The warm spell last week melted some of the snow and ice in the Grand River watershed, but not enough to reduce the risk of flooding later in the spring according to officials at the Grand River Conservation Authority.
Even with two days of warm temperatures on Feb. 17 and 18, the weather forecast Feb. 19, with Environment Canada forecasting normal temperatures and above normal precipitation over the next three months.
That means there is lots of time to replace the snow and ice that will be lost this week, said Stephanie Shifflett, a water resources engineer with the GRCA. It also means there’s still a high risk of spring flooding.
“The flood risk for spring is high due to the high amount of water contained in the snowpack,” Shifflett told municipal flood co-ordinators on Feb. 16 at their annual meeting at GRCA headquarters. “The flood risk due to ice jams is high, due to the volume and strength of ice in the river system.”
She pointed out that before that week’s brief warm spell, there was an above-average amount of snow in the northern portion of the watershed (Dufferin County) and south of Cambridge.
Snow cover was average in the central portion through most of Waterloo Region and Wellington County.
Ice covered most of the Grand River and its tributaries prior to the melt. In addition, soils in most of the watershed were either frozen or saturated with water, which results in more runoff during a melt.
“Given the high amount of water in the current snowpack and the saturated or frozen ground conditions, the potential for a major flood is higher than normal if a significant rain event occurs along with a rapid spring snow melt,” said Shifflett.
Prior to the melt, the GRCA’s reservoirs had between 50 and 85 per cent of their storage capacity available, which was normal for that time of year, she said. That allows the GRCA to hold on to some of the water generated by the thaw this week and reduce water levels downstream. Some of that water will be released from the reservoirs gradually in coming weeks to ready them to take in water during the next melt.
The meeting was the annual gathering of municipal flood co-ordinators who are responsible for their municipality’s flood response. They meet at the GRCA to review the flood monitoring and warning systems and to receive a forecast on watershed conditions.
Information on river flows is available on the GRCA website at www.grandriver.ca in the River Data section. Information on the flood warning system is in the Flood Management section.
