Two dam failures in Michigan in mid-May have led to calls for investigations as to the causes of the calamitous events as well as an examination of why the dams’ owner did not make critical upgrades in time to preclude the disaster. Although no fatalities or injuries resulted from the failures, widespread flooding forced the evacuation of thousands of central Michigan residents and significantly damaged many homes, businesses, roads, and bridges and raised concerns regarding the prospect of additional failures involving other aging high-hazard-potential dams around the United States.
On May 19, the 95-year-old Edenville Dam, situated at the confluence of the Tobacco and Tittabawassee Rivers on the border between Midland and Gladwin Counties, failed in the wake of storms that dropped as much as 8 in. of rain during 48 hours in areas of northeast Michigan. The 4.8 MW hydropower facility included an intake leading to a powerhouse located on the eastern side of the dam. The dam featured two multiple-arch spillways made of reinforced concrete. On the eastern side of the project, a 69 ft wide, 39 ft high spillway contained three tainter gates and two low-level sluice gates. On the western side, a 72 ft wide, 40 ft high spillway also contained three tainter gates. Earthen embankments totaled about 6,600 ft in length and had a maximum height of 54.5 ft. The Edenville Dam formed the 2,600-acre Wixom Lake, which had a gross storage capacity of 40,000 acre-ft.
After the breach of the Edenville Dam, high water levels surged downstream, overtopping and eventually destroying another hydropower facility, the Sanford Dam. Two other downstream facilities, the Smallwood and Secord Dams, also were damaged. The communities of Edenville, Sanford, and Midland were hit especially hard by the floodwaters. On May 19, Michigan Gov. Gretchen Whitmer declared a state of emergency for the city of Midland and Midland County. Whitmer subsequently expanded the declaration to include Arenac, Gladwin, Saginaw, and Iosco Counties. The day after the dam failures, the Michigan Department of Transportation announced that more than 20 state and local bridges would require inspections and repairs before they could reopen. On May 21, President Donald Trump issued a federal emergency declaration for Midland County.
In a May 20 statement, the owner of the Edenville Dam—Boyce Hydro Power LLC, of Sanford—cited the significant precipitation levels and stormy conditions as the reason for the dam’s failure. The “massive volume of rainfall in the drainage basins of the Tobacco and Tittabawassee [R] ivers, over an extended period of time, resulted in increasing water levels in the Wixom reservoir, to two feet below the dam crest,” according to the company’s statement. “This, combined with wave action due to high winds, eventually caused the water to penetrate the earthen dike at the east end, saturating it. This resulted in a washout of approximately 900 feet of the dam on the evening of May 19, sending large volumes of water downstream toward the Sanford [D]am. This volume was more than Sanford [D]am was capable of handling, and it was ultimately overtopped, again sending large volumes of water downstream.”
The precise reasons for the failures of the Edenville and Sanford Dams will be the subject of an investigation that Whitmer ordered the Michigan Department of Environment, Great Lakes, and Energy (EGLE) to oversee. “Among other factors, I ask that you examine the storm event, the structural integrity of the dam, the dam owner’s compliance, and the handoff of regulatory oversight from the federal to state government,” Whitmer wrote in a May 27 letter to Liesl Clark, the director of EGLE. The governor requested that she be provided a “preliminary account of what happened” at the Edenville Dam by August 31. More broadly, Whitmer directed EGLE to “review the larger issue of dam safety in Michigan and provide recommendations on policy, budgetary, legislative, and enforcement reforms that can prevent these harms from repeating elsewhere.”
The investigation ordered by Whitmer “will be conducted by an independent third-party team of experts,” said Nick Assendelft, a spokesperson for EGLE, who responded in writing to questions from Civil Engineering. The experts, who had yet to be selected as of early June, will be approved by EGLE and the U.S. Federal Energy Regulatory Commission (FERC), which regulates hydropower dams in the United States, Assendelft said.
In fact, the Edenville Dam had been subject to FERC regulation until September 2018, when the agency issued a rare order revoking the license for a hydropower facility. In 2004, companies affiliated with Boyce Hydro Power acquired the Edenville, Sanford, Secord, and Smallwood Dams on the Tittabawassee River, all of which were regulated by FERC. Beginning that year, FERC sought to have Boyce Hydro Power correct various noncompliance issues at the Edenville Dam, most notably the project’s “inability to pass the probable maximum flood (PMF) due to inadequate spillway capacity,” according to FERC’s September 10, 2018, order revoking Boyce Hydro Power’s license for the dam.
