Magazine article Risk Management

Oroville Dam Highlights Infrastructure Risks

Magazine article Risk Management

Oroville Dam Highlights Infrastructure Risks

Article excerpt

The near-collapse of the Oroville Dam in northern California in February could have been catastrophic. Communities as far as 100 miles downstream from the dam were at risk of flooding that could have resulted in $21.8 billion in structural damages, according to Risk Management Solutions. What's more, a bad situation would have been made worse by the fact that many of the properties near the dam were uninsured. Thankfully, this did not happen.

Problems at the Oroville Dam began when the dam's main water channel, or sluice, was damaged after a winter season of record rain and snowfall, following five years of drought. Torrential rainfall caused water levels to rise so quickly that large amounts needed to be released to prevent the dam from rupturing and sending a wall of water to the communities below.

But when the force of the cascading water created a large hole in the main spillway, the emergency spillway was required. This safety backup, however, also nearly failed because the dirt spillway, which had never been fortified by concrete, began to erode, increasing the risk of damage to the dam. In anticipation of a possible disaster, almost 200,000 residents living in the shadow of the dam were temporarily evacuated.

Fortunately, the crisis subsided after the California Department of Water Resources (DWR) was able to repair the main spillway by plugging the hole with large bags of rocks dropped by helicopter.

According to Rep. John Garamendi (D-Calif.), whose constituents include 150,000 of the evacuees, although there were many factors in the dam's near-failure, the situation was made worse by changing weather patterns thought to result from climate change.

Increasingly warmer weather has been melting the snowpack in the mountains and affecting the flow of the rivers that feed the dam. "The biggest reservoir in California--the snowpack--is getting smaller," Garamendi said. The warmer weather also means that precipitation that previously might have been snow that would melt in May or June is now falling as rain. These changes in precipitation alter the volume, movement, and quality of the river water, putting increased pressure on the dam. Adding to the situation is the Pineapple Express--warm storms emanating from the southwestern Pacific Ocean that are now occurring in non-El Nino years.

NEW METHOD FOR MODELING

Changing weather patterns have highlighted inadequacies in the system used to determine how much water is stored and how much is released from the reservoir. These operations are determined by a manual put together by the Army Corps of Engineers, which is responsible for the reservoir's flood management. The system used is based on historic averages of a river's hydrology, but it needs to be changed.

"We're seeing that the operational manual is not pertinent to the new circumstances of climate change," Garamendi said. "We've known this for some time."

Anticipating the need for a change, engineers began a process 10 years ago to develop a new algorithm for the American River, which flows from the Sierra Nevada Mountain Range to the Sacramento River, eventually finding its way to the Oroville Dam. The system uses real-time monitoring from satellite imaging, checking the soil's capacity for water and locating snow. The data is proving useful in anticipating problems, thereby improving flood safety and the storage capacity of the reservoir. "For example, while the historic model may say that, on April 1, the reservoir should be at a certain level based on the amount of snow on the Sierra Nevadas, it may be that warm temperatures cause the snow to melt quickly and therefore maybe we ought to have more flood capacity. …

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