An Exceptionally Wet July in the Watershed 

July 2023 was one of the wettest Julys on record in the Upper Thames River watershed. It proved challenging for Water Information Management staff to control flows and manage reservoir levels at and below the three flood control reservoirs at Pittock (Woodstock), Wildwood (St. Marys), and Fanshawe (London) Conservation Areas.   

Staff estimate that the North Thames River above the Forks watershed (including Mitchell, Stratford, St. Marys, and part of London) received 195 mm of rain in July. The Thames River above the Forks watershed (including Woodstock, Thamesford, Ingersoll, and part of London) received 142 mm, and the Thames River below the Forks watershed (Forks to Delaware) received 181 mm. We would expect this type of rain event to occur every 75 years, or about a 1.3% chance any given July.Since 1950, the most rain ever measured at the London Airport was 204 mm in 1992. The 30 year “normal” for July precipitation at the London Airport is 82.7 mm as published by Environment and Climate Change Canada. 

Fortunately, the rain was fairly spread out through the month, with no major flooding occurring. However, the elevated water levels at reservoirs interrupted recreational activities. At Fanshawe Reservoir, there are also campsites in lower parts of Fanshawe Conservation Area that can become flooded if the reservoir is needed to reduce flooding downstream. This requires staff to temporarily move several camping trailers. An added challenge this July was keeping Harris Park in London dry for the annual Rock the Park festival, which is one of the first locations in the UTRCA watershed to flood during wetter months. At Wildwood reservoir, water levels were held up to 0.9 m above what is considered normal for the end of July, which is appreciated by recreational users but can pose other challenges including managing the floating dock system on the reservoir and meeting downstream flow constraints.   

Looking East at Harris Park toward Rock the Park setuup on Friday, July 14th afternoon.