Work over half-way done on Anderson Dam tunnel in Morgan Hill

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Work on a tunnel in Morgan Hill to give more control over the water in the Anderson Reservoir is now more than half-way done, work crews said Wednesday. It’s a major milestone for the project, which aims to better protect the reservoir against earthquakes. 

This month, Valley Water crews have been using TNT to blast through the hardest bedrock and are now more than 800 feet in. 

“First, you’ll see a lot of flashes,” said Ryan McCarter, the project manager. “There’s a hole drilled about six to eight feet in with a charge at the end of it. Then you’ll hear a rumble and those are the explosives going off and the rock tumbling down.” 

Once the tunnel is completed, a pipe will be installed to better control the flow of water out of Anderson Dam. 

The flow proved to be an issue in 2017, when torrential rains hit and Valley Water couldn’t release water from the reservoir fast enough. As a result, water spilled over into Coyote Creek and flooded San Jose neighborhoods miles away. 

So far, an estimated 1,500 truckloads of rock have been carried out of the tunnel so far. And on the other side, excavators floating on barges are working to clear out the sediment. 

“We actually are already through the section of hard rock,” said McCarter. “It was about 25 to 30 feet. And now we’re back into a softer rock that’s not requiring a blasting technique, so we’re just using conventional excavation.” 

Work on the tunnel is set to finish in two years, at which point construction to retrofit the dam will begin. 

The federal and state government forced the start of the $1.4 billion project after multiple studies showed the dam was at risk of failing during a major earthquake. 

Overall, Valley Water estimates it’ll be finished by 2032. 

“This is our board of directors’ single most important project,” said John L. Varela, Valley Water’s board chair. “This is our largest dam of ten. We’re very encouraged that we’re moving forward at a rapid pace.” 

Valley Water plans to hold a public meeting in Morgan Hill on Oct. 4, updating residents on the project and the 1,000 page environmental impact report that details the impact on the surrounding community.

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