Remedial Alternatives to Address Seismic, Flood, and Reservoir Drawdown Deficiencies at Anderson Dam

Anderson Dam and Reservoir is a major water supply facility located about 18 miles southeast of San Jose, California and is owned and operated by the Santa Clara Valley Water District (District). The dam was completed in 1950 as a zoned, rockfill embankment, has a maximum height of about 240 feet, and retains approximately 90,373 acre-feet of water at its maximum reservoir operating elevation. It is subject to dam safety regulation by both the California Division of Safety of Dams (DSOD) and the Federal Energy Regulatory Commission (FERC).
Between 2008 and 2013, several dam safety deficiencies associated with seismic shaking, fault offset, flood capacity, and emergency drawdown capabilities were identified. As a result of the identification of these safety deficiencies, the Anderson Dam Seismic Retrofit Project (ADSRP) was initiated. The ADSRP consists of planning, design, and construction activities associated with correcting seismic, flood capacity, and reservoir drawdown deficiencies at Anderson Dam. The ADSRP is being conducted by the District in coordination with resource agencies, stakeholders, and the public. Due to public safety concerns (large residential area downstream), the need to utilize the full capacity of the reservoir, and the requirements of DSOD and FERC, the District has established an extremely aggressive target date of December 31, 2018 for the completion of all necessary remedial work to correct the identified deficiencies.
This paper describes the development and assessment of alternatives for the repair of the indentified deficiencies, and the selection of a preferred alternative. Included in this work was the assessment of potential fault offsets for the new outlet works, the performance of a new evaluation for the Probable Maximum Flood, a supplemental drilling investigation to evaluate foundation materials for a downstream buttress, and a risk-based cost and schedule evaluation of the alternatives.