Class 9 Geography
Drainage: The river system of an area is called drainage. The area drained by a single river system is called the drainage basin.
Depending on the slope of land, underlying rock structure and climate of an area, the streams in a drainage basin form certain patters. Different types of drainage pattern are as follows:
- a. Dendritic Drainage Pattern: When the river channel follows the slope of the terrain, it develops dendritic pattern. The stream and its tributaries resemble the branches of a tree. Hence, it is called dendritic pattern.
- b. Trellis Drainage Pattern: When a river is joined by its tributaries at almost right angles, it develops a trellis pattern. Trellis pattern develops where hard and soft rocks exist parallel to each other.
- c. Rectangular Drainage Pattern: When rocks are strongly joined, then rectangular pattern develops.
- d. Radial Drainage Pattern: When the streams flow in different directions from a central peak or dome like structure, a radial pattern is developed.
It is important to note that a combination of different patterns may develop in the same drainage basin.
The drainage systems in India can be divided into two major groups, viz. the Himalayan Rivers and the Peninsular Rivers.
The Brahmaputra River System:
- The Brahmaputra rises in Tibet; east of Mansarowar lake. It is a little longer than the Indus. Most of the course of the Brahmaputra lies outside India. It flows eastwards parallel to the Himalayas.
- After reaching Namcha Barwa, it enters India in Arunachal Pradesh through a gorge. It is known as Dihang in this region. It is joined by Dibang, Lohit, Kenula and many other tribuatries and finally forms the Brahmaputra in Assam.
- Unlike other north Indian rivers the Brahmaputra gets huge deposits of silt on its bed. This results in rising of the river bed. It also shifts its channel frequently.
The Peninsular Rivers
Most of the Peninsular Rivers are seasonal because they depend on rainfall for water. These rivers have shorter and shallower courses; compared to the Himalayan rivers. Most of the major rivers of the Peninsula flow eastwards and drain into the Bay of Bengal. These rivers make deltas at their mouths. The Narmada and Tapi are the only long rivers, which flow westwards and make estuaries. The drainage basins of the peninsular rivers are smaller in size.
The Narmada Basin: The Narmada rises in the Amarkantak hills in the Madhya Pradesh. The Narmada basin covers parts of Madhya Pradesh and Gujarat. All the tributaries of the Narmada are very short. Most of the tributaries join the Narmada at right angles.
The Tapi Basin: The Tapi rises in the Satpura ranges, in Betul district of Madhya Pradesh. The basin of Tapi covers parts of Madhya Pradesh, Gujarat and Maharashtra.
The Godavari Basin: This is the longest Peninsular river. Its drainage basin is also the largest among the peninsular river basins. The Godavari is about 1500 km long. It originates from the slopes of the Western Ghats in Nasik district of Maharashtra and drains into the Bay of Bengal. The Godavari basin covers parts of Maharashtra, Madhya Pradesh, Orissa and Andhra Pradesh. Purna, Wardha, Pranhita, Manjra, Waiganga and Penganga are the main tributaries of Godavari.
The Mahanadi Basin: This river originates in the highlands of Chhattisgarh and drains into the Bay of Bengal. It is about 860 km long. The Mahanadi basin covers Maharashtra, Chhattisgarh, Jharkhand and Orissa.
The Krishna Basin: The Krishna originates near Mahabaleshwar and drains into the Bay of Bengal. It is about 1400 km long. Tungbhadra, Koyana, Ghatprabha, Musi and Bhima are some of its tributaries. The Krishna basin covers Maharashtra, Karnataka and Andhra Pradesh.
The Kaveri Basin: The Kaveri originates in the Brahmagiri range of the Western Ghats and drains into the Bay of Bengal. It is about 760 km long. Amravati, Bhavani, Hemavati and Kabini are its main tributaries. The Kavery basin covers Karnataka, Kerala and Tamil Nadu.
A large water body which is surrounded by land is called a lake. Most of the lakes are permanent, while some contain water only during the rainy season. Lakes are formed by the action of glaciers and ice sheets, by wind, river action and by human activities.
Ox-bow Lake: A lake formed when a meandering river is cut off from the mainstream. The shape of this lake resembles an ox-bow.
Lagoon: When the lake is formed by spits and bars in coastal areas, it is called a lagoon. Chilika lake, Pulicat lake, Kolleru lake, etc. are examples of lagoon.
Glacial Lake: A lake formed by melting of glacier is called a glacial lake. Most of the lakes in the Himalayan region are glacial lakes.
Wular lake (Jammu & Kashmir) is the largest freshwater lake in India. It was formed by tectonic activity.
Benefits of a Lake: A lake helps in preventing flood by regulating the flow of river. During dry seasons, a lake helps to maintain an even flow of the river. Lakes can also be used for generating hydel power.
Role of rivers in the economy: Rivers have been the centre of human civilization since ancient times. Even today, many big cities are situated on the bank of a river. River water is used for irrigation, navigation, hydroelectricity, fisheries, etc.
River Pollution: The growing domestic, municipal, industrial and agricultural demand for water from rivers naturally affects the quality of water. As a result, more and more water is being drained out of the rivers reducing their volume. On the other hand, 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.