There’s a high risk of flooding when the spring melt takes place, says a forecast issued by the Grand River Conservation Authority (GRCA) recently.
The forecast was presented at the annual meeting of municipal flood coordinators who met at the GRCA head office in Cambridge. Though the weather was relatively dry in December and January, regular snowfalls in the last few weeks have resulted in accumulation of 20 to 50 centimetres across the watershed, said Stephanie Shifflett, a water resources engineer with the GRCA. Snow accumulation is highest in Dufferin and Wellington counties.
The snow cover equates to about 40 to 80mm of water on the ground.
The snow doesn’t have the capacity to soak up much water when spring rains hit. Underneath the snow, much of the ground is frozen, so when the melt begins, most of the water will run off rather than soak into the ground.
The persistent cold temperatures are expected to continue into March, which also raises the risk.
“The later the spring melt, the higher the likelihood of a rapid melt and river ice breakup,” Shifflett said.
Almost the entire river system is covered by ice, so a rapid melt raises the risk of ice jam flooding. An ice jam can occur when ice floating downstream accumulates at a low spot or a bend in the river, blocking the flow of water, causing it to back up and spill over the banks.
At the mouth of the river at Port Maitland, Lake Erie is largely frozen over. If that persists into the spring melt, there is a risk of flooding in the lower Grand as water and ice moving downstream are blocked from entering the lake. If that looks likely, the GRCA will work with Haldimand County to call in a Canadian Coast Guard ice breaker to clear the mouth of the river.
The GRCA operates seven reservoirs which are used to capture water from the spring melt. That has the effect of lowering river levels downstream of the reservoirs.
The reservoirs have between 60 and 90 per cent of their storage space available, which sets them up to handle large inflows of water.
The GRCA works closely with municipal officials to prepare each year for the spring melt. The authority is responsible for monitoring weather conditions and issuing warnings to municipal flood coordinators. It’s then up to the municipalities to implement their local flood response program by warning residents, closing roads, managing evacuations or taking other actions.
The meeting of flood co-ordinators on Wednesday was one of a series held during the early part of the year to get ready.
Residents can learn more about the GRCA’s flood warning and response program on the website at www.grandriver.ca. They can get flood warnings from local media, or directly from the GRCA via Twitter at @grca_flood_msg or through the GRCA’s email News service. Information on how to sign up for emails is in the Newsroom Section of the website.
