CBSE Notes | Class 9 | Social Science | Geography Chapter 3 - Drainage System of India
The chapter notes will assist you in comprehending drainage patterns and will provide an overview of Indian drainage systems. We shall study the important rivers of India, their paths, tributaries, and significance. Additionally, you will learn about lakes, their significance, the economic role of rivers, and river pollution towards the chapter's conclusion.
What is a Drainage System?
The term 'drainage' refers to natural or artificial removal of surface or sub-surface water from areas in excess of it. In geomorphological terms, the term 'drainage system' refers to a system of rivers that naturally drain the satured regions into a typically, low lying areas called 'drainage basins'.
What is a 'Water Divide'?
An elevated area such as a mountain or an upland that divides two drainage basins is called as a 'water divide'.
During the early course of a river small streams come together to form the main river which ultimately drains into a large water body such as a lake, sea or ocean.
What are the 3 courses of a river?
Upper Course : The rivers originate at a high elevation point on a mountain. It then flows rapidly through steep valleys and forms deep gorges and waterfalls. The erosional activity of river is high in this phase due to greater speed and momentum.
Middle Course : On reaching the foot of the hills, the rivers slow down due to less slope and start depositional activity. The volume of the water increases as the river is now joined by its tributaries thereby eroding the banks of the river thus making it wider. During the lower part of this course the river slows down further forming flood plains. Due to slow speed, the rivers forms meanders, ox-bow lakes, alluvial fans and riverine islands at this stage.
Lower Course : During the lower stages of its course, the rivers split into distributaries as the rate of silt deposition increases. At this point the river is said to be 'Braided'. This region is also referred to as the deltaic region and is characterised by marshy lands. Rivers meet the oceans during their last course forming deltas. Estuaries can also be found in regions where tidal action constantly washes the mouth of the river.
What are drainage patterns?
Drainage patterns are patterns of flow of a river. It depends on the slope of the land, the underlying rock structure and climatic conditions of the area. A drainage basin can have a combination of drainage patterns.
There are 4 types of drainage patterns:
Dendritic - This pattern forms when river flows along the slope of the terrain. The tributatries and the main river look like the branches of a tree, thus the name 'Dendritic'. This pattern is common for the Himalayan rivers.
Trellis - This pattern exists in regions having hard and soft rocks lying parallel to each other. The river is able to cut through the soft rocks easily and joins the other stream at right angles. These type of rivers are common in the plateau region of India.
Rectangular - Like trellis pattern, rectangular pattern also exist in rocky regions which are strongly jointed. This allows the river only the edges to flow along giving them an appearance of rectangles.
Radial - Radial patterns are common when river originates at the central peak or dome. The streams flow in all directions radially outwards resembling spokes of a wheel.
Drainage Systems in India
Role of Rivers in Economy
The banks or rivers have been areas of major settlements since ancient times. The Indus Valley Civilization along Indus, the Mespotamian Civilization along the Euphrates and Tigris and the Egyptian Civilisation are important examples.
In contemporary world, the world's major cities are located in proximity to major rivers such as Shanghai, Wuhan, Nanjing along the Yangtze river in China and Cologne,
The rivers play an critical role as they are used for irrigation, navigation, hydro-power generation, fisheries and other important economic activities. These are one of the lifelines of an economy.
Rivers have a special significance for a country like India, where agriculture is the major source of livelihood of the majority of its population.
The drainage system in India is broadly divided into 2 major groups:
The Himalayan Rivers
The Peninsular Rivers
These systems of rivers are controlled by the relief features of the Indian subcontinent.
What are the features of Himalayan Rivers?
As the name suggests, these rivers originate in the Himalayas and flow throughout the year making them perennial in nature.
These are fed by both rain water and the melting of snow.
They have high erosional activity in their upper courses as they flow from high mountains and carry lots of silt and sand.
In middle and lower courses, they flow on the northern plains and form depositional features such as ox-bow lakes and meanders.
