There was no storm. There had been no rain worth mentioning. And on 27 January the Grey Sauble Conservation Authority issued a Flood Watch for the Beaver River through Clarksburg and Thornbury, with water levels up sharply inside twenty-four hours.
What did it was ice.
What happened
Days of extreme cold on a river that had not fully frozen over produced frazil ice in the turbulent reaches upstream of the villages. Frazil is not sheet ice — it is fine crystals forming in supercooled water that is moving too fast to set, and it travels with the flow until the flow slows down.
In the reach through Clarksburg it began to collect. An obstructed channel carries less water, so the level came up, and it came up fast enough that the flood watch was issued and then updated two days later. Town of The Blue Mountains crews worked at the ice with a long-reach excavator. Lower Valley Road went under and was closed. By 3 February levels through the village had stabilised, the road reopened, and the watch expired.
Why it is worth writing down
Because it is a flood mechanism that appears on no restoration page written for the whole of Canada, and it is one of the reasons a page about water damage in Thornbury cannot honestly be the same page as one about water damage anywhere else.
It also has two practical consequences for anybody who owns property along the Beaver.
The first is that a cold snap is a reason to pay attention here, not a reason to relax. Everywhere else in our service area the winter risk is a pipe inside a building. On this river the winter risk is also the river.
The second is that the warning window is short. A rain event gives days of notice through the graded messages both authorities publish. Frazil built up inside a day.
What to do about it
Subscribe to Grey Sauble’s flood notices if you are on the Beaver, and to the Nottawasaga Valley Conservation Authority’s if you are on the Pretty River, Black Ash Creek, Lamont Creek, the Mad or the lower Nottawasaga. Both publish graded messages — a Watershed Conditions Statement, then a Flood Outlook, then a Flood Watch, then a Flood Warning — and both send them to local media.
Moving what matters off a basement floor at the Watch stage costs an hour. At the Warning stage it is usually too late.
And check your policy while you are thinking about it. Overland water is an optional endorsement in Ontario and it is separate from sewer backup, which is separate again from groundwater seepage. Whether to claim water damage on your insurance sets out which is which, and storm and overland flood cleanup covers what actually happens to the materials afterwards.
River water is contaminated water whatever it looked like arriving, so carpet and underlay that sat in it come out. That is the part people find hardest to hear, and it is better heard in February than in July.