The three dams, Rogers, Hardy, and Croton (all owned and operated by Consumers Energy), are operated in different modes but in concert give a net run of river effect on water flow. The Rogers itself has little or no impoundment and runs in run of river mode, passing through as much water as it receives. The Croton and Hardy work in concert. The Hardy, which has a larger capacity reservoir, larger turbines, and is upstream of the Croton, runs in full peaking mode, meaning that the river flow is impounded and used to generate electricity during peak demand periods. This causes wide fluctuations in water flows and reservoir levels, typically with low outflow during the night when power demand is lowest. Full peaking was once very common but because of the outflow fluctuations, is now less common. However, with the Croton immediately downstream, and with no river segment (the Croton impoundment stretches back to the Hardy outlet), it can be run in re-regulation mode, allowing a natural flow rate to exit. The Croton reservoir level fluctuates inversely with the Hardy, rising during the day and lowering at night. Since the Hardy reservoir is so large, its reservoir level fluctuates about 4 inches (10 cm) in total, while the Croton reservoir fluctuates about 9 inches (23 cm). During the winter and spring runoff, the Hardy is allowed to fluctuate much more. It can be drawn down up to 12 feet (4 m) to meet winter power demand but is required to return to normal levels by the end of April each spring.
Hardy Dam (or Hardy Hydroelectric Plant ) is an earth-filled embankment dam and powerplant complex on the Muskegon River in Big Prairie Township , Newaygo County , Michigan . At the time of its completion, it was the largest earthen dam in North America east of the Mississippi. Its impoundment forms a lake with over 50 miles of shoreline. The dam impounds a reservoir with a surface area of 4,000 acres (1,618 ha) and its power plant has an installed capacity of 31.5 MW.