50 Facts About Oroville Dam

Last updated on November 28th, 2022

The Oroville Dam is a feat of engineering. Its massive scale remains unmatched by other dams in the United States over half a century after its completion. This vital structure improved the lives of Californians by providing water, generating power, and averting disasters. It also sheds light on problems besetting the dam industry, effectively turning a crisis into an opportunity for change. Read on to learn 50 Oroville Dam facts:

The Oroville Dam at a Glance

1. What’s in a Name?

The Gold Rush started here. Near the dam was a town called “Ophir.” It was among the first gold mining sites in California. In 1854, the name changed to “Oroville,” which means “City of Gold.”

2. Claim to Fame

It’s a gigantic structure! The Oroville Dam stands as the tallest dam in the US. It rises 770 feet above the ground – significantly higher than the Hoover Dam’s height of 726.4 feet. It is also much longer at 6,920 feet versus 1,244 feet.

3. Post-war Growth

What do you do when farms turn into urban centers? After World War II, California experienced a rapid economic boom. The agriculture-focused water system proved insufficient for the developing state, leading to frequent water shortages. They needed a solution – fast!

Aerial photo of Lake Oroville, Oroville Dam, the spillway, and the Feather River
Aerial photo of Lake Oroville, Oroville Dam, the spillway, and the Feather River. Facts about Oroville Dam. Image via Wikipedia.org

4. Lighting Up the Future

California also craved energy. The population explosion meant more homes and businesses. The state had to produce more power, and a new hydroelectric power plant was on the table.

5. Solving the Shortage

Engineer Arthur Edmonston had an idea: build a dam on the Feather River. It would create a reservoir, prevent floods, and generate electricity. He sent his proposal to congress for review.

6. Push and Pull

Strong opposition delayed the project. It couldn’t get enough votes! In the following years, devastating floods changed the mind of critics. An emergency flood-control bill ensured sufficient funding.

7. Dam Ownership

Governor Goodwin Knight also had enough of the floods. In 1956, he created the California Department of Water Resources to take charge. It owns and operates the Oroville Dam.

8. Feather River

The dam impounds the 73-mile-long Feather River. In the 1800s, the river was the center of gold mining. Now it provides clean water to Southern and Central California.

9. Lake Oroville

Would you like a bit of rest? Come to Lake Oroville! It is a popular recreation area where fishing, boating, and camping are available. It formed after the dam rose, becoming the second-largest reservoir in the state.

The Thermalito Power Canal in Oroville, Butte County, North California
The Thermalito Power Canal in Oroville, Butte County, North California. Facts about Oroville Dam. Photo © Andreistanescu

10. Part of a Whole

The Oroville Dam can’t do it alone. It’s part of the massive California State Water Project that includes 21 dams and over 700 miles of canals, tunnels, and pipelines – all intended to manage this precious resource.

Design and Preparations

11. Dam Type

Whereas the Hoover Dam rose out of concrete blocks, this one maximized materials from the ground. It is a zoned earth-fill dam composed of compacted soil and rock. The core is dense and impervious, while the surface is semi-impervious and waterproof.

12. Dam Designer and Builder

Engineer Donald Thayer had two tasks: make the design and head the construction project. Meanwhile, the joint venture Oro Dam Constructors, Inc. won the primary work contract.

13. Construction Timeline

Groundbreaking happened in 1957. The first step was to relocate the tracks of the Western Pacific Railroad on the Feather River Canyon. However, construction did not begin until 1961. It opened in 1968.

14. Diversion Tunnels

Water had to go! Workers made two diversion channels to channel the water out of the dam site. Each was 4,440 ft long and 35 ft wide, lined with concrete for strength.

15. Protective Cofferdam

Staying safe and dry is the top priority. A concrete cofferdam 128 ft high rose around the site to protect it from floods. It now forms the impervious core of the Oroville Dam.

16. Rail Transport

Rail is cheap and efficient. Workers installed 11 miles of rail tracks to transport materials. Every hour, 120 train cars with soil and rock passed through – most coming from mining debris left by the 1800s California Gold Rush.


