Rising water forecast upstream of Iroquois on the St. Lawrence, and for communities along the Ottawa River

Lake St. Lawrence. Nation Valley News file photo

Latest flood watch from South Nation Conservation

NATION VALLEY — Flood waters peaked and began receding this week on the South Nation River and its tributaries — but forecasted rain this weekend might produce flooding again in low-lying areas on the local river system, says the local watershed authority.

Levels remain above average in some places, according to South Nation Conservation (SNC), which advises residents in areas prone to flooding to take necessary precautions because of the weather.

SNC’s jurisdiction also overlaps broad swaths of territory actually drained by the Ottawa River in the north and the St. Lawrence River in the south.

Upcoming peak water levels across some areas of the Ottawa River basin are expected to be similar to those experienced during the flooding of May 2017, says SNC, whose specific areas of concern include Alfred-Plantagenet and Clarence-Rockland. Those two communities are expected to peak again this Monday, April 29, at levels slightly below those observed two years ago. Levels are already high and making headlines, and SNC reports that all flood-prone areas along the Ottawa from Lac Coulonge, down to the Montreal Archipelago remain at risk.

In the south, SNC advises residents upstream (west) of Iroquois that the St. Lawrence River has been rising in concert with higher water on Lake Ontario.

While Lake Ontario’s current level is above average, it still falls within the historical range of observed levels at this time of year and currently well-bellow the extreme highs of 2017.

Water levels between the Iroquois Dam and Moses-Saunders Dam in Cornwall have been rapidly increasing due to reduced outflows from the latter dam, to limit flooding downstream near Montreal, according to SNC. However, this particular local  stretch of the St. Lawrence River — also known as Lake St. Lawrence — almost never overflows its banks because levels are tightly controlled by dams at either end of the artificial lake created during the 1950s Seaway project. Gates at Iroquois have been lowered to suppress water levels in Lake St. Lawrence.

Back in the Ottawa River basin, the Mississippi Valley Conservation Authority warns that water levels in the Constance Bay area are projected to rise another 50 to 60 cm through the end of this week. Levels were already estimated to be very close to those reached at the height of the May 2017 flooding.

Similarly, the Rideau Valley Conservation Authority says that Britannia (Grandview Road and the Belltown Community) water levels are expected to increase an additional 50 to 60 cm over the next four days.  Levels are currently forecast to be very close to those experienced at the height of the May 2017 flood.  East of Cumberland Village (Boise Village, Morin Road, Leo Lane) water levels expected to increase an additional 40 to 60 cm above the current elevation over the next four days.  Levels in those communities are currently forecast to be just below those experienced at the height of the May 2017 flood.

Due to the forecast uncertainty, officials can’t say with certainty how quickly water levels will rise and when levels  may peak.

Residents in flood-prone areas are encouraged to closely follow evolving conditions and to take necessary measures. Sandbags are available to residents in flood-prone areas.

Residents are advised to stay away from watercourses where flows are high and where banks might be unstable. Parents are encouraged to explain dangers to children.

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