The warm temperatures this week are being welcomed after a long winter, but they will also melt a lot of snow and ice causing water levels in creeks, rivers and lakes to rise.
The North Bay-Mattawa Conservation Authority (NBMCA) is issuing a "Flood Watch" for the entire watershed to highlight the potential for localized flooding, especially in low-lying areas, as the snowmelt progresses.
“Weather forecasts show warmer temperatures with minimal rain this week," said Angela Mills, NBMCA Duty Officer. "The sudden shift in weather to very warm temperatures, as high as around 20 ºC, is expected to trigger significant and rapid snowmelt. Urban watercourses in North Bay will respond more quickly to the snowmelt. Watercourses in rural areas may also experience high water levels,” Mills added.
The Chippewa Creek water level is fluctuating by around 20 cm in response to the alternating melting and freezing of the snowpack, influenced by daily high and low temperatures. Water levels on Wasi River increased by 31 cm, La Vase River increased by 23 cm, and Lake Nipissing increased by 6 cm since April 4, Water levels on the Ottawa River main stem from Mattawa to Montreal are expected to rise, per the Ottawa River Regulating Committee.
Lake-based flooding around Lake Nipissing is not expected at this time.
The snowpack water content is very high in the North Bay – Mattawa watershed, ranging between 181 mm and 238 mm of water equivalent (measured on April 6, 2023). This is an increase of 6 to 54 mm since the previous survey (March 31). Snow depths range between 51 and 60 cm in the NBMCA watershed, an increase of 5 to 10 cm since the previous survey.
For comparison, when river-based flooding occurred in April 2019, the snowpack water content was 123 mm (measured April 15, 2019). Rainfall of 31.8 mm was measured April 18, 2019. Daytime and overnight temperatures were above freezing.
Residents, especially those in low lying areas, are encouraged to monitor the conditions as they develop, and prepare accordingly. Shorelines of creeks and rivers will be very slippery at this time and, when combined with cold open water, pose a serious hazard. The public is encouraged to keep children and pets away from watercourses and off waterbodies.
Levels and flows along the Ottawa River are expected to begin increasing over the next few days as a result of the onset of the spring freshet period in the Ottawa River basin. The levels and flows in the Ottawa River are currently close to normal, but are expected to start rising. Precipitation and temperature increases throughout the spring freshet period may cause levels and flows to change rapidly.
With the snowpack being above normal for this time of year in several areas within the Ottawa River basin, flows and levels along the main stem of the Ottawa River are expected to rise above average values over the next few weeks. While it is not possible to forecast peak flow conditions at this time, meteorological events with above-normal temperatures or above-normal precipitation within the spring timeframe (next 6 to 8 weeks) can increase the risk of exceeding minor flood levels along the main stem of the Ottawa River (from Mattawa down to the Montreal Region).
