Understanding flows in the Ottawa River


THE JOURNAL FILE PHOTO/CARMEN MARIE FABIO

Hydro-Québec officials explained they do not have the ability to adjust the flow of water at the Carillon Dam in Pointe-Fortune. If the gates were closed, in a matter of hours, the water would overflow.

A team of experts and representatives from Hydro-Québec was on hand Tuesday evening for a public open-door seminar in L’Île-Perrot, aimed at reaching out to area residents and offering information on water level management in the Ottawa River basin. With the major flood events that took place in 2017 and 2019, this topic has been of great concern and a large number of people showed up for the event at the Paul-Émile-Lépine Community Centre, eager for the chance to meet face-to-face and ask questions of the people who manage the waterway.

Not as easy as turning off a tap

“There are many, many factors that contribute to water levels, and that created the ‘perfect storm’ scenario that led to the floods,” said Hydro-Québec Spokesperson Marie-France Barrette. Of the 13 reservoirs on the Ottawa River system, not all even have the capacity to control water levels. The dam at Carillon in Pointe-Fortune, for example, is built as a ‘flow through’ generator, where power is generated through the river’s natural flow and they do not have the ability to tamper with water levels from that site. “We could close the gate there, but when there is high water, in a matter of hours the dam would just overflow,” said Barrette.

PHOTO BY NICK ZACHARIAS

Hydrological Management Engineer Pierre-Marc Rondeau and Spokesperson Marie-France Barrette, both from Hydro-Québec, were on hand in L’Île-Perrot Tuesday evening to answer the public’s questions on water management in the Ottawa River basin.

Hydro-Québec (and their Ontario counterparts) do have the ability to control the flows and affect water levels starting from much further north, at facilities such as the one in Abitibi-Témiscamingue. However, according to Water Management Engineer Pierre-Marc Rondeau, only about 40 per cent of the overall shifts in water level can be influenced by the reservoir systems, while the other 60 per cent is beyond their control. “We can let the water go in the winter, and hold back in the spring,” he said, but in major events like the two in recent years there is nothing they can do to stand in nature’s way.

Difficult to predict

Smaller-scale adjustments under normal conditions are constantly made to manage water flows and attempt to maintain stable water levels in the system. Chloé Alassimone, Hydrometeorological advisor for Hydro-Québec, is part of the team tasked with assessing water levels and predicting how they will change ahead of time.

“There are a lot of factors to take into account. By taking measurements of the flow rate, by looking at the volume of snow on the ground and the temperatures in the current weather system, by seeing the amount of rainfall we are going to have, we produce previews for five to nine days ahead,” said Alassimone.

They also take into account the dryness of the surrounding landscape to predict water absorption rates. The engineers will make flow adjustments according to the short term previews, but beyond that they are no more able to predict than the weather forecast. Says Alassimone, “Beyond nine days we can only look at larger patterns and seasonal averages to try to make predictions, but it is impossible to know for sure what will happen.”

A perfect storm

Representatives acknowledged that climate change plays a role but they also said conditions that caused the recent floods were a perfect alignment of factors which worked together to cause the high waters that affected so many homeowners in different municipalities in the region. In 2019 there was about 150 to 180 per cent of the normal snow accumulation by the spring.

“If there’s a gradual melting, with a slow warming in spring, then the snow levels go down and the river can handle the extra water,” said Barrette. “But last year there was a big jump in temperature so snow melted extremely quickly, and that combined with record rains downstream in April led to far too much water to handle all at once.” She stressed that though people will point out, “…yes, there has been snow and rain for the last 40 years, and of course before that,” but it was the combination of extreme melting and far beyond normal rains that caused the problems. “In 2018 there was a lot of snow on the ground too, but the thawing was much more gradual and we did not have such high unusual rains.”

As for this spring, the representatives agreed that it is still too early to predict what will happen.

For more information consult ottawariver.ca.

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