Context: The Bihar government will try to divert the course of the mighty Kosi River in Bhagalpur district to save an archaeological site discovered recently.
Kosi River: The Sorrow of Bihar

• The Kosi is a trans-boundary river which flows through Tibet, Nepal and India.
• The river crosses into northern Bihar, India where it branches into distributaries before joining the Ganges near Kursela in Katihar district.
• Its unstable nature has been attributed course changes and the heavy silt it carries during the monsoon season, and flooding in India has extreme effects.
• It is also known as the “Sorrow of Bihar” as the annual floods affect about 21,000 km2 of fertile agricultural lands thereby disturbing the rural economy.

Why change its course?

• Several priceless artefacts have been found at the Guwaradih village in Naugachhia sub-division of Bhagalpur district during the excavation of a mound.
• These items could be 2,500-years-old and could be of interest for historians if conserved.
• The historical sites are facing threats from the Kosi floods.
• The Kosi currently flows around 300-400 metres from the site, while its old course is about two kilometres from the village.

Threats posed by the move

• Environmentalists have warned that changing the Kosi’s course could be disastrous for Bihar as seen in 2008.
• At that time, the river had breached its mud embankments at Kushaha in Nepal.
• The Kosi frequently changes its course naturally. If its course is artificially changed, it will cause floods and erosion in new areas, leading to massive displacement of people.
• It then caused extensive damage to life and property downstream in five densely populated districts of northeast Bihar.
• Some 500 people were killed and four million rendered homeless.

?Why Kosi Floods are more dangerous?

• The Kosi’s alluvial fan has fertile soil and abundant groundwater. The agricultural land in these areas is in great demand. Poverty is prevalent and farmers try to compromise on threat of floods with that of farming in flood prone area. This is the reason that this area is densely populated and subject to heavy loss of life.

Why do rivers change course?

• It’s natural for a river to keep shifting its course. It’s a part of its natural evolution. There are several factors that cause change in course of rivers. 
• Firstly, the fast flowing rivers are generally prone to silting up as they surge down the hills and spread out on the plains; thereby allowing sand and suspended matter to deposit in their slower, wider depths. Over time, the deposits create resistance, forcing the river to move to an area of lower resistance. This is why rivers change their courses. 
• Secondly,  the nature’s fury such as earthquakes, landslides and hurricanes can also change a river’s course. 
• Thirdly, human activity and climate change are also responsible for change in river course. For example, climate change has triggered the melting of glaciers more quickly thus, the volume of water in rivers has been on the rise, resulting in greater force of flow. 
• Therefore, even relatively lesser amount of rain during the monsoon can lead to a catastrophe.