Drainage Class 9 Social Science NCERT

QWhat does the term ‘drainage’ mean in geography?

In geography, ‘drainage’ describes the river system of an area. It includes the main river as well as the smaller streams that flow from different directions and join together. These combined waters ultimately drain into a larger water body such as a lake, sea, or ocean. Studying drainage helps students understand how water moves across land, how rivers connect, and how landforms influence the direction and pattern of river flow within a region.

QWhat is a drainage basin?

A drainage basin is the area drained by a single river system. This means all the land from which water flows into one main river and its tributaries belongs to the same basin. Rainwater or melted snow from within this area eventually reaches the main river and then drains into a larger water body. Drainage basins are separated from one another by higher or elevated areas such as mountains or uplands.

QWhat is a water divide and how does it separate drainage basins?

A water divide is an elevated area, such as a mountain or an upland, that separates two drainage basins. When you observe a physical map closely, you can see that rivers on opposite sides of a high ridge flow in different directions, entering different river systems. Because the highland determines which way water runs off the surface, it acts as a dividing line between basins. This explains why relief strongly controls drainage patterns.

QWhat controls the drainage systems of India?

The drainage systems of India are mainly controlled by the broad relief features of the subcontinent. Because India has distinct physiographic regions—especially the Himalayan region and the Peninsular plateau—rivers develop different characteristics depending on where they originate and the slope and structure of the land. This relief-based control is why Indian rivers are broadly grouped into Himalayan rivers and Peninsular rivers, each showing different flow and landform features.

QWhat are the two major groups of rivers in India?

Indian rivers are divided into two major groups: Himalayan rivers and Peninsular rivers. This division is based on the broad relief features and the two major physiographic regions of India from which these rivers originate. Himalayan rivers are generally long and mostly perennial, while many Peninsular rivers are seasonal and depend largely on rainfall. Their courses, erosional work, and depositional features also differ due to differences in terrain and water supply.

QWhy are most Himalayan rivers called perennial rivers?

Most Himalayan rivers are perennial because they have water throughout the year. They receive water not only from rainfall but also from melted snow from the lofty Himalayan mountains. This continuous supply helps maintain flow even in seasons when rainfall is low. As a result, Himalayan rivers often have larger volumes of water and can perform strong erosional activity in their upper courses while transporting large amounts of silt and sand downstream.

QHow do Himalayan rivers shape landforms like gorges and deltas?

Himalayan rivers cut through mountains, creating deep gorges, especially where they pass across high relief. In their upper courses, they carry out intensive erosion. As they reach the middle and lower courses, the slope decreases and deposition becomes more prominent. Here, these rivers form meanders, oxbow lakes, and other depositional features across wide floodplains. Near their mouths, many Himalayan rivers build well-developed deltas due to heavy sediment deposition.

QWhat are meanders and oxbow lakes in the context of Himalayan rivers?

Meanders are large bends that develop in a river’s course, commonly in the middle and lower parts where the slope is gentle. Himalayan rivers often develop meanders as they enter the plains and their flow spreads across wide floodplains. Over time, parts of a meander may get cut off from the main channel, forming an oxbow lake. These features are typical depositional landforms associated with mature river courses in plains.

QWhy are many Peninsular rivers seasonal?

Many Peninsular rivers are seasonal because their flow depends mainly on rainfall. During the dry season, even large rivers in the Peninsular region show reduced water flow in their channels. Unlike Himalayan rivers, they are generally not fed by snowmelt from lofty mountains. Their shorter and shallower courses also reflect the plateau nature of the region. This is why rainfall patterns strongly affect water availability in Peninsular river systems.

QHow are Peninsular rivers different from Himalayan rivers?

Peninsular rivers are generally shorter and shallower than Himalayan rivers, and many are seasonal because their flow depends on rainfall. In contrast, most Himalayan rivers are perennial, fed by both rain and melted snow. Himalayan rivers have long courses, carry heavy loads of silt and sand, and form features like meanders, oxbow lakes, and well-developed deltas. Peninsular rivers often originate in the Western Ghats and commonly drain eastwards into the Bay of Bengal.

QWhich are the major Himalayan river systems mentioned in the chapter?

The major Himalayan rivers highlighted are the Indus, the Ganga, and the Brahmaputra. These rivers are long and are joined by many large and important tributaries. A river along with its tributaries forms a river system. Each of these systems has distinct origins and courses, and together they play a major role in shaping landforms like gorges, floodplains, and deltas, as well as influencing floods and soil fertility in plains.

QWhere does the Indus River originate and what is its course in India?

The Indus River rises in Tibet near Lake Mansarowar. Flowing west, it enters India in Ladakh, where it forms a picturesque gorge. In the Kashmir region, tributaries such as the Zaskar, Nubra, Shyok, and Hunza join it. The Indus then flows through Baltistan and Gilgit and emerges from the mountains at Attock. After this, it continues southwards and ultimately reaches the Arabian Sea east of Karachi.

QName important tributaries of the Indus and where they join.

In the Kashmir region, important tributaries like the Zaskar, the Nubra, the Shyok, and the Hunza join the Indus. Further downstream, the Satluj, Beas, Ravi, Chenab, and Jhelum come together and enter the Indus near Mithankot in Pakistan. These tributaries are significant because they increase the river’s volume and expand the basin. Understanding tributaries helps students read river-system maps and identify key confluence regions.

