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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:

Geological history

Nature and structure of rocks

Topography

Slope of the land

Amount of water

Periodicity of water flow

3. Perennial & Ephemeral Rivers

Type 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

1. 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.

2. Classification of Indian Drainage

Based on direction of water discharge:

Indian Drainage → (i) Arabian Sea Drainage → (ii) Bay of Bengal Drainage

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.

3. Classification Based on Watershed Size

Category Catchment Area Examples

4. 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.

🏔️ 5. Himalayan Drainage System

Origin & Rivers

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:

Snow/glaciers

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

⭐ Exam Keywords

Himalayan rivers = Perennial + Snow & Rain fed + Deep gorges + V-shaped valleys + Rapids & waterfalls

🌊 Himalayan Drainage — Structured Short Notes

1. 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. 

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💧 4. 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