Construction is set to start next week on a $2.7-million upgrade to the Conestogo Dam near Glen Allan in Mapleton Township.
The work involves upgrades to the stilling basin, which calms the water as it surges through the dam gates. The stilling basin can currently handle flows of 700 cubic metres per second (cms), while the dam gates are capable of releasing 1,400 cms. The upgrades will bring the stilling basin up to the same capacity as the gates.
The highest flow observed at Conestogo Dam was in 1975, when the dam passed about 590 cms.
Dave Schultz, spokesperson for the Grand River Conservation Authority, said the upgrades are needed to meet safety standards set by the Ontario Ministry of the Environment.
“Since the Conestogo Dam was built, there have been cases of dam failure around the world that have drawn a lot of concerns from people who build dams,” he said. “We’re giving more thought to what kind of possible scenarios could occur in the area. It’s just not just what kind of rainfall have we ever seen, but what kind of rainfall is possible.”
Schultz said the conservation authority and the MNR are also thinking ahead to the possible effects of climate change on water levels.
Work on the stilling basin is set to be completed in the fall of 2010. The cost of the work is divided between the GRCA and the MNR through its Water and Erosion Control Infrastructure program.
The stilling basin upgrade is one of two projects to bring the dam up to MNR standards. The second project is the construction of an emergency spillway that would allow water to flow around the dam in a special channel. Without the channel, extremely high flows could run over the top of the dam, eroding it and potentially causing a collapse.
Construction of a concrete-lined spillway would cost about $20 million and take three years to build. The GRCA is currently examining how the project could be financed.