BIHAR RIVER BASINS

Part–1 : Bihar at a Glance

Introduction

Bihar is situated in the central part of the Indo-Gangetic Plain. The River Ganga divides the state into North Bihar and South Bihar. The region lying on the northern side (left bank) of the Ganga is known as North Bihar, while the region lying on the southern side (right bank) is called South Bihar.According to the Second Bihar State Irrigation Commission Report, 1994, the drainage system of Bihar has been classified into 14 river basins. These basins form the basis for flood management, irrigation planning, embankment construction, and water resource development across the state.

Classification of River Basins in Bihar

The 14 river basins identified in Bihar are:

Major Drainage Pattern

The River Ganga is the principal drainage channel of Bihar and flows from west to east across the state.The river system of Bihar is broadly divided into northern and southern drainage basins.

Northern River Basins

The rivers situated on the left bank of the Ganga are:

• Ghaghra
• Gandak
• Burhi Gandak
• Bagmati
• Kamla–Balan
• Kosi
• Mahananda

These rivers:

• Originate from the Himalayas
• Are snow-fed and perennial
• Possess large catchment areas
• Receive heavy monsoon rainfall
• Carry enormous quantities of sediment (silt)
• Are responsible for recurrent flooding across North Bihar.

Southern River Basins

The rivers situated on the right bank of the Ganga are:

• Karmanasa
• Sone
• Punpun
• Kiul–Harohar
• Badua
• Chandan

These rivers drain the southern part of Bihar before joining the Ganga.

Nature of Bihar Rivers

Most rivers of Bihar are snow-fed and perennial, particularly those originating from the Himalayas. They traverse long distances through Nepal before entering the plains of Bihar.The rivers transport huge sediment loads, which contribute to:

• Aggradation of river beds
• Meandering
• Braiding
• Frequent change of river courses
• Flooding
• Bank erosion

Monsoon Characteristics

Approximately 80–90% of the annual rainfall in Bihar is received during the South-West Monsoon season.The concentration of rainfall during a short monsoon period causes:

• Sudden rise in river discharge
• Heavy flooding
• River bank erosion
• Waterlogging
• Drainage congestion

The northern districts are particularly vulnerable because rainfall occurring in the Himalayan catchments reaches Bihar simultaneously with local rainfall.

Why North Bihar Faces Frequent Floods

North Bihar experiences severe floods almost every year because:

• Most rivers originate in the Himalayas.
• Heavy rainfall occurs over the upstream catchments.
• Rivers carry large quantities of silt.
• River beds gradually rise due to sediment deposition.
• Rivers frequently change their courses.
• Drainage becomes congested during high flows.
• Large floodplains remain inundated during the monsoon.

Salient Features of Bihar

Salient Features of Major River Basins

*Rainfall value reproduced exactly as provided in the uploaded source.

Importance of Bihar River Basins

The river basins form the backbone of Bihar's:

• Flood management
• Irrigation planning
• Water resource development
• Drainage management
• Embankment construction
• Agricultural sustainability
• Disaster mitigation
• Regional planning

They also serve as the administrative basis for planning by the Water Resources Department.

BIHAR RIVER BASINS

Part–2 : Ghaghra River Basin

Introduction

The Ghaghra River Basin is one of the 14 major river basins of Bihar identified under the Second Bihar State Irrigation Commission Report, 1994. It is a transboundary Himalayan river basin, with its catchment spread across Nepal, Uttar Pradesh and Bihar. The basin forms a part of the alluvial Gangetic Plain, and the Ghaghra finally joins the River Ganga near Chapra (Saran district).Although only a small portion of its catchment lies within Bihar, the basin significantly influences the flood regime of north-western Bihar because of its heavy sediment load, flat gradient and seasonal flooding.

Geographical Extent

The total catchment area of the Ghaghra Basin is 1,27,950 sq. km, of which:

Nearly the entire plains of the basin lie south of the Indo–Nepal border, forming a part of the Gangetic Alluvial Plain.

Districts Covered in Bihar

The Ghaghra Basin covers three districts of Bihar:

• Gopalganj
• Siwan
• Saran (Chapra)

Basin Characteristics

The basin receives rainfall ranging from 1500 mm in the Trans-Himalayan region to around 1200 mm in the lower reaches near its confluence with the Ganga.The river carries large quantities of sediment during the monsoon. As the river enters the plains, the gradient becomes extremely gentle, causing deposition of silt, meandering, and inundation of low-lying areas.

Tributary System in Bihar

Within Bihar, several rivers join the Ghaghra from the left bank.

Left Bank Tributaries

• Little Gandak
• Sondhi Nala
• Jharahi
• Daha

Right Bank Tributaries

• Nil

The tributaries contribute additional monsoon discharge and increase flood vulnerability in the downstream areas.

Flood Behaviour

Flooding in the Ghaghra Basin is mainly associated with:

• Heavy monsoon discharge
• Large-scale silt deposition
• Very flat river-bed slope
• Drainage congestion
• Meandering tendency
• Overtopping or breach of embankments

Because of the flat terrain, deposited sediments raise the river bed, making the basin highly susceptible to prolonged inundation.

Special Geomorphological Features

The basin contains numerous low-lying depressions known as "Chaurs".These Chaurs remain submerged for long periods due to poor natural drainage, causing waterlogging and delayed recession of floodwaters after the monsoon.

