WCW26

The City of Winnipeg’s Aqueduct was constructed between 1914 and 1919 and supplies potable water to a population of 800,000 from Shoal Lake at the Ontario/Manitoba border. While a majority of the 155 km length flows by gravity, the portion within the City operates under pressure, was constructed from 1650 and 1200 mm pre-cast concrete pressure pipe, and is now known as the Branch I Aqueduct, supplying 40% of Winnipeg’s potable water.
 
Winnipeg’s clay soils are high in sulphates which causes a breakdown of the cementitious matrix in concrete structures. This was a known phenomenon at the time of construction, but as sulphate resistant cement had not been invented in 1914, Engineers opted for high quality concrete and the use of an underdrain system, to control groundwater and, by extension, reduce sulphate attack on the pipe. The underdrain was constructed from 150 to 300 mm clay tile pipe with open joints to permit the infiltration of groundwater, akin to a French drain, and discharges to the Seine River, Red River, and the combined sewer system. 
 
Following a 2021 condition assessment program, the City initiated a repair program to address urgent repairs on the Branch I Aqueduct Underdrain. The project included the repair of three river outfalls, the elimination of two connections to the combined sewer system, and the repair of defects along approximately 2 km of the underdrain. Challenges, to completing the repairs included limited access to the underdrain via 750 mm manholes, repairs beneath active rail tracks, and working near the City’s GWWD railway. Repairs using trenchless technologies were prioritized where possible using both cured in place pipe (CIPP) lining and CIPP spot repairs. However, where open cut repairs were required, the Branch I Aqueduct needed to be carefully exposed and unloaded to prevent inadvertent movement of the pipe. 
 
The repair project has restored the functionality of the underdrain within the project area, focusing on maintaining the underdrain functionality by using spot repairs (external and internal), full length lining in portions where underdrain functionality is not required, and replacement where trenchless rehabilitation was not feasible. As a result of this program, the Branch I Aqueduct continues to be protected against sulphate attack by the underdrain and is expected to continue to serve the City of Winnipeg for years to come.