Rivers rarely change course. But when they do, they can bring disastrous consequences and have the potential to wipe out cities completely. Now a new study analyzing more than five decades of global data has found that changes in climate and land-use patterns may increase the risk of rivers suddenly changing their course.
The team of scientists at UC Santa Barbara, led by Sam Brooke, used 50 years of satellite imagery beginning in 1973 and documented 113 such events in rivers around the world to understand why and when they took their course. revenge. The team corroborated the satellite data with theoretical and experimental work done over the past decade and recently published the findings in the peer-reviewed journal Science.
The study also examined the 2008 incident, when the Kosi river in Bihar changed its course and caused massive flooding, killing at least 400 people and displacing nearly three million. “Around 330 million people worldwide live on river deltas, and many more live in river corridors. We need to understand how river dynamics will change in response to climate change and anthropogenic interference,” said Vamsi Ganti of UCSB’s Department of Geography, who was part of the study.
understanding disorder
A river may jump only once a decade, once a century, or even less. Scientists use the term “precipitation” to describe a rare event in which one river suddenly leaves its established channel for another, resulting in catastrophic flooding. Sometimes, even major floods can force the river to take a new course across the landscape.
Unlike the long-lasting migration of a river flow across floodplains and deltas, these stochastic and extremely unpredictable events can have all kinds of consequences, from triggering floods to creating fertile deltas. This can occur either at the base of a mountain where a river flows out of confined channels over open valleys, or downstream in a river’s backwater area where sea level affects flow, or when there is a sudden rapid flood and sediment transport. One can push a river upstream to change its course.
Scientists have long been trying to build up theories about this, using experiments and computational modeling, and some case studies to help predict these natural disasters and save lives. But, these events have been so elusive and rare that it has been challenging to make direct observations, which the team overcame through fifties of remote-sensing data and analytical techniques.
Increased risk of disasters in the upstream
a course change Much is associated with channel slope and sedimentation in the river’s backwater region – the most downstream reaches of coastal rivers where the flow is slow and the channel slope is low. However, the team found that many of the phenomena called avulsion were actually located upwards where they would normally be expected. Not only that, they also found that they are most often found in steep, sediment-rich rivers in tropical environments.
Another major concern is the increase in sediment load. Depletion occurs when and where a river is filled with sediment, which compresses the channel to the point where it juts out elsewhere, and increased sediment transport can actually push it upstream too far. All of this is disturbing, the team said, as it could expose local communities living aboveground to flood hazards they have never experienced before. Changing climate and land use could make this even worse, as they would cause more flood-driven erosion, which could make upwelling more common.
According to the team, the findings could be helpful in developing a framework to help predict when and where they might happen in the future. “However, when you’re looking at practically every single delta on Earth, you’re going to get lucky on some of them,” said co-author Austin Chadwick from the University of Minnesota.
Climate change
rising sea level Floods Known for relocating sites upstream of its historical places. The study suggests that climate and land-use changes can also increase inland encroachment on rivers. This means that disturbances confined to the backwater zone can also be upstream, exposing people to disasters.
Agriculture, deforestation, development and resource extraction are also influencing the location of these events. “If you change land use – and therefore the amount of sediment supplied to some rivers – you can take a river that is currently experiencing backwater-scaled avalanche and move it into a higher sediment supply-modulated avulsion category. Ganti said, explaining how human activities can affect the way rivers flow and gradually change their course. “This is the regime that can jump very high.”
According to lead author Sam Brooke, the study elucidates how the disorderly space on the delta is sensitive to changes in sea level, sediment load, and the duration and intensity of floods – all of which are subject to change as climate change and climate change globally. More rivers are damaged, controlled and manipulated by human development. Brooke is confident the new framework will help the team predict potentially dangerous inland migration of the river’s preferred location.
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