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| Class 9th Chapters | ||
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| 1. India – Size And Location | 2. Physical Features Of India | 3. Drainage |
| 4. Climate | 5. Natural Vegetation And Wildlife | 6. Population |
Chapter 3 Drainage
The term **drainage** refers to the **river system of an area**. Looking at a physical map, one can observe how smaller streams originating from different directions merge to form a larger river, which eventually empties into a larger water body like a lake, sea, or ocean. The entire area drained by a single river system is called a **drainage basin**.
Any elevated landform, such as a mountain or an upland, that separates two adjacent drainage basins is known as a **water divide** (Figure 3.1).
Figure 3.1 is a simple diagram illustrating a water divide, an elevated area (like a ridge) that separates two different river systems or drainage basins, directing water flow on either side into separate basins.
The Amazon river has the world's largest drainage basin. The **Ganga river** has the largest drainage basin in India.
Figure 3.2 shows a photo illustration of a Gorge, a narrow valley with steep, rocky walls carved by a river. Gorges are commonly formed by fast-flowing rivers, such as those originating in mountainous regions like the Himalayas.
Drainage Systems In India
The drainage systems of India are significantly influenced by the subcontinent's broad relief features, particularly the Himalayan mountains and the Peninsular plateau. Based on their origin and characteristics, Indian rivers are classified into two major groups:
- The **Himalayan rivers**
- The **Peninsular rivers**
These two groups differ in several ways:
- **Origin:** Himalayan rivers originate from the Himalayan mountains, while Peninsular rivers originate from the Peninsular plateau.
- **Perennial Nature:** Most Himalayan rivers are **perennial**, meaning they have water throughout the year. They are fed by both rainfall and melted snow from the high mountains. Peninsular rivers are largely **seasonal**, with their flow dependent on rainfall. Their water volume decreases significantly during the dry season.
- **Course Length and Features:** Himalayan rivers have **long courses** from source to sea. They perform intense erosion in their upper courses, forming **gorges**, and carry large amounts of silt and sand. In their middle and lower courses, they create features like **meanders**, **oxbow lakes**, and extensive **floodplains** with depositional features, finally forming well-developed **deltas** at their mouths. Peninsular rivers have **shorter and shallower courses** compared to Himalayan rivers. Most originate in the Western Ghats and flow east towards the Bay of Bengal, while a few originate in the central highlands and flow west. Some west-flowing rivers make **estuaries** instead of deltas.
Figure 3.3 illustrates different landforms created by rivers at various stages of their course: Gorges in the upper course (erosion), Meanders and Ox-Bow Lakes in the middle course (erosion and deposition), and Deltas in the lower course (deposition as the river approaches the sea).
The Himalayan Rivers
The major rivers originating from the Himalayas are the **Indus, the Ganga, and the Brahmaputra**. These are long rivers with many large tributaries, forming extensive river systems.
The Indus River System
The Indus river originates in **Tibet**, near Lake Mansarowar. It flows westwards, entering India in **Ladakh**, where it carves a picturesque gorge. Several tributaries join it in the Kashmir region, including the Zaskar, Nubra, Shyok, and Hunza. The Indus continues through Baltistan and Gilgit, emerging from the mountains at Attock.
In Pakistan, the Satluj, Beas, Ravi, Chenab, and Jhelum rivers join together to meet the Indus near Mithankot. The Indus then flows southwards, eventually draining into the **Arabian Sea** east of Karachi. The Indus plain is characterised by a very gentle slope. With a total length of **2900 km**, the Indus is one of the longest rivers in the world.
Approximately one-third of the Indus basin is located in India (in parts of Ladakh, Jammu and Kashmir, Himachal Pradesh, and Punjab), with the majority of its basin lying in Pakistan.
According to the **Indus Water Treaty (1960)** between India and Pakistan, India can utilise only 20% of the total water of the Indus river system. This water is primarily used for irrigation purposes in the Indian states of Punjab, Haryana, and the southern and western parts of Rajasthan.
