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Thunderstorm watch ends for London as high water levels remain in Thames River watershed

The Thames River and Harris Park in London, Ont. on April 5, 2023. Marshall Healey/980 CFPL

A severe thunderstorm watch has ended for London, Ont. and Middlesex County area, however rain showers and a risk of thunderstorm remains in the forecast for Wednesday evening.

A severe thunderstorm watch remained in place as of 4 p.m. for Elgin County, while watches in Huron-Perth, Oxford County, and Sarnia-Lambton had ended.

Rainfall warnings remained in place for southern Huron and southern Perth counties, calling for rainfall amounts of between 30 and 50 millimetres.

A severe thunderstorm warning was issued for the London-Middlesex area shortly before 2:30 p.m., but the warning ended shortly before 3 p.m.

“We did have one band of thunderstorms move through earlier today. Most of the other activity has stayed off to the north and the northwest of London,” Geoff Coulson, a warning preparedness meteorologist with Environment Canada, said around 2 p.m.

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“A line of thunderstorms is currently moving through the Sarnia and Detroit areas, that’s likely going to move through the London area in the next couple of hours,” he said.

Another band of thunderstorms in northern Indiana and Ohio could also move through the area in the afternoon and early evening, he said.

“There’s still that potential it could come in a very short burst, not a very long-lived period of time for the storm to move through, and still have the capability of giving a good soaking rain in that 15- to 25-millimetre range,” he said.

“The risk in terms of the heavier showers and thunderstorms is likely to be anytime through this afternoon into about 7-8 p.m. After eight this evening, there could still continue to be some showers off and on in the area, but they’re not likely going to produce much in the way of accumulation.”

Wednesday’s rainfall will come in addition to the 21 millimetres of precipitation the city saw early Tuesday, and the more than 60 millimetres it saw between early Friday morning and Saturday afternoon, according to Environment Canada data.

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The recent soaking has resulted in elevated water levels across the Thames River watershed, with ongoing flooding reported in lower-lying, flood-prone areas, such as Gibbons, Harris and Thames parks, said Eleanor Heagy of the Upper Thames Conservation Authority.

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The agency issued a watershed conditions statement for the upper Thames River area over the weekend. The statement will remain in place until at least Friday.

“There’s still high water going through London, not as high as it was last weekend, but certainly the rivers are a little bit above normal still, and we’re expecting that to continue for a little while, certainly into the long weekend,” Heagy said.

Although water levels in streams north of the city have dropped closer to normal levels, because the ground is already saturated, any rainfall the region receives on Wednesday will cause further fluctuations, she said.

“I think we should expect to see that over the day, especially if we do get that rain, but overall the trend is that creeks and rivers are slowly returning closer to normal.”

UTRCA monitors show water level spikes across the London area over the weekend, with Fanshawe Reservoir rising from 1.5 metres to just over five metres between early Saturday and early Sunday. Levels had fallen back to roughly one metre as of mid-day Wednesday.

In the Coves, a former oxbow of the Thames River near downtown, water levels rose from 0.75 metres on Friday afternoon to nearly 3.5 metres as of late Saturday night, according to UTRCA data.

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Farther downstream near Byron, the Thames River saw water levels rise from just over three metres on Friday afternoon to about 5.5 metres as of late Saturday, along with a water flow of more than 550 cubic metres per second, up from 150 as of mid-day Friday.

As of Wednesday afternoon, levels sat at just under four metres, with flow measuring 250 cubic metres per second.

Water levels remained high Wednesday in Dingman Creek near Highbury Avenue at 1.75 metres, down from 2.5 metres late Saturday, but still above the roughly 0.6 metres recorded early Friday.

“We just want to make sure people realize that, regardless of how you think of the Thames normally, at this time it is quite hazardous,” Heagy said.

“The ground is so wet and muddy it’s easy to slip. You don’t want people having any accidents and no one going into the water by accident. Also, keep pets away.”

Elsewhere in southwestern Ontario, watershed conditions statements were also in place Wednesday from Catfish Creek Conservation Authority and Kettle Creek Conservation Authority.

A flood warning remained in place by the Lower Thames River Conservation Authority, which spans an area west of London to east of Windsor.

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The warning for the Thames River and local watercourses stated that ponding, standing water and localized flooding in low-lying areas was anticipated on Wednesday as a result of the rain received over the weekend.

“Water levels on the Thames River are still high enough that flooding is occurring in the low-lying, mostly agricultural, river flats adjacent to the river from Delaware down to Chatham,” the warning, issued around the noon hour on Wednesday, reads.

“Water levels peaked around Thamesville early last evening and are slowly falling. Water levels peaked in Chatham early this morning and are now slowly falling as well. Water levels in the city should be expected to remain near peak levels throughout the day.”

The warning says water levels could remain high or rise further in the event of significant rainfall on Wednesday.

A flood warning was also in place from Long Point Region Conservation Authority.

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