Causes of Flooding

Floods in the basin generally occur because:

• Rivers spill over their banks during high discharge.
• Large quantities of silt reduce the carrying capacity of the river.
• Flat bed slope slows down drainage.
• Water accumulates in Chaurs.
• Floodwaters escape through gaps in the left embankment, particularly in Siwan and Saran districts.

Salient Features

Key Characteristics

The Ghaghra Basin is characterized by:

• Himalayan origin
• Large transboundary catchment
• Perennial river system
• Heavy sediment transport
• Extensive alluvial plains
• Presence of Chaurs
• Seasonal flooding
• Meandering river channel
• Drainage congestion
• Dependence on embankment protection

Significance for Bihar

The Ghaghra Basin is important because it:

• Contributes to the hydrology of north-west Bihar.
• Influences flood conditions in Gopalganj, Siwan and Saran.
• Forms part of the Gangetic drainage network.
• Requires continuous embankment maintenance for flood management.
• Represents a typical Himalayan alluvial river system with high sediment transport.

BPSC/UPSC Quick Revision

BIHAR RIVER BASINS

Part–3 : Gandak River Basin

Introduction

The Gandak River Basin is one of the 14 major river basins of Bihar identified under the Second Bihar State Irrigation Commission Report, 1994. It is a transboundary Himalayan river basin, with its catchment extending across Nepal, Uttar Pradesh, and Bihar. The river originates near Valmiki Nagar and finally joins the River Ganga after traversing the plains of Bihar.The Gandak is an important snow-fed perennial river carrying substantial quantities of sediment from the Himalayas. It plays a crucial role in irrigation, drainage, and flood management in north-western Bihar, while simultaneously posing major flood challenges during the monsoon season.

Geographical Extent

The total catchment area of the Gandak Basin is 40,553 sq. km, distributed across Nepal, Uttar Pradesh, and Bihar.

The basin receives its highest rainfall in the northern Himalayan region, while rainfall decreases gradually towards the southern plains.

Origin and Basin Characteristics

The Gandak River originates near Valmiki Nagar in the Himalayan region. The river flows through mountainous terrain before entering the plains of Bihar.The basin experiences its maximum rainfall during the South-West Monsoon (June–October). Annual rainfall varies considerably from about 2030 mm in the northern hilly catchment to approximately 1100 mm in the southern plains.The river has a steep gradient in the mountains, but after entering the plains the gradient decreases significantly, resulting in a reduction in flow velocity and deposition of sediments.

Sediment Characteristics

Like other Himalayan rivers, the Gandak transports large quantities of silt and sediments.As the river enters the plains:

• Flow velocity decreases.
• Sediments begin to settle.
• River bed gradually rises (aggradation).
• The river develops a tendency to spill over its banks.
• Flooding becomes more frequent during the monsoon.

Tributary System

Left Bank Tributaries

• Bhabsa
• Harha

Right Bank Tributaries

• Kakra

These tributaries contribute additional discharge during the rainy season and influence the overall hydrology of the basin.

Flood Behaviour

The Gandak River flows almost along a ridge line, making the basin particularly vulnerable to breaches in embankments.The flood situation becomes more severe when:

• The River Ganga is simultaneously in flood.
• The outfall of the Gandak is obstructed, resulting in backflow of Ganga water into the Gandak.
• Embankments fail or develop breaches.

The river has therefore been embanked on both sides, making proper maintenance of embankments essential for flood control.

Major Flood Problems

The principal causes of flooding in the Gandak Basin include:

• Heavy monsoon discharge.
• High sediment load.
• Rising river bed due to silt deposition.
• Reduced carrying capacity of the channel.
• Backflow from the Ganga during simultaneous flooding.
• Breaches in embankments.
• Overflow of river banks.

Importance of Embankments

Since the river flows close to the ridge line, any breach in the embankment may result in large-scale devastation across the surrounding floodplains.Effective flood management therefore depends upon:

• Regular inspection of embankments.
• Timely maintenance.
• Prevention of erosion.
• Strengthening vulnerable stretches before the monsoon.

Salient Features

Key Characteristics

The Gandak Basin is characterized by:

• Himalayan origin
• Perennial river system
• Large transboundary catchment
• High sediment transport
• Steep mountain gradient
• Gentle alluvial plain gradient
• River bed aggradation
• Extensive embankment system
• Backflow effects from the Ganga
• Recurring monsoon floods

Significance for Bihar

The Gandak Basin is important because it:

• Supports irrigation and water resources in north-west Bihar.
• Forms a major component of Bihar's Himalayan river system.
• Contributes significantly to the Ganga drainage network.
• Requires extensive embankment management to reduce flood risks.
• Illustrates the interaction between Himalayan sediment transport and alluvial floodplain dynamics.

BPSC/UPSC Quick Revision

BIHAR RIVER BASINS

Part–4 : Burhi Gandak River Basin

Introduction

The Burhi Gandak River Basin is one of the 14 major river basins of Bihar classified under the Second Bihar State Irrigation Commission Report, 1994. Unlike most Himalayan rivers, the Burhi Gandak joins the Ganga from its left bank within Bihar and plays a significant role in the state's floodplain hydrology.The basin has a fan-shaped catchment in its upper reaches which gradually changes into an elongated and rectangular basin downstream. Owing to its high sediment load, meandering tendency, and changing river course, the basin frequently experiences flooding, particularly during the monsoon season.

