Built in the 1950s, two intake control gates sit between the Niagara Parkway and the Niagara River, just three kilometers south of the Horseshoe Falls. The massive subterranean hydro tunnels, each 13.7 meters in diameter, start here. Water from the river is drawn through these channels to the forebays of the Sir Adam Beck 2 Generating Station 10 kilometers downstream near Queenston.
The gates stand six stories tall and 48 meters wide. When required they can be lowered into the earth to regulate the flow through the tunnels below. If an extreme emergency were to take place they can cut off the water entirely. Such a scenario has not yet arose, but the gates are closed annually as part of their regular maintenance routine.
There are similar structures across the river in Niagara Fals, New York which regulate water flowing to the Robert Moses station. While functionally they are similar to their Canadian counterparts they’re structurally quite different looking.
Standing next to the gates one can hear the water rushing through the tunnels below, moving at a rate of 1,850 meters per second and descending as deep as 101 meters beneath the city.