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Replacing an historic dam

Demolition, pilings, river diversion and major concrete pour had to be done while keeping the lock system operating

New dam under construction on the right, lock in middle and diversion system on the left. Bermingham installed two million pounds of steel sheet and combi-wall to tame and control the river during construction. Yellow floats are safety booms.
New dam under construction on the right, lock in middle and diversion system on the left. Bermingham installed two million pounds of steel sheet and combi-wall to tame and control the river during construction. Yellow floats are safety booms.

With the dam at Lock 37, one of the largest dams on the magnificent Trent-Severn Waterway, nearing the end of its service life, the Parks Canada Agency (PCA) was faced with the challenge of replacing it with a sound and serviceable structure that would both retain the historic character of its predecessor, and complement its natural surroundings.

The 386-km-long canal system known as the Trent-Severn Waterway (TSW) is a unique piece of Canadian history linking Lake Huron with Lake Ontario that was constructed in stages over a period of 87 years. Today, it is operated by the PCA and is a tourist destination that brings boaters up to cottage country between the months of May and October each year. In 2015 over 115,000 boats used the locks along the length of this well-travelled system.

Original dam built in 1903

The original dam at Lock 37 was built by Alymer and Brown in 1903 and took the better part of six years to construct utilizing the technology available at that time. Concrete was batched at the site and was not reinforced with steel. Timbers were driven to bedrock along the full length of the dam footing, and were carefully connected by tongue and groove, which were then bolted together. The process was long and time-intensive as it was all completed with manual labour. Rail lines and work horses were used to move materials around, to and from the jobsite.

Concerned about the aging dam, Public Works Government Services Canada (PWGSC) and PCA retained exp Services Inc. to undertake an assessment of the existing structure. The assessment concluded that the dam was at risk of structural failure and the decision was made to demolish the existing dam and replace it with a new one. Since the dam is a significant part of Canadian history, it was decided that some of the elements of the original dam would be incorporated into the design of the new one: modern construction practices with an historic feel. This included refurbishing the cast-iron crab winches used for moving stoplogs in and out of the sluiceways.

The original dam was constructed with four spillways and two sluiceways. There was one set of stoplogs in each of the sluiceways to be used for operation of the dam and control of water levels both upstream and downstream.

Planning and awarding contracts

The new dam was designed to have three spillways and three sluiceways. Each of the sluiceways will have two sets of stoplogs: one in the operational gains and the other in service gains. This will allow service to be done on stoplogs should they require replacement. exp worked closely with PWGSC to complete the design of the new dam structure and the project was tendered for construction.

Metric Contracting Inc., along with their team consisting of Bermingham Foundation Solutions, Priestly Demolition and Clearwater Structures Inc., was awarded the project, and work began in late 2013.

exp Services Inc. was retained by PWGSC and PCA to undertake the construction administration and site inspection of the entire dam at Lock 37 project – which until 2014 was Parks Canada’s largest engineering undertaking in eastern Canada in the past 25 years.

The scope of work included cofferdams, a water diversion system, fish rescue and relocation, excavation, demolition of the existing dam structure, steel and timber work, slope stabilization, roads and landscaping. exp’s role as design engineer changed to construction inspection and contract administration.

Bermingham builds diversion system and cofferdams

The project presented several challenges, the most critical being the ongoing operation of the lock during the demolition of the existing dam and reconstruction of the new dam. The first issue was dealing with the water that would have normally flowed through the dam. In order to address this, Bermingham Foundation Solutions along with Clearwater Structures constructed a diversion system on the south side of the lock. The diversion system was constructed with steel sheet pile (SSP) walls consisting of two concrete drop structures which included energy dissipating blocks in order to aid in the control of the velocity of water as it moved downstream, specifically during the spring melt or freshet. An inlet control structure was constructed just inside of the original shoreline which included stoplogs for controlling the water levels upstream of the dam.

Next, the upstream cofferdam was constructed using a contained bin system, made up of seven cells, that started on the north shore and was built to the south where it connected with the lock nose and thereby isolated the existing dam structure. The upstream cofferdam was made up of an SSP wall on three faces and a combiwall with pipe piles and SSPs along the upstream face. In total, more than 1,100 steel sheet piles were installed with a total length of more than 23 km for this project.

The next phase was to construct the downstream cofferdam so that the work area could be dewatered and isolated. With the area dewatered and the fish relocated, Priestly Demolition moved in and demolished the existing dam.

Construction of the new dam

Clearwater Structures then commenced construction of the new dam structure. Building and erecting forms, tying reinforcing steel and placing concrete through the winter months was challenging, but the crews didn’t stop working.

Construction of the new dam utilized modern technologies with reinforcing steel being placed within the entire 6,500+ cubic metres of concrete that was used to construct the new dam. Given the complexity of the new construction and the sequencing of work, consideration had to be given to extreme hot and cold weather protection and curing of the concrete.

In order to monitor the effects of the construction activities and to ensure that the existing lock structure would not be impacted by the ongoing work, the contractor installed three types of monitoring equipment. Inclinometers were placed in locations along the lock nose along with precision survey monuments and electrolevels. Readings were taken at various intervals with the frequency changing to reflect the work in close proximity to the lock structure.

Impacts on the environment were considered in the planning of the work activities to ensure that the work would have as little negative impact as possible. The contractor employed a variety of methods and materials to protect the environment and specifically to protect the fish-spawning area located just downstream of the dam where, for years now, several varieties of fish have spawned. The work zone at the Lock 37 dam was contained by turbidity curtains at both the upstream and downstream sides of the dam structure, while settling basins and other measures were employed throughout the work area to both minimize disruption, and meet the goal of completing the dam in 2016.


Andrew Bird, C.Tech., rcsi is supervisor of construction services at exp Services Inc.

This article originally appeared in the January/February 2016 issue of The Ontario Technologist and has been republished with the permission of the author and the Ontario Association of Certified Engineering Technicians and Technologists (OACETT).

Over 6,500 cubic metres of steel-reinforced concrete were placed in the construction of the new dam.