Increasing Flood Risks Along Ottawa River - Ottawa River Regulation Planning Board

OTTAWA/GATINEAU, Monday May 1, 2023 — The Ottawa River Regulating Committee warns that levels and flows along the main stem of the Ottawa River are increasing in response to significant rainfall received over the last few days. Minor flood levels are occurring in multiple locations between Mattawa and the Montreal region. Major flood levels are expected to be exceeded in flood prone areas over the next few days. Areas of primary concern are identified and described in more detail below. Water levels are currently expected to remain 45 cm to 1 meter below historical flood levels of 2019 on the main stem of the Ottawa River. Additional bulletins will be published if flood risk is expected to increase. 

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River Conditions Forecast / Flooding Risk*:

Weather systems from the American Midwest and the Gulf of Mexico have brought a significant amount of precipitation over much of the basin over the last few days. These events have caused most of the remaining snow in the northern portion of the basin to melt. Additional precipitation is forecasted until Wednesday. Precipitation amounts already received and forecast to occur total up to 70 mm in some parts of the basin. Runoff from this precipitation and snowmelt is bringing additional water volumes to the Ottawa River, at a time when levels have already exceeded or are near major flood thresholds in several locations. The major flood threshold is defined as the level at which one or several streets are beginning to flood, with several houses/buildings or neighbourhoods being affected.

Based on the latest weather forecast and the best information available at this time, the following conditions are expected along the main stem of the Ottawa River over the coming week(+) :

(+) Forecast levels over a four-day period are provided on our website and updated daily as conditions could change quickly. Wind and wave effects are not included.

• Mattawa: Minor flooding is already occurring. Levels are expected to continue rising until they reach a peak of about 154.55 – 154.60 m on Thursday. This corresponds to a rise in level of 45 to 50 cm compared to the observed level on Monday May 1st at 8h00.
• Pembroke: Minor flooding is already occurring. Levels are expected to continue rising until they reach a peak of about 113.30 m 113.35 m tomorrow or Wednesday. This corresponds to a rise in level of 40 to 45 cm compared to the observed level on Monday May 1st at 8h00.

• Whitewater Region: Levels are expected to exceed peak levels observed last week (April 21-23) by 50 to 55 cm. Flows at that location are expected to slightly exceed those experienced in early May 2017.

• Iles-Aux-Allumettes / Lake Coulonge: Levels are expected to exceed peak levels observed last week (April 21-23) by 50 to 55 cm. Levels at Lake Coulonge are expected to be similar to those observed in early May 2017.

• McNab/Braeside / Arnprior / Chats Lake: Levels are expected to exceed peak levels observed last week (April 21-23) by 30 to 35 cm. These levels are lower than those observed in early May 2017.

• Constance Bay / Aylmer / Lake Deschenes: Levels are expected to exceed peak levels observed last week (April 21-23) by 25 to 30 cm. These levels are lower than ththose observed in early May 2017.

• Gatineau (Hull) to the Montreal Region: Levels are expected to exceed peak levels observed last week (April 21-23) by 50 to 60 cm in Gatineau (Hull marina) and Thurso. These levels are approximately 70 cm lower than those observed in early May 2017.

If you have a flood emergency, please contact your municipality.

Reservoir Regulation Strategy

The principal reservoirs located in the northern part of the Ottawa River basin are retaining a large portion of the spring runoff caused by the ongoing rain events combined with snowmelt. Analyses will be conducted on a daily basis all through this week to optimize the use of the reservoirs to reduce river flows in downstream areas as much as possible. Dams located in the central and southern portions of the basin are essentially “run of the river” facilities with no significant storage capacity. These facilities are not able to reduce flows or the levels associated with increased spring runoff. During this critical freshet period, the Regulating Committee takes actions to mitigate the amount of flooding and will continuously monitor conditions at all points along the river.

The Regulating Committee works closely with provincial agencies responsible for issuing flood-related messages. In Ontario, Conservation Authorities and District Offices of the Ministry of Natural Resources and Forestry issue local flood-related messages and information to municipalities, Indigenous communities and other key agencies involved in flood preparedness and response. Current flood-related messages can be viewed on-line on the individual conservation authority websites and on the provincial flood webpage: https://www.ontario.ca/flooding. In Quebec, the Ministère de la Sécurité publique through the Centre des opérations gouvernementales and the Regional Directorates of Sécurité civile collaborate with municipalities to protect residents. Monitoring of flood conditions can be viewed at https://vigilance.geo.msp.gouv.qc.ca/carte.

For More Information

• Website: Current and forecast conditions on the Ottawa River along with conditions at the principal reservoirs in the system may be obtained by consulting our website. A general four-day forecast is also provided at key locations within the basin during the spring freshet period.
  • www.ottawariver.ca (English)
  • www.rivieredesoutaouais.ca/ (French)
• Telephone: You can call 1-888-621-0059 to hear a recorded message describing the river conditions forecast.
• Twitter: Follow us to be notified when press releases are issued, when we begin daily updates of the River Conditions Forecast message or the four-day forecasts at reference locations on our website, or when news bulletins are posted on our website.
  • www.twitter.com/ORRPB (English)
  • www.twitter.com/CPRRO  (French)

About the Ottawa River Regulating Committee

The group consists of the following agencies that are responsible for the collaborative flow management of the principal reservoirs within the Ottawa River watershed: Hydro-Québec, Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs du Québec, Ontario Power Generation, and Public Services and Procurement Canada. In Ontario, the Ministry of Natural Resources and Forestry, as an associate member of the Regulating Committee, contributes important hydrometeorological information and plays a key role in disseminating information in Ontario.

Frequency of Press Releases: The Regulating Committee issues a press release when the spring freshet season is starting on the Ottawa River. It issues other press releases, as needed, when it anticipates that river conditions on the main stem of the Ottawa River may exceed significant flood levels.

*Subject Area: The focus of the “River Conditions / Flood Risk” report is on the main stem of the Ottawa River (from the Lake Timiskaming outlet down to the Montreal region). River conditions in tributaries of the Ottawa River, including the Abitibi-Timiskaming area, may differ. For additional information, please communicate with the Ottawa River Regulation Secretariat using the ‘Contact us’ form on the website or leave a message at 819-303-5886 or 1-888-621-0059.