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Oroville Dam Disaster - What Really Happened?

Oroville Dam Disaster - What Really Happened?

There is a lot of conjecture relating to the disaster at the Oroville Dam recently so Rafting Magazine reached out to American Whitewater to help get the facts straight on what happened and what the implications are for the future of the hydro project.

Oroville Dam Main Spillway Breach.jpg

The first and most obvious problem was the development of a massive breach in the main spillway, compounded by a massive inflow of water from the Feather River watershed. The California Data Exchange Center reported a peak inflow to Lake Oroville at over 155,000 CFS.

The good news is that we think we have it under control.
— DWR Spokesman Doug Carlson

California Department of Water Resources (DWR) reduced the total outflow of the main spillway to 55,000 cfs causing the reservoir to fill up at an alarming rate eventually resulting in a discharge of 12,000 cfs over the emergency spillway.

Oroville Dam Emergency Spillway Discharge

Using the Emergency Spillway

According to the 2006 Federal Energy Regulatory Commission report on the concerns raised by Friends of the River the Sierra Club, and South Yuba River Citizens League (SYRCL) in 2005 the emergnency spillway was designed for the rarest of flood events. The recent high flow event, although it did result in flooding, was less then significant flood events of 1997, 95, 86, 82, and 76. All of which occurred after the construction of the dam.

The guidelines specify that in a rare flood event, it is acceptable for the emergency spillway to sustain significant damage.
— John Onderdonk, 2006 FERC Report
Oroville Dam 55,000 CFS

The problem that the aging dam faces is that the spillway was designed to 1960s flood control standards which placed the bottom of the spillway gates 50 ft below the crest of the dam. Those 50 feet at the top of a 770ft dam equates to an approximate 21.8 percent margin of error. In essence the dam operators are giving themselves only 2.5 days to come up with a solution if the river flow is 150,000 CFS. For comparison the 1997 flood had a peak inflow to late Oroville of nearly 400,000 CFS. At that flow the DWR would have just over 23 hours to respond to a failure before uncontrolled spilling of water in the hundreds of thousands of CFS over the emergency spillway would occur.

Downstream Impacts

Pollution and sediment discharge – The bottom half of the main spillway has now washed away carrying an undetermined amount of concrete, steel and asphalt debris into the Feather River watershed. This is coupled with the topsoil and vegetation erosion that has taken place resulting in the uncontrolled discharge of possibly thousands of tons of sediment into the river. This has the potential to collapse the fishery system in the waters of the Feather below the dam. It is important to note that with only 12,000 CFS, the amount of erosion in the area of the emergency spillway greatly exceeded the FERC estimates for amounts of erosion in the area.

Emergency Spillway Damage
Erosion of one to 4 feet of soil cover, and debris flow including bushes, and trees would occur during a large release in the emergency spillway.
— John Onderdonk, 2006 FERC Report
PG&E Transmission Line Work Oroville Dam

Hydro Power - The use of the emergency spillway has eroded 2 main PG&E powerlines which carry power from the Oroville Dam powerhouse. These main lines not only supply a large amount of power to northern California, but to the dam itself. Currently PG&E has cut their lower power transmission line. Luckily with all of the backups in place this has not adversely affected residents in northern California; however DWR again stated that they are drawing down spillway flows because of the potential damage to these transmission lines. Severing this transmission line reduces the 819 MW of capacity by roughly 1/3. Additionally the downstream powerhouses have been swamped with silty debris laden water forcing the shutdown and clean-up of these facilities.

Moving Salmon From the Feather River

Fishery and wetland habitat - The Department of Fish and Wildlife to perform an emergency relocation of approximately 4 million baby salmon to auxiliary fish ponds due to the high levels of sediment and turbidity the dam discharged into the Feather River hatchery. This will create a strong negative impact on the fishery for years to come and potentially impact the 2017 fishing season. This in turn will have an impact on not only private anglers, but guide services, the fishing industry, and local tourism business (hotels, campgrounds, grocery stores, fishing supply stores, and restaurants) that serve anglers.

