Flood warnings in effect along Grand River as ice jams build
Wednesday, February 6, 2019, 9:04 PM - Ice jams are raising flooding concerns along the Grand River, prompting officials to expand flood warnings on Wednesday evening.
The Grand River Conservation Authority (GRCA) issued a flood watch for much of the waterway, including the cities of Cambridge, upgrading to warnings for Brantfod and Caldeonia to Cayuga Wednesday afternoon when water levels rose and flow accelerated significantly after several ice jams gave way.
An updated statement from the authority Wednesday evening indicated flows had reached their peak along the river north of Cayuga, and were expected to reach peak flows through the day on Thursday from there south to Port Maitland, where the waterway empties into Lake Erie.
MUST SEE: DRAMATIC SCENES AS ICE CLOGS GRAND RIVER
River ice reportedly remained between Cayuga and Dunnville by Wednesday evening, and the GRCA warned ice jams and flooding were still possible before the last of the ice clears.
"The public is reminded to exercise extreme caution around all water bodies," read the conservation authority statement. "Banks adjacent to rivers and creeks are very slippery at this time and, when combined with current weather conditions, pose a serious hazard. Parents are encouraged to keep their children and pets away from all watercourses and off frozen water bodies, which will be weakened as a result of the warming trend."
WHAT IS AN ICE JAM?
An ice jam occurs when water builds up behind a blockage of ice. Ice jams form either when ice blocks a river and forms a lake, or when ice chunks in a river are blocked by something and build up to form a dam. Sometimes pieces of floating ice are carried with a stream’s current and then accumulate at any obstruction to the stream flow.
These ice jams can develop near river bends, mouths of tributaries, points where the river slope decreases, downstream of dams, and upstream of bridges. The water that is held back may cause flooding or flash flooding upstream. If the obstruction suddenly breaks then flash flooding may occur downstream.
These can result in massive flooding events. Ice jams can occur anytime from early winter to late spring depending upon changes in temperature which can cause alternate freezing and melting of water surfaces.
With files from meteorologist Jaclyn Whittal