The Ganga River System
The headstream of the Ganga, known as the **‘Bhagirathi’**, originates from the Gangotri Glacier. It is joined by the Alaknanda river at **Devaprayag** in Uttarakhand to form the main Ganga river. At Haridwar, the Ganga emerges from the mountains and enters the plains.
Figure 3.5 shows the confluence of the Bhagirathi and Alaknanda rivers at Devaprayag. This is the point where these two headstreams merge to form the main stem of the Ganga river, a significant geographical and religious site.
The Ganga is joined by numerous tributaries from the Himalayas, including major rivers like the **Yamuna, Ghaghara, Gandak, and Kosi**. The Yamuna river rises from the Yamunotri Glacier, flows parallel to the Ganga, and is a right-bank tributary, joining the Ganga at Allahabad (now Prayagraj).
The Ghaghara, Gandak, and Kosi rivers originate in the Nepal Himalaya. These rivers are notorious for causing annual floods in parts of the northern plains, leading to significant damage but also enriching the soil for agriculture by depositing fertile silt.
Several important tributaries joining the Ganga from the peninsular uplands include the **Chambal, Betwa, and Son**. These rivers rise in semi-arid regions, have shorter courses, and carry less water compared to the Himalayan tributaries.
After receiving waters from its left and right bank tributaries, the Ganga flows eastwards until **Farakka** in West Bengal, which marks the northernmost point of the Ganga delta. Here, the river bifurcates: one distributary, the **Bhagirathi-Hooghly**, flows south through the deltaic plains into the Bay of Bengal. The mainstream of the Ganga flows southwards into Bangladesh, where it is joined by the Brahmaputra.
Further downstream in Bangladesh, the combined river is known as the **Meghna**. This mighty river, carrying the combined waters of the Ganga and Brahmaputra, flows into the Bay of Bengal, forming the world's largest and fastest-growing delta, the **Sundarban Delta**. The delta is named after the Sundari tree, well-adapted to its marshy environment, and is also famous as the home of the Royal Bengal Tiger.
The total length of the Ganga river is over **2500 km**. The Ganga river system exhibits a dendritic drainage pattern. Ambala town is situated on the water divide separating the Indus and Ganga river systems. The vast plain from Ambala to the Sunderban delta stretches over nearly 1800 km, but the total drop in elevation is only about 300 metres, resulting in a very gentle slope (one metre drop for every 6 km). This gentle slope causes the river to develop large meanders.
The Namami Gange Programme, launched in 2014, is an initiative by the Indian government to address pollution, conserve, and rejuvenate the Ganga river.
The Brahmaputra River System
The Brahmaputra river originates in **Tibet**, located east of the Mansarowar lake, very close to the sources of the Indus and Satluj rivers. It is slightly longer than the Indus, and most of its course lies outside India, flowing eastwards parallel to the Himalayas.
Upon reaching **Namcha Barwa** (a peak of 7757 m), the Brahmaputra takes a sharp **'U' turn** and enters India in **Arunachal Pradesh** through a gorge. Here, it is known as the **Dihang**. In Assam, it is joined by several tributaries like the Dibang and the Lohit, forming the main Brahmaputra river.
In Tibet, where it is known as the Tsang Po, the Brahmaputra is less voluminous and carries less silt because Tibet is a cold and dry region. However, in India, it flows through a region of high rainfall, causing it to carry a large volume of water and considerable amounts of silt. The Brahmaputra is characterised by a **braided channel** throughout its length in Assam, forming many riverine islands, including Majuli, the world's largest inhabited riverine island.
During the rainy season each year, the Brahmaputra overflows its banks, causing widespread floods and devastation in Assam and Bangladesh (where it is known as the Jamuna). Unlike other North Indian rivers, the Brahmaputra is known for depositing large amounts of silt on its bed, which causes the riverbed to rise and the river channel to shift frequently.
