Upper Thames River Watershed moves to Level 2 Low Water Condition (low water update, June 9, 2021)
One Month Precipitation
The Upper Thames River watershed received an average of 29 mm of precipitation in May (about 37% of normal), ranging from approximately 50 mm near Thamesford and west of London, to 13 mm near Stratford. The long term average for May is 78 mm, measured at the London Airport and reported by Environment and Climate Change Canada (ECCC).
Three Month Precipitation
The watershed received an average of 112 mm of precipitation from March to May (about 48% of normal), ranging from approximately 160 mm in London and Mitchell, to about 31 mm in the Kilworth area. The long term three month average total for this period is 234 mm, measured at the London Airport and reported by ECCC.
A Level 2 Low Water Condition is triggered if the three month or one month total precipitation falls below 60% of the long term average value.
18 Month Precipitation
The 18 month (December 2019 – May 2021) precipitation measured by ECCC at the London Airport totaled 1242 mm, or about 86% of normal. The 18 month long term average precipitation total for the end of May is 1442 mm.
Monthly Streamflow
May stream flows were generally below 10th percentile flow rates, which indicates dry conditions for this time of year.
Reservoir Status
The UTRCA maintains three large reservoirs and several smaller ones across the watershed. Two of the large reservoirs provide flow augmentation in the summer, meaning they store spring runoff and then slowly release this water back into the river system in the dry summer months. Pittock Reservoir (South Thames River in Woodstock) reached its target summer elevation and is maintaining that level as of the beginning of June. Hopefully, that elevation can be maintained until augmentation begins later this month. Wildwood Reservoir (Trout Creek upstream of St. Marys) is typically more difficult to fill. As of the beginning of June, this reservoir is about 1.2 metres below its summer target elevation.
Two smaller reservoirs that are drawn down in the fall and filled in the spring are Lake Victoria (RT Orr Dam) in Stratford and Mitchell Reservoir in Mitchell. Lake Victoria was filled earlier this season and reached its target summer level. Mitchell Reservoir traditionally is filled a couple weeks after Orr and, at this time, has yet to be filled due to the dry conditions.
Recommendation
Based on the one month and three month precipitation totals across the watershed being below 60% of the long term average (the Level 2 Low Water Condition criteria), and below normal stream flows, it is recommended that the watershed move to a Level 2 Low Water Condition.