Geographical Extent

The total catchment area of the Burhi Gandak Basin is 12,021 sq. km, distributed between Nepal and Bihar.

The basin is fan-shaped up to the confluence of the Dhanauti River, after which it becomes elongated and rectangular.

Basin Boundaries

The Burhi Gandak Basin is bounded by:

• North: Someshwar Range of the Himalayas
• East: Bagmati Basin
• West: Gandak Basin
• South: Main Ganga Stem

This geographical setting places the basin entirely within the larger Gangetic Drainage System.

Physiography and River Characteristics

The Burhi Gandak River originates from the Someshwar Range of the Himalayas. The river initially flows through steep hilly terrain, where the bed slope ranges from about 2 m/km to 5 m/km.After entering the plains of Bihar, the gradient decreases sharply and the river flows across an extensive alluvial plain. The southern portion of the basin is comparatively flat with very little undulation.The river system has played an important role in the formation of the basin's alluvial landscape through continuous deposition of sediments.

Sediment Deposition and River Morphology

The Burhi Gandak carries large quantities of sediment from the Himalayan catchment.As the river enters the plains:

• River velocity decreases.
• Sediments are deposited extensively.
• Meandering and braiding tendencies develop.
• River channels frequently shift.

The continuous movement of the river has resulted in the formation of:

• Natural depressions known as "Mauns", created by cut-offs of meander loops.
• Numerous gullies and ridges.
• Saucer-shaped natural depressions known as "Chaurs".

These landforms are characteristic geomorphological features of the Burhi Gandak Basin.

Rainfall Characteristics

The average annual rainfall in the basin is 1283 mm.Rainfall varies significantly across the basin:

• Upper Catchment: approximately 1569 mm
• Lower Catchment: approximately 1041 mm

Most rainfall is received during the South-West Monsoon, leading to rapid increases in river discharge.

Flood Characteristics

Flooding in the Burhi Gandak Basin is caused by:

• Heavy monsoon rainfall in the upper catchment.
• Overflow of tributaries.
• Large sediment load.
• Reduction in channel carrying capacity.
• Inadequate waterway openings at bridges and culverts.
• Spilling of tributaries and streams.

Floods occurring in the tributaries often aggravate flooding in the main river channel.

Areas Frequently Affected by Floods

According to the uploaded source, the West Champaran region experiences recurring floods, particularly around:

• Plamnagar
• Narkatiaganj
• Mainatand
• Chanpatia
• Sugauli
• Semra
• Motihari
• Lalbegiaghat

The source also notes that Motihari town is frequently affected due to the spill of the Sikrahana River.Flooding also occurs because of the overflow of tributaries and smaller streams within the basin.

Tributary System

Left Bank Tributaries

• Masan
• Balor
• Pandai
• Sikta
• Balan
• Tilawe
• Tiur

Right Bank Tributaries

• Dhanauti
• Kohra
• Danda
• Fardo
• Danda-Kedane
• None-Balane

These tributaries contribute significantly to the discharge and flood behaviour of the Burhi Gandak River during the monsoon.

Salient Features

Important Geomorphological Features

The Burhi Gandak Basin exhibits several distinctive geomorphological characteristics:

• Fan-shaped upper basin
• Elongated lower basin
• Meandering river channels
• Braided river reaches
• River course shifting
• Formation of Mauns
• Formation of Chaurs
• Extensive sediment deposition
• Alluvial plains
• Natural gullies and ridges

Significance for Bihar

The Burhi Gandak Basin is significant because it:

• Forms one of the major flood-prone basins of North Bihar.
• Contributes substantially to the alluvial landscape of the state.
• Supports agriculture through fertile sediment deposits.
• Requires extensive embankment maintenance and flood management measures.
• Demonstrates the impact of Himalayan sediment transport on river morphology.

BPSC/UPSC Quick Revision

BIHAR RIVER BASINS

Part–5 : Bagmati–Adhwara River Basin

Introduction

The Bagmati–Adhwara River Basin is one of the 14 major river basins of Bihar identified under the Second Bihar State Irrigation Commission Report, 1994. It is a transboundary Himalayan river basin, with its catchment extending across Nepal and Bihar. The basin comprises the Bagmati River and the intricate network of the Adhwara Group of Rivers, making it one of the most complex drainage systems in North Bihar.The basin is characterized by low gradients, high sediment load, multiple interconnecting channels, and frequent changes in river courses. Due to these characteristics, it remains one of the most flood-prone regions of Bihar.

Geographical Extent

The Bagmati–Adhwara Basin occupies a significant portion of North Bihar.

The basin forms an integral part of the Middle Gangetic Plain and receives runoff from the Himalayan foothills before draining into the Ganga system.

Basin Characteristics

The basin consists of the Bagmati River together with numerous interconnected streams collectively known as the Adhwara Group of Rivers.Unlike a single river channel, the Adhwara system comprises several small rivers and distributaries, which frequently change their alignment and often merge or bifurcate during floods.The basin has an extremely gentle slope, resulting in:

• Slow movement of floodwater.
• Poor natural drainage.
• Long-duration waterlogging.
• Extensive floodplain inundation.

