25 August 2015

Class 9th Chapter : Drainage

CBSE NCERT Class IX (9th) | Social Studies | Geography

Chapter  : Drainage

Introduction to Drainage System

Drainage means the river system in a particular area. A river system consists of the total area covered by the tributaries and other water bodies that join the main river. A drainage basin is an area drained by a single river system. This eventually drains into a large water body, such as a lake, sea or an ocean. The drainage basin works as a funnel, by collecting all the water within the area and channeling it into a waterway.

The largest river basin in the world is the Amazon river basin. Drainage systems in India can broadly be categorized as Himalayan rivers and Peninsular rivers. The Himalayan rivers are fed by the snow melting from the mighty Himalayas and also seasonal rains, and hence these are perennial rivers.

Peninsular rivers originate in the central highlands of the peninsula, and depend solely on the rains, and, therefore, are seasonal. The four main drainage patterns are: Dendritic Drainage, Rectangular Drainage, Trellis Drainage and Radial Drainage.

The dendritic drainage pattern develops when the river follows the slope of the terrain. The rectangular drainage pattern develops on a strongly jointed rocky terrain.

A river joined by its tributaries at approximately right angles, develops a trellis pattern. The radial drainage pattern has a central peak or a dome-like elevation, from where the water flows in different directions.

Himalayan Rivers

The three important Himalayan rivers are the Ganga, the Brahmaputra and the Indus. The Indus originates in Tibet from lake Mansarovar. The main tributaries of Indus are the Satluj, the Beas, the Ravi, the Chenab and the Jhelum.

The Indus covers a distance of 2900 kilometres before reaching its destination. In 1960, Jawaharlal Nehru and Mohammed Ayyub Khan, the then President of Pakistan, signed a treaty known as the Indus Water Treaty. According to this treaty, India could use 20% of the total water carried by the Indus river system.

The river Ganga, is the longest river in India, and originates from the Gangotri glacier in the Himalayas. The Ganga starts off as the Bhagirathi, and is joined by the Alaknanda at Devaprayag. The major tributaries of Ganga are the Yamuna, the Ghaghara, the Gandak and the Kosi rivers. All these rivers originate in the Nepal Himalayas.

The peninsular tributaries that join the Ganga are the Chambal and the Betwa rivers. The interesting feature of the path of the Ganga from the Ambala water divide is that the river meanders a lot before reaching Sunderban. This is because the distance between Ambala and Sunderban is about 1800 kilometres. The slope along the path is very gentle, about one metre for every 6 kilometres.  The flow of water is very slow, and as a result, the river develops large meanders.

Like the Indus, the Brahmaputra also starts in Tibet, from the east of the Mansarovar lake. The Brahmaputra river is slightly longer than the Indus, and flows its course eastwards, parallel to the Himalayas.

A major difference with the Ganga is that the Brahmaputra flows a course mostly outside of India. It enters India from Arunachal Pradesh through a gorge. The Brahmaputra gathers strength through its tributaries, the Dihang, the Dibang and the Lohit rivers.

Peninsular Rivers

The Western Ghats make up an important water divide in peninsular India. The major rivers in peninsular India are the Mahanadi, the Godavari, the Krishna and the Kaveri, which flow eastwards and drain into the Bay of Bengal.

The two major rivers that flow westward and drain into the Arabian Sea are the Narmada and the Tapi. The tributaries of Narmada river are the Sher, the Shakkar, the Dudhi and the Tawa. The Godavari is the longest and the largest peninsular river.  It starts from Trimbak located in Nashik district of Maharashtra.

The tributaries that strengthen the Godavari are the Purna, the Wardha and the Pranhita. The major tributaries are the Wainganga, the Manjira and the Penganga.

The biggest tributary of the Mahanadi is the Shivnath river. The Krishna river is the second longest peninsular river. The main tributaries of Krishna river are the Tungbhadra, the Koyana, the Ghatprabha, the Musi and the Bhima.

The major tributaries of the Kaveri are the Amravati, the Bhavani, the Hemavati and the Kabini. The Sivanasamudram falls made by the Kaveri are the second highest waterfall in India.

Importance of Lakes and Rivers

Lakes are formed usually as a result of tectonic or glacial activity in a region.  It can also be formed by a meandering river or even artificially by human activity.

Lakes are important for various reasons, like regulating the flow of river water, storage of water during the dry seasons, to maintaining the eco-system, and also the generation of hydroelectric power. The different types of lakes in India are freshwater lakes and salt water lakes. The Wular Lake in Jammu and Kashmir is the largest freshwater lake in India.

Other freshwater lakes include the Dal in Jammu and Kashmir, the Bhimatal Lake and the Nainital Lake in Uttarakhand, and lake Kolleru in Andhra Pradesh. Lake Kolleru is officially classified as a wildlife sanctuary.

The largest salt water lake in India is the Sambhar Lake in Rajasthan. The salt produced from this lake has made Rajasthan the third largest salt producer in the country. Brackish water is a mixture of salt water and fresh water. It is not as salty as sea water and brackish water lakes are generally situated in coastal areas. The Chilika Lake in Orissa is the largest brackish water lake in India.

Rivers are considered the most basic natural resources required for human settlement. The primary reason is that we depend on rivers for fresh drinking water and water for irrigation. River water is also used for generating hydroelectric power.

The growing demand for water in agriculture, industry and domestic use is affecting the quality of water. There has been some government action to counter this by launching activities such as the National River Conservation Plan (NRCP) and the Ganga Action Plan (GAP) introduced in 1985. 

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