Climate change raises the risk of more dam failures

The dam that failed in central Michigan on Tuesday gave way for the same reason most do: It was overwhelmed by water. Almost 5 inches of rain fell in the area in the previous two days, after earlier storms had saturated the ground and swollen the Tittabawassee River, which the dam held back.

No one can say yet whether the intense rainfall that preceded this disaster was made worse by climate change. But global warming is already causing some regions to become wetter, and increasing the frequency of extreme storms, according to the latest National Climate Assessment. The trends are expected to continue as the world gets even warmer.

That puts more of the nation’s 91,500 dams at risk of failing, engineers and dam safety experts said.

“We should expect more of these down the road,” said Amir AghaKouchak, a professor of civil engineering at the University of California, Irvine. “It’s unfortunate but this is what the trend is going to be.”

Overall, he and others say, dams in the United States and elsewhere are unprepared for the changes coming in a warming world.

The dam that failed Tuesday, forcing the evacuation of about 40,000 people in and around Midland, Michigan, and threatening a chemical complex and toxic waste cleanup site, was designed a century ago, long before climate change was a concern.

The dam, at Edenville Twp. about 30 miles upstream from Midland, had severe design problems: It had been cited for having spillways that were inadequate to handle a maximum flood, whether affected by climate change or not. (A second dam at Sanford, 10 miles downstream, was overrun by the arriving floodwaters but did not collapse.)

But the Edenville Dam was hardly alone in being outdated, with design or maintenance deficiencies or other problems that might make it unsafe. The American Society of Civil Engineers, in its latest report card on infrastructure in 2017, gave the nation’s dams a “D” grade.

The average age of dams in the United States is nearly 60. And nationwide, about 15,500 are classified as having a high hazard potential; in Michigan, more than 170 dams are in that category, including the Edenville Dam. Repairing and upgrading high-hazard dams alone could cost tens of billions of dollars.

Since the mid-19th century there has been an average of about 10 dam failures a year in the United States, said Martin W. McCann Jr., a civil engineer who directs the National Performance of Dams Program at Stanford University. More than 90% of failed dams are less than about 50 feet high. (Edenville was 54 feet tall.)

Rivers and reservoirs swollen by rainfall are the cause of most of the failures. “It’s not a new thing per se,” McCann said.

But some recent dam episodes have been shown to have a climate change link. In February 2017, at Oroville Dam in California, the tallest in the nation, heavy mountain runoff into the reservoir led to the near-failure of an emergency spillway and severe damage to the main spillway.