Title
Receive an Update on the Nacimiento Dam Spillway Plunge Pool Erosion Protection Project.
Report
SUMMARY/DISCUSSION:
The Nacimiento Dam Spillway Plunge Pool Erosion Protection Project is a dam safety initiative to address ongoing erosion concerns caused by high velocity spillway flows entering the plunge pool. Past spill events have eroded the left and right banks, displaced riprap, and exposed weak underlying rock formations. Recent hydraulic modeling, a geotechnical investigation and report, and the 30% design have been completed by AECOM Technical Services, to construct a roller compacted concrete (RCC) erosion protection system to ensure spillway and dam safety during large flood events, including the Probable Maximum Flood (PMF).
The Agency contracted with GEI Consultants in September 2026 to perform environmental consulting services. The project kickoff meeting will be held in early October, and the activities will closely align with the design work. Environmental permitting and regulatory coordination with DSOD, FERC, RWQCB, CDFW, and the U.S. Army Corps of Engineers will continue as the design advances.
The Spillway Plunge Pool Erosion Protection Project is on schedule. Key milestones include:
Completed Milestones
· Topographic & bathymetric surveys: Jan 2024
· Geotechnical investigations & borings: Nov 2024 - Jul 2025
· Alternatives hydraulic modeling: 2025 - Feb 2026
· Selection of preferred alternative (Alt.?1): Feb 19, 2026
· 30% Design Report completed: Aug 28, 2026
· 30% Design Report Submission to DSOD for review: Sept 14, 2026
Upcoming Milestones
· Begin 60% design development: Nov 2026
· Complete 60% design package: Jan 2027
· Regulatory review of 60% design: Mar - May 2027
· Complete 90% design package: Jul 2027
· Final design completion: Nov 2027
· Bid package preparation: Feb - Mar 2028
· Advertise for construction bids: Mar 2028
· Issue Notice to Proceed: Jun 2028
Construction is subject to permitting, funding, and contractor proc...
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