The term drainage describes the river system of an area. Look at the physical flowing from different directions come together to form the main river, which ultímately drains into a large water body such as a lake or a sea or an ocean. The area drained by a single river system is called a drainage basin. A closer observation on a map will indicate that any elevated area, such as a mountain or an upland, separates two drainage basins. Such an upland is known as a water divide.
DRAINAGE SYSTEMS IN INDIA
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 and the Peninsular rivers
Apart from originating from the two major physiographic regions of India, the Himalayan and the Peninsular rivers are different from each other in many ways. Most of the Himalayan rivers are perennial. It means that they have water thoughout the year. These rivers receive water from rain as well as from melted snow from the lofty mountains. The two major Himalayan rivers, the Indus and the Brahmaputra originate from the north of the mountain ranges.
They have cut through the mountains making gorges. The Himalayan rivers have long courses from their source to the sea. They perform the intensive erosional activity in their upper courses and carry huge loads of silt and sand. In the middle and the lower courses, these rivers form meanders, oxbow lakes, and many other depositional features in their floodplains. They also have well-developed deltas.
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 the flow of water in their channels. The peninsular rivers have shorter and shallower courses as compared to their Himalayan counterparts. However, some of them originate in the central highlands and flow towards the west. Can you identify two such large rivers? Most of the rivers of peninsular India originate in the Western Ghats and flow towards the Bay of Bengal.
ROLE OF RIVERS IN THE ECONOMY
Rivers have been of fundamental importance throughout the human history. Water from the rivers is a basic natural resource, essential for various human activities. Therefore, the river banks have attracted settlers from ancient times. These settlements have now become big cities. Make a list of cities in your state which are located on the bank of a river.
Using rivers for irrigation, navigation, hydro-power generation significance – particularly to a country like India, where agriculture is the major source of livelihood of the majority of its population.
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.
For example, given the adequate streamflow, the Ganga water is able to dilute and assimilate pollution loads within 20 km of large cities. But the increasing urbanization and industrialization do not allow it to happen and the pollution level of many rivers has been rising. Concern over rising pollution in our rivers led to the launching of various action plans to clean the rivers. Have you heard about such action plans? How does our health get affected by polluted river water? Think about the “life of human beings without freshwater”. Arrange a debate on this topic in the class.