This text is part of the special Quebec engineering booklet
Every year, ice jams cause flooding in Quebec, with sometimes dramatic consequences for residents. Thanks to a brand new simulator, researchers from Polytechnique Montréal are improving our ability to predict and prevent these natural disasters.
In Quebec, floods cause average annual costs estimated at between $10 and $15 million. However, nearly 60% of these events come from ice jams or frazil ice (crystals or fragments of ice that float on the surface of the water). Ice jams form in spring, and more rarely in winter, when a strong mild spell causes breaks in the ice surface. The pieces break off and drift on the waterways until they hit an obstacle. The ice fragments then accumulate and create a dam, which prevents the water from flowing. The water level upstream rises and the river eventually overflows and floods the banks.
In addition to causing property damage, these events can also cost lives. And the situation could even get worse. A 2018 study of seven rivers in Quebec by researchers at Laval University predicts that the annual costs resulting from flooding caused by ice jams could increase by an average of 30% due to climate change.
Ice movements
Many municipalities try to protect themselves from these disasters by removing natural or artificial obstacles from watercourses that can block the circulation of pieces of ice. Others build boom dams to keep ice and frazil away from municipalities, add nets to retain ice without stopping the water or send mechanical shovels to break the ice near certain structures. However, it is not always easy to know which solutions are best or where to intervene to obtain an optimal result.
Ahmad Shakibaeinia, associate professor in the Department of Civil, Geological and Mining Engineering at Polytechnique Montréal, is working to solve these equations. Its laboratory is equipped with an ice behavior simulator that is unique in the country. “Our team studies ice dynamics and especially ice jams,” he explains. We want to improve our ability to discover where there is a risk of ice jams and predict the evolution of these obstructions. »
A unique simulator
The team is of course relying on digital simulations. But to properly calibrate these numerical models, researchers need experimental data. “We need to recreate on a smaller scale situations similar to those experienced on rivers, in order to generate data on several factors such as temperature, the way ice breaks up, their movements or the efficiency of structures. used to control these movements”, sums up the professor.
This simulator takes the form of a cold room about three meters wide by five meters long, in which the temperature can drop to -23 degrees Celsius. There is a circulation channel made of steel and transparent polymer. Thanks to a system of high-speed cameras, the team of researchers can follow the movement on the water of each fragment of ice, see what proportion of the pieces is retained by a structure, the force that the ice applies on the structures, among others.
Other instruments take additional measurements, for example about the volume of water flowing. Researchers can therefore determine important elements such as the optimal distance from the pillars of an ice control structure, such as a boom dam, or even the right water flow to contain an ice jam.
Teamwork
However, the use of the simulator has itself come up against an obstacle that is very different from ice jams: COVID-19. Indeed, the construction of this equipment was completed at the beginning of 2020, just before the arrival of the pandemic in Quebec. The lab was subsequently closed for several months. It was only recently that the researchers were able to start putting their device to the test.
Ahmad Shakibaeinia’s team is now collaborating on a research project on the effectiveness of ice jam control structures with colleagues from Laval University and the Ministry of Public Security. “Our work is used to calibrate and validate numerical models that will be used by researchers at Laval University, who will apply them to real situations,” explains the Polytechnique professor.