Koshi River of Purnea (Bihar)

The Kosi River is one of the largest tributaries of the Ganga River . Kosi river is called Koshi in Nepal and is a Tran boundary river between Nepal and India. The river basin is surrounded by the ridges separating it from the Brahmaputra in the north, the Gandaki in the west, the Mahananda in the east, and by the Ganga in the south. Kamlā, Bāghmati (Kareh) and Budhi Gandak are major tributaries of Koshi in India, besides minor tributaries like Bhutahi Balān. Over the last 250 years, the Kosi River has shifted its course over 120 kilometres from east to west. The Kosi River (The Sorrow of Bihar) is one of two major tributaries, the other river being Gandak, draining the plains of north Bihar, the most flood-prone area of India. This river is mentioned in the epic Mahabharata as Kauśiki.

The Kosi is known as the “Sorrow of Bihar”  when it flows from Nepal to India, as it has caused widespread human suffering in the past through flooding and very frequent changes in course. The Kosi Barrage has been designed for a peak flood of 27,014 m³/s ,Kosi Barrage, also called Bhimnagar Barrage after the name of the place where it was built between the years 1959 and 1963 straddles the Indo-Nepal border. It is an irrigation, flood control and hydropower generation project on the Kosi river built under a bilateral agreement between Nepal and India: the entire cost of the project was borne by India. The catchment area of the river is 61,788 sq.km  in Nepal at the Barrage site.

On August 18, 2008, the Kosi river picked up an old channel it had abandoned over 100 years ago near the border with Nepal and India. Nearly 27 lakhs people were reported affected as the river broke its embankment at Kusaha in Nepal, thus submerging several districts of Nepal and India. The worst affected districts included Supaul, Araria, Saharsa,Madhepura, Purnea, Katihar, parts of Khagaria and northern parts of Bhagalpur, as well as adjoing  regions of Nepal. The floods caused by the breach in the eastern afflux embankment at upstream Kuaha village in Nepal on August 18 is the worst in the region.  The Saura is the principal tributary of the Kosi. It rises in some lowland to the north-west of Jalalgadh and joins the Kosi near Mirganj. The river flows to the eastern side of the Purnea town and separates old Purnea City and new Purnea Town.