Pariksha SaathiLesson 6 of 10 · Bihar General Knowledge
Rivers of Bihar, Floods and River Projects
Drafted with AI assistance and fact-checked on 28 October 2026; not yet read line by line by a human editor. Spotted a mistake? Tell us. Editorial standards & corrections
The Ganga, Bihar's spine
Almost all of Bihar drains into the Ganga. The river enters the state at Chausa in Buxar district, where the Karmanasa meets it on the Uttar Pradesh border, flows east past Buxar, Patna, Mokama, Munger and Bhagalpur, and leaves for Jharkhand's Sahibganj on its way to West Bengal. Its northern tributaries come from the Himalaya, are fed by snow and monsoon rain, carry huge loads of silt and often change course; its southern tributaries come from the Vindhyan and Chota Nagpur uplands, are rain-fed and shrink in summer. The stretch through Patna is part of National Waterway 1 (Haldia to Prayagraj, formerly Allahabad), declared in 1986.
Northern tributaries
From west to east, the Ghaghara (Saryu) joins the Ganga near Chhapra, close to Chirand. The Gandak, called the Narayani or Shaligrami in Nepal and the Sadanira in ancient texts, enters Bihar at Valmikinagar and meets the Ganga at Sonepur-Hajipur opposite Patna. The Burhi Gandak rises in West Champaran near the Someshwar hills, flows east of the Gandak through Muzaffarpur and Samastipur, and joins the Ganga near Khagaria. The Bagmati comes from the Kathmandu valley and flows through Sitamarhi, Muzaffarpur and Darbhanga; the Kamla-Balan drains Madhubani and Darbhanga; the Kosi enters near Bhimnagar in Supaul and joins the Ganga near Kursela in Katihar; and the Mahananda drains the far north-east (Kishanganj, Purnia, Katihar) before meeting the Ganga beyond Bihar.
The Kosi, the Sorrow of Bihar
The Kosi, or Saptakoshi, is formed in Nepal by seven Himalayan streams, chiefly the Sun Kosi, the Arun and the Tamur. Carrying one of the heaviest silt loads of any river, it has shifted westward by more than 100 km over about two centuries, burying farmland under sand and leaving old channels behind. Under the Kosi Agreement of 1954 between India and Nepal, a barrage was built near Hanuman Nagar on the Nepal side of Bhimnagar, with embankments on both banks and the Eastern and Western Kosi canals. On 18 August 2008 the eastern embankment breached at Kusaha in Nepal and the river swung into an old course, flooding Supaul, Madhepura, Araria, Saharsa and Purnia.
Gandak and Son projects
The Gandak Agreement of 1959 with Nepal led to a barrage at Valmikinagar whose canals irrigate Champaran, Saran and Tirhut in Bihar, parts of Uttar Pradesh and part of Nepal. Of the tributaries that join the Ganga in Bihar from the south, the Son is the largest: it rises near Amarkantak in Madhya Pradesh and joins the Ganga near Maner, west of Patna. Its waters feed one of India's oldest modern canal systems: the anicut (weir) at Dehri-on-Sone was built in the 1870s, and the Indrapuri barrage upstream later replaced it. The Son canals made the old Shahabad region, especially Rohtas and Kaimur, the rice bowl of Bihar.
Other southern rivers
The Punpun rises in the Chota Nagpur plateau and joins the Ganga at Fatuha, east of Patna; its banks are also used for pind-daan. The Falgu (Phalgu) is formed near Bodh Gaya by the union of the Niranjana (Lilajan) and the Mohana; Gaya and its Vishnupad temple stand on its bank, and because water flows under its sandy bed for most of the year it is called antahsalila. The Karmanasa, regarded in tradition as an unholy river, forms part of the boundary with Uttar Pradesh. The Kiul drains Jamui and Lakhisarai, and the Ajay rises near Jamui and flows into West Bengal.
Floods and embankments
North Bihar is among the most flood-prone regions of India, because heavy monsoon rain over Nepal, steep Himalayan slopes, heavy silt and a flat plain combine. After the floods of 1954 the government relied mainly on embankments, and their length has grown many times since, yet flood damage has not fallen: embankments trap silt and raise riverbeds, cause waterlogging behind them, and fail disastrously when breached. A long-discussed answer is a high dam on the Kosi at Barahkshetra in Nepal, which would also store water and generate power, so Bihar's floods are partly an India-Nepal question.
Bridges and wetlands
The Ganga in Bihar is crossed by the Rajendra Setu at Mokama (1959), the state's first rail-cum-road bridge over the river; the Mahatma Gandhi Setu between Patna and Hajipur (1982), more than 5.5 km long and long counted among India's longest river bridges; and the Vikramshila Setu at Bhagalpur. The plains hold many wetlands: Kanwar Lake (Kabar Taal) in Begusarai, Bihar's first Ramsar site (2020) and often described as Asia's largest freshwater oxbow lake; the Kusheshwar Asthan wetland in Darbhanga; and Baraila Lake in Vaishali, all three also bird sanctuaries.
Key facts
- The Ganga enters Bihar at Chausa (Buxar), where the Karmanasa joins it, and flows west to east past Patna, Munger and Bhagalpur.
- Northern tributaries from west to east: Ghaghara, Gandak, Burhi Gandak, Bagmati, Kamla-Balan, Kosi, Mahananda.
- Southern rivers: Karmanasa, Son, Punpun, Falgu, Kiul and Ajay; they are rain-fed and shrink in summer.
- Confluences: Ghaghara near Chhapra, Gandak at Sonepur-Hajipur, Son near Maner, Punpun at Fatuha, Burhi Gandak near Khagaria, Kosi near Kursela.
- Kosi: Saptakoshi of Nepal (Sun Kosi, Arun, Tamur); Sorrow of Bihar; Kosi Agreement 1954; barrage near Hanuman Nagar; Kusaha breach on 18 August 2008.
- Gandak Agreement 1959; the Valmikinagar barrage irrigates Bihar, Uttar Pradesh and Nepal.
- Son: rises near Amarkantak; anicut at Dehri-on-Sone (1870s), later the Indrapuri barrage; the Son canals make Rohtas-Kaimur the rice bowl of Bihar.
- Falgu: formed by the Niranjana (Lilajan) and the Mohana near Bodh Gaya; Gaya's Vishnupad temple is on its bank; called antahsalila.
- Ganga bridges: Rajendra Setu, Mokama (1959); Mahatma Gandhi Setu, Patna-Hajipur (1982); Vikramshila Setu, Bhagalpur.
- Kanwar Lake (Kabar Taal), Begusarai: Bihar's first Ramsar site (2020), often described as Asia's largest freshwater oxbow lake.
Quick revision
Ganga enters at Chausa (Karmanasa), NW-1 1986; north: Ghaghara, Gandak (Valmikinagar to Sonepur), Burhi Gandak, Bagmati, Kamla, Kosi (Kursela), Mahananda; south: Son (Amarkantak, joins near Maner), Punpun (Fatuha), Falgu (Niranjana + Mohana), Karmanasa, Kiul; Kosi = Sorrow of Bihar, Agreement 1954, Kusaha breach 2008; Gandak Agreement 1959; Dehri anicut 1870s, Indrapuri barrage; Rajendra Setu 1959, Gandhi Setu 1982; Kanwar Lake Ramsar 2020.