The Peninsular Rivers
The primary **water divide** in Peninsular India is formed by the **Western Ghats**, which run along the western coast from north to south. Most of the major rivers of the Peninsula, including the **Mahanadi, Godavari, Krishna, and Kaveri**, flow **eastwards** from the Western Ghats and drain into the **Bay of Bengal**. These east-flowing rivers form **deltas** at their mouths.
In contrast, there are numerous smaller streams that flow **west** of the Western Ghats into the Arabian Sea. However, only the **Narmada and the Tapi** are long rivers that flow west and make **estuaries** (where river meets the sea, unlike a delta). The drainage basins of the Peninsular rivers are generally smaller in size compared to those of the Himalayan rivers.
The Narmada Basin
The Narmada river originates in the **Amarkantak hills** in Madhya Pradesh. It flows westwards through a **rift valley** formed by faulting (cracking and sinking of the Earth's crust). Along its course to the sea, the Narmada creates several picturesque locations, such as the 'Marble rocks' near Jabalpur, where it flows through a deep gorge, and the 'Dhuadhar falls', where the river plunges over steep rocks.
All tributaries of the Narmada are relatively short and mostly join the main river at right angles. The Narmada basin covers parts of Madhya Pradesh and Gujarat. The government of Madhya Pradesh has initiated the Namami Devi Narmade mission for the conservation of the Narmada river.
Two large rivers that originate in the central highlands and flow towards the west are the Narmada and the Tapi.
The Tapi Basin
The Tapi river rises in the **Satpura ranges**, in the Betul district of Madhya Pradesh. Like the Narmada, it also flows in a **rift valley** parallel to the Narmada, but it is considerably shorter in length. The Tapi basin covers parts of Madhya Pradesh, Gujarat, and Maharashtra.
The coastal plains between the Western Ghats and the Arabian Sea are very narrow, resulting in short coastal rivers. Other main west-flowing rivers, besides Narmada and Tapi, include the Sabarmati, Mahi, Bharathpuzha, and Periyar.
The Godavari Basin
The Godavari is the **largest Peninsular river**. It originates from the slopes of the **Western Ghats** in the Nasik district of Maharashtra. Its total length is approximately **1500 km**, and it drains into the **Bay of Bengal**. The Godavari basin is also the **largest drainage basin** among the Peninsular rivers, covering parts of Maharashtra (about 50% of the basin area), Madhya Pradesh, Odisha, and Andhra Pradesh.
The Godavari is joined by a number of tributaries, including the Purna, Wardha, Pranhita, Manjra, Wainganga, and Penganga (the last three being quite large). Due to its large size and extensive basin, the Godavari is also known as the **Dakshin Ganga** (Southern Ganga).
The Mahanadi Basin
The Mahanadi river rises in the **highlands of Chhattisgarh**. It flows through Odisha to reach the **Bay of Bengal**. The river has a length of about **860 km**. Its drainage basin is shared by Maharashtra, Chhattisgarh, Jharkhand, and Odisha.
The Krishna Basin
Rising from a spring near Mahabaleshwar, the Krishna river flows for approximately **1400 km** before reaching the **Bay of Bengal**. Its major tributaries include the Tungabhadra, Koyana, Ghatprabha, Musi, and Bhima. The Krishna basin is shared by Maharashtra, Karnataka, and Andhra Pradesh.
The Kaveri Basin
The Kaveri river originates in the **Brahmagiri range of the Western Ghats** and flows southeast to reach the **Bay of Bengal** south of Cuddalore in Tamil Nadu. The river's total length is about **760 km**. Its main tributaries are Amravati, Bhavani, Hemavati, and Kabini. The Kaveri basin drains parts of Karnataka, Kerala, and Tamil Nadu.
The Kaveri river is known for the **Shivasamudram Falls**, which is the second biggest waterfall in India. Hydroelectric power generated from these falls is supplied to areas like Mysuru, Bengaluru, and the Kolar Gold Field.
Besides these major Peninsular rivers, several notable smaller rivers flow eastward into the Bay of Bengal, including the Damoder, Brahmani, Baitarni, and Subarnarekha.
