Key California reservoir to be drained due to earthquake risk

[PeteS in CA]

https://www.bakersfield.com/ap/national/key-california-reservoir-to-be-drained-due-to-earthquake-risk/article_24654552-0272-5057-80bf-033b1d3f7099.html

Key California reservoir to be drained due to earthquake risk

SAN JOSE, Calif. — In a dramatic decision that could significantly impact Silicon Valley’s water supply, federal dam regulators have ordered Anderson Reservoir, the largest reservoir in Santa Clara County, to be completely drained starting Oct. 1.

The 240-foot earthen dam, built in 1950 and located east of Highway 101 between Morgan Hill and San Jose, poses too great of a risk of collapse during a major earthquake, the Federal Energy Regulatory Commission, which regulates dams, has concluded.
...
Anderson Reservoir is owned by the Santa Clara Valley Water District, a government agency based in San Jose. When full, it holds 89,278 acre feet of water — more than all other nine dams operated by the Santa Clara Valley Water District combined.
...
“With these new requirements, we expect to see an impact to groundwater basins that are replenished with water released from Anderson Reservoir, including South County and southern San Jose,” Camacho said. “Staff is already exploring other sources of water that will have to come from outside of the county. While residents have done an excellent job of conserving water since 2013, another drought during this time frame could require everyone to significantly decrease their water use.”

Camacho also said that draining the reservoir starting in seven months is likely to kill wildlife downstream in Coyote Creek, including endangered steel head trout, amphibians and reptiles. Coyote Creek flows from the dam through downtown San Jose to San Francisco Bay.

I suppose the loss of this water for a few years (repair time and refill time) is less awful than the flood that would result from a dam collapse, but this has the possibility of being painful.

[Elderberry]

https://www.valleywater.org/anderson-dam-project

Schedule

Start FY 2014 / Finish FY 2028

Progress of the Anderson Dam Seismic Retrofit Project work

Following the seismic stability evaluation, Valley Water initiated the Anderson Dam Seismic Retrofit Project in 2012 as a permanent fix to the risks identified by the seismic study. In addition to seismically retrofitting the dam embankment, the planning phase of the project identified the need to:

    Replace the existing outlet pipe that runs below the dam to improve capacity and reliability

    Increase the wall height of the concrete spillway to approximately 9 ft and the height of the dam crest to 7 ft to provide more freeboard required to pass the revised Probable Maximum Flood (PMF)

This project is currently in the design phase. Geotechnical and geologic investigations have been performed in many areas around the dam to collect data for the retrofit project and to complete the design of the additional project elements. As part of this investigation previously unidentified seismic deficiencies were discovered:

    The upstream embankment shell materials are also susceptible to liquefaction during a MCE. Liquefaction describes a phenomenon whereby a soil loses strength in response to earthquake shaking, causing it to behave like a liquid.

    The existing Transition Zones (special material placed between the clay core and the rockfill shells to protect the core) were determined to be inadequate to prevent failure due to possible fault offset leading to seepage and erosion through the bedrock foundation beneath Anderson Dam during a major earthquake

These findings have resulted in modifications to the reservoir restriction and the extent of necessary retrofit work to stabilize the dam. The maximum water surface elevation in the reservoir was restricted an additional 10 feet in January 2017 to accommodate greater potential deformation due to liquefaction of the upstream shell. The retrofit project which was originally planned to include large upstream and downstream buttresses has been modified to a nearly complete replacement of Anderson Dam in place. This replacement will ensure the post-project facility has removed all liquefiable material in and beneath the embankments and will be built to the most modern design standards and with rigorous quality control. Finally, a new high level outlet will also be constructed to allow rapid drawdown of the upper portion of the reservoir in case of an emergency.

[PeteS in CA]

It looks like there was no thread about it back in early 2017, but the flooding in parts of south San Jose in that time frame was on Coyote Creek, and was due to the heavy rainfall at that time that forced releasing a large amount of water from Anderson reservoir. Parts of Hellyer Park and the Coyote Creek Trail through the park were flooded, as were neighborhoods around and in Coyote Creek and Kelley Parks. Parts of Hellyer Park and the Coyote Creek Trail remained flooded for a couple of months after.

[Elderberry]

I know what that's like. I have a place on the Trinity River just north of Liberty Tx. I think it was 83-84. I was unable to reach my place by vehicle due to the release from the Lake Livingston dam from around November to March. I think it was El Nino dumping so much rain on us. I did boat in once just to take a look at the place. It was fine.

[Cyber Liberty]

https://www.bakersfield.com/ap/national/key-california-reservoir-to-be-drained-due-to-earthquake-risk/article_24654552-0272-5057-80bf-033b1d3f7099.html

Key California reservoir to be drained due to earthquake risk

I suppose the loss of this water for a few years (repair time and refill time) is less awful than the flood that would result from a dam collapse, but this has the possibility of being painful.

Who said anything about "repair and refill?"  The Environmental Wackos have been itching to breach dams and drain as many reservoirs as they can in Cali.  They will block any project to repair the dam for years and years.

[IsailedawayfromFR]

All of the recent scientific and engineering findings were undoubtedly performed prior to the dam being built to start with.

This is not an exercise based upon science or engineering.

It is purely political.

[PeteS in CA]

All of the recent scientific and engineering findings were undoubtedly performed prior to the dam being built to start with.

This is not an exercise based upon science or engineering.

It is purely political.

The dam was built in 1950 and designed with what was known at the time. Since then faults have been discovered and liquefaction has become much better understood. I do not think this is at all political.

[IsailedawayfromFR]

The dam was built in 1950 and designed with what was known at the time. Since then faults have been discovered and liquefaction has become much better understood. I do not think this is at all political.

I saw no new faults in the writeups I read, just some new soil borings about the base rock.

Prior to dam construction, it is an absolute certainty that numerous soil borings were made to establish the dam's foundation.  That is how dams are properly designed.

So am unsure exactly how much 'new' data is being relied upon and instead just new engineering studies.  @PeteS in CA - do you know?

Also, this appears to be a dam built by a local governmental agency, so I wonder on what authority a federal agency can come in and over-rule the actions of a state and governmental agencies for something that appears wholly within the confines of California?

[sneakypete]

Hmmmm,could they possibly build some sort of pipeline to SF,and use the water to flush the streets of junkies and other turds?

[sneakypete]

   The Environmental Wackos have been itching to breach dams and drain as many reservoirs as they can in Cali.  They will block any project to repair the dam for years and years.

@Cyber Liberty

That IS the nature of that particular beast.