They have well developed deltas
The 3 major rivers in the Himalayan system are Indus, Ganga and Brahmaputra.
What are the features of Peninsular Rivers?
Most of the rivers originate in Western Ghats and flow eastward towards the Bay of Bengal. Major rivers being Godavari, Krishna and Kaveri.
Some rivers such as Narmada and Tapi originate in the Central Highland and flow westwards through a rift valley into the Arabian sea.
Many of the rivers are fed by rainwater and are thus seasonal.
They have shorter and shallower courses as compared to Himalayan rivers.
The Himalayan Rivers
The 3 major river systems originating in the Himalayas are:
The Indus River System
The Ganga River System
The Brahmaputra River System
1. The Indus River System
Source: It river Indus originates in Tibet, near Mansarover lake.
Drains in: The Arabian Sea
Length : 2900 - 3200 Km (From Various Sources)
Drainage Basin : Ladakh, Jammu and Kashmir, Himachal Pradesh, Punjab and Pakistan
Major Tributaries
- Zanskar, Nubra, Shyok and Hunza - They join Indus in the Ladakh and Kashmir region.
- Jhelum, Satluj, Beas, Ravi, Chenab - These tributaries form the river 'Panjnad' before they join Indus in the Punjab plains of Pakistan near Mithankot.
Route: The river originates in the Tibetan plateau near Lake Mansarover and flows in north-west direction entering India through Ladakh. Here it is joined by the rivers Zanskar, Nubra and Shyok. It then enters Kashmir where the river Hunza joins it.
It then flows though the Gilgit-Baltistan region and takes a sharp bend north of Nanga Parpat in a deep gorge near Attock. The direction of flow now changes to south-west and it continues into Pakistan where it is joined by its 5 major tributaries - Jhelum, Satluj, Chenab, Ravi and Beas.
2. The Ganga River System
Source : The river Ganga forms when the rivers Alaknanda and Bhagirathi join at Devprayag.
As per hindu mythology, Bhagirathi is considered the source of the Ganga and is fed by the Gangotri glacier.
Alaknanda being longer and having greater discharge is the however the main source. Alaknanda is fed by the Satopnath glacier.
Drains in: The Bay of Bengal
Length : Over 2500 Km
Drainage Basin : The river Ganga flows through Uttrakhand, Uttar Pradesh, Bihar, Jharkh and West Bengal. Its basin which is drained by many of its tributaries extends to other states of the Indian plains as well.
Major Tributaries
Yamuna, Ghaghara, Gandak, Kosi- These rivers rise in the Himalayas and join Ganga in the Northern plains. These rivers flood the northern plains every year and cause widespread damage to life and property. These floods are however benefitial in increasing the fertility of the soil.
Yamuna originates from Yamunotri glacier and flows as a right bank tributary parallel to Ganga. It joins Ganga at Allahabad.
Ghaghara, Gandak and Kosi rise in the Nepal Himalayas.
Chambal, Betwa and Son - These tributaries have limited water as they rise from semi arid regions of the peninsular uplands. They flow in the north east direction towards the northern plains and join Ganga as its left bank tributarties.
Route: River Ganga forms after the confluence of rivers Bhagirathi and Alaknanda at Devprayag. It enters the plains at Haridwar and is joined by its right and left bank tributaries as it flows through the northern plains. The river develops large meanders in the plains as the river traverses a distance of 1800 Km with only 300 meters in falling slope.
It then flows eastward till Farakka in West Bengal, where it bifurfactes into Bhagirathi-Hooghly rivers which flow southward into West Bengal.
The main stream which is now called Padma enters Bangladesh where it joins the river Brahmaputra to form Meghna. This mighty river then drains into the Bay of Bengal forming the famous Sunderban Delta.
3. The Brahmaputra River System
Source : The river Brahamputra rises from Tibet close to source of Indus and Satjul near Mansarover Lake.