Physiography

The Bagmati–Adhwara Basin is predominantly composed of recent alluvial deposits brought by Himalayan rivers.The terrain is:

• Flat and low-lying.
• Poorly drained.
• Rich in fertile alluvial soils.
• Highly susceptible to river migration.

Numerous abandoned river channels, marshes and natural depressions are found throughout the basin.

Rainfall Characteristics

The basin receives substantial rainfall during the South-West Monsoon.

Most precipitation occurs between June and September, causing rapid increases in river discharge.

River Behaviour

The rivers of the Bagmati–Adhwara system exhibit:

• Frequent meandering.
• Channel shifting.
• Heavy silt deposition.
• Braided river reaches.
• Formation of multiple distributaries.
• Overflow into adjoining floodplains during the monsoon.

Because of the extremely low gradient, floodwaters often remain stagnant for prolonged periods.

Flood Characteristics

Flooding in the Bagmati–Adhwara Basin is primarily caused by:

• Heavy rainfall in Nepal.
• Simultaneous monsoon rainfall in Bihar.
• Large sediment load.
• Poor drainage.
• Frequent river course changes.
• Overflow of interconnected channels.
• Waterlogging in low-lying areas.

Unlike flash floods, flooding in this basin is generally prolonged, with water remaining over agricultural fields for extended periods.

Drainage Characteristics

The Adhwara rivers form a network drainage pattern rather than a single well-defined river.During high discharge:

• Rivers frequently overflow.
• Channels interconnect.
• New flow paths develop.
• Floodwaters spread over extensive floodplains.

This dynamic drainage pattern makes flood management particularly challenging.

Salient Features

Major Characteristics

The Bagmati–Adhwara Basin is distinguished by:

• Transboundary Himalayan basin
• Complex river network
• Adhwara group of rivers
• Low-gradient floodplain
• Recent alluvial deposits
• High sediment transport
• River migration
• Waterlogging
• Long-duration floods
• Frequent channel changes

Importance of the Basin

The Bagmati–Adhwara Basin is important because it:

• Forms one of the most significant floodplain ecosystems of North Bihar.
• Supports agriculture through fertile alluvial soils.
• Receives Himalayan runoff from Nepal.
• Influences groundwater recharge.
• Requires integrated flood and drainage management because of its interconnected river network.

Challenges

Major challenges in the basin include:

• Recurring floods.
• Drainage congestion.
• River course migration.
• Waterlogging.
• Heavy sediment deposition.
• Poor natural drainage.
• Agricultural losses during prolonged inundation.
• Complex management of multiple interconnected channels.

BIHAR RIVER BASINS

Part–6 : Kamla–Balan River Basin

Introduction

The Kamla–Balan River Basin is one of the 14 major river basins of Bihar identified under the Second Bihar State Irrigation Commission Report, 1994. It is a transboundary Himalayan river basin, with its catchment extending across Nepal and Bihar. The basin comprises the Kamla River, Balan River, and their associated tributaries, which together form one of the important drainage systems of North Bihar.The basin is characterized by high monsoon discharge, heavy sediment transport, frequent channel migration, and recurring floods. After entering the plains of Bihar, the rivers lose gradient rapidly, resulting in widespread deposition of sediments and inundation of low-lying areas.

Geographical Extent

The Kamla–Balan Basin extends from the Himalayan foothills of Nepal into the alluvial plains of North Bihar.

The basin forms an integral component of the Middle Gangetic drainage system.

Basin Characteristics

The Kamla–Balan Basin consists of the Kamla River and the Balan River, along with their associated drainage network.After descending from the Himalayan region, the rivers enter the plains where the slope becomes very gentle. As a result:

• Flow velocity decreases.
• Sediment deposition increases.
• River channels become unstable.
• Frequent meandering develops.
• Floodwaters spread over extensive floodplains.

The basin has fertile alluvial soils but remains highly vulnerable to seasonal floods.

Physiography

The basin is predominantly composed of recent alluvial deposits.The terrain is characterized by:

• Flat topography.
• Extensive floodplains.
• Low natural gradient.
• Poor drainage conditions.
• Numerous abandoned channels.
• Waterlogged depressions in several locations.

The geomorphology of the basin is continuously modified by river migration and sediment deposition.

Rainfall Characteristics

The basin receives substantial rainfall during the South-West Monsoon.

Most rainfall occurs during June to September, leading to a rapid increase in river discharge.

River Behaviour

The Kamla–Balan River System exhibits:

• Meandering river channels.
• Frequent shifting of river courses.
• Heavy silt deposition.
• Overflow during peak monsoon.
• Formation of floodplain deposits.
• Seasonal inundation of adjoining agricultural lands.

Because of the gentle slope, floodwaters remain in the basin for extended periods before draining into the Ganga system.

Flood Characteristics

Flooding in the Kamla–Balan Basin results from:

• Heavy rainfall in Nepal.
• Simultaneous rainfall over North Bihar.
• Large sediment load.
• Reduced carrying capacity of river channels.
• Poor drainage.
• Frequent channel migration.
• Overflow of embankments during high discharge.

Floodwaters generally spread over wide areas due to the flat terrain.

Drainage Characteristics

The drainage pattern of the basin is influenced by:

• Himalayan runoff.
• Low-gradient alluvial plains.
• Multiple distributaries.
• Natural depressions.
• Seasonal flood channels.

