Chapter - 3 Drainage
What is Drainage?
- Drainage refers to the river system of an area.
- A drainage basin is the area drained by a single river system.
- A watershed is the boundary that separates two drainage basins.
Drainage Basin
- A drainage basin is the area of land where all the water drains into a single river system.
- It includes the main river and all its tributaries.
- Think of it like a bowl: all the rain falling inside it flows toward the bottom (the main river).
Water Divide (Watershed)
- A water divide is a highland or elevated area that separates two drainage basins.
- Water falling on one side of the divide flows into one river system, and on the other side, it flows into another.
2. Drainage Systems in India :- India has two major types of drainage systems:
a. Himalayan Rivers
- Perennial (flow all year round)
- Fed by glaciers and rain
- Long courses from source to sea
- Example: Ganga, Brahmaputra, Indus
b. Peninsular Rivers
- Seasonal (depend on rainfall)
- Shorter and shallower
- Flow through plateaus and hills
- Example: Godavari, Krishna, Narmada, Mahanadi, Kaveri
Indus River System
Origin:
The Indus River originates in Tibet, near Lake Mansarovar, on the northern slopes of the Kailash Range.
Path / Course:
- Flows northwest into Ladakh (India) through the Ladakh region of Jammu & Kashmir.
- Then enters Pakistan near the town of Leh at Gilgit-Baltistan.
- Flows through Pakistan and finally drains into the Arabian Sea near Karachi.
Length:
- Total Length: Approximately 2,900 km
- One of the longest rivers in the world.
Main Tributaries:
On the left bank:- Sutlej, Beas, Ravi
On the right bank: - Jhelum, Chenab
Governed by the Indus Water Treaty (1960) between India and Pakistan, brokered by the World Bank.
Ganga River System (Ganga River Basin)
Origin:
- The Ganga River originates from the Gangotri Glacier in the Uttarakhand Himalayas.
- Its initial name is Bhagirathi.
- At Devprayag, Bhagirathi meets Alaknanda, and from there it is called the Ganga.
Length:
- About 2,500 km long.
- One of the longest rivers in India.
Tributaries: - Left Bank Tributaries (join from the north):
Ghaghara, Gandak, Kosi,
These come from the Himalayas and often cause floods.
Right Bank Tributaries (join from the south):
Yamuna (most important; joins at Prayagraj / Allahabad), Son River, Tons River
Course / States it Flows Through:
- Uttarakhand → Uttar Pradesh → Bihar → Jharkhand → West Bengal
- In West Bengal, it splits into two:
- Bhagirathi-Hooghly (flows through India)
- Padma (flows into Bangladesh)
Mouth (Where it Ends):
The Ganga empties into the Bay of Bengal, forming the Sundarbans Delta – the largest delta in the world.
Brahmaputra River System
Origin:
- The Brahmaputra River originates in Tibet, near Lake Mansarovar.
- In Tibet, it is called Tsangpo (or Yarlung Tsangpo).
Entry in India:
- The river enters India through Arunachal Pradesh, where it is known as Dihang.
- After entering Assam, it is called the Brahmaputra.
Length:
- Approx. 2,900 km (like the Indus).
- Flows through Tibet → India → Bangladesh.
Tributaries:- In Arunachal Pradesh & Assam:
Dibang, Lohit, Subansiri, Kameng, Manas, Teesta (joins in Bangladesh)
These tributaries increase the volume and strength of the river, especially during the monsoon.
Riverine Island:
- Majuli Island in Assam is formed by the Brahmaputra.
- It is the largest riverine island in the world (now shrinking due to erosion).
Features of Brahmaputra:
- Unlike other Himalayan rivers, it carries more water and silt during the monsoon.
- Causes frequent floods in Assam and surrounding areas.
- Has a braided channel and shifts course often:- Braided channel reduced stream flow or an increase sediment loads.
The Peninsular Rivers:-
Narmada and Tapi Rivers :- Both are important west-flowing rivers in India that drain into the Arabian Sea.
