100-Year-Old Thunder Bay Dam Refurbished with Precast Elements

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The original Boulevard Lake Dam in Thunder Bay, Ontario, was built in 1901-1902 and the current
structure was built in 1906-1907. It was originally constructed to generate electricity for the surrounding area. Some of the electricity generated was used to power streetcars that ran up and down Cumberland Street. The dam created a reservoir, Boulevard Lake, which includes surrounding parkland as well as a 5km pedestrian loop around the lake and over the dam. Boulevard Lake has become one of the most popular recreational spaces in the City of Thunder Bay. It is also home to the Thunder Bay Canoe Club.

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The City of Thunder Bay decided that, included in the rehabilitation of the Boulevard Lake Dam structure, the pedestrian walkway would be widened to allow for the increase in pedestrian traffic as well as
facilitate snow removal in the winter months.

During the Municipal Class EA leading up to the dam construction/refurbishment, the dam was identified as a heritage structure. The City of Thunder Bay was directed to study and maintain the characteristics of the original dam. A number of deck (pedestrian) panels would be required to have an arch incorporated in the element as well as a sloped broom finish for the walking surface.

The City of Thunder Bay specified precast concrete for the new walkway slabs and arches. Precast concrete provides both the long-term durability and the inherent characteristics of accelerated construction, two important factors for this project. Additionally, the high level of quality control that is achieved in a precast manufacturing facility helped ensure that the resulting structural elements would maintain the heritage characteristics of the original structure. Miller Precast Ltd., a local Thunder Bay precast concrete producer who supplies precast elements across northern Ontario, reviewed the project requirements and submitted pricing to construct the custom precast concrete slab and arch elements.

Miller Precast utilized its technical manufacturing expertise to construct custom formwork that would enable the rapid production of the arched walkway segment. The main challenge with the arch walkway elements was that each span was different. Miller designed the formwork to allow for flexibility in span of the arch sections while ensuring that each element met the required tolerances. A total of 18 arched deck panels and 11 regular deck panels were needed to complete the project. Each deck panel was 3.66 m wide by up to 4.3 m long. The weight of each panel was up to 10,000 kgs each. The variation in the length and the weight was due to the arch sections which were required to have a different length in order to meet the required span from abutment to abutment.

To add enhanced durability and ensure a service life of 100 years, the City of Thunder Bay required that each element would be temperature-controlled and wet cured for 96 hours. Since the elements were precast, they could be produced and stored prior to the contractor requiring them.

The installation of the panels was coordinated with Miller’s logistical team. Elements were shipped to the site and a crane was used to drop them into their final position. The precast concrete slabs and arch elements allowed the contractor to install up to five elements per day. The last elements were installed in mid-August 2021.

The refurbished Boulevard Lake Dam is now in operation providing local residents with walking
trails and parkland for years to come. The City of Thunder Bay would like to thank Miller Precast for providing custom structural elements that met both the heritage requirements and the expected long service life of the Boulevard Lake Dam.

Mike Vogrig, P.Eng.
Project Engineer, Infrastructure & Operation Division
City of Thunder Bay
Precast Producer: Miller Precast Ltd.