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Chapter 16. Drainage (Geography Notes)


➤ The Drainage refers to a body of flowing water, ranging in scale from a rill to river.
➤ The evolution of drainage system in a particular region is determined by the nature of the original surface and the Geological structures.
➤ There are broadly two categories of drainage – Sequent Drainage System and Insequent Drainage System.
(1) Sequent Drainage System
(a) Consequent Stream : In the region of flooded structure, stream formed in the synclinical troughs is called synclinical consequent stream.
Consequent stream follows the direction of the slope. Most of the stream draining the coastal plains of India are of this type.
(b) Subsequent Stream : When the master consequent stream is joined by its tribuatary at right angles it is called subsequent stream. For of Yamuna and river “Son” a tributary of the Ganga are the subsequent streams.
(c) Obsequent Stream : It is the stream which flows following the direction of the slope opposite to master consequent stream. For example : the Mahabharat Range of lesser Himalayas, Ganga, Yamuna etc.
(d) Resequent Stream : Such stream follows the direction of master consequent stream that meets the subsequent stream at right angles.
(2) Insequent Drainage System
The streams which do not follow the regional slopes and drain across the geological structure are called insequent or inconsequent streams.
(a) Antecedent Drainage : The stream which originated before the upliftment of the surface on which they flow. For example, Indus, Sutlej and Brahmaputra are antecedent rivers as they originated before the upliftment of Himalayan Range and hence create deep Gorge, along the Mountain Range.
(b) Superimposed Drainage : It is formed when the nature and characteristics of the valley and flow direction of a consequent stream develop on the upper geological formulation and structure are superimposed on the lower geological formation of the entirely different characteristics.
For example, river Subarnarekha is superimposed on Dalma hills on the west of Chandil in the Chhotanagpur plateau region of Jharkhand.
➤ Hydrosphere is the water surface which includes the oceans, lakes and rivers.
➤ It is estimated that the hydrosphere contains about 1,460,000 cubic km of water.
➤ Of this 97.3% is in the oceans and inland seas. The rest 2.7% is found as glaciers and ice caps, fresh water lakes, rivers and underground

ReservoirVolume (Million Km3)Percentage of the Total
Ice Caps and Glaciers292.05%
Ground Water9.50.68%
Soil Moisture0.0650.005%
Streams and Rivers0.00170.0001%

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