How Climate Change Could Challenge California's Dam Infrastructure

As climate change continues to intensify, California’s dam infrastructure could be put to the test.

Dam safety has always been a high-stakes operation — when the St. Francis dam gave way in 1928, over 450 people died as billions of gallons of water crashed down the San Francisquito Canyon. More recently, In 2017, Oroville Dam in Butte County was at risk of failure, and 180,000 people were evacuated.

Karla Nemeth, the director of California’s Department of Water Resources (DWR), which includes the state's Division of Dam Safety, said that each year the DWR inspects the 1,200 dams within its jurisdiction, and she told LAist's radio news program "AirTalk" that with California’s historic rainfall levels last winter, this year’s inspection provided an opportunity to understand how the state’s dams perform when full, and what potential repairs and improvement might be needed to reinforce these critical piece of infrastructure as our climate becomes hotter and wetter.

High-capacity design

Dams are typically designed to withstand much more severe storms than we typically see, according to David Gutierrez, the vice president of engineering and consulting firm GEI Consultants. Gutierrez said that California has typically seen storms whose severity might have a 1/100 or 1/200 chance of occurring — while dams are designed to withstand storms with a 1/10,000 chance, or less, of occurring.

Gutierrez, who previously worked for California’s Division of Dam Safety, said that it extremely important that dams do not overtop — or release water uncontrollably over parts of the dam that are not designed to pass flow — since that could lead to erosion of the dam.

But weighing the probability of these risks is not always straightforward. JT Raeger, an earth scientist with NASA’s Jet Propulsion Laboratory, said that climate change is causing the probabilities of various storm levels to shift, and that the statistical distribution of these weather events could change in unpredictable ways over the next decades.

Changing seasonal patterns

As a result, Raeger said, the seasonality of our water events could change — which could pose an issue, as our infrastructure is built around certain seasonal patterns. As temperatures rise, snow will melt faster and earlier in the season, causing warmer springs and winters.

This April, the snowpack from the Sierra Nevadas would have been enough to cover the entire state of California with five inches of water, according to Raeger.

“With earlier snowmelt, that means there's a cascade of consequences. That means the reservoirs are going to fill earlier in the year. And then that water is going to be used or led out of those reservoirs earlier in the year,” Raeger said.

The question, the, Raeger said, is whether the reservoir can be managed in such a way that the snowmelt and stores water can get the state through the entire summer.

The key, Gutierrez said, is maintaining the infrastructure well. One safety measure proposal has been lowering the spillways, or the part of the dam where the water actually flows. That would lower the risk of water approaching the top, and could be an excellent tool for preventing flooding of the communities that reside downstream, Gutierrez said.

Though Gutierrez said that California has not yet seen storms at the level that would threaten the dam’s safety allowance, understanding the changing climate and its effects on the water system will be key for both dam safety and prevention of flooding.

“As [dam engineer], our job is to actually understand what that risk is,” Gutierrez said. “There's always going to be risks, you can't eliminate them.”

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