A river runs through it
Associate Professor Pascale Biron (Geography, Planning and Environment) is a fluvial geomorphologist. She studies how and why rivers are shaped as they are, “although it is a bit more complex than that.”
Consider, for instance, the Quebec practice of straightening rivers. “The natural path for rivers in the St. Lawrence Lowlands tends to be a meander,” a back-and-forth, S-shaped water flow formed over time by the natural build up of sediment and erosion on alternating banks of a river.
In Quebec, the seigneurie system established during French colonization created long, skinny farms that backed onto rivers or lakes. Fast forward 400 or so years and 21st-century farmers are taxed for land that extends all the way to a body of water. If that water meanders in and out of a field’s back end, farmers are being taxed, in part, for non-productive ground. A solution widely implemented from the 1960s through the ’80s was the straightening of rivers to reclaim arable land.
Straightened rivers, however, tend to flow faster and cause more bank erosion, so banks must then be frequently reinforced and stabilized to ensure they don’t collapse. “These projects are very expensive,” Biron said. In addition, the loss of a buffer zone between worked land and rivers, combined with contemporary fertilization and drainage practices, causes other problems.
“Many ditches were dug in the fields to get rid of the water from the spring flood as early as possible, with the result that drainage density in agricultural areas of Quebec has increased markedly in the last 40 years,” Biron said. “In some places, you can almost watch the algae blooms grow where these ditches meet the main river.”
Phosphorous run-off from farms is thought to be largely responsible for the growing blue-green algae problem in Quebec lakes and rivers.
While Biron is one of the few geographers working in this area (“It’s mostly biologists and engineers”), it isn’t her primary research area. She currently holds two NSERC grants that focus on combining fieldwork with Geographic Information Systems and numerical modelling.
The first grant is for three-dimensional modelling of the impact of stream deflectors. Stream deflectors are structures that alter water flow in a river to help recreate a natural underwater habitat for fish like trout. Rivers naturally have a series of deep pools (where fish hide and find cooler water during hot summer days) and faster, shallower reaches with coarse bed particles called riffles (where fish spawn).
Soil and other sediments, which enter the river from agricultural run-off, tend to fill in these spaces and give rivers a more “uniform profile” that isn’t conducive to the maintenance of a proper fish habitat. By examining what type of deflector design works best and doesn’t get washed away, “we’re trying to bring some fundamental science to a field that is very practical,” Biron explained.
The second grant is an NSERC strategic grant in which Biron is the co-principal investigator with André Roy at Université de Montréal and Michel Lamothe at Université du Québec à Montréal. It focuses on the impact of climate change on the St. Lawrence River and five of its tributaries – the Yamachiche, the St. Maurice, the Batiscan, the Richelieu and the St. François.
“We have a broad database of information about the St. Lawrence,said Biron, “but very little information about its tributaries.” The first step in the project was to gather extensive field data about each tributary’s topography, velocity, sediment size, etc., along with ongoing monitoring of water levels.
A PhD student at Université de Montréal whom Biron supervises is now conducting numerical analyses on the results to determine how tributaries will adjust to changes in the water level of the St. Lawrence River based on different climate models.
While it is early, Biron says there are already some clear results. “All of the models are indicating earlier floods in the tributaries and less time of ice cover.” How that information transfers into usable data for municipalities looking at infrastructure needs 30, 50, or 100 years down the road is not clear yet.
“We expect a long-term adjustment which will deepen river beds, generate more bank erosion, bring more sediments into the St. Lawrence River, undercut some bridge foundations and really impact sensitive environments like shallow lakes (for example, Lake St. Pierre) and wetlands. Many watershed management agencies really want to know what’s going to happen and have provided us useful information for this project.”