Drains in: The Bay of Bengal
Length : Over 3200 Km, but most of its course lies outside of India
Drainage Basin : The river and its tributaries flow through Arunachal Pradesh, Assam and Bangladesh.
Major Tributaries
Dibang and Lohit - The Brahmaputra is called Tsangpo in Tibet and is known as Dihang upon entering Arunachal Pradesh. It then joins Dibang and Lohit in Assam to form Brahamaputra
Route: From its source in Tibet, It flows eastward parallel to the north of Himalayas. It has low volume in Tibet as its a cold and dry desert.
It then takes a 'U-turn' on reaching the peak Namcha Barwa and enters India from Arunachal Pradesh. Here its volume increases as it flows through rainshed regions and carries along with the huge amount of silt.
The deposition of silt in the Assam plains makes it flow in braided channels which result in formation of many riverine islands. The largest inhabited riverine island of Majuli has been formed due to silt deposition by Brahmaputra.
From here the river enters Bangladesh and finally drains into Bay of Bengal after joining the main stream of Ganga.
Why does Brahmaputra cause devastation due to floods?
The river Brahamaputra carries with it large amounts of silt which get deposited on its bed causing it to rise. Thus, during the rainy season the river overflows its banks and causes widespread devastation due to floods. It also changes its channel several times due to the higher river bed.
The Peninsular Rivers
The main source of rivers in the Indian peninsular plateau is the Western Ghats. They run parallel to the west coast of India and act as barriers for the southwest monsoons. As a result they act as a water divide with rivers flowing in both western and eastern directions from it.
Why do most long rivers in peninsular pleteau flow eastward?
The Vindhya, Satpura ranges and Western Ghats on the northwestern and western edges are higher in elevation. The southern part of the plateau called the Deccan has an eastward tilt and therefore most rivers that originate in the Western Ghats flow eastwards towards the Bay of Bengal forming deltas at their mouths.
Major rivers flowing eastward are : Mahanadi, Godavari, Krishna and Kaveri
Smaller Rivers flowing eastward : Damoder, Brahmani, Baitarni and Subarnrekha
Which rivers flow westward in the peninsular plateau?
Many rivers that originate on the western side of the Western Ghats drain into the Arabian sea. They have smaller courses as the western coastal plains are a narrow strip and closer to the source of the rivers. Due to tidal action on the western coast, these rivers form estuaries rather than deltas.
Some important rivers are:
Zuari and Mandovi (Goa)
Mahi (Madhya Pradesh, Rajasthan and Gujarat)
Sabarmati (Rajasthan and Gujarat)
Bharathpuzha and Periyar (Kerela and Tamil Nadu)
Other than these, two long rivers Narmada and Tapi also flow westward. They originate in the Central Highlands region of the peninsular plateau and flow through through rift valleys that have been formed due to faulting.
What are some of the major river basins of Peninsular Plateau?
Narmada Basin
Tapi Basin
Mahanadi Basin
Godavari Basin
Krishna Basin
Kaveri Basin
1. Narmada Basin
Source : It rises in Amarkantak hills in Madhya Pradesh
Drains in : The Arabian Sea
Length : 1300 Km
Drainage Basin : Madhya Pradesh and Gujarat
Route : It flows westward though a rift valley between the Vindhya and Satpura ranges. It flows through gorges in a region of 'Marble Rocks' near Jabalpur and the 'Dhuadhar' falls where it falls over steep rocks creating beautiful views.
The tributaries joining Narmada are very short and join it at right angles in a trellis pattern as the underlying rocks are a combination of hard and soft.
2. Tapi Basin
Source : It rises in Satpura ranges near Betul in Madhya Pradesh
Drains in : The Arabian Sea
Length : 700 Km
Drainage Basin : Madhya Pradesh, Gujarat and Maharashtra
Route : It also flows westward though a rift valley south of Narmada.
