Message # 2020-11
Issued: 11:30 a.m., Tuesday February 11, 2020
Subject: FLOOD WATCH issued for Otonabee River.
Issued to: Municipalities of Selwyn, Douro-Dummer, Asphodel-Norwood, Otonabee-South Monaghan, Cavan Monaghan, City of Kawartha Lakes, City of Peterborough and Trent Hills, and Otonabee Conservation’s other partners in flood emergency management.
This FLOOD WATCH is issued to alert municipalities, residents and businesses that flood conditions are a possibility.
This past weekend, extreme cold air temperatures resulted in frazil ice generation and jamming that, in turn, caused water levels on the Otonabee River to rise about 0.7 metres. Then, on Sunday, above-seasonal air temperatures brought relief. Since, water levels have receded about 0.4 metres and continue to slowly go down. However, this downward movement in water levels is expected to reverse as the current calm, mild weather will give way to accumulating snow and some of the coldest temperatures of the year so far.
Beginning Wednesday overnight, and continuing into Thursday, a low pressure system will invade the Region bringing snow. Then, starting Thursday afternoon and continuing through much of the Family Day weekend, a mass of Arctic air will dominate the Region resulting in a significant temperature drop, accompanied by bitter wind chills ranging from -20 to -30 degrees Celsius. Snow, cold air temperatures, and wind chill will cool the surface water temperature of the Otonabee River below the freezing point (i.e., super-cooled). The Otonabee River flows are too fast and too turbulent to form a solid cover of ice, and instead, the super-cooled water will form “frazil” ice crystals – a kind of sticky slush ice.
As frazil ice is carried downstream it will eventually come to rest against obstructions (e.g., islands and bridges), in low velocity areas (bends and slope reductions) or in areas of channel constrictions. Where it comes to rest, it will accumulate. Where frazil ice accumulates, it is likely to cause a restriction of water flow downstream, thereby resulting in a rise of water and possibly flooding behind the frazil ice jam.
There is potential for flooding on the Otonabee River due to frazil ice generation, accumulation and jamming during this coming period of snowfall, extreme cold air temperatures and wind chill. Therefore, residents and businesses in low-lying areas along the shores of the Otonabee River are strongly encouraged to take action to limit or prevent damages well ahead of the start to the Family Day weekend.
Milder Pacific air is expected move into the Region next week, and therefore, this FLOOD WATCH message will expire TUESDAY, February 18th, 2020.
Gord Earle | Flood Forecasting & Warning Duty Officer | 705-745-5791 x 214
250 Milroy Drive, Peterborough, ON K9H 7M9
firstname.lastname@example.org | Flood Watch Hotline 705-745-5791 x 228