The Kosi River is the Himalayan river known as the “Sorrow of Bihar” because of its devastating floods.
The Kosi rises in the Himalayas of Tibet and Nepal, where its upper tributaries include the Sun Kosi, Arun and Tamor. These rivers meet in Nepal before the Kosi flows southward into India and joins the Ganges near Kursela in Bihar.
The river carries heavy sediment from the young, rapidly eroding Himalayas. This material raises the riverbed and contributes to channel shifts across the alluvial plains. Over roughly two centuries, the Kosi’s main channel moved about 120 kilometres westward, creating a wide zone of flood risk.
A major flood in August 2008 followed a breach near Kusaha in Nepal, sending the river into an old channel and affecting millions of people. The nickname refers to the river’s destructive flooding, not to its length or water volume.