Wednesday, August 5, 2020

Flooding expected to start Saturday in Chatham

colour Foundation

Here is the latest information from the St. Clair Region Conservation Authority, regarding the conditions of the Sydenham River:

Sydenham River is still frozen but slowly deteriorating

The Lower Thames Valley Conservation Authority issued this information about the conditions along the Thames River:

Starting yesterday, warm temperatures arrived in the region and daytime high temperatures are not expected to dip below freezing again. Most weather forecasts are calling for 10-20 mm of rainfall from Thursday through Sunday for the Lower Thames watershed. The warm temperatures and rain will melt the remaining snow in the Lower Thames over the next few days. The Thames River will begin to rise and local flooding may occur in the low lying areas and on the region’s smaller watercourses as some roadside and agricultural ditches are still filled with snow and ice making it difficult for the water to drain off the landscape.

While the Lower Thames watershed has lost most of its existing snowpack, the same can’t be said for the Upper Thames. Recent snow surveys suggest that there is around 100 mm of rainfall equivalent stored in the snowpack upstream of London. The warm temperatures and the expected 20-35 mm of rainfall predicted for Thursday through Sunday in the Upper Thames watershed will cause that snowpack to start melting and that runoff to make its way downstream. The river flats (those being the low lying areas adjacent to the river) from Delaware to Chatham are expected to flood starting Saturday. Water levels in the downstream reaches can be expected to remain high all week. Persons undertaking agricultural activities in the river flats should be advised of these conditions.

With peak flows not expected to reach Chatham before some time mid next week, there is a lot of uncertainty with how this spring melt may progress. Weather forecasts become more uncertain the further out they get and rainfall predictions can change quickly. At this point, the Authority anticipates having to operate the 6th St. Backwater Dam at the mouth of McGregor Creek sometime mid-next week. If some of the higher predictions come to pass, there may be basement flooding for the businesses along King St.

From the Prairie Siding Bridge downstream to the mouth at Lighthouse Cove, there is still some ice on the Thames River. Lake St. Clair at the mouth is also still iced in. While this does still present some risk of ice jam related flooding, there is still 4 or 5 days available for melting in the forecast before flows capable of creating flooding reach the mouth. There are also some stretches of ice upstream of Chatham, but they do not appear significant enough to cause any issues.

People should take extra caution and avoid the river, lakes, ditches, streams, and ponds. Any remaining ice cover will be unstable and dangerous. A combination of slippery banks, moving/melting ice and cold water is particularly dangerous. Parents should pay special attention to keep their children and pets away from the water.

The Lower Thames Valley Conservation Authority will continue to monitor conditions and will issue additional messages as required.

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