In May 2023, heavy rainfall caused more than 20 levees to fail in the Emilia-Romagna region of northern Italy, unleashing floods that killed 17 people, displaced nearly 37,000 others, and caused more than 8.5 billion euros in damages. After the disaster, researchers pointed to a surprising and preventable contributing factor: burrowing mammals, whose cozy homes along riverbanks had made many levees unstable.
Now, amateur scientists in Italy and other flood-prone parts of the world can help unearth these furry culprits before they cause more disasters by spotting and reporting levee dens with a mobile app.
Ten years ago, most people had to be convinced this was a problem, said Stefano Orlandini, a civil and environmental engineer at the University of Modena and Reggio Emilia in Italy. People told him he was crazy, telling Orlandini that “this failure isn’t reported in any hydraulics textbook.” In 2015, Orlandini and his colleagues showed that the dens of crested porcupines, badgers, and red foxes significantly weakened the integrity of levees that had failed in another flood in northern Italy the previous year.
After a decade of calling attention to the danger, Orlandini and other researchers released the Burrow Tracker app this year. The group will present the app’s features on 11 December at AGU’s Annual Meeting 2024 in Washington, D.C.
Poking Holes in Flood Defenses
“Especially after the disasters in Romagna, people see this as one of the major problems.”
For diggers with big appetites, river levees provide easy living. Burrowing mammals are often attracted to the softer soil and ample food found near riverbanks. They build their dens in the sloping terrain, which provides extra protection from rainfall and other harsh weather conditions.
Small pockets of air maintain a negative pressure in the animal burrow that makes it structurally sound. But when soil water levels start surging during intense storms, the dirt holding up the walls of the burrow becomes saturated, removing the air and releasing the tension.
“It is the same principle with a sandcastle,” Orlandini said. “You cannot build a castle with dry sand or totally wet sand. But you can build a wonderful castle with unsaturated or humid sand.” Once the walls are oversaturated, water rushes into the tunnel systems excavated by the animals, and the levees start eroding internally. Then, they fail.
“Especially after the disasters in Romagna, people see this as one of the major problems,” Orlandini said. “They want to contribute to the solution.”
Dishing the Dirt on Dens
“It is much more impactful than a scientific paper.”
Dirt-dwelling creatures leave behind tracks, trails, and tunnels. Residents strolling along levee banks can snap photos of these markers and upload them to the Burrow Tracker’s database. The app asks users to include details about the photos, such as the animal type, time, date, coordinates, and relevant observations about each den.
“We felt that it was important to involve citizens to raise awareness about the problem,” Orlandini said. “It is much more impactful than a scientific paper.” Burrow Tracker, now available for download, had nearly a dozen photos mapped within the first 2 weeks of its launch.
The researchers hope to give the data to people responsible for maintaining levees and moving problem animals away from riverbanks.
Any solution the app facilitates must keep animal ethics in mind, said Luca Börger, a professor of ecology and biodiversity at Swansea University in the United Kingdom who was not involved in the study. Once burrows are identified, filling up the holes might make it undesirable to build dens in levees, he suggested. “The combination of deterring and making other areas more attractive [to the animals] might be the way forward.”
Using crowdsourced data to track burrows has challenges. “You need to find ways to understand what the sampling effort is,” Börger said. “Often with citizen science, you have someone who has recorded something, but you don’t know how often they are going out.” In areas where no data have been recorded, it may be difficult to know what to attribute the absences to: a lack of burrows or a lack of people there to report them.
Because the Burrow Tracker app geolocates images, it is easy for the researchers to verify the data, Börger noted. Orlandini said the team vets each photo before accepting submissions and applies statistical analysis to check for multiple submissions from the same burrow.
Orlandini said he hopes that anyone living in floodplains can use this tool in partnership with engineers in their communities.
—Carly Kay (@carlykkay), Science Writer