Failed Michigan Dam Had Longstanding Spillway Deficiencies

The Edenville dam, which failed on March 19 flooding Midland, Michigan, and forcing as many as 10,000 residents to evacuate their homes, had its license revoked by the Federal Energy Regulatory Commission (FERC) on Sept. 10, 2018, due to a “longstanding failure to increase the project’s spillway capacity to safely pass flood flows,” among other things.

The Edenville project consists of earthen embankments totaling about 6,600 feet in length and having a maximum height of 54.5 feet. The project spans both the Tittabawassee and Tobacco Rivers, creating a 2,600-acre reservoir known as Wixom Lake, with a gross storage capacity of about 40,000 acre-feet and a 49-mile-long shoreline at full pool. The project is owned by Boyce Hydro Power LLC.

The dam is located on the county line between Midland and Gladwin counties. It is about 21 miles upstream from Midland. Edenville dam is flanked by two concrete spillways. The Tittabawassee spillway is on the east side of the dam and the Tobacco spillway is on the west. The spillways permit the release of surplus water from the reservoir to the downstream side of the dam. Such releases are intended to prevent water from overtopping and damaging or destroying the dam.

Deficiencies Identified More Than 20 Years Ago

In January 1999, the regional engineer in FERC’s Office of Energy Projects, Division of Dam Safety and Inspections issued a letter to Wolverine Power Corp., the licensee at the time, describing the project’s need to increase its spillway capacity. Of particular concern was the project’s inability to pass the “Probable Maximum Flood” (PMF) due to inadequate spillway capacity. The PMF event is defined as “the flood that may be expected from the most severe combination of critical meteorologic and hydrologic conditions that is reasonably possible in the drainage basin under study.”

As much as four-and-a-half inches of rain reportedly fell in some parts of the Edenville dam area during a 36-hour period beginning May 17. This was on the heels of more than an inch of rain a few days earlier, resulting in a surge in runoff. It’s unclear if the conditions matched or exceeded the modeled PMF, but at about 6 p.m. on May 19, the dam failed.

History of Noncompliance

When the Edenville spillway deficiencies were first identified in 1999, Wolverine Power requested time to study the problem. In June 2002, the regional engineer issued a letter requiring the company to file a detailed plan for spillway upgrades by July 31, 2002, and complete required modifications by Dec. 31, 2006.

FERC documents do not specify if Wolverine Power met the July 2002 deadline, but in June 2004 the company transferred the Edenville project license to Boyce. The following month, Boyce sent a letter to the regional engineer stating that it planned to complete construction of an auxiliary spillway on the Tittabawassee River in 2004 and was studying whether it also needed to construct a second auxiliary spillway on the Tobacco River.

Soon thereafter, Boyce fell into a regular habit of requesting extensions, missing deadlines, and receiving letters of violation. For years, the company delayed action while conducting studies, and evaluating design and construction options.

In 2008, Boyce claimed it could not perform work on the spillway because it did not have the money or ability to borrow the necessary funds. It then agreed to commit funds to an account dedicated to improvements, report semi-annually on the status of funds, and make upgrades over a three-year period beginning in June 2010.

Following several more years of Boyce failing to make any significant progress, in February 2014 the regional engineer accepted a new schedule that would allow Boyce to complete construction of its proposed auxiliary spillways by the end of 2015. Although the spillway designs that Boyce submitted were not sufficient to pass the full PMF, the regional engineer wrote that he would accept them as an interim risk reduction measure.

Still, Boyce failed to make progress on improvements and “numerous extensions” were granted, according to FERC documents. On June 15, 2017, FERC staff issued a compliance order detailing Boyce’s failure to remediate spillway deficiencies, as well as its failure to comply with a number of other license and regulatory requirements.

Ordered to Cease Generation

The Edenville project includes a 50-foot-long intake leading to the powerhouse located at the dam on the eastern side. The powerhouse contains two 2.4-MW Francis-type turbine generator units for a total installed capacity of 4.8 MW. On Nov. 20, 2017, FERC staff issued an order requiring Boyce to cease generation at the project.

Boyce filed a motion with the U.S. Court of Appeals for the D.C. Circuit requesting a stay of the cease generation order; the stay was granted on Feb. 7, 2018. However, on Feb. 18, 2018, FERC proposed revoking the license, concluding there was no reason to believe that Boyce intended to come into compliance with previously issued orders. On Sept. 10, 2018, the Edenville project’s license was revoked, effective Sept. 25, 2018.

As part of the order, Boyce was required to permanently disable the project’s generating equipment and file written notification, providing the date and time that generation ceased, the generator meter reading at that time, and a photograph of the reading on the meter. Boyce petitioned the U.S. Court of Appeals for the D.C Circuit asking the court to enjoin FERC from enforcing the license revocation, but the request was denied on Sept. 20, 2018.

POWER found no record of physical work being completed to increase the capacity of spillways beyond that which they were capable of in 1999.

Aaron Larson is POWER’s executive editor (@AaronL_Power, @POWERmagazine).

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