The drainage system refers to the system of flow of surface water mainly through rivers. An area drained by a river and its tributaries is called a drainage basin. The drainage system is related to a number of factors like slope of land, geological structure, amount and velocity of water.

On the basis of the origin the drainage can be divided in to two parts:

(a) The Himalayan drainage system (b) The Peninsular drainage system

Tributary: A stream or river that flows into a larger river. e.g. Yamuna

Delta: A triangular shaped land at the mouth of a river formed from the deposition of silt, sand and small rocks that flow downstream in the river. eg. Ganga delta.

Estuary: A partially enclosed coastal body of water where the salty tidal water mixes with the fresh water of the river. eg. Narmada river makes an estuary

The Himalayan Drainage System:

Most of the Himalayan Rivers are perennial. This means they have water throughout the year. This is because most of these rivers originate from the glaciers and snowy peaks. They also receive water from the rainfall. The main river system in this category are:

The Indus River System Jhelum, Ravi, Beas and Satluj
The Ganga Rivers System Yamuna, Ramganga, Ghaghara, Gomti, Gandak and Kosi etc.
The Brahmaputra River System Dibang, Lohit, Tista and Meghna etc

The Peninsular Drainage System:

Most of the Peninsular rivers flow eastwards and enters into Bay of Bengal. Only Narmada and Tapi rivers which flow westwards of the Western Ghats.

The main Peninsular rivers are Narmada, Tapi, Godavari, Krishna , Kaveri and Mahanadi.

Drainage Patterns:

The streams within a drainage basin form certain patterns, depending on the slope of land, underlying rock structure as well as the climatic conditions of the area. These are dendritic, trellis, rectangular, and radial patterns. The dendritic pattern develops where the river channel follows the slope of the terrain. The stream with its tributaries resembles the branches of a tree, thus the name dendritic. A river joined by its tributaries, at approximately right angles, develops a trellis pattern. A trellis drainage pattern develops where hard and soft rocks exist parallel to each other. A rectangular drainage pattern develops on a strongly jointed rocky terrain. The radial pattern develops when streams flow in different directions from a central peak or dome like structure.

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