Why is the Kosi River called the “Sorrow of Bihar”?

The Kosi River is infamously known as the “Sorrow of Bihar” due to its long history of devastating and unpredictable floods.

The primary reasons for this are:

• High Sediment Load: The Kosi originates in the high Himalayas and carries an enormous amount of silt and sediment.
• Riverbed Aggradation: As the river enters the flat plains of Bihar, it slows down and deposits this silt, causing its own riverbed to rise.
• Frequent Avulsion (Course Changing): Once the riverbed becomes too high, the river breaches its embankments during peak monsoon flow and carves a new channel. Over the last 200 years, the Kosi has shifted its course over 120 km westward.

This constant course-changing and the massive, silt-laden floods inundate vast areas of northern Bihar, destroying crops, homes, and infrastructure, which is why it is called the sorrow of Bihar.