JML Engineering was retained by the City of Thunder Bay to complete the structural assessment, detailed design, regulatory approval process, tendering, and contract administration/site inspection for the Boulevard Lake Dam Rehabilitation project.

The 106 m long, 5.7 m high Boulevard Lake Dam was constructed in the early 1900’s and consists of 12 sluiceways and 17 spillways. Over the past century, the dam had been rehabilitated numerous times.  However, significant rehabilitation had not occurred at the dam for nearly 50 years and was long overdue.

Boulevard Lake was lowered to facilitate inspection of all dam elements below normal water level. Significant structural deficiencies were observed, as most of the concrete faces were in poor to very poor physical condition.

Numerous functional deficiencies were also observed, including a very narrow walkway over which one of Thunder Bay’s most popular recreational trails passes, and an aged stop log system controlling sluiceways for flow passage.

JML Engineering completed detailed hydraulic analyses of the dam in accordance with the Lakes and Rivers Improvement Act (LRIA). The Hazard Potential Classification of the dam using the Inflow Design Flood (Regulatory Flood) (IDF) was determined. Hydraulic modelling of the dam and the downstream reach was done using HEC-RAS software to determine the effects of dam breach during normal conditions and during the IDF to determine the incremental losses associated with dam failure.

In accordance with the LRIA, numerous stability calculations were done at the dam. Sliding and overturning of the dam were checked for the following conditions: normal summer operation, normal winter operation, operation during the IDF, operation during the IDF including wave effects, and normal summer water level plus effects from the 1:1000-year wind.

JML Engineering obtained regulatory approvals for this project, including a Permit to Take Water for Construction Dewatering, Environmental Compliance Approval, MNRF Work Permit through the LRIA, Fisheries Act Approval through the Department of Fisheries and Oceans, and approval through the Lakehead Region Conservation Authority. In addition, the dam has been designated an historically important structure. Maintaining the heritage features of the dam were an important aspect to be considered in the design of this rehabilitation project.

JML Engineering completed the detailed design for the following scope of work items for this project:

• Cofferdams, temporary flow passage system, and dewatering plan.

• Maintaining water surface elevations and flow through the dam during construction in accordance with regulatory approvals.

• Refacing all sluiceway buttresses, wingwalls, and sluiceway/spillway aprons.

• New cast-in-place concrete sluiceway buttress extensions, spillway buttresses, and north face wall extensions.

• New post-tensioning rods at each buttress to ensure stability during the IDF.

• New precast concrete sluiceway deck panels and spillway deck panels c/w arch beams to maintain heritage aspects. The new deck panels significantly widened the walking surface for recreational users.

• New continuous stainless steel railing system.

• Designed new electrically actuated weir gates at each sluiceway to allow improved control over normal flows and rapid response to the IDF.

• Improved lighting throughout the dam designed.

• Social gathering area featuring salvaged historical components.

The project has been tendered to be completed over a two-year period. Construction began in June 2020 and was Substantially Complete in May 2023.