These characteristics make flood forecasting and drainage management particularly important.

Salient Features

Major Characteristics

The Kamla–Balan Basin is distinguished by:

• Transboundary Himalayan basin
• Snow-fed perennial river system
• Heavy sediment transport
• Recent alluvial floodplain
• Meandering river channels
• Frequent river migration
• Low-gradient terrain
• Seasonal flooding
• Waterlogging in low-lying areas
• Fertile agricultural plains

Importance of the Basin

The Kamla–Balan Basin plays a significant role in:

• Supporting agriculture through fertile alluvial soils.
• Recharging groundwater.
• Sustaining riverine ecosystems.
• Providing irrigation potential.
• Maintaining the hydrological balance of North Bihar.

Despite these benefits, effective flood management remains a major challenge due to the basin's geomorphological characteristics.

Challenges

Major issues affecting the basin include:

• Annual floods.
• Heavy silt deposition.
• River course changes.
• Drainage congestion.
• Waterlogging.
• Agricultural losses.
• Bank erosion.
• High maintenance requirement of flood-control infrastructure.

BIHAR RIVER BASINS

Part–7 : Sone River Basin

Introduction

The Sone River Basin is one of the 14 major river basins of Bihar identified under the Second Bihar State Irrigation Commission Report, 1994. It is one of the largest southern river basins of Bihar and extends across Madhya Pradesh, Uttar Pradesh, Jharkhand and Bihar. The river Sone is a major right-bank tributary of the Ganga and drains a vast plateau region before entering the Gangetic plains.Unlike the rivers of North Bihar, the Sone Basin is not severely affected by silt deposition, although flooding occurs in its lower reaches due to over-bank spilling and backwater effects of the Ganga.

Geographical Extent

The Sone Basin covers a vast inter-state catchment.

The basin extends across:

• Madhya Pradesh
• Uttar Pradesh
• Jharkhand
• Bihar

The basin is roughly rectangular in shape, having:

• Maximum East–West Length: 460 km
• Maximum North–South Width: 220 km

Physiography

Except in its lower reaches, where it enters the Gangetic Plain in Shahabad district, the Sone flows through:

• Hilly terrain
• Forested regions
• Plateau landscape of Madhya Pradesh and Uttar Pradesh

The upper basin has comparatively steeper gradients, while the lower basin becomes flatter as the river approaches the Ganga.

Rainfall Characteristics

The basin experiences considerable spatial variation in rainfall.Rainfall ranges from:

• 1472 mm in the upper catchment
• Around 954 mm in the plains where the Sone joins the Ganga.

River Behaviour

Flooding is generally not widespread throughout the basin but is concentrated in the lower reaches, where the river leaves the hilly terrain and enters the plains.The river usually spills:

• Below Daudnagar on the right bank.
• Below Nasriganj on the left bank in Bhojpur district.
• Further downstream near Koilwar Bridge, causing inundation in adjoining low-lying areas.

The principal cause of over-bank spilling is:

• Heavy rainfall in the upper catchment, and
• Insufficient carrying capacity of the river within its banks.

Flood Management Measures

Several important embankment schemes have been constructed for flood protection, including:

• Buxar–Koilwar Embankment (Part)
• Sone Left Embankment from Koilwar to Harpur Lock
• Sone Right Embankment Schemes

These structures help reduce flood damage in vulnerable downstream regions.

Flood Characteristics

Flooding becomes particularly severe when:

• The Sone River is simultaneously in flood.
• The Ganga is also flowing at high stage.

Under such conditions:

• Drainage congestion develops.
• Floodwater remains trapped for longer periods.
• Duration and extent of inundation increase considerably.

Historical Flood

A major flood occurred in 1975, when the Sone overflowed in its lower reaches.The flood resulted in inundation of:

• Entire Danapur
• Most parts of Patna town

The event caused extensive damage to private and public property.

Sediment Characteristics

Unlike many Himalayan rivers, the Sone Basin does not experience a significant silt problem because:

• Annual silt load does not follow a regular pattern.

This distinguishes the Sone from rivers such as the Kosi, Gandak, and Bagmati.

Districts Covered in Bihar

The basin covers the districts of:

• Rohtas
• Bhojpur
• Aurangabad
• Patna

Salient Features

Major Characteristics

The Sone Basin is characterized by:

• Inter-state river basin
• Plateau-origin river system
• Rectangular basin shape
• Hilly upper catchment
• Forested terrain
• Lower Gangetic plains
• Limited silt deposition
• Over-bank spilling in lower reaches
• Backwater flooding due to Ganga
• Embankment-based flood protection

Importance of the Basin

The Sone Basin plays a significant role in:

• Supporting agriculture in southern Bihar.
• Providing irrigation potential.
• Maintaining water availability in plateau and plain regions.
• Contributing to the Ganga river system.
• Protecting urban centres through embankment infrastructure.

Challenges

Major issues affecting the basin include:

• Flooding in lower reaches.
• Over-bank spilling.
• Drainage congestion during simultaneous floods of the Sone and Ganga.
• Damage to low-lying settlements.
• Requirement of continuous embankment maintenance.

