Classification of Drainage System of India
Let’s begin with the basic idea.
Imagine a country like a large roof. When it rains, the water needs a path to flow down and reach the ground. This flow doesn’t happen randomly. Water naturally chooses a route—lowest in elevation—and this forms a pattern.
That pattern of how water from rainfall or melting snow flows across the land, eventually collecting into rivers and streams, and finally reaching oceans, lakes, or drying up in deserts—is called a Drainage System.
India’s drainage system is one of the most complex and vast in the world—like a giant, interconnected web of veins and arteries.
To understand the Indian drainage system in a structured way, let’s divide it into four categories, each based on a different criterion:
1️⃣ Based on Origin (Source of the River)
We ask: Where is the river born?
A. Himalayan Rivers
- Origin: These rivers begin in the snow-covered Himalayas.
- Example: Ganga, Indus, Brahmaputra.
- Feature: They are perennial, meaning they flow throughout the year—because they are fed by both rain and glacial meltwater.
👉 Analogy: Imagine a river that has two salaries—one from monthly income (rainfall) and another from a fixed deposit (glacier). So, they never run out of water 😊
B. Peninsular Rivers
- Origin: These arise from the Western Ghats or Central Highlands.
- Example: Godavari, Krishna, Cauvery, Mahanadi.
- Feature: They are mostly non-perennial—they rely primarily on rainfall, so many dry up or reduce flow in summers.
👉 These rivers are like freelancers 😊—they work great during the monsoon season, but might be off-duty in dry months.
2️⃣ Based on the Type of Drainage (Where They Drain)
We ask: Where is the river going?
A. Exorheic Drainage (Into the Sea)
- Most Indian rivers drain into the Bay of Bengal or Arabian Sea.
- Example: Ganga (Bay of Bengal), Narmada (Arabian Sea).
B. Endorheic Drainage (Inland Drainage Basin)
- These rivers do not reach the sea. Instead, they end up in salt lakes or simply get absorbed into the ground.
- Example: Luni River (Rajasthan), Sambhar Lake basin streams.
👉 Think of these like short-term trips—they don’t go abroad (sea), they stay within city limits (inland) 😊
3️⃣ Based on Size of Catchment Area
We ask: How big is the area from which the river collects water?
| Type of River | Catchment Area (sq km) |
| Major | More than 20,000 |
| Medium | 2,000 – 20,000 |
| Minor | Less than 2,000 |
- Catchment area is the area from where rainfall flows into a river.
- The Ganga, for instance, has a massive catchment, while small seasonal rivers in Tamil Nadu or Rajasthan may cover only a few hundred sq km.
4️⃣ Based on Water Contribution by Rivers
We now ask: Which rivers bring the most water to the Indian system?
Here’s the actual percentage contribution of different rivers to India’s total water flow:
| River | % Contribution of Water |
| Brahmaputra | ~40% (Highest) |
| Ganga | ~25% |
| Godavari | ~6.4% |
| Mahanadi | ~3.5% |
| Krishna | ~3.4% |
| Narmada | ~2.9% |
| Rest Combined | ~20% |
👉 The Brahmaputra, despite its shorter stretch in India (~916 km), brings the highest volume of water—thanks to its origin in Tibet, heavy rainfall in the Northeast, and huge tributaries.
Drainage System of Indian Rivers based on Orientation to the Sea.
Let’s begin with a simple question:
When rain falls in India, where does that water finally go?
Well, based on which side of the subcontinent the rivers drain, we can classify Indian rivers into two broad systems
1️⃣ The Bay of Bengal Drainage System (East-Flowing Rivers)
2️⃣ The Arabian Sea Drainage System (West-Flowing Rivers)
🧭 Let’s Understand This Through Geography First
If you look at the map of India, you’ll notice something interesting:
The eastern side is broader and flatter, while the western side is narrower and has the Western Ghats (Sahyadris) running parallel to the coast.
This geographical difference determines the flow of rivers:
- East-flowing rivers from central India and the Himalayas flow into the Bay of Bengal.
- West-flowing rivers, mainly originating in the Western Ghats, descend quickly into the Arabian Sea.
🗺️ Comparative Chart: Bay of Bengal vs Arabian Sea Drainage
| Feature | Bay of Bengal Drainage | Arabian Sea Drainage |
|---|---|---|
| Direction | East-flowing | West-flowing |
| Drainage Area | ~77% of India’s drainage area | ~23% of India’s drainage area |
| Major Rivers | Ganga, Brahmaputra, Mahanadi, Godavari, Krishna, Cauvery, Penneru, Vaigai, etc. | Indus, Narmada, Tapti, Mahi, Sabarmati, small Sahyadri rivers |
| Flow Character | Long course, large deltas, meandering flow | Shorter course, steep gradients, estuaries |
| End Region | Forms deltas before meeting the sea | Forms estuaries; no large deltas |
| Rainfall Support | Receives both Southwest and Northeast monsoon + cyclonic rain | Limited monsoon, mostly Southwest monsoon |
| Water Contribution | ~90% of India’s river water drains here | Much smaller share of water |
🧭 Interesting Case: Narmada and Tapti
- These rivers are exceptions.
- Even though they flow almost parallel, they drain westward, into the Arabian Sea.
- They cut through rift valleys, and create fertile valleys rich in alluvial soil and dense teak forests—especially in Madhya Pradesh and Maharashtra.
👉 You can say they are like the rebels of the Indian drainage system—flowing against the general trend.
💡 Why Is There a Lopsided Water Distribution?
Now here comes a crucial question:
Why do more rivers, and more water, drain into the Bay of Bengal, despite the Arabian Sea getting a decent share of the western coastline?
✅ Factors Responsible:
- Rainfall Pattern:
- The Bay of Bengal side gets rain from both Southwest and Northeast monsoons.
- The Arabian Sea side, especially Rajasthan, Haryana, and Punjab, gets much less rainfall.
- Cyclonic storms (which are frequent in the Bay of Bengal) also increase rainfall here.
- Himalayan Rivers Drain East:
- Most perennial rivers from the Himalayas—Ganga, Brahmaputra—flow into the Bay of Bengal.
- These rivers carry enormous volumes of water throughout the year.
- Western Rivers are Seasonal:
- Rivers like Luni, Sabarmati, Mahi are often non-perennial or highly dependent on monsoon.
- Less rainfall means less discharge into the Arabian Sea.
- Geographical Tilt and Landform:
- The general slope of the Indian plateau is towards the east, naturally pushing more rivers in that direction.
🧠 Quick Facts for Prelims
- Ganga is the longest river entirely within India, draining into the Bay of Bengal.
- Indus, though flowing westward, is mainly in Pakistan, with only part of its course in India.
- Only about 10% of India’s river water flows into the Arabian Sea, despite it covering 23% of drainage area.
