Anderson Dam Seismic Retrofit Project

The construction of the Diversion Outlet Structure slabs and walls was successfully completed in April 2024 and the construction of the Diversion Outlet Structure roofs was completed in June 2024.

In February 2024, Valley Water achieved a signification project construction milestone with the completion of the excavation of the 24-foot diameter Low-Level Outlet Tunnel. In August 2024, an 8-foot diameter Micro-Tunnel Boring Machine was launched to advance the lake tap for the stage 1 diversion, completing the tunneling operations for the Anderson Dam Tunnel Project.

As mentioned in the previous environmental review process update and discussed at the public meeting held on June 6, 2024, Valley Water has been working expeditiously to move the Anderson Dam Seismic Retrofit Project forward, with the goal to begin construction in April 2026. Valley Water recently met with the project Board of Consultants (BOC), which reviews the project and makes recommendations to FERC to discuss updated design plans and provides construction sequencing. In response to that meeting and BOC recommendations, Valley Water now proposes to make certain construction changes such as extending work hours, adding some weekend days, and to begin work on certain project components sooner. These proposed changes would allow Valley Water to construct planned project components within the planned construction timeline before the wet season each year to improve our ability to complete this important health and safety project on schedule.

Because these construction changes would cause additional impacts, Valley Water has decided to revise and partially recirculate the Draft Environmental Impact Report (EIR) to update project impacts on air quality, greenhouse gas emissions, noise, and aesthetics, and allow additional public comment on the construction changes and updated impact analyses. While taking this approach would extend Valley Water’s certification of the Final EIR from September 2024 to February 2025, this would not delay the overall project construction schedule that is planned to begin in spring 2026.

In accordance with the California Environmental Quality Act Guidelines, Valley Water has released the Partially Recirculated Draft EIR with an updated project description, air quality, greenhouse gas emissions, noise, and aesthetics sections, together with two revised technical appendices, for additional public comment before finalizing the document. The Partially Recirculated Draft EIR is available for public review on Monday, August 5, 2024, for a 45-day public review period. The Notice of Availability and Partially Recirculated Draft EIR can be accessed here: https://www.valleywater.org/public-review-documents. (Please note there has been a minor correction to the NOA that was mailed and published in the newspaper the week of July 29th.)

Separately, Valley Water is considering making other changes to the project description and environmentally superior alternative, including changes to post-construction flows and certain conservation measures to further reduce fisheries impacts, in response to comments and recommendations from regulatory agencies such as National Marine Fisheries Service (NMFS). These other project description changes, which also include other minor clarifications and additions, would appear in the Final EIR.

Q: What is Anderson Dam and Reservoir?

A: Anderson Dam creates Santa Clara County’s largest surface water reservoir—Anderson Reservoir—that stores local rainfall runoff and imported water from the Central Valley Project. With a capacity of nearly 90,000 acre-feet, enough water to supply almost a million people for a year, the reservoir is a critical part of the region’s water supply system. The reservoir provides water to drinking water treatment plants and for groundwater recharge. Anderson Dam, located in Morgan Hill, was built in 1950 to the seismic and dam safety standards of the day. Studies have shown a large earthquake could damage the dam, causing an uncontrolled release of water that could inundate cities and rural areas from San Francisco Bay south to Monterey Bay, including much of Silicon Valley.

Q: What is the Anderson Dam Seismic Retrofit Project?

A: The Anderson Dam Seismic Retrofit Project (ADSRP) looks to rebuild the dam in compliance with today’s seismic safety standards and regulations. The project will increase the dam’s outlet capacities to allow a rapid, controlled reduction of the reservoir levels in an emergency. The spillway capacity will be increased to safely carry water from severe flood events. Valley Water initiated the project in 2012 following a seismic stability evaluation. Then in 2016, additional studies revealed previously unidentified fault lines, extending the length of time to complete the work. In February 2020, the Federal Energy Regulatory Commission (FERC) directed Valley Water to immediately reduce water levels in Anderson Reservoir with the goal to speed up work to replace the dam. Anderson Reservoir is currently limited to 3% capacity.

The ADSRP includes not just constructing the seismic retrofit components to minimize seismic risks, but also conservation measures to minimize environmental impacts and provide environmental benefits, post-construction operations that improve Coyote Creek fisheries conditions, and a long-term adaptive management program.

Q: How long will construction take?

A: Construction of the ADSRP, which consists of building new outlet pipes and removing and reconstructing the spillway and the dam embankment, will begin after the first stage is completed and the required permits are received. ADSRP construction is estimated to start in 2026 and to take seven years.

A critical part of the project schedule depends on the acquisition of environmental permits from state and federal agencies, such as the National Marine Fisheries Service (NMFS), U.S. Army Corps of Engineers (USACE), U.S. Fish and Wildlife Service (USFWS), California Department of Fish and Wildlife (CDFW), and the California State Water Resources Control Board (SWRCB).

