endangered steelhead trout, amphibians and reptiles. Coyote Creek flows from the dam through downtown San Jose to San Francisco Bay.

Three years ago, San Jose city officials ordered more than 14,000 residents to evacuate as water from swollen Coyote Creek flooded homes and temporarily shut down a portion of a major freeway.

Complicating the issue, California may be heading into a new drought. On Monday, amid a dry winter, Anderson Reservoir was just 29 % full.

The water stored there is an important part of the southern San Francisco Bay area's water supply - with enough water for the annual needs of at least 130,000 people plus what the district considers an emergency supply.

"While residents have done an excellent job of conserving water since 2013, another drought during this time frame could require everyone to significantly decrease their water use," Camacho said.

Staff is already exploring other sources of water that will have to come from outside of Santa Clara County, Camacho said.

Copyright 2020 The Associated Press.

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