Globally, 71% of the Earth's surface is covered by water, but 97% of this is saltwater. Only 3% is freshwater, and three-quarters of that freshwater is trapped as ice.
Lakes
India has numerous lakes, which vary in size and characteristics. Lakes are not only attractive tourist spots, but also serve various purposes for human beings.
Many lakes are permanent, while some are seasonal, containing water only during the rainy season (e.g., lakes in inland drainage basins of semi-arid regions). Lakes can be formed by glacial action, wind, river action, or human activities (like damming rivers).
Natural lakes in India include:
- **Ox-bow lakes:** Formed when a meandering river across a floodplain cuts off a bend.
- **Lagoons:** Formed in coastal areas by spits and bars, such as the Chilika lake, Pulicat lake, and Kolleru lake.
- **Saltwater lakes:** Found in regions of inland drainage, sometimes seasonal, like the Sambhar lake in Rajasthan, used for salt production. Lakes of very large extent are also called seas (e.g., Caspian, Dead, Aral Seas).
- **Freshwater lakes:** Most are in the Himalayan region and are of glacial origin (formed when glaciers dug out basins filled with snowmelt). The Wular lake in Jammu and Kashmir, the largest freshwater lake in India, is an exception, formed by tectonic activity. Other important freshwater lakes include Dal lake, Bhimtal, Nainital, Loktak, and Barapani.
Figure 3.6 shows a photo of Loktak Lake, a large freshwater lake in Manipur, famous for its floating phumdis (heterogeneous mass of vegetation, soil, and organic matter). As a natural freshwater lake, it serves ecological functions and can be important for local livelihoods and tourism.
Apart from natural formations, lakes are also created by human activities, such as the damming of rivers for hydroelectric power generation. **Guru Gobind Sagar** (associated with the Bhakra Nangal Project) is an example of such an artificial lake.
Lakes are valuable for several reasons:
- They help **regulate the flow of rivers**, preventing floods during heavy rains and maintaining an even flow during dry seasons.
- They can be used for **generating hydel power**.
- They help moderate the local climate.
- They maintain aquatic ecosystems.
- They enhance natural beauty, promote tourism, and provide recreational opportunities.
Role Of Rivers In The Economy
Rivers have played a fundamental role throughout human history and continue to be crucial for the economy. Water from rivers is a basic natural resource essential for various human activities. Consequently, riverbanks have been attractive sites for human settlements since ancient times, with many settlements evolving into large cities today.
Rivers are particularly significant for India's economy, where agriculture is the primary source of livelihood for the majority of the population. Rivers provide water for **irrigation**, which is vital for agricultural productivity. They are also used for **navigation** (transportation) and **hydro-power generation**.
Using rivers for irrigation, navigation, and power generation is especially important in a country like India, where a large population depends on agriculture for subsistence.
River Pollution
The increasing demand for water from rivers for domestic, municipal, industrial, and agricultural use significantly impacts the quality of river water. More water is drawn out, reducing the rivers' volume. Simultaneously, a heavy load of untreated sewage and industrial effluents is discharged into rivers.
This discharge of pollutants not only degrades the water quality but also overwhelms the river's natural **self-cleansing capacity**. While a river like the Ganga might be able to dilute pollution loads within a certain distance of large cities under adequate flow conditions, increasing urbanisation and industrialisation prevent this, causing pollution levels to rise in many rivers.
Concern over rising river pollution has led to the launch of various **action plans** to clean rivers.
National River Conservation Plan (NRCP)
The river cleaning initiative in India began with the launch of the **Ganga Action Plan (GAP) in 1985**. This plan was later expanded to include other rivers under the **National River Conservation Plan (NRCP) in 1995**. The main objective of the NRCP is to improve the water quality of the major rivers across the country by implementing projects aimed at reducing pollution. This primarily involves undertaking pollution abatement work, such as setting up sewage treatment plants and controlling industrial discharges.
The NRCP website provides more details on the plan's objectives and implementation strategies.