Mid-month Update: Upper Thames River Watershed moves back to Level 1 Low Water Condition (low water mid-month update, June 23, 2021)
30 Day Precipitation
In the past 30 days (to June 22), the Upper Thames River watershed received an average of 66 mm of precipitation or about 83% of normal, ranging from approximately 106 mm west of Stratford, to 41 mm near Ingersoll. The long term average for June is 80 mm, measured at the London Airport and reported by Environment and Climate Change Canada (ECCC).
90 Day Precipitation
In the past 90 days (to June 22), the watershed received an average of 159 mm of precipitation (about 66% of normal), ranging from approximately 213 mm in Mitchell, to about 104 mm in the Woodstock area. The long term three month average total for this period is 240 mm, measured at the London Airport and reported by ECCC.
A Level 1 Low Water Condition is triggered if the three month or one month total precipitation falls below 80% (but above 60%) of the long term average value.
Monthly Streamflow
30 day average streamflow was generally between the 10th and 25th percentile flow rates, which indicate moderately 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 June 22. Drawdown begins at Pittock Reservoir on July 01. Wildwood Reservoir (Trout Creek upstream of St. Marys) is typically more difficult to fill. As of June 22, Wildwood Reservoir is about 1.0 metre below its target elevation for that date.
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 in the early spring and reached its target summer level. Mitchell Reservoir traditionally is filled a couple weeks after Orr. At this time, this reservoir has not filled due to the dry spring, although recent rains have raised the level to about 0.6 metres below its target summer level.
Recommendation
It is recommended that the Upper Thames River watershed move from a Level 2 to a Level 1 Low Water Condition based on the following factors:
- average 30 day precipitation has improved to within the normal range,
- three month precipitation totals across the watershed generally between 60% and 80% of the long term average, and
- stream flows improving from earlier in the spring.
Find out more about the Ontario Low Water Response program.
Contact: Eleanor Heagy, Communication Specialist