Avulsions across Kosi River

Avulsions across Kosi River

News: Recently a research study reported that instability in Kosi River has been observed after the construction of embankments on either side of it.

What are avulsions?
• Avulsion refers to the phenomenon of change in the course of river flow causing the abandonment of the old established river channel and formation of a new channel.

Where are we likely to see Avulsions?
• Rivers lining tropical and desert regions are more prone to avulsions.
• Avulsions occur less frequently, only once a decade or century, or even less.
• The rare occurrence of avulsions makes them less discussed despite their catastrophic effects as compared to more frequent extreme weather events and the continuous effect of sea-level rise.

Key Findings of the Research:
• 113 avulsions have been documented worldwide as per the satellite imagery from 1973-2020 and historical maps.
• Rivers altered routes in the mountain bases while descending onto unconfined valleys or open oceans in 33 instances. Kosi river falls under this category.
• The change can also occur in the delta regions. One is along backwater zones, part of the river that flows differently because of the effects of the downstream sea.
• Along some of the world’s largest waterways, such as the Orinoco, Yellow, Nile and Mississippi Rivers, 50 instances occurred on low sloping deltas.
• In 30 instances, avulsions occurred in rivers with extreme sediment load. River beds are filled-up with the sediments causing the rivers to seek new channels during floods.
To read more about history of Kosi River and Projects along the same do refer this article:
https://www.firstpost.com/long-reads/a-dammed-history-of-the-kosi-5221841.html