17. Averting Disasters

Ready or not, challenges will come. In 1964, the unfinished dam dealt with heavy inflows after days of rain. It almost overflowed, but the dam somehow reduced peak flow by 40% and kept everyone safe. Not bad for a rookie.

18. Dam Tough!

Don’t worry about earthquakes. They designed the Oroville to last, even under the strongest earthquake in the region. Hundreds of instruments measure its vital signs to provide reassurance.

19. The Final Touches

All the hard work paid off. Workers completed the embankment of the dam on October 6, 1967. The last push required 155 million tons of material, sent via 40,000 train trips.

20. Dam Dedication

The Oroville Dam is a crown jewel of California. Naturally, its dedication ceremony in 1968 drew notable figures like Gov. Ronald Reagan and Chief Justice Earl Warren. Almost 50,000 people attended the weeklong festivities.

Spillway Facts

21. Expect the Worst, Hope for the Best

Pessimism is an engineer’s best friend. They have to anticipate the worst thing that could happen and find ways for the project to handle it. In the case of the Oroville Dam, they calculated the so-called “Probable Maximum Flood” – the most rain that can fall from the sky.

22. Spillway Dimensions

The weather model showed them what to do. Designers included a service spillway 180 feet wide and 3,000 feet long to guide excess water down the river, preventing dam overflows from most storms.

Close View of a Dam Spillway
Close view of a dam spillway on a Rainy Day (representational image). Facts about Oroville Dam. Photo © Alpegor

23. Visualizing the Volume

What goes in must come out – pronto! As rain intensifies, the main spillway must release water to the Feather River. The max rate is 300,000 cubic feet per second – enough to fill an Olympic-sized swimming pool every two seconds.

24. Shooting for the Moon

If the spillway outflow passed through an ordinary garden hose, it could achieve 15% of the speed of light. That could shoot the water up to the moon within 9 seconds!

25. Unicorn Events

An emergency spillway takes care of extreme events. It increases outflow capacity if the main spillway is inadequate or out of service. In the Oroville Dam, the emergency spillway is a simple concrete weir.

26. A Fatal Flaw

Warning signs were everywhere. In 2005, environmental groups found a flaw: the emergency spillway leans on the exposed earth. It can erode if water overflows, causing the concrete weir to collapse.

27. Ignorance is Bliss

A quick solution? Cover the side of the emergency spillway with hard concrete. The groups brought this up with the Federal Energy Regulatory Commission. However, officials said it was costly and unnecessary. They would learn their lesson the hard way.

28. Early Signs of Trouble

In 2013, civil engineers found cracks in the main spillway. In an interview, they dismissed it as a typical incident frequently caused by faulty drainage systems. They patched things up and swept them under the rug.

29. Questionable Inspection

Regular checks aren’t enough. Engineers must perform thorough inspections as close as possible to the action. Unfortunately, the team was happy to inspect from a distance in 2015.

30. Improved Dam Safety

Darkness can always turn to light. Later, investigations revealed all the lapses. These served as a wake-up call for dam safety regulators. It improved industry practices in California and the rest of the United States.

The Oroville Dam Crisis

31. The Wettest Winter

In late 2016, Northern California experienced its heaviest winter rainfall in over a century. It continued throughout the season, testing the limits of the Oroville Dam in early 2017.

32. Main Spillway Damage

In January, the spillway opened to protect the dam. Engineers discovered damage to the spillway foundation the following month, but rising water prevented repairs. The worsening situation forced the operator to press the “emergency button.”

33. Unintended Consequences

It was time for Plan B: the untested emergency spillway. The mounting pressure left them with no choice. Water overflowed to the hillside as designed, improving the situation. However, it also eroded the soil supporting the spillway. The predictions of environmentalists were coming true.

34. Mandatory Evacuation

Erosion had to stop. Otherwise, the wall may collapse, triggering flash floods in low-lying areas. On February 12, the government ordered residents to evacuate as a precautionary measure. It affected almost two hundred thousand people.

35. Return and Relief

Both spillways were in danger, but the second one was becoming more of a headache. They increased flow to the damaged main spillway to reduce erosion on the other side. It worked! The mandatory evacuation ceased on February 14.

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