CITY COUNCIL STAFF REPORT
MEETING DATE: January 25, 2017
PREPARED BY: Karl Bjarke, Engineering and Utilities
APPROVED BY: City Manager
Title
ANDERSON DAM SEISMIC RETROFIT UPDATE
END
RECOMMENDATION(S)
RECOMMENDATION
Receive report from Santa Clara Valley Water District representative on status of the Anderson Dam Seismic Retrofit project.
BODY
COUNCIL PRIORITIES, GOALS & STRATEGIES:
Ongoing Priorities
Enhancing public safety
Protecting the environment
Preserving and cultivating public trust
2016 Focus Areas
Planning Our Community
Developing Our Community
Participate in Regional Issues
REPORT NARRATIVE:
Anderson Dam is located in the foothills east of Morgan Hill and contains the largest water storage reservoir in the Santa Clara Valley Water District (SCVWD) inventory. SCVWD intends to re-construct the dam to bring it up to current state seismic standards. In 2011, a consultant hired by the SCVWD performed a seismic study of the dam, which indicated that the material at the base and foundation of the dam embankment would weaken due to liquefaction during what is estimated to be the maximum credible earthquake (7.25 magnitude quake) on the Calaveras Fault. Such a quake and the subsequent liquefaction could significantly deform the dam embankment, risking an uncontrolled release from Anderson Reservoir.
The SCVWD initiated the design of the retrofit project 2012. Geotechnical studies during the design have exposed more of a fault risk than originally anticipated and in June of 2016 District staff informed the SCVWD Board of Directors that the design would have to accommodate a more extensive retrofit. District staff presented to the Board a revised schedule and scope for the project at their December 13, 2016 meeting. The purpose of this presentation by District staff to the City Council is to update the Council and the community on the status of the project.
It should be pointed out that the SCVWD is currently operating the dam and reservoir under strict rules issued by the State Division of Safety of Dams (DSOD) due to the known seismic risk. Among those rules is that the reservoir volume not exceed approximately 2/3 of ultimate capacity. This is accomplished by not allowing the surface elevation of the water to rise higher than 45' below the crest of the dam.
COMMUNITY ENGAGEMENT: Involve
The SCVWD has held several community meetings since the design of the retrofit began in 2012. These community meetings will continue throughout the design and construction of the project
ALTERNATIVE ACTIONS:
This is an information only item.
PRIOR CITY COUNCIL AND COMMISSION ACTIONS:
N/A
FISCAL AND RESOURCE IMPACT:
N/A
CEQA (California Environmental Quality Act):
Not a Project
LINKS/ATTACHMENTS:
None