Watershed Conditions Statement – Flood Outlook
Watershed Conditions Statement – Flood Outlook gives early notice of the potential for flooding based on weather forecasts calling for heavy rain, snow melt, high wind or other conditions that could lead to high runoff, cause ice jams, lakeshore flooding, or erosion.
If you have a flood emergency, please contact your municipality. If you live in an unincorporated township, please contact the Ministry of Natural Resources and Forestry (MNRF) – North Bay District.
A Watershed Conditions Statement – Flood Outlook is in place for the North Bay-Mattawa Conservation Authority watershed.
Current Conditions:
Significant rainfall associated with intense thunderstorms yesterday (Jul 15) triggered flash floods in urban parts of North Bay and caused road washouts in Chisholm. Additional thunderstorms are forecast for this evening through tomorrow.
Water levels in the Wasi River and Kaibuskong River (Lake Nosbonsing) subwatersheds increased in response to this rain and remain high for this time of year. Water levels in other areas of the watershed are normal for this time of year.
Current water levels can be viewed by searching Station Names “Ottawa River”, “Mattawa River”, “Chippewa Creek”, “La Vase River”, “Wasi River”, and “Lake Nipissing” at https://wateroffice.ec.gc.ca/search/real_time_e.html
Forecasted Conditions:
Environment Canada has issued a Severe Thunderstorm Watch and the Ministry of Natural Resources and Forestry has issued a Provincial Flood Watch for the NBMCA area. Unstable weather is forecast to continue through this evening (Jul 16) as multiple frontal systems push through, bringing rainfall and the risk of strong thunderstorms, high winds, and hail. There is a risk of strong thunderstorms that could bring 25-60+ mm of rain throughout the Lake Nipissing to Mattawa area and extending southward.
Water levels on the Ottawa River are managed by upstream dams and reservoirs operated by provincial and federal governments. Forecasts are available at https://ottawariver.ca/
The water level on Lake Nipissing is regulated by dams operated by the federal government. Forecasts are available at https://www.tpsgc-pwgsc.gc.ca/ontario/eaux-water/renseignement-information-eng.html
Historic Flood Conditions:
For comparison, in response to intense rainfall of 25 mm in 45 minutes, and a total of 37 mm on June 26, 2023, water levels on Chippewa Creek rose by 120 cm in 90 minutes. Additional rain of 53 mm on June 27 caused water levels to rise again by 108 cm, with most of the increase occurring in less than three hours.
Additionally, approximately 50 mm of rain was recorded near Astorville over a span of 3 hours yesterday, and the Wasi River responded by an increase of 56 cm in six hours. This corresponds to an increase in flow from 2.3 m3/s to 11.3 m3/s.
Risk:
High-intensity and/or significant amounts of rainfall can lead to increased runoff, streamflow and flooding. Areas that were impacted by yesterday’s storms may be more vulnerable to additional rainfall. Forecast rainfall over the next two days is likely to cause higher flows and localized flooding in low-lying and flood-prone areas, as well as overland flow during high-intensity rainfall.
All residents, especially those in low lying areas, are encouraged to monitor the conditions that are developing. Banks adjacent to rivers and creeks are 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.
Municipalities are encouraged to monitor water crossings for debris that may affect the movement of water through culverts and bridges. A close watch on local conditions and updated forecasts and warnings from Environment Canada is also recommended.
Staff at the North Bay-Mattawa Conservation Authority will continue to monitor weather and watershed conditions and update this message based on the changing weather and streamflow conditions.
This message will be in effect until (or updated before) Thursday, July 18, 2024 at 4:00 PM EDT.
