Upper Thames River remains in Level 1 Low Water Condition (low water update, August 26, 2022)

The Low Water Response Team declared a Level 1 Low Water Condition in the Upper Thames River watershed on July 15, 2022. The following provides an update on precipitation, flows, and reservoir levels.

Precipitation

• 30 Day: The Upper Thames River watershed received an average of 89 mm of precipitation between July 27 and August 26 (about 114% of normal). The long term average for this period is 78 mm, measured at the London Airport and reported by Environment and Climate Change Canada (ECCC).
• 90 Day: The watershed received an average of 182 mm of precipitation between May 28 and August 26 (about 77% of normal). The long term average total for this period is 238 mm, measured at the London Airport and reported by ECCC.

A Level 1 Low Water Condition is triggered if the three month (90 day) total precipitation falls below 80% of the long term average value.

• 18 Month: The 18 month (January 15, 2021 – July 15, 2022) precipitation measured by ECCC at the London Airport totaled 1420 mm, or about 98% of normal. The 18 month long term average precipitation total for August is 1443 mm.

Monthly Streamflow

The August 26th 30 day average stream flows were generally between the 25th and 50th percentile flow rates, indicating little concern regarding low water in most locations, but the Middle Thames River, Thames River above Woodstock, and Fish Creek were within the range of a Level 1 Low Water Response condition.

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. Both Pittock and Wildwood Reservoirs (South Thames River in Woodstock and Trout Creek above St. Marys, respectively) reached target summer elevations this spring and are currently augmenting downstream flow, with their levels slowly decreasing. The water levels at both reservoirs are near the operating guideline elevation (0.08 m above at Pittock, 0.2 m below at Wildwood).

Recommendation

Based on the 90 day precipitation totals across the watershed being below 80% of the long term average (Level 1 trigger), and with still relatively normal 30 day stream flow in most locations, it is recommended that the Upper Thames River watershed remain in a Level 1 Low Water Condition.