The Daily

The Sunday Read: ‘The Trillion- Gallon Question’

Sun Jul 23 2023

Oraville DamCalifornia damsArc Storm scenarioDam safetyFlood controlHistorical floodsSeven Oaks DamClimate change

Description

This comprehensive summary explores the crisis faced by Oraville Dam in Northern California in 2017 due to heavy rain causing its concrete spillway to disintegrate. It delves into the risks faced by California's dams, the dismissive response to the Arc Storm scenario predicting severe flooding, and the challenges in assessing dam weaknesses. The summary also covers the response to the crisis, future preparations for flood control, historical floods in California, and the vulnerability of Seven Oaks Dam. It concludes with a reflection on the aftermath and hope for the future.

Insights

Outdated flood data and lack of consideration for climate change pose risks to California's dams

California's dams were built to store water from wet years and distribute it during dry periods, but they face risks due to outdated flood data and lack of consideration for climate change.

Arc Storm scenario predicted devastating flooding in California

The Arc Storm scenario predicted severe flooding throughout California, with water depths of up to 20 feet in the Central Valley and economic losses of $725 billion. However, the response from authorities was dismissive and demoralizing.

Dam safety is often overlooked or underestimated

Dam failures can be deadly, but dam safety is often overlooked or underestimated by experts in various fields. Responsibility for dam safety lies with multiple state and federal agencies, creating challenges in coordinating efforts and understanding water distribution across California.

Efforts are being made to improve flood control

Efforts are being made to improve flood control through programs like 'Forecast informed reservoir operations' and the construction of new spillways. However, challenges remain in addressing erosion and catastrophe risks.

Historical floods and future predictions

Research indicates that major floods occur on average every 120 years in California. The next major flood event is predicted to happen soon based on computer models and sediment cores. Historical evidence from the Great Flood of 1862 supports the possibility of catastrophic storms.

Vulnerability of Seven Oaks Dam

Seven Oaks Dam, located on the San Andreas Fault, faces the challenge of being an earth-filled dam instead of concrete. It has experienced more droughts than floods, but heavy rain in 2005 caused a significant rise in the reservoir. The potential failure of Seven Oaks Dam could have devastating consequences for nearby areas.

Changing where and how we live may be necessary

California's vulnerability to floods and the increasing severity of storms due to climate change may require changes in where and how people live to mitigate risks.

Summary

Transcript

The Oraville Dam Crisis

00:00 - 08:06

The tallest dam in the US, located in Oraville, Northern California, faced a crisis in 2017 when heavy rain caused its concrete spillway to disintegrate.
If the dam failed, it could send a wall of water 300 feet high towards the town below.
California's dams were built to store water from wet years and distribute it during dry periods, but they face risks due to outdated flood data and lack of consideration for climate change.
Embankment dams, common in California, are resilient to earthquakes but vulnerable to over-topping.
In 2017, Oraville Dam faced the risk of being over-topped and potentially washing away like a sand castle.
After investigating the risks posed by other dams in California, experts warned that storms could bring unprecedented destruction and devastating flooding if a dam fails.
A story titled 'The Trillion-Galen Question' explores what would happen if California's dams fail.

The Crisis Unfolds

07:44 - 16:06

For days, the group in the conference room tried to figure out how to stop Lake Oraville from rising despite the steady rain.
They put the hobbled spillway back in service, but the stream dove into the hole and threw even more concrete into the air.
Nearly half of the spillway was gone and erosion started creeping toward Orville's emergency spillway.
The emergency spillway had never been used in 50 years since the dam was completed.
On February 10th, DWR decided to reduce outflow on the main spillway, ensuring that the emergency spillway would be used.
At around seven o'clock in the morning on February 11th, water started flowing down the emergency spillway.
The geologists warned about unstable rock below the weir and discussed head cutting and erosion traveling up the hill.
On February 12th, it was judged that within two to four hours, the weir could topple over and cause a wall of water as high as 50 feet rushing toward town.
A mandatory evacuation order was issued at 4.27 pm on February 12th for an evacuation zone determined by Honi with input from Bill Croyal.
As many as 180,000 people had to leave their homes due to evacuation orders.
The sheriff's department evacuated inmates from jail using any available vehicles and saved limited handcuffs for violent prisoners.
After stabilization of dam conditions due to reduced rain and damaged but functioning main spillway, townspeople returned home.
The dam now has two new spillways that have survived major rains without problems, but residents remain traumatized by past events.
The Independent Forensic Report identified faults in DWR's culture and decision-making regarding repairs and design flaws in dams across California.
Dams across America are being reassessed for hidden weaknesses due to increasing extreme weather events.
California's dams are unprepared for extreme weather due to miscalculations and underestimations of flooding risks.
The design of California's infrastructure does not account for climate change and the increasing severity of storms.
Flood data used in dam design is based on a century of unusually placid weather, ignoring the impact of atmospheric rivers that bring massive amounts of water to California.
A study called 'arc storm' predicted devastating flooding in California with economic losses of $725 billion, but the response from authorities was demoralizing.

