Heavy Rain Leads to High Water Levels Across Thames River Watershed
Watercourses across the Upper Thames River watershed were on the rise in early April, thanks to heavy spring rain. With weather forecasts calling for up to 75 mm of rain on saturated ground, there was the potential for a significant flood event.
The Upper Thames River Conservation Authority (UTRCA) issued a Water Conditions Statement – Flood Outlook on Tuesday, April 1st, to alert municipal flood coordinators that the rainfall could cause anything from minor flooding in low-lying areas to more significant flooding similar to the February 2018 event, depending on how much rain materialized.
By Thursday, April 3rd, rain gauges across the watershed reported 35-55 mm of rain, with many measuring more than 55 mm. Streams and rivers responded quickly to the runoff, peaking on Thursday afternoon in upstream communities including Mitchell, Stratford, and Tavistock. Peak flows moved through London later that evening and into the early hours of Friday. Additional rainfall on April 5th kept river levels high into the following week.
UTRCA staff closely monitored the evolving conditions and operated flood control reservoirs at Fanshawe, Wildwood, and Pittock Conservation Areas to reduce flooding in communities downstream.
While significant flooding was avoided, there was extensive localized flooding in low-lying areas, highlighting the importance of keeping development away from flood-vulnerable areas.
Dingman Drive at Highbury Avenue, London, April 3, 2025.
This event was the first spring flood for the safety boom installed last fall above Fanshawe Dam. The boom prevents reservoir users from getting too close to the dam and the turbulent water around it but also proved effective in preventing significant debris from going through, and potentially getting caught in, the dam gates.
Safety boom above Fanshawe Dam, April 4, 2025.
In terms of the frequency of this flood event, the Medway Creek subwatershed experienced a 1 in 10-year flood (10% chance of occurring in any given year) while the rest of the watershed saw anywhere from a 5-year flood (20% chance) to a 2-year flood (50% chance).
Medway Creek at 12 Mile Road, Middlesex Centre, April 3, 2025.
This was the second flood event of the year. The winter of 2024/2025 saw extensive snow cover — UTRCA’s snow survey and weighing gauge data indicated the watershed snowpack contained the equivalent of 100 mm of water, on average. This amount had the potential to cause significant flooding if accompanied by rain or rapid thaw. Fortunately, March brought ideal melting conditions: daytime temperatures were not too warm, overnight lows dipped below freezing, and there was no significant rainfall near the end of the month. As a result, the snowpack melted gradually.
Still, the melt, combined with several rain events and rising temperatures into March, contributed to elevated water levels. By early April, there was limited capacity in the soil to absorb additional moisture, leading to faster runoff and more widespread flood impacts.
Since late February, the UTRCA has released eight flood bulletins. Throughout each flood event, the UTRCA has reminded residents to stay clear of watercourses. Fast-moving, cold water combined with unstable banks creates dangerous conditions, and people are urged not to take shelter along riverbanks or in flood-prone areas. Parents are especially reminded to keep children and pets well away from waterways.
The UTRCA continues to monitor watershed conditions and encourages residents to stay informed about future flood events on our website: thamesriver.on.ca/water-management/flood-bulletins.