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A look at the $2.3 billion tunnel being built at Anderson Dam

An 1,800-foot tunnel is being dug up underneath the Anderson Dam in Morgan Hill and those working on the $2.3 billion project hope it’ll prevent devastating floods in the future. 

Ryan McCarter is the manager for the Anderson Dam Seismic Retrofit Project and said a large steel pipe will go inside the 20-foot-wide tunnel.

It’ll allow Valley Water to better control the amount of water being released from the reservoir into Coyote Creek — something that may have prevented the South Bay floods in 2017.

Back then, water managers couldn’t release water fast enough during a storm – leading to a spillover that triggered devastating flooding in San Jose.

The new valve will be able to release 15 times more water than the current system.

“When storms stack up successively, when we can’t empty the reservoir back down to allow space for the next storm that’s when we run into issues,” McCarter said. “So this will give us the ability to lower after a storm prior to an additional storm.”

So far, 1,400 feet have been excavated. The final phase of this digging project kicks off in the summer. 

That’s when they’ll be boring through the final 350 feet right into the reservoir.

“So this is the point in which we change types of equipment and we use a micro-tunnel boring machine which is basically a giant drill,” McCarter said. “It’s an eight-foot in diameter machine that has a cutter head at the front of it.” 

It’s all part of a major retrofit for the aging dam.

That retrofit was mandated by the federal government after studies found the structure could fail in a major earthquake. And if that quake struck while the reservoir was full, there would be widespread destructive flooding across Santa Clara Valley.

“This project is Valley Water’s top priority. Once completed, it would help ensure public safety, protect our regional water supply, and provide environmental benefits for future generations,” John L. Varela, Valley Water board director, said.

“So really, this is all designed to take the largest possible earthquake and the largest possible flood that we could dream up,” McCarter said.  

The valve will also keep the water level low throughout the rest of the retrofit .

While the entire project isn’t set to finish until 2032, for this phase, there’s finally light at the end of the tunnel.

Source: NBC Bay Area

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