Students’ infiltration tests with Rémi Clément (INRAE). © Maxence Grugier
In July, the Infiltration Process summer camp invited international post-graduate students in rainwater management, urban hydrology and eco-engineering to the open-air lab “Eco-Campus” at the University of Lyon in France. On the agenda: developing open source hardware, data analysis, distributing information, and above all sharing, in order to raise awareness among policy-makers and the general public of effective water treatment in urban areas.
Water is at the core of our concerns. This is especially true in recent years, as epic droughts and catastrophic floods threaten both human infrastructures and the land itself. Managing and distributing water in urban areas is also a pressing issue: How can we better manage wastewater (grey water, black water, sludge)? How can we improve rainwater infiltration in urban areas? What solutions do we have for decanting spaces, on the scale of a village, a city, or at home? How can we sensitize both policy-makers and citizens, so that pratices evolve alongside legislation?
These were just a few of the questions that were raised and discussed during the three days of Infiltration Process, which was held on the Eco-Campus LyonTech La Doua in Villeurbanne/Lyon on July 4-6, 2022. The summer program, funded by H2O’Lyon university research school, invited Master and Ph.D. students from around the globe (Israel, Austria, Norway, Singapore…) to inform, exchange, share and make open source autonomous monitoring tools for experimenting in the open-air Eco-Campus.
Promoting and optimizing
The idea for Infiltration Process initially came out of a thematic collaboration between two environmental laboratories: REVERSAAL (“reduce, reuse, promote residual water resources”), a unit founded in 2018 to research methods of recycling and treating urban wastewater, and DEEP (“waste, water, environment”), a research unit whose “environmental engineering skills are mobilized to meet the challenges of ecological and energy transitions” and who “prefigure future waste management by helping to develop innovative, compact, energy-efficient and intelligent eco-technologies”.
Given the current climate crisis, the researchers were tasked with responding quickly to various environmental conditions and climate contexts. By focusing on managing future wastewater, initiatives such as Infiltration Process help prepare to reduce polluting emissions and diffuse toxic substances in the soil and groundwater, while promoting better reuse of water.
LyonTech La Doua, a model Eco-Campus
It’s no coincidence that this first session of Infiltration Process took place on the Eco-Campus of La Doua in Villeurbanne. Considered to be an environmental model ever since the renovation work began in 2017, the campus has invested in innovative rainwater management that reduces pollution while nurturing greenery.
The Infiltration Process summer program kicked off with a tour of the Eco-Campus. Students visited the various on-site installations dedicated to water infiltration: dry rivers or marshes alongside greenways, drains to collect rainwater from parking lots and sports facilities, ditches, green roofs, etc. Among these, a highlight was the resident water infiltration basin built in the late 1960s, which collects water from the surrounding two hectares of impermeable surfaces. This was the main site for most of the tests and experiments monitoring the groundwater, where students analyzed water quality and learned different ways of collecting data.
When asked about the local facilities, Helen K. French, hydrogeology professor at the Norwegian University of Life Sciences, was surprised at how similar these initiatives were to those in Norway: “Where I work, we use the campus as a laboratory. We also developed experimentation sites that are a lot like the one we visited today, infiltration basins that we call “rain gardens”. The aim, as where I’m from, is to render the soils permeable in order to restore their natural capacity to filter rainwater and feed the soils. It’s reassuring to see that in terms of research, we’re going in the same direction.”
Making good use of water
In natural environments, 0% to 10% of the ground surface is impermeable; in urban areas, it’s 75% to 100%.
The summer camp focuses on the infiltration of rainwaters, as current events show that the massive impermeability of soils is a major factor in floods and overflows, as well as environmental damage (concentrating water currents and pollution, decreasing groundwater infiltration, reducing evapotranspiration and creating heat islands).
The effects are even more convincing when expressed in numbers. If we observe the phenomena of evapotranspiration, streaming, superficial and deep infiltration in forested areas, almost 25% of rainwater ends up as groundwater (40% evaporates and 25% infiltrates the surface). In urban areas, due to impermeable soils, only 5% of rainwater ends up as groundwater, while 55% streams (and provokes flooding), and only 30% evaporates, creating heat islands. The reason is that in natural environments, 0% to 10% of the ground surface is impermeable, while in urban areas, it’s 75% to 100%. It is therefore necessary to dewater urban areas.
The second morning of Infiltration Process was dedicated to methods of quantifying water infiltration and collecting data. Assisting the students in these geophysical and hydrological measurements were Rémi Clément (geophysicist, INRAE), Laura Delgado-Gonzalez (postdoctoral researcher, INRAE) and Laurent Lassabatere (researcher, ENTPE, school of sustainable land use planning). Together, they helped the students conduct an in situ infiltration experiment using open source tools developed by the researchers themselves.
