Shifting rivers threaten millions of people worldwide

An abrupt alteration in a river’s course, known as a river avulsion, is a natural phenomenon that often leads to catastrophic flooding. These events upset the delicate balance of ecosystems and human settlements.

Sudden shifts in the paths of rivers have shaped landscapes and human history, leaving communities vulnerable to devastating impacts.

To address this global issue, a dedicated team of researchers has worked to decode the enigma of river avulsions. The study has potential implications for millions of people around the world.

Framework for predicting river avulsions

The research was led by Led by James “Jake” Gearon, a PhD candidate in the Department of Earth and Atmospheric Sciences (EAS) at Indiana University Bloomington.

“Measuring topography around a river is difficult and time-consuming because of the dense vegetation,” explained Gearon. “We took advantage of a new satellite that uses lasers to measure topography.”

The advanced lidar technology allowed the team to gauge bare-earth elevations, thus mapping the landscape features around rivers with increased accuracy.

This feat in technology has allowed the research team to create a unique framework for predicting river avulsions – a problem humanity has grappled with for centuries.

River avulsions threaten millions

“Avulsions, which are possibly the inspirations for ancient flood myths, have created the largest floods in human history and continue to threaten millions of people today,” noted Professor Douglas Edmonds.

Given the rise in climate change and human expansion into disaster-prone areas, understanding river avulsions is more crucial than ever.

River avulsions, often birthed from a combination of rising water levels and sediment buildup, can wreak havoc on nearby communities. They often cause severe flooding as the river carves a new path across the floodplain.

Factors influencing river avulsions

Previous assumptions suggested that avulsions were a result of either an elevated riverbed or a more alluring path offered by the adjacent land.

However, the researchers determined that both factors work together and play different roles depending on the river’s location.

“We can now actually test these two 80-year-old ideas with the topography data we have collected from space,” noted Professor Edmonds. “We were surprised to find that both factors work collaboratively.”

The experts found that near coasts, rivers avulse when the slope away from the channel is steeper – not because they are perched.

“The opposite is true near mountain fronts; on fans, the alternative paths are similarly steep to the downstream path, so rivers avulse when they are perched above the surrounding landscape,” noted the researchers.

Mapping avulsion corridors

The team analyzed data from 174 river avulsions across the globe, using satellite imagery to track river movements over the past several decades. 

Avulsions are frequently found near mountain ranges and coastal areas, where sediment buildup is rapid. Seventy-four percent of the studied avulsions occurred in these regions, where rivers are more prone to sudden shifts.

Utilizing this knowledge, the team has developed a model to map “avulsion corridors” – potential paths that rivers might take during an avulsion.

This tool will help governments and planners identify high flood-risk areas and allocate resources accordingly.

“Traditional flood models focus on rising water levels from heavy rains, but avulsions can occur without warning, even in areas where rainfall isn’t a major concern. This makes them particularly dangerous and difficult to predict, much like earthquakes,” said Gearon.

Guarding the south against river avulsions

The value of these findings multiplies in the Global South, where geological factors and infrastructure challenges make communities particularly vulnerable to avulsions.

In many regions, a combination of natural conditions and underdeveloped infrastructure intensifies the impact of river shifts.

“The 2008 Kosi River avulsion in Northern India directly affected over 30 million people, killing hundreds and causing over $1 billion in damage,” said Professor Edmonds.

Significance of the study

The newly developed model could help countries prepare for disasters, potentially saving lives and cutting down economic damage.

As we march into a future where climate change continues to disrupt weather patterns and escalate flood hazards, river avulsions are expected to become more common. This is because climate change accelerates the factors that contribute to avulsions.

For example, rising sea levels can impact coastal rivers and deltas by reducing the slope of river channels, slowing water flow, and increasing sediment deposition. This buildup of sediment can encourage avulsions as rivers seek new, steeper courses.

The study is published in the journal Nature.

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