3. Mahanadi Basin
Source : It rises in highlands of Odisha
Drains in : Bay of Bengal
Length : 860 Km
Drainage Basin : Maharashtra, Chhattisgarh, Jharkhand,
and Odisha.
4. Godavari Basin
Source : It rises on slopes of Western Ghats near Nasik, Maharashtra
Drains in : Bay of Bengal
Length : 1500 Km ( Longest Peninsular River)
Drainage Basin : Maharashtra, Madhya Pradesh, Odisha and Andhra Pradesh
Major Tributaries : Purna, Wardha,Pranhita,Manjra, Wainganga and
the Penganga. It is also called as 'Dakshin Ganga' because of its length and the large area it drains.
5. Krishna Basin
Source : It rises near Mahabaleshwar, Maharashtra
Drains in : Bay of Bengal
Length : 1400 Km
Drainage Basin : Maharashtra, Karnataka and Andhra Pradesh
Major Tributaries : Tungabhadra, Koyana, Ghataprabha, Musi and Bhima
6. Kaveri Basin
Source : It rises at Talakaveri in the Brahmagiri range in Karnataka
Drains in : Bay of Bengal, south of Cuddalore in Tamil Nadu
Length : 760 Km
Drainage Basin : Karnataka, Kerela and Tamil Nadu
Major Tributaries : Amravati, Bhavani, Hemavati and Kabini
Role of Rivers in Economy
Lakes
How are lakes formed?
Lakes can be formed as a result of the action of glaciers and ice sheets, action of wind, river action, and human activities.
Examples of different forms of lakes in India
Meandering rivers form cut-offs and form ox-bow lakes - Kanwar Lake near Begusari in Bihar
Spits and bars form lagoons in coastal areas - Chilika Lake, Pulicat Lake and Kolleru Lake
Glaciers dug out basins which get filled with water from melting snow - Mansarover Lake, Pangong Lake
Tectonic Activity - Wular Lake
Artificial Lakes by creating dams and despressions - Guru Gobind Sagar ( Bhakra Nangal Project), Rana Pratap Lake, Hirakud Lake
India has many lakes which differ from each other in the size, and other characteristics.
Most lakes are permanent; while some contain water only during the rainy season, like the lakes in the basins of inland drainage of semi-arid regions.
Lakes can also be categorised into salt water or fresh water lakes:
Salt Water Lakes in India
Salt water lakes could be formed either due to formation fo lagoons as the brackish water is cut off from the sea by spits and bars. Such lakes can also be found inland in semi-arid regions where high rates of evaporation make the lakes saltier.
Examples : Sambhar Lake, Chilika Lake, Pangong Lake, Kolleru Lake, Pulicat Lake, Lonar Kale, Pachpadra Lake
Fresh Water Lakes in India
Most fresh water lakes in India are in the Himalayan region. They are mostly formed due to glacial origin with few exceptions such as the Wular lake which formed due to tectonic activity.
Examples: Dal lake, Bhimtal, Nainital, Loktak and Barapani
Importance of Lakes
Lakes are of great value to human beings and also help in maintaining ecological balance.
Regulate the flow of a river : During heavy rainfall, it prevents flooding and during the dry season, it helps to maintain an even flow of water.
Developing Hydel Power : Lakes at higher elevation can act as reservoirs for hydel power projects.
Influence on Climate : They have a moderating effect on the climate of their surroundings
Ecological Balance : They help in maintaining the aquatic ecosystem, enhance natural beauty and act as biodiversity hotspots.
Tourism : They help in promotion and development of tourism and provide recreational activities.
River Pollution
The growing consumption of water has reduced the volume of water in rivers and also affected its quality. Increase in urbanization and industrialisation has further stresses the supply of water.
In addition, the discharge of sweage and industrial affluents is also adversely affecting the self-cleansing capacity of the rivers.
The Government of India has launched several programs and schemes in order to clean the rivers such as National River Conservation Plan.