The length of the forebay is full of bright green water. On the left is the exterior stone wall with regular columns and windows to the outside. On the right are the angled steel grates that prevent ice and trash from entering the penstocks.

Forebay Green Water And Ice Racks Nov 23, 2006

One of the most significant challenges with a hydro-electric power station in a cold climate is ice.

There are two keys issues to worry about:

  1. A buildup of ice can prevent enough water from entering the penstocks, thereby preventing the turbines from rotating at an optimal speed
  2. Large pieces of ice can enter the penstocks and damage the turbines
A small boat is in the water (the exterior forebay) in front of the exterior wall of Rankine Generating Station. Archival photo from 1906.
Rankine Station ice breaker boat: This archival photo from 1906 shows the original ice breaker tug boat, sitting in the exterior forebay of the station. Its job was to ensure that no large ice buildup could occur that would limit the quantity of water flowing into the station.

Stopping ice from getting in

Ice management was a key requirement at Rankine and there were a variety of steps taken to address it. The angled racks inside the forebay are metal channels that try to prevent large pieces of ice from entering the penstocks. There are smaller ‘junk racks’ that can be lowered to prevent additional debris (garbage, tree branches, etc.) from the entering the penstocks as well.

Breaking up ice dams

Outside the forebay the ice could sometimes build up in significant ways that required it to be cleared. Workers would operate a boat outside the forebay that would be used to ram, breakup and dislodge ice buildup. In some cases this also involved using explosives to break up the ice.

An ice breaker tug boat is surrounded by thick ice in the water, pressed up against the exterior wall of the Rankine Generating Station. Archival photo from 1936.
Tug boat and ice: The ice breaker tug boat is surrounded by thick ice in the exterior forebay. Behind the boat is the exterior facade of the generating station.