Mio Dam
| Company type | Hydroelectric facility |
|---|---|
| Industry | Energy, Hydroelectric power |
| Founded | 1916 |
| Headquarters | Luzerne , United States |
| Products | Hydroelectric power (4.96 MW capacity) |
| Owner | Consumers Energy |
Mio Dam is a hydroelectric facility situated on Michigan's Au Sable River with an installed capacity of 4.96 MW. It represents the fourth installation among six dams built by Consumers Power between 1906 and 1924 along this river and is positioned furthest upstream. Finished in 1916, the structure includes earthen embankments on both sides linked by a spillway, while the powerhouse and an outdoor substation lie to the north of the spillway. Consumers Energy ensures public access to Mio Pond through a boat launch and provides portage routes for canoeists and kayakers to circumvent the dam.
Recognition and Significance
MICHIGAN HISTORIC SITE: In 2005, Mio Dam earned designation as a Michigan Historic Site due to its pioneering design that channels surplus river flow through conduits embedded within the powerhouse foundation (known as an under-sluice), eliminating the need for expensive above-ground gated spillways. In 1988, modifications were made to comply with federal safety regulations by adding a concrete spillway above ground.
HYDRO HALL OF FAME: Mio Dam was inducted into the Hydro Hall of Fame by HydroVision International in June 2017, honoring its innovative conduit spillway concept and more than 100 years of reliable service. This under-sluice approach was subsequently applied to other Consumers Power dams, including the downstream Alcona Dam completed in 1924.
AU SABLE CANOE MARATHON: The dam is one of six that participants must portage around during the annual overnight 120-mile Au Sable River Canoe Marathon, an event that required two years of preparation.
Technical Information
Constructed as an earth embankment dam with a reinforced concrete core wall, Mio Dam creates a water head of 29 feet. The original machinery remains functional, consisting of two Allis-Chalmers vertical turbines and generators, each rated at 2,500 KW operating at 2,500 volts and 80 RPM. The powerhouse is a brick structure measuring 30 by 75 feet with a flat roof. Building the dam in the remote Luzerne region presented logistical difficulties, necessitating transport of heavy equipment over long distances without railway support. The dam features an innovative "conduit spillway" patented by William W. Tefft, then Chief Engineer at Consumers Power Company; it employs two steel tubes, each 60 inches in diameter, to convey water beneath the powerhouse. There is also a smaller concrete spillway equipped with a single tainter gate.
To mitigate environmental impacts, Consumers Energy uses an underwater air bubbler system that blends cooler water into turbine intakes to maintain temperatures at or below the mandated 68 degrees Fahrenheit. Compressors generally operate for about six hours daily to replicate natural cooling cycles but may run continuously during periods of elevated temperatures.
River Flow and Safety
Consumers Energy closely monitors river flow rates and water temperatures to maintain safe operation of the hydroelectric dam, releasing surplus water when necessary. The USGS operates six real-time streamflow monitoring stations along the Au Sable River as part of its National Streamflow Information Program; these data support the National Weather Service’s Advanced Hydrologic Prediction Service. One such gauge (ID: MIOM4) is positioned at Mio Dam.
Dam safety status is classified into three levels: "Condition C" indicating high flow without emergency, "Condition B" signaling potential failure risk, and "Condition A" denoting imminent or actual failure. Condition C occurrences are infrequent on dams along the Au Sable River. Local emergency response agencies conduct regular drills and maintain coordinated contingency plans for possible failures. In July 2020, officials emphasized that failure at Mio Dam could lead to sequential failures of five downstream dams, creating significant hazards for public safety.