BIHAR RIVER BASINS

Part–8 : Punpun River Basin

(Complete BPSC/UPSC Notes)

Introduction

The Punpun River Basin is one of the 14 major river basins of Bihar identified by the Second Bihar State Irrigation Commission Report, 1994. It is an important southern tributary basin of the Ganga, extending across Bihar and Jharkhand. The basin is elongated in shape and is characterized by comparatively low banks, inadequate channel capacity in its lower reaches, and frequent over-bank spilling during the monsoon season.The basin significantly influences the flood situation in Patna and the Mokama Tal region, especially when high flood levels in the Ganga coincide with floods in the Punpun River.

Geographical Extent

The Punpun Basin extends across Bihar and Jharkhand.

The basin mainly covers the districts of:

• Patna
• Jehanabad
• Gaya
• Aurangabad

The basin is elongated in shape, influencing the concentration and movement of floodwaters toward the lower reaches.

Rainfall Characteristics

Approximately 85% of the total annual rainfall is received during the south-west monsoon (June–September).Rainfall varies considerably from the upper reaches to the confluence with the Ganga.

• 954 mm near the confluence with the Ganga.
• 1,817 mm in the uppermost reaches.

Hydrological Characteristics

The lower reaches of the Punpun Basin are characterized by:

• Low river banks.
• Inadequate channel capacity.
• Frequent over-bank spilling even during normal floods.

Floodwater spills occur on both banks of the river.

Course of Floodwaters

North-eastward flowing floodwaters from the Punpun meet the spill waters of its two important tributaries:

• Morhar River
• Dardha River

Important spill locations include:

Morhar River

• Floodwaters spill north of Taregana–Bharatpur Road.

Dardha River

• Floodwaters spill north of Taregana–Dumari Road.

The combined floodwaters increase inundation in downstream areas.

Flood Control Measures

Flooding along the left bank of the Punpun has been considerably reduced after construction of:

• Left Bank Embankment under the Patna Town Protection Scheme

This embankment has helped protect major urban areas from floodwaters.

Flooding in Mokama Tal Region

Part of the floodwater from the right bank of the Punpun flows into the:

• Dhoba River System

This aggravates flooding in the Mokama Tal Area.The situation becomes particularly severe when:

• The Ganga is flowing at high flood stage.
• Backwater from the Ganga enters:
  • Punpun
  • Dardha
  • Dhoba River System

This causes widespread inundation over large areas surrounding the Mokama Tal.

Causes of Flooding

The major causes responsible for flooding include:

• Low river banks.
• Inadequate channel capacity.
• Simultaneous flooding of the Ganga.
• Backwater effect from the Ganga.
• Spill from tributary rivers.
• Heavy monsoon rainfall.

Important Tributaries

The principal tributaries mentioned for the basin are:

• Morhar
• Dardha
• Dhoba River System (receives spill water from the right bank)

Districts Covered

The Punpun Basin mainly covers:

• Patna
• Jehanabad
• Gaya
• Aurangabad

Salient Features

Major Characteristics

The Punpun Basin is characterized by:

• Southern tributary basin of the Ganga.
• Elongated basin shape.
• Low banks in lower reaches.
• Inadequate river channel capacity.
• Frequent over-bank spilling.
• Significant backwater influence from the Ganga.
• Flood interaction with Morhar and Dardha rivers.
• Flood impact on Mokama Tal.
• Urban flood protection through embankments.

Importance of the Basin

The Punpun Basin is important because it:

• Drains a large part of south-central Bihar.
• Influences flood conditions in Patna.
• Plays a major role in the hydrology of the Mokama Tal region.
• Supports agriculture through seasonal water availability.
• Contributes to the drainage network of the Ganga Basin.

Challenges

Major challenges include:

• Frequent flooding in lower reaches.
• Low carrying capacity of the river channel.
• Simultaneous flooding with the Ganga.
• Backwater-induced inundation.
• Floodwater convergence from tributaries.
• Need for continuous embankment maintenance and flood management.

BIHAR RIVER BASINS

Part–9 : Kiul–Harohar River Basin

Introduction

The Kiul–Harohar River Basin is one of the 14 major river basins of Bihar identified under the Second Bihar State Irrigation Commission Report, 1994. It is a river system extending across Bihar and Jharkhand, comprising numerous interconnected streams that frequently bifurcate and reunite during their course. Unlike the major Himalayan rivers of North Bihar, the Kiul–Harohar Basin is primarily a plateau-fed basin, with rivers largely remaining non-perennial and exhibiting regime flow characteristics.Although flooding is comparatively less severe than in North Bihar, the basin experiences flash floods, over-bank spilling, and local flooding due to inadequate channel capacity and poorly maintained embankments.

Geographical Extent

The Kiul–Harohar River System drains extensive areas of Bihar and Jharkhand.

The upper catchment lies within the Chotanagpur Plateau, characterized by:

• Low hills
• Gentle slopes
• Depressions
• Valleys

The river system is composed of numerous small streams that frequently bifurcate and reunite, making the exact river length difficult to determine.

Physiographic Characteristics

The upper basin possesses:

• Plateau terrain
• Low hills
• Undulating topography
• Depressions and valleys

As the rivers descend into the plains, they spread through multiple interconnected channels.The river network is highly complex because several small streams divide and later merge repeatedly.

Rainfall Characteristics

The basin receives an average annual rainfall of 1,104 mm.The lower catchment receives comparatively less rainfall than the upper catchment.Approximately 90% of the annual rainfall occurs during the south-west monsoon (June–October).

