Powerhouse stabilization overview

One of the historic gate valves after refinishing.

By Brendan Hodgson and Svenja Hansen

This is the third in a series of stories about the Powerhouse, which sits at the core of the Sault Ste. Marie Canal National Historic Site. Work to stabilize the structure began in December 2023, and is expected to continue for approximately two years. Now is the time to have a look at the technology that was cutting edge 130 years ago and is usually hidden.

Building next to water comes with an inherent risk of flooding and erosion. In the case of the historic Powerhouse, it had to be situated in close proximity to the Sault Canal. In fact, in its heyday, Lake Superior water was intentionally diverted from the upper canal through the building to generate electricity to operate the lock and provide lighting for the site.

What few visitors realize is that a huge underground pipe, known as the penstock, runs alongside the original lock. Water continuously flowed through this pipe to the hydro-electric generating equipment, which was housed on the first floor of the Powerhouse.

The penstock intake is located West of the westernmost motorhouses. The eastern motorhouses mark the spot where this 304m (1,000 ft) long pipe divides to channel the water into two symmetrical pipes, each leading into the Powerhouse. In 1911, the Y-junction was removed and replaced by a reservoir. The work to stabilize the building is focused on capturing and managing the water flow in and around the Powerhouse rather than in the building itself.

The existing reservoir is being removed and the soil has been excavated to bedrock. A new reservoir made of reinforced concrete is being poured and weeping tile is being added around the reservoir to channel any remaining water away from the Powerhouse, thereby limiting further erosion of the building’s foundation.

The waterflow through the penstock and the Y-pipes is controlled using large valves. The penstock will have a new butterfly valve added, which controls waterflow by turning a metal disk 90-degrees to either an open or closed position. The flow into the Powerhouse is controlled by two original gate valves, which have been machined and completely restored off-site. They function by lifting a metal disc up and down in a protective housing.

Eventually, the penstock reservoir will be covered so that much of this historic infrastructure will once again be hidden. For the time being, however, it is open, and visitors can look through the construction fence to catch a glimpse of the inner workings of this national historic site which was designated for its many technological firsts. We invite you to join us on a site tour to learn more!

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