The Kosi River is known as the “Sadness of Bihar” because of its annual floods that affect about 21,000 square kilometers (8,100 sq mi) of fertile farmland, disrupting the rural economy.
On August 18, 2008, the Kosi River restored an old canal it had abandoned more than 100 years earlier near the border with Nepal and India.
The Kosi River is one of the largest tributaries of the Ganges.
Kosi is known as “The Sorrow of Bihar” because it has caused a lot of human suffering in the past due to floods and very frequent changes in flow as it flows from Nepal to Bihar.
Final Answer:
Hence, the following is the reason the Kosi river is known as the ‘Sorrow of Bihar’.kosi river was abandoned more than 100 years ago and it is the largest tributaries.it caused a lot of human suffering due to blood.