Friday, 5 February 2016

DRAINAGE

SOURCE: 9TH NCERT
Drainage:
The river system of an area is called drainage. The area drained by a single river system is called the drainage basin.

Drainage Patterns:

·        Depending on the slope of land, underlying rock structure and climate of an area, the streams in a drainage basin form certain patters. Different types of drainage pattern are as follows:
a. Dendritic Drainage Pattern:
·        When the river channel follows the slope of the terrain, it develops dendritic pattern.
·        The stream and its tributaries resemble the branches of a tree. Hence, it is called dendritic pattern.
b. Trellis Drainage Pattern:

·        When a river is joined by its tributaries at almost right angles, it develops a trellis pattern.
·        Trellis pattern develops where hard and soft rocks exist parallel to each other.
c. Rectangular Drainage Pattern:

·        When rocks are strongly joined, then rectangular pattern develops.
d. Radial Drainage Pattern:

·        When the streams flow in different directions from a central peak or dome like structure, a radial pattern is developed.
·        It is important to note that a combination of different patterns may develop in the same drainage basin.
LAKES
·        A large water body which is surrounded by land is called a lake.
Most of the lakes are permanent, while some contain water only during the rainy season.
·        Lakes are formed by the action of glaciers and ice sheets, by wind, river action and by human activities.
Ox-bow Lake:
 A lake formed when a meandering river is cut off from the mainstream. The shape of this lake resembles an ox-bow.
Lagoon:
 When the lake is formed by spits and bars in coastal areas, it is called a lagoon. Chilika lake, Pulicat lake, Kolleru lake, etc. are examples of lagoon.
Glacial Lake:
 A lake formed by melting of glacier is called a glacial lake. Most of the lakes in the Himalayan region are glacial lakes.
Wular lake (Jammu & Kashmir) is the largest freshwater lake in India. It was formed by tectonic activity.
Benefits of a Lake:
 A lake helps in preventing flood by regulating the flow of river. During dry seasons, a lake helps to maintain an even flow of the river. Lakes can also be used for generating hydel power.
Role of rivers in the economy:
Rivers have been the centre of human civilization since ancient times. Even today, many big cities are situated on the bank of a river. River water is used for irrigation, navigation, hydroelectricity, fisheries, etc.
River Pollution:
 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.







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