Researchers have made significant discoveries regarding the perilous issue of ‘river avulsion,’ providing insights into predicting when and where rivers might abruptly change their paths.
Investigators from Indiana University have made important discoveries about the hazardous phenomenon known as “river avulsion,” which can help anticipate the sudden and drastic shifts in river courses. This research, published in Nature, illuminates a process that has impacted human civilization through catastrophic floods and continues to endanger millions globally.
Under the leadership of James “Jake” Gearon, a doctoral candidate in the Department of Earth and Atmospheric Sciences (EAS) within the College of Arts and Sciences at Indiana University Bloomington, the research team has for the first time detailed the conditions that lead to river avulsions. The co-authors include Harrison Martin (Ph.D. EAS ’23), a postdoctoral fellow currently at CalTech; Clarke DeLisle (Ph.D. EAS ’23) now at EVS, Inc; Eric Barefoot, a postdoctoral researcher at IU Bloomington and now a faculty member at UC-Riverside; and Professor Douglas Edmonds, the Malcolm and Sylvia Boyce Chair in Geological Sciences in the Earth and Atmospheric Sciences department.
The team employed cutting-edge satellite technology to analyze how certain landscape characteristics increase the likelihood of avulsions. “Assessing the topography around a river can be challenging and labor-intensive due to thick vegetation,” noted Gearon. “We harnessed a new satellite equipped with lasers for topographical measurement.” This technology, known as lidar, penetrates through vegetation to provide accurate measurements of ground elevations.
This research introduces a groundbreaking framework for forecasting when avulsions might occur, an issue humanity has faced for thousands of years. “Avulsions are potentially the basis for ancient flood legends, have caused history’s largest floods, and still pose a threat to millions today,” explained Edmonds. “As climate change modifies global water cycles and more people settle in flood-prone areas, understanding and predicting avulsions is crucial.”
What Triggers River Avulsions?
River avulsions happen when the water level rises above the surrounding land, often due to sediment accumulation in the riverbed. When this occurs, the river can overflow, carving out a new path across the floodplain, presenting severe flooding risks as it floods regions that are not equipped to handle such volumes. For instance, the 2008 avulsion of the Kosi River in Northern India impacted over 30 million people, resulted in hundreds of fatalities, and inflicted damages exceeding $1 billion.
Historically, scientists believed that avulsions were primarily caused by two factors: either the riverbed rising above the floodplain or the land alongside the river shaping a steeper path for the water. “We can now actually examine these two long-standing theories using the topographical data we collected from space,” said Edmonds, “and we were surprised to learn that both elements interact differently depending on the river’s specific situation.”
Hazard Prediction for Avulsions – A New Approach to Mapping Flood Risks
The research team evaluated data from 174 river avulsions worldwide, using satellite imagery to observe river shifts over the past decades. Their findings indicate that avulsions are significantly more frequent near mountainous regions and coastal zones compared to areas in the river’s central stretch. About 74 percent of the avulsions were found near mountain fronts or coastlines, where sediment tends to accumulate rapidly.
Additionally, by utilizing topographic data, the researchers created a new model to delineate what they call “avulsion corridors” — potential paths that rivers could take if they deviate from their current course. This tool could assist governments and planners in pinpointing regions at high risk for sudden flooding, especially in areas lacking effective flood management systems.
The study underscores the necessity of accounting for avulsions in flood hazard evaluations, an aspect that traditional flood models typically overlook. “Standard flood models concentrate on rising water levels caused by excessive rainfall, but avulsions can occur unannounced even in regions where rainfall isn’t a predominant concern. This unpredictability makes them especially hazardous and challenging to forecast, akin to earthquakes,” stated Gearon.
Consequences for the Global South
The findings hold particular significance for the Global South — the less developed segments of Africa, Latin America, and Asia — where avulsions are more frequent and frequently more lethal. In numerous cases, geological factors coupled with inadequate infrastructure heighten community vulnerability to abrupt river alterations. For example, the flooding related to the 2010 avulsion of the Indus River in Pakistan affected over 20 million individuals.
The new model, which relies on limited data requirements, could enable countries to prepare for disasters linked to avulsions, potentially saving lives and diminishing economic repercussions. By equipping scientists, policymakers, and practitioners with a fresh perspective on flood risks — particularly as climate change continues to alter weather patterns and exacerbate flood threats globally — this study offers vital tools for comprehending and mitigating the risks associated with river avulsions.
