Valley Water making progress on work at Anderson Dam

For the past several months, Valley Water construction crews drilled 244 holes deep into the hillside next to Anderson Dam in Morgan Hill. Inside each hole, workers placed a 120-foot-long bar, up to 2-1/4 inches in diameter. The steel bars, each weighing about 1,600 pounds, were covered with 12-inches of concrete.

This work to reinforce roughly 15,000 square feet of hillside was a milestone in an overall effort to build a new outlet tunnel at Anderson Dam. This new tunnel will allow Valley Water to draw down the reservoir reliably and quickly, providing greater control over the water levels in the reservoir and increasing public safety.

“This tunnel is a major part of getting Anderson Dam back online as a stronger facility so it can protect public safety and again serve as Santa Clara County’s largest drinking water reservoir,” said Valley Water Chair Pro Tem John L. Varela, who represents South County. 

Later this summer, Valley Water will begin digging a tunnel reaching 24.5′ in diameter through the 12-inch concrete layer and hillside. Once the tunnel is complete, Valley Water will be able to release water from Anderson Reservoir five times more quickly than previously and 12 times more quickly once the whole project is finished.

“We needed to make sure the hill can withstand the tunneling process,” Valley Water Deputy Operating Officer Chris Hakes said. “The strength of the steel bars will hold the hill in place.”

The existing outlet pipe runs underneath the dam and crosses fault lines. This pipe would be unable to withstand movement caused by a large earthquake and must be replaced. The new outlet tunnel replacing the existing old pipe is designed to withstand an earthquake.

Once the tunnel is complete, Valley Water will begin retrofitting the dam embankment and spillway. That project is estimated to start in 2025 and will last about seven years. Once completed, Valley Water will again be able to fill Anderson Reservoir to capacity.

Rebuilding Anderson Dam to ensure public safety is Valley Water’s highest priority. We are working with numerous state and federal agencies to obtain the necessary permits to move forward with the project as quickly as possible.

For more information about our work at Anderson Dam, visit the project webpage at

  • Reinforced hillside at Anderson Reservoir


  1. Good information, but with all the documents posted to the site, I do not see a single comprehensive schedule. All you share is 3 bars several years long each. Where can I get a copy of a more detailed schedule? Knowledge fosters understanding and a significantly more comprehensive schedule would help that.
    Thank you.


    1. Valley Water is exploring options to increase the amount of water it can store in local reservoirs.
      One of these projects, the proposed expansion of Pacheco Reservoir in south Santa Clara County, would double the amount of water we can store in local reservoirs. Valley Water would rely on this local supply during future droughts and emergencies. The Pacheco project has already been awarded $504 million in conditional funding from the state’s Prop 1 Water Storage Investment Program.
      You can learn more at


  2. Thanks for the update, but 10 years to complete the task — it took 4 years to build the Golden Gate. Where is/ are the new reservoirs being built as part of that billion dollar bond issue past, years ago. It would appear the monies will be exhausted just in evaluating a site. This state will return to a desert with it’s present hydro/aquatic system built to support a population of 30 million, now approaching 45 million. Have a great 👍 day!!


    1. So the bay area lost is best recreational lake until 2032??!!? Who approved this and why is it taking so long. Last year park staff were telling everybody it was going to take two years to complete. In 1936 it took us five years to build the Hoover dam, why the hell will this take 12 years!? California bureaucracy at its finest!!! I’m really starting to lose faith in our government.


  3. I also have a problem with the planning and scheduling. President Kennedy said we would be on the Moon in 10 years, and we can’t rebuild an earthen dam in 12 years (and extending). I understand there is a large effort to move the existing materials to a location north of the Boy’s ranch and this will take time. Why wait three years to start this effort and do it concurrently with the tunnelling effort. Taking the top off the dam should not hinder the tunneling work.


  4. As of 1/17/2023 the Anderson reservoir is 43% full. I thought that it has to be nearly empty until the dam retrofit is complete. Could you explain?


    1. Thanks for the question.
      The recent series of atmospheric river storms – described by the Mercury News as the second wettest 21-day stretch in the Bay Area since 1849 – filled many of Valley Water’s 10 reservoirs. Rainfall was significant across Santa Clara County, including watersheds around Anderson Dam in Morgan Hill, where between 13 and 17 inches of rain fell.
      These storms resulted in significant rainfall runoff into Anderson Reservoir. The amount of water that entered the reservoir exceeded the amount that could be released through the existing outlet pipe, which was open during the storms. Between Dec. 31 and Jan. 18, the amount of water stored in Anderson increased from 3.9% to about 45% of capacity. It will take Valley Water about two months to bring Anderson Reservoir back down to 3.7% capacity without additional rainfall.
      The existing outlet pipe at Anderson Dam can release up to 1,000-acre feet (or 325 million gallons) of water daily.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: