Runoff from Forecast Rain and Warm Temperatures will Raise Water Levels (flood bulletin, March 21-27, 2023)
FLOOD WATCH
Issued March 21, 2023, at 5:50 p.m.; Valid until March 27, 2023
On Wednesday, a low-pressure system is expected to move into the province. This warm moist air mass will bring showers and periods of rain for most of southern Ontario, with total rain accumulation across the Upper Thames River basin potentially reaching 20 – 25 mm. An additional 20 mm of rain is possible on Saturday. Above zero temperatures are generally expected from now into the weekend.
The Upper Thames River Conservation Authority (UTRCA) conducted a watershed-wide snow survey on Tuesday which measured an average of 46 mm of water equivalent. This snow is already beginning to melt and release water. Ground conditions are saturated from the rain and snowmelt over the past weekend.
The UTRCA expects water levels to be elevated starting early Thursday, and to remain high over the weekend and into next week. If temperature and precipitation forecasts materialize, runoff totals and corresponding water levels are expected to surpass events experienced earlier this year, including this past weekend. Traditional low-lying floodplain areas are expected to be inundated and there is the potential for more serious flooding in some areas. UTRCA officials will be watching the event and forecasts closely.
Municipal staff are asked to monitor areas with drainage problems and low-lying flood prone areas for potential road and recreational trail closures.
The UTRCA’s flood control reservoirs at Fanshawe, Wildwood, and Pittock Conservation Areas are at seasonal levels and will be operated to reduce downstream flooding. Use of reservoir storage will consider the potential of more precipitation on Saturday and into next week. UTRCA officials are monitoring the situation and will update this bulletin as the event progresses and more data becomes available.
Residents are reminded to use extreme caution near all watercourses and caregivers are reminded to keep children and pets away from watercourses. Stream banks can be slippery and unstable and the water is extremely cold, fast-moving, and higher than normal. Any ice cover will be weakened and unstable. Flood control reservoirs are especially hazardous due to fluctuating water levels.
As water levels rise, it is not safe to take shelter along riverbanks or in low lying areas that are prone to flooding.