3. DRAINAGE

The term drainage describes the river system of an area. Look at the physical map. You will notice that small streams flowing from different directions come together to form the main river, which ultimately 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.

Drainage refers to how rivers and streams collect and move water from an area. When looking at a physical map, you can see how smaller streams merge to create a larger river that eventually empties into a bigger body of water, like a lake or ocean. The region where all the water from these streams is collected and drained is called a drainage basin. This means that all the rainfall and water runoff in this area flows into one main river.

Think of how a funnel works when you pour liquid into it. The funnel collects the liquid at the top before channeling it into a bottle below. In the same way, a drainage basin collects water from all its parts before directing it into one main river, much like the funnel directs the flow into a single place.

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.

A water divide is a geographical boundary that separates one drainage basin from another. Typically, this is an elevated area like a mountain. When rain falls on either side of a divide, the water will flow into different drainage basins. For example, if it rains on one side of a mountain, the water will flow towards one river system, while rainfall on the other side will drain into a completely different river system.

Imagine you have a toy car driving on a sloped toy board. If you pour water on one side, it will roll down that side, filling a container below. But if you pour water on the other side, it will flow in the opposite direction into another container. The slopes of those two sides represent the water divide.

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.

In India, the various river systems can be categorized based on their geography. The two primary categories are Himalayan rivers, which originate from the mountains, and Peninsular rivers, which arise from the plateaus and hills. The unique geographical features in these regions influence how these rivers flow and the characteristics they exhibit.

Think of India as a giant playground with hills, mountains, and flat areas. Just like different play areas can lead to different games, the geographical features of India create two distinct types of river systems. One set of rivers runs down from the mountains (Himalayan), while the others flow from the ups and downs of the land (Peninsular).

Most of the Himalayan rivers are perennial. It means that they have water throughout the year. These rivers receive water from rain as well as from melted snow from the lofty mountains.

The Himalayan rivers are known for being perennial, meaning they have a continuous flow of water throughout the year. This water comes from two main sources: rainfall and the melting of snow from the mountains during warmer months. This consistent flow ensures that these rivers remain full even in dry periods.

Think of a garden hose. When you turn it on, water flows out continuously, keeping the plants watered. Similarly, the Himalayan rivers keep flowing year-round, much like the garden hose provides a steady supply of water, whether from rainfall or melting snow.

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 flow of water in their channels. The Peninsular rivers have shorter and shallower courses as compared to their Himalayan counterparts.

In contrast to the Himalayan rivers, many Peninsular rivers depend on seasonal rainfall for their water supply. This means that during the dry season, their water levels drop significantly, leading to much lower flow rates. Additionally, these rivers are generally shorter and less deep compared to the more mighty Himalayan rivers.

Consider a fountain that only operates during rainy days. On sunny days, the fountain has little or no water. Peninsular rivers work similarly: they flow abundantly during the rainy season but may dwindle to mere trickles in dry months.

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