Scientists pioneer flood prediction model to combat river course changes

Creating a new river channel (avulsion) is a natural geomorphological process. Catastrophic changes in river courses can threaten millions of people around the world. New research allows for better prediction of these phenomena and taking appropriate actions reports the journal "Nature."

Thanks to pioneering research, scientists from Indiana University have discovered a way to predict when and where rivers might drastically change their course. The results of this research shed light on a process that has had a significant impact on human history. It contributes to the creation of destructive floods and continuously poses a threat to millions of people worldwide.

Water flows downward, following the path of least resistance, often creating bends and meanders, especially on plains, which isn’t always synonymous with flowing straight. In mountainous areas, rivers may find new, steeper channels. This process causes erosion on one bank of the river and sediment accumulation on the other. Water flow depends on climate variables, such as rainfall and air temperature. River channel formation is also influenced by local topography, land use, and other variables.

Meanders typically occur in lowland areas, in rivers' lower and middle sections. Over time, they can shift toward the river mouth, increasing their curvature. When the water level rises, they can be cut off from the main river channel, forming oxbow lakes.

For the first time, a research team led by James "Jake" Gearon, a PhD student in the Department of Earth and Atmospheric Sciences (EAS) at Indiana University Bloomington, developed conditions that lead to changes in river courses. The team includes Harrison Martin, Clarke DeLisle, Eric Barefoot, and Professor Douglas Edmonds. The research utilized advanced satellite technology for terrain imaging. The scientists emphasized that measuring topography around a river is challenging due to vegetation. To this end, they used a satellite that utilizes lasers for measurements.

Changes in river courses, which could have inspired ancient flood myths, have caused some of the most significant floods in history and still threaten many people. Edmonds emphasized, "As climate change alters global water cycles and human expansion into flood-prone areas increases, understanding and predicting avulsions has never been more critical."

River course changes occur when the water level surpasses the surrounding landscape, often due to sediment accumulation. This can result in uncontrolled water spilling over the banks and creating a new channel. This leads to flooding because the new channel often appears in areas unprepared for such a volume of water.

Scientists previously believed that sudden changes in river courses resulted from two main factors: the riverbed rising above the floodplain or a steeper path on the sides of the river. Edmonds stated "We can now actually test these two 80-year-old ideas with the topography data we have collected from space." The data showed that both factors interact and depend on the river's location.

Analysis of data from 174 river avulsions worldwide, using satellite images, reveals that course changes are more common near mountain ranges and coastal areas, where sediments accumulate rapidly. In these regions, 74 percent of avulsions occurred.

Utilizing topographic data, the research team developed a model for mapping "river avulsions" – potential paths that rivers might follow if they change their courses. This model can help governments and planners identify areas at high risk of sudden flooding, especially in regions with limited resources.

– 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.

The research results can be valuable for the Global South, where sudden changes in river courses are more common and can have more catastrophic effects. The flood associated with the avulsion of the Indus River in Pakistan in 2010 affected over 20 million people.