Class 9 Geography Notes: Drainage
Class 9 Geography Notes: Drainage
Welcome back to our Class 9 Geography study series! Today we are exploring Chapter 3: Drainage.
When you hear the word "drainage," you might think of the pipes in your house. But in geography, the term drainage describes the river system of an area. In this chapter, we will look at how water flows across the beautiful landscapes of India, the major rivers, and why they are the lifelines of our country.
Let’s dive right into the flow!
1. Important Terms You Need to Know
Before we jump into the rivers, let's clear up some basic geographic vocabulary that frequently appears in exams:
Drainage Basin: The area drained by a single river system. (Fun fact: The Amazon River has the world's largest drainage basin!).
Water Divide: Any elevated area, such as a mountain or an upland, that separates two drainage basins. A classic example is the Ambala water divide between the Indus and Ganga river systems.
2. Drainage Systems in India: The Big Two
The drainage systems of India are mainly controlled by the broad relief features of the subcontinent. Accordingly, the Indian rivers are divided into two major groups:
The Himalayan Rivers
The Peninsular Rivers
The Himalayan Rivers
These rivers originate from the snow-covered Himalayan mountains.
Perennial Flow: They have water throughout the year because they receive water from rain as well as from melted snow from the lofty mountains.
Features: They have long courses from their source to the sea. They perform intensive erosional activity in their upper courses and form spectacular gorges, V-shaped valleys, meanders, oxbow lakes, and well-developed deltas.
The Peninsular Rivers
These rivers originate from the Peninsular Plateau and central highlands.
Seasonal Flow: A large number of the Peninsular rivers are seasonal, as their flow is dependent on rainfall. During the dry season, even the large rivers have reduced water flow in their channels.
Features: They have shorter and shallower courses compared to their Himalayan counterparts. Most of them flow eastwards and drain into the Bay of Bengal, forming deltas at their mouths.
3. The Himalayan River Systems
There are three main Himalayan river systems you need to memorize:
A. The Indus River System
Origin: Rises in Tibet, near Lake Mansarovar.
Flow: Enters India in the Ladakh district of Jammu and Kashmir. It flows through Baltistan and Gilgit and emerges from the mountains at Attock.
Tributaries: The Zaskar, the Nubra, the Shyok, and the Hunza join it in the Kashmir region. The Satluj, the Beas, the Ravi, the Chenab, and the Jhelum join together to enter the Indus near Mithankot in Pakistan.
End: Drains into the Arabian Sea, east of Karachi.
(Exam Note: According to the regulations of the Indus Water Treaty (1960), India can use only 20% of the total water carried by the Indus river system.)
B. The Ganga River System
Origin: The headwaters of the Ganga, called the Bhagirathi, is fed by the Gangotri Glacier and joined by the Alaknanda at Devaprayag in Uttarakhand.
Emergence: At Haridwar, the Ganga emerges from the mountains onto the plains.
Tributaries: Major tributaries from the Himalayas include the Yamuna (arises from Yamunotri glacier), the Ghaghara, the Gandak, and the Kosi. Tributaries from the peninsular uplands include the Chambal, the Betwa, and the Son.
End: It flows eastwards till Farakka in West Bengal. Here, the river bifurcates. The mainstream flows southwards into Bangladesh and is joined by the Brahmaputra (forming the Meghna river) before flowing into the Bay of Bengal.
The Delta: The mighty river forms the Sunderban Delta, which is the largest and fastest-growing delta in the world, and the home of the Royal Bengal Tiger.
C. The Brahmaputra River System
Origin: Rises in Tibet east of Mansarovar lake, very close to the sources of the Indus and the Satluj. In Tibet, it is known as the Tsangpo.
Flow: It flows eastwards parallel to the Himalayas. On reaching the Namcha Barwa peak, it takes a 'U' turn and enters India in Arunachal Pradesh through a gorge. Here, it is called the Dihang.
Features: In India, it carries a large volume of water and a considerable amount of silt. It forms many riverine islands. (Did you know? Majuli, in the Brahmaputra, is the largest inhabited riverine island in the world!)
4. The Peninsular River Systems
The main water divide in Peninsular India is formed by the Western Ghats. We can divide these rivers based on where they flow:
West-Flowing Rivers (Flow into the Arabian Sea)
These rivers form estuaries instead of deltas.
The Narmada Basin: Rises in the Amarkantak hills in Madhya Pradesh. It flows towards the west in a rift valley formed due to faulting. It creates beautiful locations like the 'Marble Rocks' near Jabalpur and the 'Dhuadhar falls'.
The Tapi Basin: Rises in the Satpura ranges, in the Betul district of Madhya Pradesh. It also flows in a rift valley parallel to the Narmada but is much shorter in length.
East-Flowing Rivers (Flow into the Bay of Bengal)
These rivers make well-developed deltas at their mouths.
The Godavari Basin: This is the largest Peninsular river. It rises from the slopes of the Western Ghats in the Nasik district of Maharashtra. Because of its length and the area it covers, it is also known as the Dakshin Ganga.
The Mahanadi Basin: Rises in the highlands of Chhattisgarh. It flows through Odisha to reach the Bay of Bengal.
The Krishna Basin: Rises from a spring near Mahabaleshwar. Its major tributaries are the Tungabhadra, the Koyana, the Ghatprabha, the Musi, and the Bhima.
The Kaveri Basin: Rises in the Brahmagiri range of the Western Ghats and reaches the Bay of Bengal in south of Cuddalore in Tamil Nadu.
5. Lakes in India
Lakes are of great value to human beings. India has many lakes, which differ from each other in size and other characteristics.
Freshwater Lakes: Most are in the Himalayan region and are of glacial origin. The Wular lake in Jammu and Kashmir is the result of tectonic activity and is the largest freshwater lake in India. Other important freshwater lakes are Dal lake, Bhimtal, Nainital, Loktak, and Barapani.
Saltwater Lakes: The Sambhar lake in Rajasthan is a salt water lake, and its water is used for producing salt. The Chilika Lake (Odisha) is the largest saltwater lake in India.
Artificial Lakes: Damming of rivers for the generation of hydel power has also led to the formation of lakes, such as Guru Gobind Sagar (Bhakra Nangal Project).
6. Role of Rivers in the Economy & River Pollution
Why are rivers important?
Rivers have been of fundamental importance throughout human history. Water from rivers is a basic natural resource, essential for various human activities. They provide water for irrigation, navigation, hydro-power generation, and basic domestic needs.
The Problem: River Pollution
The growing domestic, municipal, industrial, and agricultural demand for water from rivers naturally affects the quality of water.
More and more water is being drained out of the rivers reducing their volume.
A heavy load of untreated sewage and industrial effluents are emptied into the rivers.
This affects not only the quality of water but also the self-cleansing capacity of the river. To combat this, the government has launched various action plans like the National River Conservation Plan (NRCP) to clean the rivers.
Quick Revision Summary 📝
Himalayan Rivers (Indus, Ganga, Brahmaputra) are perennial and form large deltas.
Peninsular Rivers (Narmada, Tapi, Godavari, Krishna, Kaveri, Mahanadi) are seasonal.
Godavari is known as the Dakshin Ganga.
Narmada and Tapi flow west into the Arabian Sea and form estuaries.
Rivers and lakes are vital for the economy, but
industrial and domestic pollution is a major threat that needs immediate conservation efforts.
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