The Ottawa River Regulation Planning Board (ORRPB) says as of yet, there are no indications this year’s spring thaw will cause any significant flooding, but that it is too early to predict how the thaw will affect water levels throughout the river’s watershed.
The ORRPB is a collaborative body made up of representatives from federal, Quebec and Ontario governments, as well as the agencies responsible for operating the large reservoirs in the Ottawa River basin.
As the body that works to monitor and manage water levels throughout the basin, it releases regular information about water levels and expected thaw conditions across the watershed.
The board’s most recent river conditions forecast, published Mar. 14, said while water levels downriver of Pembroke are expected to increase slightly due to the weekend’s heavy rain and warmer temperatures, levels should return to normal by the end of this week.
Despite this temporary increase in water levels, the board stated spring thaw conditions, including the amount of water in the snow and the average temperatures around zero degrees over the past two weeks, are more or less average for this time of year, and are conducive to moderate melting of the snow.
“It is too early to predict the magnitude and timing of the peak in the main stem of the Ottawa River. At this time, there are no indicators of concern,” concluded the board’s overview of early spring conditions, also published Mar. 14.
“However, the possibility of significant flooding cannot be excluded at this early stage of spring, as weather conditions, such as snowfall and heavy rain, in the coming weeks will influence the intensity of the freshet [spring thaw]. These conditions are often known only a few days before they occur.”
According to historical data available publicly through the ORRPB’s website, spring freshet usually begins around the start of April.
MRC Pontiac public security coordinator Julien Gagnon said the biggest factor leading to flood risk during freshet is heavy rainfall.
“The ground is so saturated with water at that time of year that any water isn’t soaking into the ground. It’s just running off into the streams, creeks and rivers that then all end up in the Ottawa River,” he said.
Gagnon said Monday that despite the weekend’s rain, he’s not yet concerned about spring flooding.
“These are mostly due to bad drainage or no ditches on these roads,” he said. “One day of rain has not drastically increased my concerns for flooding in the Pontiac [ . . . ] I remain optimistic so far.”
On Mar. 17, the observed water level at Lac Coulonge was 106.44 metres above sea level, which is also the historical median level for that date.
The low-level flood limit at Lac Coulonge is 107.5 metres, which affects certain residences very close to the shoreline. The critical water level for this location is 108 metres, at which point many homes begin to flood.
ORRPB’s next forecast will be published Mar. 18 on ottawariver.ca.
Local officials monitoring flooding risks
In the past month, the MRC Pontiac’s flood prevention task force has been ramping up its meetings to prepare for the upcoming freshet.
Gagnon said at the group’s last meeting in February, members observed the ORRPB’s water levels and forecast, as well as the drawdown of the water out of the reservoirs.
He said at their next meeting on Mar. 25, in addition to regular water level checks, they will begin discussing a communications plan for the mayors to take back to their municipalities.
“We will be talking about emergency response preparedness because most of the mayors attend this task force,” he said. “We’ll start talking about municipal preparation and ensuring that we talk about it with the administration and each municipal office.”
In 2017 and 2019, flooding from the Ottawa River and its tributaries caused widespread damage across the Pontiac, destroying homes and forcing people to evacuate.
According to the MRC Pontiac’s public security department, over 1,100 residences were flooded, during the 2017 and 2019 floods, while over 800 people were evacuated.
A combined $4.3 million was given by the province in emergency assistance to individuals affected by those floods, and over $100,000 to municipalities.
Gagnon said the MRC and local municipalities learned a lot about flood prevention during the 2017 floods.
“Municipalities did not have the knowledge or skills of how to manage the effects of flooding, and allowed many people to remain in their homes while it may have been imprudent to do so,” he wrote in an email.
“By 2019, evacuation of entire neighbourhoods was made mandatory in many municipalities to protect those residents.”
Gagnon added that now, three-quarters of Pontiac’s municipalities have emergency systems in place to alert citizens of evacuation orders or of essential flooding-related information.
He said that going into the flooding season, members of the public should be aware about their own personal flooding situation, and encouraged them to check the ORRPB website for updates, as well as a document available on the MRC’s website about how to prepare and react to flooding.
