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Federal Energy Regulatory Commission




 
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Anderson Dam


FERC issued a dam safety directive on February 20, 2020, requiring Santa Clara Valley Water District (SCVWD) to immediately lower the reservoir restriction to elevation 565.0 (the reservoir is currently below this elevation, so no immediate action is required by SCVWD). Further, we directed SCVWD to begin lowering the reservoir to elevation 488.0 (Deadpool) on October 1, 2020. This will allow Valley Water time to find alternative emergency water supply in addition to engaging in environmental consultation over the next 7 months.

Additionally, we asked for a plan and schedule within 30 days from the issuance of the directive for the design and construction of a new Low-Level Outlet structure. SCVWD indicated that implementing this project first would help to mitigate some risk, and we agree.

Why Now?

  • New information provided by SCVWD in the November 1, 2019 submittal shows the project features are more vulnerable in a 100-year earthquake than previously understood.
  • There is no guarantee for the current scheduled dam rehabilitation. The reservoir restriction has already been in place almost 10 years and SCVWD’s estimate is that construction could start in 2022.
  • The risk at this project to downstream life and property is extreme. A catastrophic dam failure could potentially affect tens of thousands of people. Decisions must be made with public safety being the paramount factor.

Why Full Drawdown?

  • With the current small outlet capacity, the project can’t keep the reservoir from rising rapidly during periods of heavy precipitation such as occurred in 2017. If an earthquake occurs with a high reservoir level, the dam could sustain serious damage and potentially fail.
  • After identifying the greater vulnerability to earthquakes, SCVWD has not proposed any alternative lower reservoir restriction over the past three months. There is no “safe” reservoir level until the dam is fully remediated. Risks remain to the downstream population even with a fully drained reservoir. But a full drawdown reduces the risk as much as possible with the current condition of the dam.
  • Damage to any structures from an earthquake is much more critical with the reservoir elevated. Therefore, with a lowered reservoir, there is additional time to address any damage before impacts begin to occur downstream.

Impacts from Drawdown

  • Emergency Water supply---SCVWD must find alternate sources. SCVWD would need to have worked through this issue anyway due to the reservoir needing a full drawdown for three years during the rebuild. SCVWD must now expedite work on addressing this now.
  • Environmental—All parties (SCVWD, FERC, National Marine Fisheries Service, United States Fish and Wildlife Service, United States Army Corps of Engineers, United States Environmental Protection Agency, state and local agencies) will be working to mitigate potential environmental impacts between now and October. Once again, these environmental issues would need to be addressed in the future as the reservoir will be drained during the rebuild.