The Arc Storm Scenario

15:39 - 23:57

The Arc Storm scenario predicted severe flooding throughout California, with water depths of up to 20 feet in the Central Valley and economic losses of $725 billion.
The response from emergency managers, municipal authorities, and dam owners was dismissive and demoralizing.
The authors of the report pointed to the Great Flood of 1862 as evidence that such a catastrophic storm is possible.
Cox, who initiated the project, had a background in journalism and was skilled at bridging disciplines and asking critical questions.
Researchers used historical high watermarks to estimate peak discharge during the flood, which exceeded the median flow of the Mississippi River.
State officials showed little interest or willingness to address the potential risks outlined in the Arc Storm scenario.
Flooding is often overlooked compared to more dramatic disasters like earthquakes, but it exposes human flaws and vulnerabilities.
The Department of Water Resources (DWR) abruptly ended their involvement in the Arc Storm project for political reasons.
Dam failures can be deadly, but dam safety is often overlooked or underestimated by experts in various fields.
Responsibility for dam safety lies with multiple state and federal agencies, creating challenges in coordinating efforts and understanding water distribution across California.

Assessing Dam Weaknesses

23:30 - 30:35

For any dam receiving federal funding, the Army Corps of Engineers plays a role.
The Corps helps write the water control manual for each dam, which dictates when to hold on to water and when to release it.
Folsom Dam came within six hours of overtopping in 1986, and something similar happened in 2017.
There were significant risks of dams being over-topped in other locations as well.
A project called ArcStorm 2.0 aims to examine how a warmer climate would strengthen atmospheric rivers and its impact on flood control in California.
A paper predicted a supercharged storm sequence with high odds of occurring in the next 40 years.
Preliminary analysis by the Army Corps showed astounding results for six major reservoirs during this storm sequence.
Emergency spillways of Auravil Dam and Don Pedro Dam would be tested, potentially causing floods beyond previous levels.
Bryant Dam and New Melonus Dam are likely to overtop, leading to unprecedented destruction if projections are correct.
The Army Corps stressed that the model is theoretical and not meant to demonstrate real consequences.

The Response and Future Preparations

30:11 - 38:13

In one memorable moment, the California Governor's Office of Emergency Services sent a copy of the 'Northern California Catastrophic Flood Response Plan' that downplayed the risks involved.
The flooding models for Arc Storm 2.0 were sent to Cox, who shut down the discussion quickly and asked to lose his email address.
DWR agreed to fund hydrological studies based on Arc Storm 2.0 and admitted that some dams in the state were 'not up to snuff.'
During a meeting at Oraville, DWR representatives discussed reforms and improvements made after 2017, including independent audits and risk assessments.
A tour of Oraville's new spillways revealed changes made since 2017, but questions about erosion and catastrophe remained unanswered.
Efforts are being made to improve flood control through programs like 'Forecast informed reservoir operations' and the construction of new spillways.
The Ark spillway for atmospheric river control could have mitigated damage during past floods in Yuba River.

Historical Floods and Future Predictions

37:46 - 46:06

A study commissioned by Yuba suggests that the ark spillway could have lowered the water level in the Yuba River during the floods of 1997, potentially preventing levee failures and home destruction.
Folsom Dam opened an auxiliary spillway to release water earlier and increase capacity for extreme floods, but it came with a high price tag of $900 million.
Research conducted by scientists at Indiana University and the University of Michigan using sediment core samples indicates that major floods occur on average every 120 years in California.
The next major flood event is predicted to happen soon based on computer models and sediment cores.
The Agwamansa Pioneer Cemetery in Colton, California holds evidence of a flood in 1862, which can help determine the flow rate of the Santa Ana River during that time.
Seven Oaks Dam was built to withstand a probable maximum flood inflow of 180,000 cubic feet per second, but has experienced more droughts than floods since its construction.

The Vulnerability of Seven Oaks Dam

45:40 - 53:34

The San Andreas Fault runs through the dam, making it necessary for Seven Oaks to be an earth-filled dam instead of concrete.
Seven Oaks had a quiet 20 years with more droughts than floods.
In 2005, heavy rain caused the reservoir to rise 120 feet overnight.
The lead engineer for the dam, Robert Kwan, doesn't think the spillway will be used in his lifetime.
If 300,000 cubic feet per second drained into the reservoir, it would overflow both the spillway and the top of the dam.
The Army Corps denies that such a sustained and extreme flow is possible at Seven Oaks.
The inundation map shows that if the dam were to fail, many areas including fire stations, police stations, schools, and houses would be affected.
If Prado Dam also failed, all of Anaheim would be added to the inundation zone before reaching the sea.
Changing where and how we live may be necessary due to climate change and California's vulnerability to floods.

The Aftermath and Hope

53:20 - 53:34

The storms are intense, but after each one passes, the land around them, done and brittle and dusty for years now, blooms with a million newborn flowers and endless gold-green grasses.