QWhat is the length of the Indus and how much of its basin lies in India?

The Indus is about 2900 km long, making it one of the longest rivers in the world. A little over a third of the Indus basin is located in India, covering areas such as Ladakh, Jammu and Kashmir, Himachal Pradesh, and Punjab. The rest of the basin lies in Pakistan. The Indus plain has a very gentle slope, which influences the river’s flow and the development of plains along its course.

QWhat is the Indus Water Treaty (1960) and how does it affect India’s use of Indus waters?

According to the Indus Water Treaty (1960), India can use only 20 percent of the total water carried by the Indus river system. This regulation affects how the river’s water is managed and shared. The water that India is allowed to use is mainly used for irrigation in Punjab, Haryana, and the southern and western parts of Rajasthan. The treaty is an important example of how river waters can be governed by international agreements.

QWhat are the headwaters of the Ganga and how is the Ganga formed?

The headwaters of the Ganga are called the Bhagirathi. They are fed by the Gangotri Glacier and are joined by the Alaknanda at Devaprayag in Uttarakhand. After this confluence, the river is known as the Ganga. At Haridwar, the Ganga emerges from the mountains onto the plains. This transition from mountains to plains influences river speed, sediment deposition, and the formation of features like meanders in later stretches.

QWhich major tributaries join the Ganga from the Himalayas?

Major tributaries that join the Ganga from the Himalayas include the Yamuna, the Ghaghara, the Gandak, and the Kosi. The Yamuna rises from the Yamunotri Glacier and flows parallel to the Ganga before meeting it as a right bank tributary at Allahabad. The Ghaghara, Gandak, and Kosi rise in the Nepal Himalaya and contribute significantly to the Ganga system, including influencing floods in the northern plains.

QWhy do the Ghaghara, Gandak, and Kosi cause floods and also help agriculture?

The Ghaghara, Gandak, and Kosi rise in the Nepal Himalaya and flood parts of the northern plains every year, causing widespread damage to life and property. At the same time, these floods also enrich the soil for agricultural use because rivers deposit fine sediments over the floodplains. This shows a dual impact of rivers: they can be destructive during high flow but beneficial by improving soil fertility through deposition, supporting farming in river plains.

QWhich tributaries of the Ganga come from the peninsular uplands?

The main tributaries of the Ganga that come from the peninsular uplands are the Chambal, the Betwa, and the Son. These rivers rise from semi-arid areas, have shorter courses, and do not carry much water compared to the Himalayan tributaries. Their origin in drier regions affects their discharge and sediment load. Knowing these tributaries helps differentiate between Himalayan-fed and Peninsular-upland-fed contributions to the Ganga river system.

QWhat is the Namami Gange Programme and what are its objectives?

The Namami Gange Programme is an Integrated Conservation Mission approved as a ‘flagship programme’ by the Union Government in June 2014. Its twin objectives are effective abatement of pollution and the conservation and rejuvenation of the national river, Ganga. This connects river geography with environmental management. The programme highlights that rivers face pollution challenges and need planned efforts to improve water quality and restore river health for ecosystems and human use.

QWhat happens to the Ganga at Farakka and how does the Sundarban Delta form?

Farakka in West Bengal is the northernmost point of the Ganga delta. Here, the river bifurcates: the Bhagirathi-Hooghly distributary flows southwards through the deltaic plains to the Bay of Bengal, while the mainstream flows into Bangladesh. In Bangladesh, it is joined by the Brahmaputra and further downstream is known as the Meghna. The combined waters form a vast delta that flows into the Bay of Bengal, called the Sundarban Delta.

QWhy does the Ganga develop large meanders in the plains?

The Ganga develops large meanders in the plains because the slope is extremely gentle over a long distance. The plains from Ambala to the Sundarban stretch nearly 1800 km, but the fall in slope is only about 300 metres. With such a small gradient, the river flows more slowly and begins to swing from side to side, creating broad bends. This is a key example of how slope controls river behavior and landform development.

QWhere does the Brahmaputra originate and how does it enter India?

The Brahmaputra rises in Tibet, east of Mansarowar lake, close to the sources of the Indus and the Satluj. It flows eastwards parallel to the Himalayas. On reaching Namcha Barwa (7757 m), it takes a ‘U’ turn and enters India in Arunachal Pradesh through a gorge. In Arunachal Pradesh it is called the Dihang, and later becomes the Brahmaputra in Assam after meeting key tributaries.

QWhy does the Brahmaputra form braided channels and cause frequent floods in Assam?

In Tibet, the Brahmaputra carries less water and less silt because the region is cold and dry. In India, it passes through a high rainfall region, so it carries a larger volume of water and a considerable amount of silt. In Assam, it has a braided channel throughout its length and forms many riverine islands. During the rainy season it overflows its banks, causing widespread floods in Assam and Bangladesh. Heavy silt deposits raise the riverbed and lead to frequent channel shifting.

QWhat are the main characteristics of Peninsular rivers and which are major examples?

The main water divide in Peninsular India is formed by the Western Ghats. Most major Peninsular rivers—Mahanadi, Godavari, Krishna, and Kaveri—flow eastwards and drain into the Bay of Bengal, forming deltas at their mouths. The Narmada and Tapi are the only long rivers flowing west and they form estuaries. Peninsular rivers are often seasonal and rainfall-dependent, with shorter and shallower courses than Himalayan rivers, reflecting the plateau relief.

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