Plans to drain Anderson Reservoir amid seismic safety concerns

Bay Area

MORGAN HILL, Calif. (KRON) – Feds have demanded that Anderson Reservoir be emptied amid seismic safety concerns.

Could that lead to a water shortage or rationing? 

Are there any risks associated with pulling the plug on the south bay’s largest water supply?

The dam looms over the neighborhood here. 

The Calaveras fault runs through and if the dam were to fail in a large earthquake, the consequences could be disastrous.  

Here’s a look at what could happen unless the reservoir is drained completely as demanded by the federal government.

This newly released video shows how a magnitude 6.6 or larger earthquake near Anderson Dam, when the reservoir is full, could unleash a wall of water 35 feet high into downtown Morgan Hill within 14 minutes claiming thousands of lives.  

Water managers are well aware of the risk says Valley Water C.O.O. Nina Hawk.

“The video does show essentially the importance of this project, why we need to move this project along very quickly because there is potential there, there is risk,” Hawk said.

The dam is to undergo a seismic safety retrofit, but it isn’t happening fast enough to satisfy the federal government, which is now demanding the reservoir be completely drained.  

Exactly how that will happen remains unclear.

“So the risk is that the reservoir itself has water behind the dam and so if the water does come throughout of the outlet into the creek, we want to make sure that it’s done at a speed and magnitude is done in a safe way so that it’s not done too quickly and also to make sure that there’s no concern about additional water that would not be behind the dam moving forward,” Hawk said.  

Anderson Reservoir is now about 29-percent full.  

Water managers hope to avoid any shortages this year but with another drought looming, more water may have to be imported and new calls for conservation or rationing may eventually be needed.

“But it will really depend on mother nature, how much water will come down into our reservoirs and how much will be available from that imported supply I just spoke about and then from there we’ll be able to determine if we need to call for any additional conservation,” Hawk said. 

It’s not clear how long it will take to drain the remaining 8-billion gallons of water in the reservoir.  

Some will be saved or diverted into underground storage but the remainder, although much, much slower than the flood in that video, will be released into Coyote Creek and make its way out to the bay eliminating the risk of disaster.

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