1. Narmada River
- Origin:- Rises from the Amarkantak Plateau in Madhya Pradesh.
- Flow Direction:- Flows westward through a rift valley between the Vindhya and Satpura ranges.
- Drains Into:- Arabian Sea
- Creates:- Estuary (not delta) at its mouth.
- Beautiful waterfalls like:- Dhuandhar Falls near Jabalpur.
- Special Features:- Forms many gorges and waterfalls.
- Area Covered:- Madhya Pradesh, Gujrat
2. Tapi (Tapti) River
- Origin:- Rises from the Satpura ranges near Multai in Madhya Pradesh.
- Flow Direction:- Flows westward through a rift valley. Parallel to Narmada.
- Drains Into:- Arabian Sea
- Area Covered:- Passes through Madhya Pradesh, Maharashtra, and Gujarat.
3. Godavari River
- Origin:- Rises from the Trimbak Plateau in the Nashik district of Maharashtra.
- Length:- About 1,465 km – Longest river in Peninsular India.
- Flow Direction:- Flows eastward and drains into the Bay of Bengal.
- Drains Into:- Bay of Bengal, forming a large delta.
- Major Tributaries:- Left Bank: Purna, Pranhita, Indravati, Sabari
- Right Bank:- Manjira, Maner
- Also Known As:- The Dakshin Ganga or Ganga of the South because of its size and cultural importance.
- States it Flows Through:- Maharashtra, Telangana, Andhra Pradesh, Chhattisgarh, Odisha
4. Mahanadi River
- Origin:- Rises in the Sihawa hills of Chhattisgarh.
- Length:- Around 860 km.
- Flow Direction:- Flows eastward and drains into the Bay of Bengal.
- Drains Into:- Bay of Bengal, forming a delta.
- States it Flows Through:- Chhattisgarh and Odisha
5. Krishna River
- Origin:- Rises from Mahabaleshwar in the Western Ghats, Maharashtra.
- Length:- Approximately 1,400 km long.
- Major Tributaries: -Left Bank: Bhima, Musi
- Right Bank: Koyna, Tungabhadra, Ghatprabha, Malaprabha
- States it Flows Through:- Maharashtra, Karnataka, Telangana, Andhra Pradesh
- Drains Into:-Bay of Bengal, forming a delta.
6. Kaveri (Cauvery) River
- Origin:- Rises from Talakaveri in the Brahmagiri Hills, Western Ghats, Karnataka.
- Length:- About 760 km long.
- Major Tributaries:- Left Bank: Harangi, Hemavati, Shimsha
- Right Bank: Lakshmana Tirtha, Amaravati, Bhavani
- Flow Direction:- Flows southeast and drains into the Bay of Bengal.
- States it Flows Through:
- Karnataka, Tamil Nadu (also touches Kerala and Puducherry)
Lakes:- A lake is a naturally occurring, relatively large and fixed body of water on earth surface and surrounded by land.
Lagoons:- A lake of salt water that is seperated from the sea by sand or rock.
Ox-bow Lake:- An ox-bow lake is the crescent-shaped lake that forms when a cut-off meander gets completely isolated from the river.
Why called "Ox-bow"?:- Because its shape looks like the yoke (bow) used on oxen.
Cut-off:- A cut-off is formed when a river changes its course, usually during a flood. Rivers in plains often meander (take winding curves). When a meander becomes very curved, the river may cut across the narrow neck during floods, creating a new, shorter channel.
Value of Lakes and Rivers for Economy
1. Source of Water
2. Irrigation
3. Hydroelectric Power
4. Fishing
5. Recreation & Tourism
6. Climate Control
7. Flood Control
8. Habitat for Wildlife
Reasons for River Pollution
1. Industrial Waste
2. Sewage Disposal
3. Religious Activities
4. Agricultural Runoff
5. Plastic and Garbage
6. Bathing and Washing
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