As there is necessarily a direct link between infiltration and soil quality, different methods must be used in tandem. Among them were the methods of “infiltration” and “electric resistivity” (where soil resistance is measured instead of measuring infiltration directly). The latter provided an opportunity to introduce an open source hardware tool specially developed by the INRAE researchers, called the OhmPi.
Rémi Clément: “There are proprietary components in this device, but the point is to design a system that’s perfectly adapted to research in local infiltration using materials that are available commercially, with documentation so that anyone can build it simply by themselves.”
Poorly treated water
In urban areas, wastewater is generally treated using “grey water” techniques. Nicolas Forquet, engineer-researcher at Reversaal (INRAE), explains: “Right now the concept is to get rid of wastewater by reprocessing it in huge purifying stations, or even in some parts of the world, by sending it down pipes that pour into rivers, with all the environmental problems that that implies.”
Today, the 19th century hygiene techniques that consisted of evacuating water through simple canals are showing their limits. The water networks quickly become saturated.
“We know the limitation of these techniques that require building larger and larger infrastructures with a notable impact on the environment,” Forquet continues. Therefore, we need to find other solutions. “Regarding the infiltration processes used here, the idea is to avoid pouring rainwater down pipes, to instead let it naturally infiltrate the soils,” he says. “These techniques are cheaper and limit the risks of pollution. We plan to use infiltration basins, ditches or dry rivers, to allow the water to accumulate and infiltrate naturally.”
“To be pirated without moderation”
The afternoon was reserved for an Arduino workshop given by Frédéric Cherqui, educator-researcher at DEEP laboratory (INSA Lyon), where participants learned to design a low-cost sensor using an Arduino microprocessor. They then calculated the infiltration rate in situ in experimental conditions. At the end of the workshop, the collected data is uploaded to a server, as part of the commons.
“Our goal is not just to do experiments, but also to share our results online,” says Cherqui. “At INSA, we have 20 years of collected data on our servers, and we invite anyone who is interested in these topics to download them. The same goes for our equipment. We build our own hardware tools because it’s more adapted to our research, and we distribute the blueprints, sketches and manuals on our websites, so that everyone can make them.”
“At INSA, we have 20 years of collected data on our servers, and we invite anyone who is interested in these topics to download them.”
Frédéric Cherqui, educator-researcher and lecturer at DEEP
Méli Mélo, the multimedia project developed by Graie, an association that informs the public about water management issues by interfacing between researchers and decision-makers, introduces itself as “a website to be pirated without moderation”. This spirit can be found at all levels of Infiltration Process, in its program, activities and actors.
According to Laetitia Bacot, project manager at Graie and executive director of OTHU (laboratory for observing urban waste and its impact), “All the work done by the various actors described here is mainly designed to help communities make the right choices. So it’s important for them to have models, tools that they can use to play, simulate, explore hypotheses. This is what our students have in mind as they work during Infiltration Process. It’s also the motor behind the Graie project and the Méli Mélo website – to help people understand these processes and appropriate them as citizens. So we reach out to make things accessible and attractive. For example, we made several short films with the team from the Kaamelott series, which were very well received by the general public.”
Episode 14 of the web series (in French) by Graie, 2015:
Uncertainties
The last day was spent building models. In the research field, when you want to extrapolate results from different kinds of sites and create a trend, you need to design models (here, physically based conceptual models, where we know the processes and design equations that are like a simplification of these processes that allow us to extrapolate possible scenarios). For this, students used the open source software Shiny to go all the way to the dissemination phase – designing content that is accessible through a graphical interface that can be consulted online and understood by decision-makers working in public authorities and various regional institutions. Between the moment that the data is acquired and the moment that it’s validated, there is a lot of work to be done sorting and analyzing. Data is volatile and vulnerable to all sorts of restrictions, so it’s important to reconduct an experiment several times and to do a long, in-depth analysis to make sure it’s accurate.
On the third morning, we contemplated the problem of uncertainty in processing this data with Jean-Luc Bertrand-Krajewski, professor at DEEP specialized in the notion of uncertainties. The talk was really interesting, even if it quickly became very technical, as it perfectly reflected the complex research field of applied sciences, which is so dependent on experimental, environmental, material (human and machine), methodological and other conditions.
As the British philosopher Francis Bacon (1561–1626) wrote: “If a man will begin with certainties, he shall end in doubts; but if he will be content to begin with doubts, he shall end in certainties.” In the case of research based on data as complex as hydrology data (restricted by factors as volatile as meteorology, geophysics, anthropic alteration, etc.), we are clearly navigating between determinism and indetermination. Based on the principle that having knowledge is always temporary and that there is a vast scale between proven knowledge and total ignorance, a whole generation of future engineers or educator-researchers in this field must learn to share and exchange in order to build perennial and reusable models… as well as they can.
Infiltration Process Summer School website
Data sharing website, sketches, etc. to build your own OhmPi and other open source hardware
Maxence Grugier is the Chronicler-in-residence of Rewilding Cultures, a project co-funded by the Creative Europe programme of the European Union.