C1: Anderson Dam Seismic Retrofit*

Anderson Dam creates the county’s largest surface water reservoir—Anderson Reservoir— which stores local rainfall runoff and imported water from the Central Valley Project. The reservoir is an important water source for treatment plants and the recharge of the groundwater basin. Besides restoring drinking water supplies, the upgrade also supports compliance with environmental regulations. Valley Water’s regular reservoir releases ensure that downstream habitat has healthy flows and temperatures to sustain wildlife.

A breach of Anderson Dam at full capacity could have catastrophic consequences, including inundation of surrounding land more than 30 miles northwest to San Francisco Bay, and more than 40 miles southeast to Monterey Bay.

In December 2016, the Board was informed by Valley Water staff that findings from the geotechnical and geologic investigations performed during the project’s design phase led to the conclusion that a more extensive dam retrofit than had originally been envisioned would have to be performed. Further, the Board was informed that the more extensive retrofit work would double the previous project’s estimated cost. Valley Water staff presented the Board with a water supply cost-benefit analysis that showed the benefits of the more extensive retrofit project significantly outweighed the cost of not proceeding with the retrofit, which would require Valley Water to purchase additional imported water every year to make up for the loss of long-term storage at Anderson Reservoir. Based upon this information and analysis, the Board directed Valley Water to continue work on this critical infrastructure project.

Anderson Reservoir is the largest of the 10 Valley Water reservoirs and provides a reliable supply of water to Santa Clara County. It has a total storage capacity of approximately 90,000 acre-feet (one acre-foot is 325,851 gallons of water, enough to serve two households of five for one year). Anderson Dam was built in 1950 and named after the key founder and first president of Valley Water, Leroy Anderson. A long, deep natural gorge located three miles east of U.S. 101 in Morgan Hill provided a suitable dam site. 

Findings of the original seismic stability evaluation completed in 2011 on Anderson Dam indicated that the downstream and upstream embankments could become unstable during a very large magnitude earthquake and the rupture of faults underlying the dam may have adverse impact on the outlet pipe and intake structure.

About the Safe, Clean Water and Natural Flood Protection Program

In November 2020, voters in Santa Clara County overwhelmingly approved Measure S, a renewal of Valley Water’s Safe, Clean Water and Natural Flood Protection Program.

The program was first passed by voters in 2000 as the Clean, Safe Creeks and Natural Flood Protection Plan, then again in 2012 as the Safe, Clean Water and Natural Flood Protection Program. The renewal of the Safe, Clean Water Program will continue to provide approximately $47 million annually for local projects that deliver safe, clean water, natural flood protection, and environmental stewardship to all the communities we serve in Santa Clara County.

While evaluating ways to improve the 2012 program, Valley Water gathered feedback from more than 21,000 community members. That helped Valley Water create the six priorities for the renewed Safe, Clean Water Program, which are:

Priority A: Ensure a Safe, Reliable Water Supply

Priority B: Reduce Toxins, Hazards and Contaminants in our Waterways

Priority C: Protect our Water Supply and Dams from Earthquakes and Other Natural Disasters

Priority D: Restore Wildlife Habitat and Provide Open Space

Priority E: Provide Flood Protection to Homes, Businesses, Schools, Streets and Highways

Priority F: Support Public Health and Public Safety for Our Community

Each year, Valley Water prepares a report providing a progress update for each of these program priorities, along with fiscal year accomplishments.

To ensure transparency and accountability to the voters, the ballot measure also created an Independent Monitoring Committee, appointed by the Santa Clara Valley Water District Board of Directors. The Independent Monitoring Committee annually reviews the program’s progress to ensure the outcomes are achieved in a cost-efficient manner and reports its findings to the Board. Additionally, the IMC also reviews each proposed 5-year implementation plan prior to its submittal for Board approval.

In addition, the program requires three independent audits.

View the Safe, Clean Water Program’s annual reports, annual IMC audit reports, and independent audits, including a staff response, on the Valley Water website.