After a cold, snowy winter, area residents could be facing a spring of high water.
The possibility of flooding in the Grand River system is the highest it has been in years, according to flood control staff at the Grand River Conservation Authority (GRCA).
Municipal flood coordinators were told recently the snow pack is higher than it has been in about 30 years. Almost the entire river system is covered in ice, as is Lake Erie.
“The overall flood risk is high this spring,” Stephanie Shifflett, a GRCA water resources engineer, told flood coordinators at a recent meeting held at the GRCA office in Cambridge.
“A rapid melt or a rapid melt in combination with rainfall will result in very high runoff, high river flows and break up river ice,” said Shifflett.
The high volume of ice in the river system increases the risk of ice jams, she said.
Ice jam flooding can result in a very quick rise in water levels which means there is sometimes little opportunity to issue flood warnings.
A further complicating factor this year is the debris left behind by the December ice storm. As branches and trees are carried downstream, there is the chance they will clog bridges and culverts, resulting in localized flooding.
The GRCA does regular surveys of the amount of snow on the ground at 12 locations throughout the watershed. This gives flood engineers a good reading on how much water is contained in the snow.
This year, many of the snow survey locations are recording two or even three times as much water content in the snowpack as the long-term average.
Across the watershed the ground is already saturated with water as a result of the exceptionally wet year in 2013. Much of the ground is frozen. That means that when the spring melt starts, most of the water will run off into the river system rather than soak into the ground.
To prepare for the spring melt, the GRCA has been lowering the water levels in its reservoirs to create more storage space and allow the reservoirs to capture as much water as possible in order to reduce downstream flows.
The reservoirs can sometimes cut flows by 50 per cent.
However, there are limits to the amount of water they can hold, so sometimes it becomes necessary to release water from the reservoirs to protect the dams from overtopping.
GRCA staff are also keeping a close eye on weather conditions and testing the flood warning system to ensure that it’s working properly. Meetings have been held with municipal and emergency service personnel to ensure they’re ready for the spring melt.
Residents can get flood warnings from the GRCA website at www.grandriver.ca (to sign up for emails visit the “Newsroom” section).
