Kosi River course change

Subject: Geography

Section: Maping

Context: Kosi River course change

Content

In India, a large flood forced the Kosi River to abandon its established channel for an older one in 2008, displacing 3 million people and claiming more than 250 human lives; such events are called avulsions.
Based on satellite data on 113 such avulsions, in 33 instances, rivers changed routes in the bases of mountains while descending onto unconfined valleys or open oceans.
Kosi river belongs to this category.
In the other two categories, the change occurs in the delta regions.
One is along the backwater zones, part of the river that flows differently because of the effects of the downstream sea.
The last category occurs in rivers with extreme sediment load.

Kosi River

The Kosi is a trans-boundary river which flows through China, Nepal and India.
It drains the northern slopes of the Himalayas in Tibet and the southern slopes in Nepal.
From a major confluence of tributaries north of the Chatra Gorge onwards, the Kosi River is also known as Saptakoshi for its seven upper tributaries.
These include the Tamor River originating from the Kanchenjunga area in the east and Arun River and Sun Kosi from Tibet.
The Sun Koshi’s tributaries from east to west are Dudh Koshi, Bhote Koshi, Tamakoshi River, Likhu Khola and Indravati.
The Saptakoshi crosses into northern Bihar, India where it branches into distributaries before joining the Ganges near Kursela in Katihar
Its unstable nature has been attributed to the heavy silt it carries during the monsoon season, and flooding in India has extreme effects.
Peaks located in the basin include Mount Everest, Kangchenjunga, Lhotse, Makalu, Cho Oyu and
The Kosi alluvial fan is one of the largest in the world. It shows evidence of lateral channel shifting exceeding 120 km (75 mi) during the past 250 years, via at least twelve major channels.
The river, which flowed near Purnea in the 18th century, now flows west of Saharsa.