1. Drainage
Drainage = Flow of water through well-defined channels such as rivers, streams, nalas and channels.
A drainage system is the network of rivers and their tributaries.
Poorly defined or choked channels may cause flooding.
2. Drainage Pattern
The arrangement of rivers and streams in an area is called a drainage pattern.
It depends on: /factors
Geological history -saraswati river
Nature and structure of rocks - Hard/soft rocks affect river courses
Topography- Himalayan and Peninsular regions
Slope of the land-Rivers generally flow from higher to lower areas
Amount of water-Ganga has a large water volume
Periodicity of water flow- Himalayan rivers are generally perennial; many Peninsular rivers are seasonal.
3. Perennial & Ephemeral Rivers
Meaning ?
Perennial Rivers that have water throughout the year
Ephemeral Rivers/streams that flow mainly during the rainy season and remain dry otherwise
4. Catchment Area
The area from which a river collects/drains water is called its catchment area.
5. Drainage Basin
The area drained by a river and its tributaries is called a drainage basin.
Important Drainage Patterns
(i) Dendritic Pattern 🌳
Resembles the branches of a tree.
Common where the underlying rocks have uniform resistance.
Example: Rivers of the Northern Plains.
(ii) Radial Pattern
Rivers flow in all directions from a central hill or elevated area.
Example: Rivers originating from the Amarkantak Range.
(iii) Trellis Pattern
Primary tributaries flow parallel to each other.
Secondary tributaries join them at right angles (90°).
(iv) Centripetal Pattern
Rivers flow from all directions towards a central lake or depression.
Water is collected in the central low-lying area
Dendritic → Tree branches
Radial → From centre outward
Trellis → Parallel + right-angle tributaries
Centripetal → From all directions towards centre
Basic Terms
Watershed: Upland/highland separating one drainage basin from another.
River Basin: Catchment area of a large river and its tributaries.
Watershed vs River Basin: Watersheds are relatively small; river basins cover larger areas.
Activities in one part of a basin can affect the whole basin, so river basins are useful for planning.
Classification of Indian Drainage Based on direction of water discharge:
Bay of Bengal: about 77% of India's drainage area.
Arabian Sea: about 23%.
Main rivers flowing towards Bay of Bengal:
Ganga,Brahmaputra,Mahanadi,Krishna,Godavari, etc.
Main rivers flowing towards Arabian Sea:
Indus,Narmada,Tapi,Mahi,Periyar
They are separated by: Delhi Ridge, Aravalli Range and Western Ghats.
Classification Based on Watershed Size
Important Observations
•Many rivers of North India originate in the Himalayas.
•Large rivers of the Peninsular Plateau generally originate in the Western Ghats.
•Narmada and Tapi are exceptions—they flow towards the Arabian Sea.
•Many short rivers of the western coast also drain into the Arabian Sea.
•Western coastal rivers extend from the Konkan to Malabar coast.
Himalayan Drainage System
The Himalayan drainage system mainly includes:
Indus
Ganga
Brahmaputra
Main Features
•Has evolved over a long geological period.
•Rivers are mainly perennial because they receive water from:
i.Snow/glaciers
ii.Rainfall
•Rivers have cut deep gorges through the Himalayas.
•Formed due to the erosional activity of rivers and uplift of the Himalayas.
•Rivers form V-shaped valleys.
Common features include:
•Gorges
•Rapids
•Waterfalls
Himalayan Drainage —
Himalayan Rivers: Main Features
In the plains, Himalayan rivers form:
•Flat valleys
•Ox-bow lakes
•Flood plains
•Braided channels
•Deltas near river mouths
•In the Himalayan region, rivers are highly tortuous.
•In the plains, they show strong meandering and frequently change their course.
Kosi River is called the “Sorrow of Bihar” because it frequently changes its course due to heavy sediment deposition.
2. Evolution of Himalayan Drainage
Ancient River Theory
•Geologists believe a mighty river called Indo-Brahma once flowed along the entire Himalayas.
•It flowed from Assam → Punjab → Sind → Gulf of Sind.
•This happened around 5–24 million years ago during the Miocene period.
•Evidence: continuity of the Siwalik formations and deposits of sand, silt, clay, boulders and conglomerates.
Later Division
The Indo-Brahma river is believed to have divided into three major drainage systems:
1. Indus system
Indus + its five western tributaries
2. Ganga system
Ganga + Himalayan tributaries in the central part
3. Brahmaputra system
Brahmaputra in Assam + Himalayan tributaries in the eastern part
Why did it divide?
•Probably due to Pleistocene uplift of the Western Himalayas.
•Potwar Plateau (Delhi Ridge) became a water divide between Indus and Ganga systems.
•Down-thrusting of the Malda Gap diverted the Ganga and Brahmaputra systems towards the Bay of Bengal.
3. Indus River System
•Indus = Sindhu
•One of the largest river basins in the world.
•Total basin area: about 11,65,000 km²
•Total river length: about 2,880 km
•It is the westernmost Himalayan river in India.
Origin
•Originates from a glacier near Bokhar Chu in the Tibetan region.
•Approximate location: 31°15′N, 81°40′E
•Altitude: about 4,164 m
•Near the Kailash Mountain Range.
Course
Tibet → Ladakh → Baltistan → Jammu & Kashmir → Pakistan
In Tibet, it is known as Singi Khaban (Lion’s Mouth).
Flows northwest between the Ladakh and Zaskar ranges.
Forms a spectacular gorge near Gilgit.
Enters Pakistan near Chillar in the Dardistan region.
Tributaries of Indus
Himalayan Tributaries
Shyok,Gilgit,Zaskar,Hunza,Nubra,Shigar
Gasting, Dras
Other Important Tributaries
Kabul,Kurram,Tochi,Gomal,Viboа
Sangar
Five Rivers of Punjab
Sutlej + Beas + Ravi + Chenab + Jhelum
Q. The five rivers of Punjab and their ancient names are ? (mentioned in rig veda)
Jhelum → Vitasta
Chenab → Asikni
Ravi → Parushni
Beas → Vipasha
Sutlej → Shutudri
Comments
Post a Comment