Published on 25 October 2024
Intense rainfall events linked to climate change generate dynamic runoff which, through erosion, removes materials from the soil, including contaminants. At IMT Nord Europe, research teams are carrying out complementary measurement and modeling work to understand how this displaced matter enters the water cycle, and how to better manage territories.
Climate change is reflected not only in changes in global temperature, but also in rainfall patterns. Increased rainfall, particularly in winter, leads to runoff and pollutants spilling into river basins – areas that naturally receive flowing water. Suspended or dissolved loads in water negatively impact its quality: simply look at the recent difficulties around cleaning the Seine for the upcoming Paris 2024 Olympic and Paralympic Games.
The study of the transfer of materials, and in particular contaminants, into river basins is of interest to many scientists, including Claire Alary, a geosciences researcher at the Energy and Environment Center for Education, Research and Innovation (CERI EE) at IMT Nord Europe. The researcher is working on the confluences of the Canche, a coastal river in the Pas-de-Calais region north of the Seine. Her aim is to understand how solid matter coming from soil, and likely to contain contaminants, is transported to outlets, or conversely, deposited in aquatic environments to form what geologists call “sediment compartments”.
To understand the phenomena at work, Claire Alary sets up measurement networks on several scales in river basins, in order to observe the dynamics of water and sediment flows. The Planquette is a tributary of the Canche, a sub-river basin of some 50 square kilometers, which can itself be broken down into elementary river basins. The researcher and her team installed instruments on a small scale, in a 54-hectare (0.54 square kilometer) elementary basin of the Planquette, and on a larger scale, in the Planquette itself at its nearby outlet.
These devices use turbidity probes to record water flow and opacity, and also monitor runoff dynamics and material loads. The instruments record constant measurements and are supplemented by automatic sampling of suspended matter, which is used to perform various physico-chemical analyses to assess environmental quality or characterize pollutant loads.
“This highly detailed approach to hydro-sedimentary dynamics in river basins is then linked to the local context, such as soil typology – and possible pesticides, in the case of agricultural river basins – or rainfall patterns,” says Claire Alary. In partnership with Navigable Waterways of France (VNF), the researcher is also studying the presence of contaminants in sediment layers, and the sources of the suspended matter that settles and silts in the river channels of the Nord region.
Topographic map of the Canche Basin. Crédits : Creative Commons / Boldair.
Using all these measurements, scientists are attempting to model current and future transfers. Claire Alary uses certain models with her team, but river basins are complex environments to describe. “There are many factors that influence the type of runoff or transport of matter: the nature of the soil, the intensity of rainfall, but also the season, for example”, says the researcher. “These are very large-scale systems. Even the elementary river basins,” adds Éric Duviella, an automation researcher at the Digital Systems Center for Education, Research and Innovation (CERI SN) at IMT Nord-Europe.
For several years now, this specialist in systems modeling and control has been working with Claire Alary on water management applications. Éric Duviella uses data collected in the field to help create digital twins of ecosystems, using powerful, differentiating “black box” models that complement those used by the CERI EE team. “Our aim is to provide models that are simple to implement and dependent on where the measurements were taken, but still generic enough to be deployed in other systems, such as other lakes or rivers,” says the researcher. These models are then simulated to replay past scenarios, and possibly predict future pollutant-spreading scenarios.
That said, taking measurements at a given point shows temporal dynamics, not spatial ones. In addition to deploying tools for measuring and steering aquatic environments, Éric Duviella and his team use a robotic solution to complement the fixed-point sensors: aquatic drones! These robots provide an image of aquatic pollution across the entire environment in which they are deployed, thereby defining temporal and spatial maps.
These “mobile laboratories”, supplied by start-up Bathy Drone Solution (BDS), are fitted with sensors that can be adapted to suit the research topic and types of measurement to be carried out. In collaboration with Claire Alary once again, Éric Duviella used these drones to carry out experiments at the confluence of the Planquette and Canche rivers, to visualize the lines of contaminants spreading from the tributary to the sub-river basin. Recently, the researcher and his team also produced a map characterizing water quality in lake Héron, to the east of Lille. “As the outlet into the lake is highly charged, we can visualize how loads spread using the measurement gradient,” he says.
Aquatic drone used by Éric Duviella’s team for dynamic measurement of various parameters (temperature, pH, etc.) in several areas of lake Héron. Credits: CERI SN.
At present, these aquatic drones are remotely operated, i.e. steered by a human operator, but Éric Duviella and his team aim to develop fleets of automated, autonomous robots for even more effective mapping. The drones also carry out their grid of measurements on the surface – around 30 cm below the water – but could operate lower down in the water column, i.e., deeper down. “By striving to better record these spatial and temporal evolutions, we aim to improve our knowledge of the phenomena at play and our predictions, while maintaining the simplicity of our models. The next step would be to use these predictive models as a basis for decision-making and steering tools for local stakeholders,” says Éric Duviella.
Claire Alary also believes in this dialog. Both are involved in a regional research consortium bringing together scientists from many disciplines – sociology, chemistry, toxicity, and more – to provide societal responses to the issue of water resources throughout the Nord region. The collaboration between these two colleagues at IMT Nord Europe is far from over. “It’s work we would very much like to continue,” they agree.
At present, these aquatic drones are remotely operated, i.e. steered by a human operator, but Éric Duviella and his team aim to develop fleets of automated, autonomous robots for even more effective mapping. The drones also carry out their grid of measurements on the surface – around 30 cm below the water – but could operate lower down in the water column, i.e., deeper down. “By striving to better record these spatial and temporal evolutions, we aim to improve our knowledge of the phenomena at play and our predictions, while maintaining the simplicity of our models. The next step would be to use these predictive models as a basis for decision-making and steering tools for local stakeholders,” says Éric Duviella.
Claire Alary also believes in this dialog. Both are involved in a regional research consortium bringing together scientists from many disciplines – sociology, chemistry, toxicity, and more – to provide societal responses to the issue of water resources throughout the Nord region. The collaboration between these two colleagues at IMT Nord Europe is far from over. “It’s work we would very much like to continue,” they agree.
When assembly lines become circular