Boyce Hydro Power, in its May 20 statement, cited cost constraints as the reason why it never increased the spillway capacity of the Edenville Dam. “The cost estimate for construction of the modified spillway plans that were approved by FERC in 2012 exceeded $8 million, which Boyce did not have the ability to finance,” the company said. “Boyce sought funding help from the community, without success.”
Although the company sought to work with FERC to develop potential alternatives, no solutions came to pass, prompting the commission to revoke its license for the Edenville Dam. “Boyce Hydro has, for more than a decade, knowingly and willfully refused to comply with major aspects of its license and the commission’s regulatory regime, with the result that public safety has been put at risk and the public has been denied the benefits, particularly project recreation, to which it is entitled,” FERC stated in its 2018 order. “The record demonstrates that there is no reason to believe that Boyce Hydro will come into compliance; rather, the licensee has displayed a history of obfuscation and outright disregard of its obligations.”
The precise reasons for the failures of the Edenville and Sanford Dams will be the subject of an investigation. Subjects will include the storm event, the structural integrity of the dams, and the owner’s compliance with safety regulations.
In a May 20 letter to Boyce Hydro Power, FERC directed the company “to immediately begin formation of a fully independent forensic investigation team to focus on the Sanford Dam, Smallwood Dam, and Secord Dam.” After reviewing project operations at the dams, conducting field investigations, and reviewing project documents, the team is to prepare a forensics analysis report discussing the “root cause of the overtopping damage to Sanford Dam as well as any other contributing causes,” the letter states.
After FERC’s revocation of the company’s license for the Edenville Dam, regulatory authority for the structure reverted to the State of Michigan, specifically EGLE, which was known then as the Department of Environmental Quality. In October 2018, department staff visited the dam to assess its current condition but not its capacity to meet the state’s safety standards. Subsequently, the department began “reviewing decades’ worth of records and inspection reports that had been previously unavailable because they were protected under federal critical infrastructure laws,” according to EGLE’s fact sheet.
The disasters prompted discussions about the age and deficiency of dams across the nation.
The department required that Boyce Hydro Power “complete a comprehensive analysis of the dam’s structural integrity and ability to meet state safety rules,” according to the fact sheet, particularly the requirement that the dam have the ability to manage one-half the PMF, a 50-percent reduction compared with FERC’s standard. The department “had not received that report from the owners at the time the dam failed,” the fact sheet states.
In late 2018 and 2019, Boyce Hydro Power lowered water levels by several feet in Wixom Lake. The company did so “to ensure the safety of the dam and the operators under hazardous winter conditions,” according to its May 20 statement. In the springs of 2019 and 2020, Boyce Hydro Power restored the lake elevation to its normal levels, the result of “pressure” to do so from residents living along the lake’s shoreline, EGLE, and the Michigan Department of Natural Resources (DNR), according to its statement. The State of Michigan has denied this charge. For its part, the state maintains that the two drawdowns of the impoundment harmed mussel populations in the reservoir and damaged adjacent wetlands. On April 29, 2020, Boyce Hydro Power sued the State of Michigan, alleging harm as a result of the state’s oversight of the Edenville Dam. The next day, the state sued the company, seeking compensation for alleged natural resources damages.
On June 9, Michigan’s Department of Attorney General filed a separate lawsuit against Boyce Hydro Power, seeking compensation for expenses incurred as a result of the flooding after the dam failure. With its suit, the state also aims to compel the company to pay for efforts to clean up debris caused by the dam failures, including hazardous materials. Separately, a group of residents and business owners is suing Boyce Hydro Power and Michigan’s EGLE and DNR.
Congress also has gotten involved. On June 1, members of the House Committee on Energy and Commerce sent letters to FERC and EGLE, asking detailed questions regarding the regulatory history of the Edenville Dam and their roles in it.
The disasters prompted discussions about the age and deficiency of dams across the nation. “This could be a sign of things to come in the U.S.,” said Mark Ogden, a technical specialist for the Association of State Dam Safety Officials, of Lexington, Kentucky, who provided written responses to questions from Civil Engineering. “We know that there are more than 2,300 high-hazardpotential dams identified as deficient” in the National Inventory of Dams, he said. “We also are experiencing more frequent storms that are exacerbating identified vulnerabilities with aging dams, and there is a lack of funding to repair these vulnerabilities.”
This news article first appeared in the July/August 2020 issue of Civil Engineering.