Nature of the River System

The rivers of the Kiul–Harohar Basin differ significantly from the Himalayan rivers of North Bihar.Major characteristics include:

• Mostly non-perennial.
• Predominantly regime rivers.
• Plateau-fed drainage.
• Numerous bifurcating channels.
• Frequent channel rejoining.

Flood Characteristics

The basin generally experiences less severe flooding than the river basins of North Bihar.However, flash floods occur during periods of heavy rainfall in the upper catchment.Flooding mainly results from:

• Low bank capacity.
• Inadequate carrying capacity of river channels.
• Overflow of tributaries.
• Poorly maintained embankments.

Rivers Responsible for Flooding

The principal rivers contributing to flood problems include:

• Kiul
• Harohar
• Sakari
• Falgu
• Mohane
• Paimar

These rivers often spill over their banks because their channels cannot safely accommodate high monsoon discharge.

Embankment Condition

Flood protection in several locations depends upon Zamindari embankments.However, these embankments are generally:

• Inadequate in cross-section.
• Poorly maintained.
• Incapable of withstanding medium flood conditions.

Consequently, breaches and over-bank flooding occur frequently.

Major Flood Problems

The important flood problems identified within the basin include:

1. Kiul River

• The Kiul River spills over its banks in the lower reaches near Lakhisarai, causing flooding in surrounding areas.

2. Sakari River

• The Sakari River, a tributary of the Harohar, is a shallow river carrying a large amount of silt.
• During flash floods, water frequently overtops the banks.
• Existing local Zamindari embankments below Sakari Weir contain several gaps through which floodwater escapes.

3. Falgu River

• The Falgu River occasionally creates flood situations due to flash floods generated by heavy rainfall in its upper catchment.

4. Panchane River

• The Panchane River also produces local flooding because of the inadequate carrying capacity of its several bifurcated channels.

Causes of Flooding

The major causes responsible for flooding are:

• Flash floods in the upper catchment.
• Inadequate channel capacity.
• Poorly maintained embankments.
• Overflow of tributary rivers.
• High silt load in shallow channels.
• Numerous bifurcating river channels.
• Heavy monsoon rainfall.

Important Rivers of the Basin

Major rivers forming the basin include:

• Kiul
• Harohar
• Sakari
• Falgu
• Mohane
• Paimar
• Panchane

Salient Features

Major Characteristics

The Kiul–Harohar Basin is characterized by:

• Plateau-fed drainage basin.
• Upper catchment in the Chotanagpur Plateau.
• Numerous interconnected streams.
• Frequent bifurcation and rejoining of channels.
• Mostly non-perennial rivers.
• Regime river characteristics.
• Flash floods rather than prolonged Himalayan floods.
• Dependence on local embankments.
• Comparatively lower flood severity than North Bihar basins.

Importance of the Basin

The Kiul–Harohar Basin is important because it:

• Drains a large portion of south-central Bihar.
• Forms an important plateau drainage network.
• Supports agriculture through seasonal runoff.
• Connects multiple river systems before ultimately joining the Ganga Basin.
• Influences flood management in Lakhisarai and adjoining districts.

Challenges

Major challenges include:

• Flash floods during heavy rainfall.
• Weak and poorly maintained embankments.
• High silt deposition in tributaries.
• Inadequate channel carrying capacity.
• Flooding due to bifurcated river channels.
• Need for modernization of flood-control infrastructure.

BIHAR RIVER BASINS

Part–10 : Badua River Basin

Introduction

The Badua River Basin is one of the 14 major river basins of Bihar identified in the Second Bihar State Irrigation Commission Report, 1994. It is a comparatively small southern river basin situated in the Munger–Bhagalpur region of Bihar. The basin is formed primarily by the Badua River and the Belharana River, both of which have been grouped together for hydrological studies and basin planning because of their close geographical association.The Badua River ultimately drains into the Ganga, while the Belharana River also independently joins the Ganga upstream of the Badua outfall.

Geographical Location

The basin lies between:

• Latitude: 24°35' N to 25°25' N
• Longitude: 86°22' E to 86°55' E

The basin occupies the south-eastern part of Bihar and forms an important drainage system for the Munger region before joining the Ganga.

Origin and Course of the River

The Badua River originates from the hills of Chakai Block in Munger District.After originating in the hilly terrain, it flows northward and ultimately joins the Ganga near Nathnagar (west of Bhagalpur) through Chanan Nadi.

Belharana River

The Belharana River flows almost parallel to the Badua River on its left bank.Important characteristics include:

• Falls independently into the Ganga.
• Joins the Ganga about 26 km upstream of the Badua outfall.
• Hydrologically grouped with the Badua Basin for planning and study purposes.

Catchment Characteristics

The basin is comparatively small among Bihar's river basins.

The drainage areas of the Badua and Belharana rivers are considered together for basin management.

Hydrological Characteristics

The river originates in hilly terrain before entering the plains.The basin primarily drains:

• Munger region
• Nathnagar area
• Western Bhagalpur region

Both the Badua and Belharana eventually discharge into the Ganga through separate outlets.

Basin Planning Significance

Although the Badua and Belharana are separate rivers, they are treated as one hydrological unit because:

• Their drainage areas are closely connected.
• Their outfalls are located near each other.
• Joint basin planning is more effective for flood management and water resource development.

