Dams in distress: Partial failure in Minnesota offers a nationwide warning

The partial failure of Minnesota’s 114-year-old Rapidan Dam highlights risks that many communities face as the number of dams in disrepair rises and climate change makes rainfall more frequent and severe.

Before the breach, which led floodwaters to carve away at the bank of the Minnesota River and swallow a waterside home, local leaders in Blue Earth County, Minnesota, had been contemplating whether to tear down the old structure or perform costly long-term repairs. Regulators considered the dam a “significant” hazard, and it was graded as in “poor” condition as of April 2023, according to the National Inventory of Dams.

Almost 4,100 dams are categorized at the same risk level and condition — or worse — according to an NBC News analysis of the inventory’s data. Every state has at least one such dam. Ohio has the most at 373.

As a whole, America’s dams — more than 91,000 in total — are aging. Many need expensive rehabilitation. Few were designed for today’s climate, with a warmer atmosphere that can hold — and dump — more water. The number of people living in inundation zones below these dams continues to grow.

Heavy rains cause high water levels at the Rapidan Dam near Mankato, Minnesota, on Monday. Mark Vancleave / AP

The average U.S. dam is 57 years old, and dam safety experts say the pace of investment has been too slow to keep the infrastructure up to the standards it was built for, much less for worsening climate hazards.

“It’s falling behind,” said Sharon Tapia, president of the Association of State Dam Safety Officials. “We’re in a situation where we’re seeing more and more dams needing to be rehabilitated or repaired to meet current standards.”

The association estimated in a report last year that it would take $157.5 billion to bring nonfederalU.S. dams up to par. That pertains just to today’s safety standards — it does not factor in enhancements to address additional, future risks from climate change, she said.

President Joe Biden’s 2021 infrastructure bill included $3 billion for dam safety projects — a sliver in comparison to the overall need.

It’s too early for scientists to say whether global warming played a role in the Rapidan Dam’s partial failure, but it made the conditions that led to it more likely.

For every degree Fahrenheit of warming, the atmosphere can hold and deliver about 3% to 4% more moisture, giving storms a stronger punch and making rainfall totals that were once considered rare much more common. That, in turn, raises the risk of devastating floods.

Views of the Rapidan Dam on Sept. 6, 2011, and on June 26, after floodwaters overcame parts of the structure.Maxar Technologies via AP

The Rapidan Dam, built in 1910 and managed by Blue Earth County, was described on the county’s website as in a “state of disrepair.” After flooding in 2019 and 2020, a power generation company stopped leasing the dam, leaving it without a hydropower operator.

But the Federal Energy Regulatory Commission, which regulates the dam, was not overly concerned about the structure’s integrity as recently as last month. According to FERC documents, the dam was inspected May 21 and “found to be in overall satisfactory condition.”

“No major dam safety deficiencies were observed that would require immediate remedial action,” the letter said, though it noted severe concrete deterioration, exposed rebar and cracking that it said should be closely monitored.

The inspection, an analysis of the structure’s safety and stability, was separate from the assessment by the National Inventory of Dams, which considers the full performance of the project, a FERC spokesperson said.

Blue Earth County officials had been weighing whether to remove the dam, at a cost of more than $82 million, or repair it for around $15 million. Both options had downsides: Repairs might only last 40 years, while removal could take five years to plan and secure permits, according to engineering documents from 2021. A county spokesperson said officials were not able to respond to questions, beyond providing updates at news conferences.

A riverside home seen on Tuesday before it partially collapsed, near at the Rapidan Dam in Minnesota. Andrew Weinzierl / AW Aerial via AP

The dam’s partial failure came after three days of intense rainfall that left the Minnesota River at its third-highest flood height since at least 1881, according to Brennan Dettmann, a National Weather Service meteorologist based in the Twin Cities.

In the Mankato area, where the dam is located, 7 to 8 inches of rain fell over three days, based on an analysis from Kenny Blumenfeld, a senior climatologist at the Minnesota State Climate Office.

“That elbow of the Minnesota River got hit pretty hard,” he said, adding that in southern Minnesota, such heavy rainfall would have between a .5% and 2% chance of happening each year.

Bill McCormick, who led the state of Colorado’s dam safety program from 2011 to 2021, said that extreme rainfall has added strain across the nation.

“We’re getting more frequent, intense storms that are testing the aging infrastructure. Spillways and dams that maybe didn’t see as many storms in a given year are now seeing more storms,” he said. “All those aging systems are now being tested more and more.”

Housing development is raising hazard levels for some dams, too, McCormick added, as people settle in once-rural areas, where dams constructed for farmland are now guarding subdivisions.

Hiba Baroud, an assistant professor of civil and environmental engineering at Vanderbilt University, said the Rapidan’s partial failure, among others, should prompt lawmakers to take a hard look at how to bolster dam infrastructure and triage repairs.

“We really need to think proactively to project potential scenarios for all the dams in the U.S. and start prioritizing which dams need to be rehabilitated or upgraded to avoid a situation like this,” she said, “as opposed to witnessing a big event and using it as a wake-up call about this particular dam.”

Floodwaters continue to carve a channel around the Rapidan Dam on Thursday. Mark Vancleave / AP

From 2013 to 2023, 283 dams in the U.S. experienced some kind of failure, according to data provided by the Association of State Dam Safety Officials and analyzed by NBC News. Some didn’t cause sizable problems, but others had grave consequences. In 2019, a blizzard precipitated a dam failure that washed away the home of a Nebraska man, drowning him.

Tapia said dam rehabilitation is too often constrained by insufficient funding and lengthy environmental permitting processes.

“They’re just taking too long to get fixed because of the funding issues and the permitting issues,” she said. “The engineering is typically the easiest part.”

Evan Bush

Evan Bush is a science reporter for NBC News. He can be reached at [email protected].