Anderson Reservoir is the largest of the ten water district reservoirs and provides a reliable supply of water to Santa Clara County. It has a total storage capacity of 89,073 acre-feet (one acre-foot is 325,851 gallons of water, enough to serve two households of five for one year). Anderson Dam and Reservoir was built in the 1950s and named after the key founder and first president of the water district, Leroy Anderson. A long, deep natural gorge located three miles east of U.S. 101 in Morgan Hill provided a suitable dam site.
Currently, a storage restriction of about 45 feet below the dam crest has been put in place to protect the public with a reduced storage capacity of 61,810 acre-feet. Water district staff and the regulatory agencies (California Division of Safety of Dams and the Federal Energy Regulatory Commission) have approved the restriction and believe that this would prevent the uncontrolled release of water in case of a failure after a major earthquake.
Findings of a seismic stability evaluation performed in 2007 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 pipes and intake structure. The water district has initiated a capital project, the Anderson Dam Seismic Retrofit Project (ADSRP), to complete the planning, design and construction of the seismic retrofit of the dam.
Progress of the Anderson Dam Seismic Retrofit Project work
The water district initiated the Anderson Dam Seismic Retrofit Project in 2012. In addition to seismically retrofitting the dam embankment, the planning phase of the project identified the need to:
• Replace the intake structure in the reservoir and the existing outlet pipe that runs below the dam
• Increase the wall height of the emergency concrete spillway
• Increase the height of the dam crest to provide more freeboard
This project is currently in the design phase. Geotechnical and geologic investigations have been performed in many areas around the dam over the past several years as part of the necessary data collection to prepare the design plans for the embankment retrofit and to complete the design of the additional project elements.
The water district is working very closely with the State’s Division of Safety of Dams and the Federal Energy Regulatory Commission. Both agencies have jurisdictional authority for this dam and reservoir, and the water district must obtain their review and approval for all design plans for the project. Environmental documents must also be prepared to comply with federal and state regulations, and permits must be obtained from several regulatory agencies for water diversion activities during construction including dewatering of the reservoir. The current plan for start of project construction is spring 2018.
Boating and Recreational Activities
For boating and recreational activities, contact the Santa Clara County Park at 408-355-2200 or www.parkhere.org. To ensure that the county has enough drinking water during the drought, the water district has been pumping water from San Luis Reservoir into Anderson Reservoir since February until June 2014, which raised the water level for recreational activities, but has suspended the pumping until further notice.
Answers to most commonly asked questions about the project can be found in the following link:
Anderson Dam Seismic Stability Study completed
In July 2011, the Santa Clara Valley Water District completed a seismic stability evaluation of Anderson Dam. The evaluation found that the dam is subject to significant damage if a large earthquake were to occur close to the dam.
A storage restriction of 25.5 feet below the spillway has been put in place to protect public safety. The dam’s two regulatory agencies, the California Division of Safety of Dams and the Federal Energy Regulatory Commission approved the restriction. The restriction will allow the dam to fill to 67 percent of its full storage capacity. Staff believes that this will prevent the uncontrolled release of water after a major earthquake.
The water district has initiated a capital project, the Anderson Dam Seismic Retrofit Project, to complete the planning, design and construction of a seismic retrofit by the end of 2018. The operating restriction will remain in place until the project is completed.
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