Crews have finished a $307 million outlet tunnel at Anderson Dam near Morgan Hill, giving Valley Water a much faster way to drain Santa Clara County's largest reservoir and cutting flood risk along Coyote Creek in San Jose ahead of a strong El Niño winter.
The tunnel is 1,736 feet long and 24 feet high, with a 13-foot-diameter steel pipe inside, the Mercury News reported Monday. Crews tested it Oct. 30, releasing 4 million gallons into Coyote Creek. The new outlet can release 6,000 cubic feet of water per second, 13 times the old pipe's 450.
"We'll be able to drain the reservoir now in a more controlled way, reducing the chance of a flood event like in 2017," said Ryan McCarter, Valley Water's deputy operating officer. In 2017, the full reservoir spilled into Coyote Creek and flooded San Jose neighborhoods including Rock Springs and Naglee Park.
What's next
The 13-foot outlet replaces the dam's old 4-foot pipe, Valley Water said in July. Work on haul roads and temporary bridges starts Jan. 1. Crews plan to tear down the 1950 earthen dam from 2028 to 2030 and finish a new, quake-resistant dam in 2033. Valley Water put the total project cost at about $2.8 billion in July; the Mercury News puts it at $3.2 billion. Federal regulators ordered the reservoir held at 3% full, where it remains. Background: Anderson Dam construction starts in 2027.