By Julie Strupp of ConstructionDive,
Following the rare and dramatic collapse of the Edenville and Sanford dams in Midland County, Michigan, in May 2020 that forced 10,000 residents to evacuate, a newly released preliminary report sheds light into why they failed, and offers safety lessons for other aging, earthen infrastructure.
The independent investigation from the Federal Energy Regulatory Commission (FERC) covers the physical mechanisms involved in the accident but doesn’t place blame; a final report expected in several months will delve into human factors.
The report says poor construction and ignored upkeep, combined with intense rainfall, were the primary causes of the failure. Experts previously assumed that only an earthquake could cause a dam embankment to liquify the way it did in Edenville.
A series of failures
On May 19, 2020, water poured into the Wixom Lake reservoir, filling it to a record high. This waterlogged the dam’s embankment, which caused it to liquify and collapse, per the report. This overwhelmed the downstream Sanford Dam, causing it to fail as well. The problems started long before that day though: The two dams were built in the 1920s, but a key embankment wasn’t compacted the way it was supposed to be, setting it up for failure about 100 years later.
Boyce Hydro bought the Edenville, Sanford, and two other central Michigan dams as tax shelters in 2006 and owned them at the time of the collapse, Bridge Michigan reported.
After the company failed for decades to repair spillways that are supposed to prevent flooding, the FERC revoked the license to generate power for the Edenville dam a year and a half before the accident. The Sanford Dam was an active hydroelectric facility at the time of the incident.
A 2012 report by Boyce says that the company knew since at least 2012 that the section of the dam that failed lacked the tile drains that were supposed to line the entire bottom, leaving that soil vulnerable to saturation. The company disputes it is to blame. It also argues area landowners and federal regulators are responsible for rules that made it unable to preemptively drain the lake to make room for the additional rainwater.
Other dams at risk
While the liquification seen at Edenville is rare, dam failure is unfortunately not unique: The 2017 Oroville Dam incident in California forced 180,000 people to evacuate, and in 2019 the Spencer Dam failure in Nebraska killed one person. Both failures were also sparked by heavy rain.
The Michigan dam failures caused about $175 million in damage to homes and buildings and left two lake beds empty. Victims of the incident are suing Boyce Hydro (as well as state and federal regulators) but the company has filed for bankruptcy, thus plaintiffs are unlikely to receive much compensation from it.
Experts don’t know exactly how many U.S. dams might have the same issues as Edenville, said Mark Ogden, technical specialist for the Association of State Dam Safety Officials, and information is sparse about the many dams that were constructed a century ago.
"We know there are likely about 4,000 high hazard-potential dams that have an assessment rating of poor or are not rated, and it’s likely that a good percentage of those require some remedial action," Ogden said. "The need for action to get these dams upgraded and improved is really significant."
More than half of dams are privately owned, and lack of upkeep is sometimes an issue, according to Ogden. Plus, climate change-related extreme weather will put increasing stress on aging dams in coming years, and could cause more breakdowns unless remedial measures are taken, he said.
Policy, engineering remedies
Going forward, engineers will look for lessons from the incident, according to Ogden.
"Any time we see a failure or incident at a dam, it’s really important to investigate... I think that we will see that dam owners will look at these types of dams and will make decisions based on this new info to make sure it doesn’t happen again," said Ogden. "There are definitely dams out there in a similar situation [as Edenville], and hopefully dam owners and regulators and others in the dam safety field can work together."
One of the issues with preventing dam failures is that there isn’t enough funding for inspections and upkeep, according to Ogden. The Twenty-First Century Dams Act, introduced by Sen. Dianne Feinstein (D-CA) in July, would provide $21.1 billion to rehabilitate, retrofit and remove dams as needed, as well as to fund inspections and state safety programs. States regulate about 70% of dams in the U.S.
"Many dam safety programs are terribly under-resourced," Ogden said. "[The 21st Century Dam Act] is an important piece of legislation that could help in terms of improving the safety of dams."