Q: What will be the impact on Rosendin Park be?

A: Due to blasting activities, there will be a full and partial closure of Rosendin Park during the ADSRP construction. A full closure of Rosendin Park is anticipated to last up to four months during the initial blasting work with partial closure of Rosendin Park planned for the remaining efforts. Valley Water anticipates the park closure to last up to three years. Park closures could potentially occur during years four, five and six of the ADSRP construction.

Q: Wildfire Emergency Access

A: Valley Water is coordinating with CalFire, Santa Clara County Parks, and the City of Morgan Hill regarding any impacts construction would have on an emergency vehicle’s ability to access wildfires using emergency evacuation routes. Local jurisdictions do not recognize Rosendin Park as an evacuation route; Dunne Avenue will remain the designated emergency evacuation route throughout construction.

Throughout construction, Coyote Reservoir will retain water for potential aircraft wildfire response.

Q: How is Valley Water addressing the concerns about feral pigs?

A: Valley Water understands the community’s concern regarding the presence of the feral pigs and acknowledges the request to work with the community to help improve the situation. Valley Water has received a large number of comments from the public on the Anderson Dam Seismic Retrofit Project (ADSRP) Draft Environmental Impact Report and the Draft Petition for Surrender of Exemption regarding the feral pig presence within the vicinity of the project area. Valley Water is currently in the process of addressing the comments that were submitted for these two public documents, including those that addressed the nuisance of the feral pigs.

The increase in feral pig numbers and activity is part of a larger regional issue that is occurring throughout Santa Clara County and the greater San Francisco Bay Area. There is strong evidence through recent documentation, online sources, and agency coordination that the statewide and regional feral pig presence has been and continues to increase over time. In fact, the passage of SB 856 in 2022, relaxing restrictions on feral pig hunting, reflects the statewide growing feral pig population and the need for better management of feral pigs, thus demonstrating that the issue is not restricted to the vicinity of Anderson Reservoir. There are ample access routes by which pigs could have dispersed from Coyote Canyon to neighborhoods adjacent to the reservoir without having to cross Coyote Creek or Anderson Reservoir.

The increased presence of and disturbance caused by feral pigs have been reported in many other areas of Santa Clara County. In 2020, there were news reports of significant feral pig damage at the Coyote Creek Golf Club. This location is four miles northwest of Anderson Dam, and there is no expectation that the presence of feral pigs at the golf course was related to the drawdown of Anderson Reservoir.

Although California Department of Fish and Wildlife (CDFW) could issue Valley Water a depredation and trapping permit, Valley Water is limited on depredation and trapping efforts depending on property boundaries, agency limitations, and use of trapping and depredation equipment. To help with this issue, Valley Water continues to work with other agencies and to research and consider options for region-wide solutions to help address the feral pig issue.

Q: What is the cost of the project and what makes this project so expensive?

A: As of 2024, the total cost of the ADSRP has increased by $894.41 million to approximately $1.9 billion. Approximately $2.3 billion is the current combined cost of the Federal Energy Regulatory Commission (FERC) ordered Compliance Project (FOCP), which includes Anderson Dam Tunnel Project (ADTP), Cross Valley Pipeline Extension, Coyote Percolation Dam Replacement, Coyote Flood Management Measures, Coyote Creek Chillers Project and the ADSRP.

FERC requiring that the FOCP be implemented before the ADSRP, new FERC and environmental regulatory requirements, and inflation and worker shortages are driving the project costs up.

Q: Why did the cost increase so dramatically?

A: Several developments over the last 10 years have greatly expanded the scope of the ADSRP and extended the project schedule.

Initially, the dam was planned to be seismically stabilized by adding additional material. However, investigations during the design phase found active faulting under the dam’s foundation which meant that the existing dam embankment could liquify and potentially fail during a large earthquake. This led to a change in the design. The project evolved into the complete removal of the existing dam and its replacement with a new dam. This change was approved by federal and state dam regulators, FERC, and the Division of Safety of Dams (DSOD), and by the FERC mandated body of experts, the Board of Consultants.

Additionally, the dam spillway was originally set to undergo spot repairs as opposed to a full replacement. However, after the nation’s tallest dam, Oroville Dam, partially failed in 2017 and forced downstream evacuations, environmental damage, and costly emergency repairs, the DSOD imposed stricter standards for spillway design. This revision to spillway design standards requires removing and replacing the existing spillway and extending the spillway through the unlined portion.

Given all this, design documents prepared in 2018 planned for a 5-year construction period for the Anderson Dam Seismic Retrofit Project (ADSRP) starting in 2022. The total project cost was estimated at $576 million.

However, subsequently, the Federal Energy Regulatory Commission (FERC) ordered Valley Water to build the outlet tunnel and complete other related projects within the next three years as a part of the FERC Compliance Project (FOCP), and then begin construction of the embankment replacement. This resulted in extending the total construction duration for FOCP and ADSRP to 10 years. Although Valley Water’s initial discussions with FERC centered around addressing the potential impacts resulting from the reconstruction of the dam, the National Marine Fisheries Service (NMFS) has requested that potential impacts related to post-construction dam operations, also be considered. As a result, the five subprojects mentioned above were added to the scope of the ADSRP.