Evacuating Salmon Feather River Hatchery

Displacement of residents – Nearly 200,000 residents were ordered to immediately evacuate with less than 60 minutes notice. This not only strained the resources of emergency services in the area, but it has had a profoundly detrimental impact on businesses. The evacuation and ensuing confusion essentially forced the shutdown of the local economy of effected communities. Emergency shelters were set up, but in the wake of this many families were forced to stay in hotels or alternative accommodations. This detriment to residents is further impacted by the disaster forcing local businesses to temporarily close causing the residents to be put out of work for a short time.

Cost of Prevention

In 2005 Friends of the River, the Sierra Club, and SYRCL lead the way in requesting that FERC require the emergency spillway be armored. Unfortunately as Paul Rogers of the Mercury New reports: “A filing on May 26, 2006, by Thomas Berliner, an attorney for the State Water Contractors, and Douglas Adamson, an attorney for the Metropolitan Water District of Southern California, discounted the risk. It urged FERC to reject the request to require that the emergency spillway be armored, a job that would have cost tens, if not hundreds, of millions of dollars.”

Shoring up the emergency Spillway

Cost to Rebuild

Figures are currently being floated that California taxpayers will be bearing the burden of repair costs spiraling Up to $200 million to fixed the damaged spillway. This includes possible rate hikes to consumers and any bond measures / emergency relief efforts that are sent to help repair the dam. The extensive damage to the infrastructure will also require extensive demolition and redesign of both of the spillway systems.

Potential Impacts

If California experiences another major rain event in the near future and the emergency spillway is again required, it could cause significant damage to facilities that are already in a precarious state.

Crews have been working to shore up the emergency spillway and the primary spillway along with cleaning up the mess of concrete and sediment. Unfortunately if there is a second failure in these temporary emergency measures DWR will only serve to dump more concrete, sediment, and rock into the watershed.

Oroville Dam Emergency Spillway

A failure of the second power transmission line due to erosion will result in serious power issues to the local power grid along with requiring some major overhauls in the transmission lines.

Repeating such disaster with higher flows even has the potential to damage levees and put even more people in jeopardy. If both spillways failed creating a massive uncontrolled discharge of water the full force of the 150,000 CFS flood event would be placed on the down river levee system.

The levees improvement, paid for through local cost share and Proposition 1E funds, provide protection for a once-in-200-year flood. This means the system can handle about 170,000 cubic-feet per second of water.
— Michael Bessette, director of engineering Sutter Butte Flood Control Agency

170,000 CFS is not a far cry from the 150,000 CFS coming into Lake Oroville. Based on SBFCA’s engineering standards an uncontrolled release from the recent event’s peak inflow plus a 12% increase in those flows would easily overtop the levees and put even more residents at risk for property damage and injury. Had the emergency spillway eroded and failed as well this hypothetical situation would quickly turn into reality.

Sediment Filled Discharge

Although prevention of this disaster has been championed by environmental groups in the past, this is exactly the kind of management, oversight, and financial disaster that laws like the California Environmental Quality Act and The Clean water Act sought to avoid. This disaster will surely have far reaching economic consequences for the State of California. Voters in California are continuously convinced that measures like California’s Proposition 1, which directed 7.5 Billion dollars to new water storage proposals rather than investing that money into California’s current infrastructure, is a good investment.  Upgrading and modernizing our current infrastructure would go a long way to prevent ecological and economic disasters like this incident. Unfortunately this whole incident will end up costing at least twice as much to fix it as it would have to perform proper maintenance and upgrades with the American tax payer getting stuck with the bill.


We would like to thank Dave Steindorf of American Whitewater for his contributions and time discussing the issues in this article. For more up to date information please follow American Whitewater on Facebook. All images are courtesy of California Department of Water Resources under public domain copyright.

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