Updated for BPSC Prelims 2026Bihar's river system is one of the most important topics in the Geography and Environment sections of the 72nd BPSC Combined (Preliminary) Competitive Examination (26 July 2026). Questions are frequently asked on river basins, tributaries of the Ganga, catchment areas, protected areas, Ramsar sites, dams, and river origins. This article provides a one-stop revision guide.
The topic covers multiple subjects simultaneously:
A single question can combine two or three of these areas.
| Rank | River Basin | Catchment Area in Bihar (sq. km) |
|---|---|---|
| 1 | Main Ganga Stem | 15,205 |
| 2 | Kiul–Harohar | 12,806 |
| 3 | Kosi | 11,410 |
| 4 | Burhi Gandak | 9,601 |
| 5 | Punpun | 7,536 |
| 6 | Bagmati–Adhwara | 6,500 |
| 7 | Mahananda | 6,150 |
| 8 | Karmanasa | 5,127 |
| 9 | Kamla–Balan | 4,488 |
| 10 | Gandak | 4,188 |
| 11 | Ghaghra | 2,995 |
| 12 | Chandan | 2,371 |
| 13 | Badua | 2,215 |
| 14 | Sone | 1,483 |
These rivers originate mainly from the Himalayas or Nepal and join the Ganga from its northern side.
| West → East | River | Origin | Meets Ganga |
|---|---|---|---|
| 1 | Ghaghra | Mapchachungo Glacier, Tibet | Doriganj (Saran) |
| 2 | Gandak | Devghat, Nepal | Hajipur–Sonepur |
| 3 | Burhi Gandak | Chautarwa Chaur, West Champaran | Khagaria |
| 4 | Bagmati | Bagdwar, Shivapuri Hills, Nepal | Joins Kosi near Beldaur |
| 5 | Kamla–Balan | Mahabharat Range, Nepal | Joins Kosi near Beldaur |
| 6 | Kosi | Sapta Kosi, Nepal | Kursela, Katihar |
| 7 | Mahananda | Mahaldiram Hills, Darjeeling | Manihari, Katihar |
These rivers mainly originate from the Peninsular Plateau and join the Ganga from the southern side.
| West → East | River | Origin | Meets Ganga |
|---|---|---|---|
| 1 | Karmanasa | Kaimur Hills | Chausa, Buxar |
| 2 | Sone | Amarkantak Plateau | Maner (Patna) |
| 3 | Punpun | Palamu Plateau | Fatwah |
| 4 | Kiul | Giridih Hills | Near Surajgarha |
| 5 | Badua | Chakai Hills | Nathnagar, Bhagalpur |
| 6 | Chandan | Deoghar Hills | Near Kahalgaon |
| River | Important Protected Area |
|---|---|
| Gandak | Valmiki Tiger Reserve |
| Gandak | Valmiki Wildlife Sanctuary |
| Burhi Gandak | Kanwar Lake Bird Sanctuary |
| Ganga | Vikramshila Gangetic Dolphin Sanctuary |
| Badua | Bhimbandh Wildlife Sanctuary |
| Chandan | Bhimbandh Wildlife Sanctuary |
| River Basin | Ramsar Site |
|---|---|
| Burhi Gandak | Kanwar Taal |
| Ganga Basin | Kabar Taal |
| Ganga Basin | Kusheshwar Asthan |
| Kiul–Harohar Basin | Nagi–Nakti Bird Sanctuary |
| River | Structure |
|---|---|
| Gandak | Valmikinagar Barrage |
| Kosi | Bhimnagar (Kosi) Barrage |
| Sone | Indrapuri Barrage |
| River | Feature |
|---|---|
| Badua | Bhimbandh Hot Springs |
| Chandan | Bhimbandh Hot Springs |
Candidates should revise the following topics thoroughly:
Main Ganga Stem
Kiul–Harohar
Kosi
Valmiki Tiger Reserve (Gandak Basin)
Vikramshila Gangetic Dolphin Sanctuary (Ganga)
Kanwar Taal
Ghaghra → Gandak → Burhi Gandak → Bagmati → Kamla–Balan → Kosi → Mahananda
Karmanasa → Sone → Punpun → Kiul → Badua → Chandan
The Bihar River System is among the most scoring Geography topics in BPSC. Questions are often framed by combining river sequence, origin, confluence, Ramsar Sites, wildlife sanctuaries, and dams. A clear understanding of these interconnections can help candidates answer multiple questions correctly in the Preliminary Examination.
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