Work is progressing on finalizing the project’s design, permitting process and environmental review so that construction can start in early-2026.

Q: Will my water bill increase? If so, when and by how much?

A: In the fiscal year 2023, preliminary water rates to help pay for the $1.9 billion Anderson Dam Seismic Retrofit Project are projected to go up by less than $1 per month for the average Santa Clara County household. Though Valley Water is the countywide wholesaler, it relies on local water retailers to deliver water directly to homes and businesses, in addition to determining their own billing rates. This projection does not account for potential increases due to drought impacts, other projects costs or external factors. Valley Water is rigorously pursuing state and federal grants to help subsidize this project and reduce the impact on ratepayers.

Q: Will the last parcel tax help pay for this increased price tag?

A: Yes, this project was voter-approved as part of the Safe, Clean Water, and Natural Flood Protection Program. The total funding available from this source for the Anderson Dam Seismic Retrofit Project is $54.1 million.

Q: How will water supplies be impacted by this project?

A: Valley Water will supplement its water supplies through additional imported water purchases and conservation to ensure adequate supplies for groundwater recharge and water treatment plants.

Q: What is Valley Water doing to reduce public safety risks until the new dam is constructed?

A: Valley Water continues to work closely with state and federal regulators to maximize public safety. Anderson Reservoir has been operating at levels required by regulators so that if the dam were to slump during an earthquake, the top of the dam would still remain higher than the water levels behind the dam. Valley Water’s priority is to compete construction of the new outlet that will allow quick reservoir drawdown, providing greater control over the water levels and increased public safety.

Valley Water expects increased deliveries for the critical outlet tunnel project at Anderson Dam in Morgan Hill, beginning Tuesday, October 1, 2024, and continuing through the end of the month.

During that time, increased daily truckloads carrying rock, concrete, and equipment will be traveling from U.S. Highway 101 to the construction site off Cochrane Road. These deliveries are for activities that include the demobilization of the micro-tunnel boring operation, installation of the diversion system, channel armoring along Coyote Creek and the construction of the north weir.

When completed, the Anderson Dam Tunnel Project will give Valley Water greater control over reservoir levels.

Valley Water recognizes the inconvenience and impacts of these activities on residents near the dam and reservoir. We will make every effort to redirect construction lighting away from homes and minimize noise from our trucks and equipment. Thank you for your patience.

Our largest water reservoir has been drained while we retrofit it so it can withstand a large earthquake. Learn more about the project's timeline and how our region can benefit from a reconstructed Anderson Dam.

Please watch the video or click this link to view the new video about the history and scope of the Anderson Dam Seismic Retrofit Project.

While the Anderson Dam Tunnel Project is under construction, large portions of the Anderson Lake County Park will remain open, including the Live Oak Picnic area, the Rosendin area, the Anderson Lake Park Visitor Center and the Coyote Creek Parkway. However, some areas of the park will be closed, impacting recreational activities such as angling, boating, hiking and picnicking around the dam and reservoir. These activities will be limited or completely closed.

During construction, please check out these alternative recreational spots nearby:

• Coyote Lake Harvey Bear Ranch County Park. Located just upstream of Anderson Reservoir, the park provides power and non-power boating, fishing, hiking, picnicking, nature trails, camping and biking opportunities around Valley Water's Coyote Reservoir.
• Calero County Park. Boating, fishing, hiking and picnicking is available. The park surrounds the nearby Calero Reservoir.
• Henry Coe State Park. Located about three miles east of Anderson Reservoir, the park is the largest state park in northern California and protects and preserves 87,000 acres of scenic hills and mountain ridges in the Diablo Mountain Ridge. The largely undeveloped park welcomes backpackers, equestrians, mountain bikers, day hikers and anyone seeking solitude in a nearly untouched setting.
• Coyote Valley Open Space Preserve. This preserve offers a scenic overlook from the western edge of the Coyote Valley in addition to multi-use trails and picnicking areas.
• Rancho Canada del Oro Open Space Preserve. Located in the foothills of the Santa Cruz mountains in South Santa Clara County, the preserve has 12 miles of easy to challenging trails. The multi-use trails are open to hikers, mountain bikers and equestrians.

For a listing of city parks and trails, visit the Parks and Open Space page on the city of Morgan Hill's website.

Valley Water has lowered the water levels at Anderson Reservoir to 3 percent capacity in accordance to the FERC directive. This allows for the start of construction on the 1,700-foot long tunnel, up to 24-feet in diameter, on the left side of the dam looking towards the reservoir. The new tunnel will allow Valley Water to increase the amount of water that can be released by five times during an emergency. Construction is scheduled to begin summer 2021 and run through December 2023.