Drainage Detailed Chapter Notes - Social Studies (SST) Class 9

Introduction

The term "drainage" refers to the river system within a specific area. On a physical map, the convergence of small streams from various directions is evident, forming the main river that eventually empties into a larger water body, such as a lake, sea, or ocean. The region drained by a single river system is termed a "drainage basin." A detailed map examination reveals that elevated features, such as mountains or uplands, act as dividers between two distinct drainage basins.  

Drainage Patterns

The streams within a drainage basin form certain patterns, depending on the slope of the 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.

A combination of several patterns may be found in the same drainage basin.

Types of Drainage Patterns

Drainage System in India

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:

(i) The Himalayan Rivers and                                                  
(ii) The Peninsular Rivers.

The Himalayan Rivers

The major Himalayan Rivers are the Indus, the Ganga and the Brahmaputra. These rivers are long and are joined by many large and important tributaries.

The Indus River System

The river Indus rises in Tibet, near Lake Mansarovar. Flowing west, it enters India in the Ladakh district of Jammu and Kashmir. Several tributaries, the Zaskar, the Nubra, the Shyok and the Hunza, Join it in the Kashmir region. The Indus flows through Baltistan and Gilgit and emerges from the mountains at Attock. The  Satluj, the Beas, the Ravi, the Chenab and the Jhelum join together to enter the Indus near Mithankot in Pakistan. Beyond this, the Indus flows southwards eventually reaching the Arabian Sea, east of Karachi. The Indus Plain has a very gentle slope. With a total length of 2900 km, the Indus is one of the longest rivers in the world. a little over a third of the Indus Basin is located in India in the states of Jammu and Kashmir, Himachal Pradesh, and Punjab and the rest are in Pakistan.

The Peninsular Rivers

Lakes

• Sambhar Lake is the largest inland salt lake in India situated in Rajasthan. Other salt lakes in Rajasthan are Didwana, Degana, Pachadra, Kucha man, and Lunkaransar.
• Lunar Lake situated in Maharashtra is a crater lake.
• Chilka Lake situated in the Puri district of Orissa & south of the Mahanadi delta is the biggest lake in the country.

Loktak Lake 

• Kolleru Lake is a deltaic Lake of Andhra Pradesh situated between the Krishna & Godavari delta.
• Pulicat Lake situated in the north of Chennai is a shallow lagoon. it has been barred by a long sandpit which is actually Sri Harikota island.
• Loktak Lake situated in Manipur is the largest freshwater lake in North East India. Keibul lamjao, the only floating National Park of the country is situated here.
• Vembanad Lake is a lagoon in Kerala and is an important tourist spot. coconut islands are located in it.
• Gohna Lake situated near Devprayag in Garhwal has been formed by a huge landslide across a tributary of the Ganga.
• Wular Lake & Dal Lake are tectonic lakes formed by faulting activities.

Importance of Lakes

• Lakes are very important to man.
• A lake helps to regulate the flow of a river.
• During heavy rainfall they prevent flooding and during the dry season, they help maintain an even flow of water.
• Lakes are also used for developing hydel power.
• Lakes are a valuable source of water.
• They moderate the climate of the surrounding areas.
• They maintain the aquatic ecosystem.
• They enhance natural beauty, helps in developing tourism.
• They provide recreation through boating and swimming.

Role of Rivers 

• Rivers have formed fertile northern plains and deltas containing alluvial soils which are the most productive agricultural lands of India.
• Water from rivers is a basic natural resource essential for the survival of humans, plants and animals, for agricultural and industrial activities.
• The banks of rivers have been cradles of civilization all over the world. For example Indus civilization in India.
• Rivers have provided cultural and economic progress since ancient times.
• Rivers provide an inland transportation system. They also dilute and transport wastes from settlements.
• Industrial; development has flourished along rivers. Most industrial processes depend on water as raw material, as a coolant, and for generating hydroelectricity.

River Pollution

Rapidly growing domestic, Municipal, industrial and agricultural demand for water from rivers naturally affects the quality of water. Today more and more water is drained out of the rivers. It has resulted in reducing their volume. A heavy load of untreated sewage and industrial effluents is emptied into the rivers.

• This affects not only the quality of water but also the self-cleansing capacity of the river. For example, if there is adequate streamflow, the Ganga water is able to dilute and assimilate pollution loads of large cities within 20 km.
• The result is that the pollution level of many rivers is rising.
• Concern over the rising pollution of our rivers has launched of various action plants to clean the rivers.

National River Conservation Plan (NRCP)

• The activities of Ganga Action Plan (GAP) phase-l were started in 1985.
• They declared closed on 31^st March 2000.
• The steering committee of the National River Conservation Authority reviewed the progress of the GAP and necessary corrections were made on the basis of lamed and experiences gained from GAP phase l.
• They have been applied to the major polluted rivers of their country under the NRCP.
• The Ganga Action Plan (GAP) Phase-ll has been merged with the NRCP. The expanded NRCP now covers 152 towns located along 27 interstate rivers in 16 states. Under this action plan, pollution abatement work is being taken up in 57 towns. a total of 215 schemes of pollution abatement have been sanctioned. so far, 69 schemes have been completed under this action plan. A million liter of sewage is targeted to be intercepted, diverted, and treated.

[Intext Question]

For a detailed understanding of this chapter, check the video below.

Some Interesting Knowledge

• The world’s largest drainage basin is the River Amazon which is situated in South America.
• According to the regulation of the Indus Water Treaty (1960), India can use only 20 per cent of the total water carried by the Indus River system. This water is used for irrigation in the Punjab, Haryana, and the southern and western parts of Rajasthan.
• The Sundarban Delta derived its name from the Sundari tree which grows well in marshland. it is the world’s largest and fastest-growing delta. it is also the home of the Royal Bengal Tiger.
• The Brahmaputra is known as the Tsang Po in Tibet and Jamuna in Bangladesh.
• The river Kaveri is the second biggest waterfall in India. it is known as Sivasmudram. the fall supplies hydroelectric power to Mysore, Bangalore, and the Kolar Gold Field.
• 71 percent of the world’s surface is covered with water, but 97 percent of that is saltwater. Of the 3 percent that is available as freshwater, three-quarters of it is trapped as ice.
• Lakes of large extent are called the seas, like the Caspian, the Dead, and the Aral seas.