en.Wedoany.com Reported - The Michigan Senate has passed legislation increasing the flood flow capacity that dams must withstand, part of a series of measures to strengthen dam safety standards in the state. This spring, multiple rivers experienced floods exceeding the 500-year event level, pushing some high-risk dams to the brink of failure.
Senate Bill 947, sponsored by Democratic Senator Mallory McMorrow of Royal Oak, has been sent to the Republican-led Michigan House of Representatives. The House is simultaneously advancing House Bill 5485, introduced by Republican Representative Bill Schuette of Midland, though the measure has not yet passed a full vote.
Current law requires high-hazard dams to withstand a 200-year flood. Luke Trumble, head of the Dam Safety Program at the Michigan Department of Environment, Great Lakes, and Energy (EGLE), stated that the new legislation would raise the standard to the Probable Maximum Flood, the theoretical worst-case scenario. Trumble noted that most high-hazard and significant-hazard dams currently only need to withstand a 200-year flood, while the new law would increase capacity requirements for high-hazard dams to the Probable Maximum Flood.
This standard applies to dams classified by the state as high-hazard, a designation based on the consequences of a failure, not the dam's physical condition. Trumble revealed that the list includes approximately 90 high-hazard dams, 150 significant-hazard dams, and about 700 low-hazard dams. The potential hazard rating is unrelated to a dam's condition or likelihood of failure, only assuming the downstream impact if a breach occurs. Engineers assign separate condition ratings after inspections: satisfactory, fair, poor, or unsatisfactory. About 15% to 20% of the state's dams fall into the poor or unsatisfactory categories.
The legislation increases inspection frequency for high-hazard dams from every three years to annually, for significant-hazard dams from every four years to every two years, while maintaining the five-year interval for low-hazard dams. Trumble pointed out that the state currently lacks the authority to require higher flood standards, even for dams in good condition. He cited an example: "A dam in very good structural condition and well-maintained, but only capable of withstanding a 200-year flood, is prone to failure during extreme flood events."
The April floods on the Cheboygan, Manistee, and Au Sable rivers exposed this gap. Trumble, citing data from U.S. Geological Survey (USGS) stream gauges, stated that flows on these rivers even exceeded the 500-year flood event. Dams on these rivers, federally regulated hydropower dams, are already required to meet the Probable Maximum Flood standard. Trumble noted that this helped them better withstand the April floods compared to state-regulated dams built to lower standards.
Similar legislation was proposed after the 2021 failures of the Edenville and Sanford dams in Midland County but failed to pass committee. Trumble said the current bill was introduced before the April floods and gained momentum due to them. He noted that some high-hazard and significant-hazard dams were "pushed to the brink of failure," prompting the dam safety industry and legislature to consider whether it is appropriate for high- and significant-hazard dams to be pushed to the verge of failure if a flood occurs.
The legislation also requires dam owners to register structures and demonstrate sufficient funding for maintenance and repairs, addressing decades of underinvestment in dams primarily built between the 1930s and 1960s. Trumble stated that if owners have been planning and have the financial capacity to repair or replace dams before problems arise, registration should proceed smoothly. The bill would establish a permanent dam safety emergency fund, replacing a version created through budget appropriations that is set to expire. Trumble noted that the legislation does not include new appropriated funds, with funding still dependent on future budget decisions.
Cost estimates for bringing dams statewide up to standard vary widely depending on scope. Trumble cited the 2023 American Society of Civil Engineers (ASCE) Infrastructure Report Card, which estimated $225 million to $400 million over 20 years to address dams currently in significant, poor, or unsatisfactory condition. A study by the Association of State Dam Safety Officials (ASDSO) suggests the cost to bring all dam infrastructure in Michigan to satisfactory condition approaches $1 billion. Trumble emphasized that a $1 billion investment is not needed next year, but efforts must begin moving toward that figure to match investment speed with dam degradation rates. He noted that upgrading dams costs far less than the consequences of failure, citing the 2020 Edenville dam failure causing approximately $200 million in structural damage, and that the risk cost of accepting lower design standards far exceeds the potential cost of improved design.
