Drainage

The River system of an area is called drainage. Now let us try to understand – What is the ‘River System’? A large river originates from a place then travels a long distance and finally falls into a large water body like ocean, sea or lake. During the course of its flow the large river is joined by different small streams and small rivers. In other words we can say that large river obtains water from different sources through small streams and small rivers from different areas or regions. This entire system is called ‘River System’. If a river obtains water from a pond then that pond is also the part of that river system. There may be a different condition If a small river is separated from a large river which is known as distributary, then that distributary is also the part of the river system. For example river Ganga is drained by many streams and rivers like Bhagarathi, Mandakini, Alaknanda, Nandakini, Pindar, Yamuna, Ghaghara, Gandak, Son, Kosi etc. Before arriving Bay of Bengal river Hooghli gets separated from river Ganga. So, in this case river Hooghli is a distributary of Ganga, which is also the part of the Ganga River System.

Drainage Basin:

The area drained by a single river system is called ‘Drainage Basin’.

Water Divide:

An elevated area such as mountain or upland which separates two drainage basin is called ‘water divide’.

The concept of water divide will become more clear from the map given below. There are two river systems on the given map- i. Ganga River System and ii. Brahmaputra River System which are highlighted by light green colour. These two river systems are separated by the Himalayan Mountain ranges. Therefore in case of river Ganga and river Brahmaputa the Himalayan Ranges are example of ‘water divide’.

Drainage System in India

Indian rivers are divided into two major groups:

1. The Himalayan Rivers

2. Peninsular Rivers

1. The Himalayan Rivers: The rivers which originate from the Himalayan ranges are categorised as the Himalayan rivers. The Himalayan rivers have water throughout the year. That’s why the Himalayan rivers are known as perennial rivers. The rivers which flows throughout the year is known as perennial river. There are three important perennial rivers. 1. The Indus, 2. The Ganga and 3.The Brahmaputra.