9th Class Social Science Drainage Important Terms and Concepts - Drainage

IMPORTANT TERMS AND CONCEPTS

1.  Watershed.  A higher ground (upland) separating two adjoining drainage systems or a river basin.

2. Dendritic drainage. It is a river system in which a number of streams (tributaries) join the main river to form a pattern that looks like a tree with its spreading branches.

3. Trellis drainage. It is a river system in which the main river is joined by (streams tributaries), flowing in sub-parallel valleys. The streams form a rectangular or trellis pattern, e.g., River Narmada basin in India.

4. Radial drainage. It is a river system in which streams flow outwards in different directions from central dome-shaped watershed. It is formed in areas of conical hills.

5. Inland drainage. When the rivers do not have sufficient water to reach a sea or an ocean but instead flow into a lake or end up in an arid region, it forms inland drainage. The Aksai Chin area in Ladakh is an Inland drainage.

6.            Gorge.  It is a deep river valley with steep walls. It is much deeper than it is wide. It is cut by river action in areas of low rainfall where the river has a plentiful supply of water from a source higher up.  The lack of rainfall means that there is little erosion of the rocky sides of the river valley.

 7.   Braided river. Rivers carrying large amount of silt form silt islands, e.g., Brahmaputra river.

8.   Estuary.  A partially enclosed stretch of water that is subjected to marine tides and fresh water drainage from land. River enters into the sea depositing all the silt into the ocean and does not form delta.

 9.   Perennial rivers. Rivers which are snow-fed and have constant volume of water throughout the year, e.g., Ganga, Yamuna, Indus, etc.

 10. Rain basin. An area drained by a single river with its tributaries is known as a river basin. e.g.. River Ganga with its tributaries flows through Haridwar, Varanasi and Patna etc. The area is called river basin.

 11.  Peninsula rivers. All the rivers flowing in the Deccan plateau, e.g., Mahanadi, Krishna, Godavari etc. are Peninsula rivers. They are non-perennial because their flow is mainly dependent on rainfall. They are rain-fed and therefore fluctuate in volume.

 12.  Himalayan rivers. These rivers originate in the Himalayas. They are snow-fed. The volume of water does not fluctuate much, hence they are perennial rivers, e.g., Yamuna, Ganga, Kosi, etc.

 13.  Lagoons.   Shallow salt water lakes almost cut off from the sea by a beach or reef, e.g., Lake Chilika in Orissa and Lake Pulicat in Tamil Nadu. Malabar coast is studded with number of lagoons.

 14. Delta.  A roughly triangular area of sediments formed at the mouth of a river. It contains large quantity of alluvium. It is favourable for doing agriculture. There are number of distributaries in the. delta region, e.g., Ganga-Brahmaputra delta, Nile delta.

 15. Silt.  A layer of very fine particles, coarser than clay but finer than sand. Silt is often carried and deposited by rivers.

 16. Large dam. Barriers are constructed on river bed to hold back flow of water. River water gets collected in reservoir. Such a reservoir is known as a dam. A huge dam or a series of small dams are built on a river and its tributaries. These man-made lakes help in impounding huge amount of rainwater. Water from these dams is used in Hirakud dam on river Satluj and river Mahanadi respectively.

17.  Trough.  Lower part of a wave between crests. An elongated low area made by erosional activity of river.

 18.  Centrifugal drainage system pattern. Areas with inland drainage, in arid regions. Streams converge from all sides towards a central depression, where there is a lake.

 19.  Seasonal rivers. Their flow is dependent on rainfall. During the dry season, they have reduced flow of water. Peninsular rivers are seasonal rivers.