Tributaries

The important tributaries of the Badua River are:

• Belharana
• Gobra Nala
• Chanan
• Barne Nala
• Kamjori

Flood Characteristics

The uploaded data indicates that the Badua Basin has comparatively limited flood management infrastructure.The basin records:

• No embankments
• No flood-protected area

Flood-prone area exists despite the absence of embankment construction.

Salient Features

Major Characteristics

The Badua Basin is characterized by:

• Small river basin of south Bihar.
• Origin from the hills of Chakai Block.
• Outfall into the Ganga near Nathnagar.
• Parallel drainage by the Belharana River.
• Joint hydrological planning of Badua and Belharana rivers.
• Absence of embankments.
• Moderate flood-prone area despite limited flood-control infrastructure.

Importance of the Basin

The Badua Basin is important because it:

• Forms an important drainage network of Munger and Bhagalpur.
• Connects hilly catchments with the Ganga plains.
• Supports agriculture in south-eastern Bihar.
• Contributes seasonal runoff to the Ganga.
• Represents one of Bihar's smaller but significant independent river basins.

Challenges

Major challenges include:

• Absence of embankment infrastructure.
• Flood-prone low-lying areas.
• Small basin with seasonal runoff concentration.
• Requirement of integrated basin management with the Belharana River.
• Dependence on natural drainage channels.

BIHAR RIVER BASINS

Part–11 : Chandan River Basin

Introduction

The Chandan River Basin is one of the 14 major river basins of Bihar identified under the Second Bihar State Irrigation Commission Report, 1994. It is an independent river basin situated in the south-eastern part of Bihar, draining primarily through the Chandan River, Chir River, and Bilasi River. These three rivers together form a common watershed before ultimately joining the Ganga River.The basin originates from the hills of Deoghar (Jharkhand) and represents an important plateau-fed drainage system flowing into the Gangetic plains.

Geographical Location

The Chandan Basin lies between:

• Latitude: 24°30' N to 22°51' N
• Longitude: 84°36' E to 87°27' E

The basin occupies parts of Jharkhand and south-eastern Bihar, draining into the Ganga after traversing hilly and plain regions.

Origin and Course of the River

The Chandan River originates from the hills of Deoghar in Jharkhand at an elevation of approximately 274 metres above mean sea level (MSL).From its source, the river:

• Travels approximately 110 km.
• Enters the plains after descending from the plateau.
• Bifurcates into several small distributary channels before reaching the Ganga.
• Finally joins the Ganga River through Jamunia Nala.

River System

The Chandan Basin is drained by three principal rivers:

• Chandan River
• Chir River
• Bilasi River

Important characteristics include:

• Bilasi River flows almost parallel to the Chandan River on its left bank.
• Bilasi finally merges into the Chandan before the river enters the Ganga.
• These three rivers form a single hydrological watershed.

Catchment Characteristics

The basin forms a medium-sized drainage system in south Bihar.

Hydrological Characteristics

The river begins in hilly terrain and gradually enters the alluvial plains.Before reaching the Ganga, the river develops:

• Numerous distributary channels.
• Delta-like drainage characteristics.
• Multiple small channels connected through Jamunia Nala.

Important Tributaries

The important tributaries of the Chandan River are:

• Orhni
• Kuldar
• Chatri

These tributaries contribute seasonal runoff and strengthen the drainage network of the basin.

Basin Characteristics

The Chandan Basin is characterized by:

• Plateau-fed origin.
• Independent drainage into the Ganga.
• Parallel flow of Bilasi River.
• Deltaic river characteristics near its lower reaches.
• Bifurcation into several distributary channels before joining the Ganga.

Flood Characteristics

The available data indicates that the basin has limited flood management infrastructure.Although flooding occurs in portions of the basin, the extent is comparatively lower than the major North Bihar river basins.

Salient Features

Major Characteristics

The Chandan Basin is characterized by:

• Independent river basin of south Bihar.
• Origin in the Deoghar Hills (Jharkhand).
• Source elevation of 274 metres above mean sea level.
• Approximately 110 km course before reaching the plains.
• Formation of distributary channels in lower reaches.
• Final outfall into the Ganga through Jamunia Nala.
• Common watershed comprising the Chandan, Chir, and Bilasi rivers.
• Parallel flow of the Bilasi River on the left bank.

Importance of the Basin

The Chandan Basin is important because it:

• Drains the south-eastern plateau region into the Ganga.
• Connects the Deoghar uplands with the Gangetic plains.
• Supports agriculture through seasonal runoff.
• Forms an important drainage system in the Munger–Bhagalpur region.
• Demonstrates a transition from plateau drainage to deltaic distributary channels.

Challenges

Major challenges include:

• Seasonal flooding in low-lying areas.
• Management of distributary channels.
• Maintenance of embankments.
• Flood regulation during intense monsoon rainfall.
• Integrated management of the Chandan–Chir–Bilasi watershed.

Reference

Government of Bihar, Water Resources Department.Bihar Embankment Asset Management System (BEAMS): Bihar Basins at a Glance. Flood Management Improvement Support Centre (FMISC). Available at: https://beams.fmiscwrdbihar.gov.in/glance/glancemaster.aspx (Accessed: 04 July 2026).