Title
Consider receiving a presentation on the Nacimiento Dam and San Antonio Dam Spillway Condition Assessment. (ADDED VIA ADDENDA)
Report
RECOMMENDATION:
It is recommended that the Monterey County Water Resources Agency Board of Supervisors:
Receive a presentation on the Nacimiento Dam and San Antonio Dam Spillway Condition Assessment.
SUMMARY:
This presentation will provide a description of Nacimiento and San Antonio Dam hazard classification, construction and operational history of both spillways, spillway condition assessment report conclusions and recommendations, and spillway work planned for the present fiscal year.
DISCUSSION:
Monterey County Water Resources Agency (MCWRA) owns and operates Nacimiento and San Antonio Dams. Nacimiento Dam is regulated with regard to dam safety matters by California Department of Water Resources, Division of Safety of Dams (DSOD), and the Federal Energy Regulatory Commission (FERC) because a hydroelectric plant is located at the dam. San Antonio Dam is regulated with regard to dam safety matters by DSOD. Based on downstream potential for loss of life and infrastructure in the event of dam failure, DSOD classifies Nacimiento and San Antonio Dams as “Extremely High Hazard” and FERC classifies Nacimiento Dam as “High Hazard.” DSOD and FERC have authority to restrict water storage at regulated dams if unsafe conditions occur.
After the 2017 Oroville Dam spillway incident, DSOD and FERC directed all high hazard (and higher) classification dam owners to complete focused spillway inspections and condition assessment reports. MCWRA hired GEI Consultants, Inc., a firm with extensive dam sector experience, to inspect and prepare condition assessment reports for both spillways. Inspections were completed in July 2017. The condition assessment report for San Antonio Dam spillway was completed in May 2018 and submitted to DSOD on May 23, 2018. The condition assessment report for Nacimiento Dam spillway was completed in June 2018 and submitted to DSOD and FERC on July 6, 2018.
GEI Consultants’ overall conclusion for Nacimiento Dam spillway is that it is “judged to be in good operable order at the time of inspection (July 2017).” Additional investigation and maintenance work at the spillway are needed, and a work plan was submitted to DSOD and FERC on July 31, 2018 requesting approval to proceed. DSOD has provided notice to proceed with the work plan; FERC work plan approval has not yet been received. DSOD and FERC have not yet responded to the Nacimiento Dam spillway condition assessment report.
GEI Consultants’ overall conclusion for San Antonio Dam spillway is that it “is in generally poor to fair operable condition.” DSOD has not yet officially responded to the San Antonio Dam spillway condition assessment report, however has indicated verbally that total or near-total replacement of the spillway will be the likely direction provided.
This presentation to the MCWRA Board of Supervisors will provide a description of dam hazard classification, construction and operational history of both spillways, spillway condition assessment report conclusions and recommendations, and spillway work planned for the present fiscal year.
OTHER AGENCY INVOLVEMENT:
The California Department of Water Resources, Division of Safety of Dams (DSOD) and the Federal Energy Regulatory Commission (FERC) ordered the condition assessments, review the reports, and provide concurrence with or rejection of report recommendations, and/or additional directions.
FINANCING:
The spillway condition assessment report contract amount was $126,611. Estimated cost of spillway work planned for this fiscal year is approximately $250,000.
Prepared by: Chris Moss, Senior Water Resources Engineer, (831) 755-4860
Approved by: __________________________________________________
David E. Chardavoyne, General Manager, (831) 755-4860
Attachments:
Presentation slides