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CA Dam Starts Draining for Seismic Retrofit

Wednesday, October 7, 2020

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At the beginning of the month, officials from the Santa Clara Valley Water District started taking the first steps in its $576 million Anderson Dam Seismic Retrofit Project to remove and replace the existing infrastructure.

The project is slated to close portions of the Anderson Lake County Park for roughly a decade.

About the Project

Built in 1950 along the Calaveras Fault, the Anderson Dam is a 240-foot earthen dam built to operate a 90,373 acre-feet-capacity, seven-mile-long reservoir in Santa Clara County, California. Since 2009, the reservoir has been reportedly kept—at most—74% capacity, as it was found that the dam could fail in the event of a 7.2 earthquake.

Tom Pavel, CC-BY-2.0, via Wikimedia Commons

At the beginning of the month, officials from the Santa Clara Valley Water District started taking the first steps in its $576 million Anderson Dam Seismic Retrofit Project to remove and replace the existing infrastructure.

By 2012, the SCVWD began looking at efforts to strengthen the dam’s infrastructure and approved the Safe, Clean Water and Natural Flood Protection Program. The program was developed to ensure residents and stakeholders that Santa Clara would address five priorities regarding its water:

  • Priority A: Ensure a Safe, Reliable Water Supply;
  • Priority B: Reduce Toxins, Hazards and Contaminants in our Waterways;
  • Priority C: Protect our Water Supply from Earthquakes and Natural Disasters;
  • Priority D: Restore Wildlife Habitat and Provide Open Space;
  • Priority E: Provide Flood Protection to Homes, Businesses, Schools and Highways; and
  • Other: Six projects from the Clean, Safe, Creeks Plan have been carried forward into the Safe, Clean Water Program.

However, a few years later, officials found that the dam itself required a greater retrofit than first thought. By May 2015, $14 million of Safe, Clean Water funding was approved to be transferred to the Water Utility Enterprise Fund as reimbursement for the Anderson Dam project. Although, funds up to $45 million could be used to help restore the reservoir to full operating capacity.

In 2017, the state Division of Safety and Dams changed the design criteria for spillways, which required the existing spillway at Anderson be completely replaced as opposed to repaired.

By 2019, the SCVWD began working with the Federal Energy Regulatory Commission on the evaluation of existing risk reduction measures for the project. After obtaining additional interim risk reduction measures in December and January 2020, FERC announced in February that the water district would have to fully drain its reservoir to 488 feet (Deadpool) by Oct. 1.

The announcement arrived after new information regarding the infrastructure showed that the project features are more vulnerable in a 100-year earthquake than previously understood, potentially negatively affecting tens of thousands of people.

According to FERC, the safety risks at Anderson Dam are “unacceptably high” and that an elevation of no higher than 565 feet must be maintained at the reservoir.

David Capka, Director of the Division of Dam Safety and Inspections at the FERC, wrote in a letter to the SCVWD, “Once begun, you must lower it safely to elevation 488 as quickly as you can. Again, you must take all appropriate measures to maintain and quickly lower the reservoir to Deadpool in the event of significant inflow once the elevation is reached.”

What Next

With draining efforts in place, agency officials hope to lower the reservoirs capacity to just 3%, which could be achieved as early as December if the weather stays dry, according to The Mercury News.

During draining efforts, the SCVWD will remove the water at rates measuring roughly 200-acre feet, or 65 million gallons per day. However, should the project endure winter storms, the process could last until April 2021.

After draining tasks are completed, the project calls for the construction a 1,700-foot-long tunnel, up to 24-feet in diameter, on the left side of the dam looking towards the reservoir. The infrastructure is expected to increase the release of water during an emergency by five-fold.

A full draining plan for the project can be viewed, here.

Over the next several months, the SCVWD plans to find and alternative emergency water supply in addition to engaging in environmental consultation. Construction on the Anderson Dam Seismic Retrofit Project is expected to begin sometime in 2022.


Tagged categories: Federal Energy Regulatory Commission (FERC); Health & Safety; Health and safety; Locks and dams; NA; North America; Project Management; Reservoir; Safety; Upcoming projects

Comment from Tom Schwerdt, (10/7/2020, 8:35 AM)

A decade seems like an awfully long project timeframe.

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