Watershed Conditions Statement - Flood Outlook

Message Number: 2024-15

Issued: July 16, 2024, at 4:00 PM EDT

From: NBMCA Duty Officer, Angela Mills

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.

The general public is advised of these messages through the www.nbmca.ca website with the flood status icon and a link to information about current conditions. NBMCA also circulates these messages to local media and social media, posting on Twitter (@theNBMCA), Instagram (nbmcainfo), and Facebook (NBMCA).

The public is invited to share photos of watershed conditions on social media using #NBMCAFlood.

Media Release issued July 16, 2024

https://www.nbmca.ca/watershed-management/flood-forecasting/flood-watch-status-terminology/

North Bay-Mattawa Conservation Authority Subwatershed map — *^{NBMCA Subwatershed Map}*

Lake Nipissing

Flows through the dams are based on daily analysis of the current status of the lake and river and as agreed to by the Sturgeon-Nipissing-French-Wanapitei Water Management Group. Weather forecast is considered, along with the inflows from the upper watersheds and outflows through the dam to the French River.

You can view the current level on Lake Nipissing at North Bay on the graph below and the French River at the Water Survey of Canada (WSC) website. Fluctuations in the levels are a result of the strong winds affecting the movement of surface water. Water level and flow information for the South River and Sturgeon River systems is available from Ontario Power Generation (OPG).

Flood warnings for Ontario can be found on the Ontario Flood Forecasting and Warning website.

Why the fluctuation in water level readings on Lake Nipissing? Lake Nipissing can sometimes act like a bathtub, with water shifting in the lake, depending upon wind direction, speed and atmospheric pressure - known as a wind surge or seiche. At times the wind can have such an impact that it may result in the level being higher or lower at the French River gauge compared to the gauge located on the North Bay shoreline.

Mattawa River

The current Ottawa River water level may be viewed at the Water Survey of Canada (WSC) website (note that there is a delay of several hours, and 100m should be added to the gauge reading for metres above sea level).

The Ottawa River Regulation Committee and Ontario Power Generation which operates the Otto Holden Dam provide information online regarding the management of water levels on the Ottawa River. To view water levels and current conditions on the Ottawa River visit the Ottawa River Regulation Planning Board and Ontario Power Generation.

Watercourses and Monitoring throughout the Watershed

There are other watercourses within the NBMCA jurisdiction which are monitored by NBMCA and other agencies. These gauges are maintained by Water Survey Canada - Environment Canada and can be viewed in real-time online.

In addition to the Water Survey of Canada gauges, there are other staff gauges which are monitored by NBMCA or the Ministry of Natural Resources and Forestry: