Physiography and Drainage Systems

Why This Topic Matters for NDA

Indian physiography and drainage appear in the NDA General Ability Test almost every year. The questions are usually direct and factual: which river is a tributary of the Ganga, which pass connects to which region, where the Western and Eastern Ghats meet, or which division has the youngest mountains.

Because the answers are recall-based and rarely change, this is one of the most efficient areas to revise — no calculation, no diagrams to draw, just organised facts. If you can hold a clear mental map of India in your head, you can convert almost every such question into a sure mark.

The Six Physiographic Divisions

On the basis of relief and geological structure, India is divided into six major physiographic divisions. Knowing this list in order is the backbone of the whole topic.

• The Northern and North-Eastern Mountains (the Himalayas)
• The Northern Plain (Indo-Gangetic-Brahmaputra plain)
• The Peninsular Plateau
• The Indian Desert (the Thar)
• The Coastal Plains (Western and Eastern)
• The Islands (Andaman-Nicobar and Lakshadweep)

Each division has a distinct origin. The Himalayas and the Northern Plain are young features formed by the collision of the Indian and Eurasian plates and the deposition of river sediment. The Peninsular Plateau is one of the oldest and most stable landmasses on Earth, made of ancient hard rocks.

The Himalayas: Three Parallel Ranges

The Himalayas are the world's youngest fold mountains, formed where the Indian Plate collided with the Eurasian Plate. They stretch about 2,400 km in a great arc from the Indus gorge in the west to the Brahmaputra gorge in the east. Running lengthwise (longitudinally), they are made of three roughly parallel ranges.

The Great Himalayas (Himadri)

The northernmost and highest range, with an average height above 6,000 m. It holds the loftiest peaks including Mount Everest (Sagarmatha) and Kanchenjunga. Its core is composed of granite, and it is perennially snow-bound, feeding many glaciers.

The Middle Himalayas (Himachal or Lesser Himalaya)

Lying south of the Himadri, these ranges average 3,700–4,500 m. They contain famous hill stations and valleys — the Pir Panjal, Dhaula Dhar and Mahabharat ranges, and the well-known Kashmir, Kangra and Kullu valleys.

The Shiwaliks (Outer Himalayas)

The southernmost and lowest range (900–1,100 m), made of unconsolidated sediment brought down by rivers. The longitudinal valleys between the Shiwaliks and the Lesser Himalaya are called Duns — for example, Dehra Dun.

Regional Divisions and Passes

From west to east, the Himalayas are also divided regionally by the rivers that cut across them: the Punjab Himalayas (Indus to Sutlej), Kumaon Himalayas (Sutlej to Kali), Nepal Himalayas (Kali to Tista) and Assam Himalayas (Tista to Dihang). Beyond the Dihang, the range bends sharply southward as the Purvanchal or Eastern Hills — the Patkai, Naga, Manipur and Mizo hills. Key passes include Zoji La (Kashmir to Ladakh), Nathu La and Jelep La (Sikkim to Tibet), Shipki La (Himachal) and Bomdi La (Arunachal Pradesh).

The Northern Plain

South of the Himalayas lies the Northern Plain, formed by the deposition of alluvium (fine river-borne sediment) by three river systems — the Indus, the Ganga and the Brahmaputra. It is one of the most fertile and densely populated regions on Earth.

Based on relief, the plain is divided into belts from north to south:

• Bhabar — a narrow belt of pebbles along the Shiwalik foot where streams disappear underground.
• Tarai — a wet, marshy zone south of the Bhabar where the streams re-emerge.
• Bhangar — the older alluvium, slightly raised; it often contains lime nodules called kankar.
• Khadar — the newer, fertile alluvium of the floodplains, renewed every flood.

The Peninsular Plateau

The Peninsular Plateau is a tableland of old crystalline, igneous and metamorphic rocks — part of the ancient landmass of Gondwana. It is the oldest and most stable physical unit of India. It has two broad parts.

The Central Highlands

North of the Narmada river, covering the Malwa plateau. They are bounded by the Aravallis on the north-west — one of the world's oldest fold mountain systems, now worn down to low hills.

The Deccan Plateau

A triangular landmass south of the Narmada. It is bordered by the Western Ghats (Sahyadris) on the west and the Eastern Ghats on the east. The north-western Deccan is covered by the famous black soil formed from lava — the Deccan Trap.

Desert, Coastal Plains and Islands

The Indian Desert (Thar)

Lying to the west of the Aravallis, the Thar Desert is an undulating sandy plain with crescent-shaped dunes called barchans. Rainfall is below 150 mm a year. The Luni is the only large, mostly seasonal river of the region.

The Coastal Plains

The plateau is flanked by narrow coastal plains. The Western Coastal Plain is narrow and divided into the Konkan, Kannad and Malabar coasts. The broader Eastern Coastal Plain includes the Northern Circar and the Coromandel coast, and is rich in deltas built by the Mahanadi, Godavari, Krishna and Kaveri. Chilika Lake, India's largest coastal lagoon, lies on the eastern coast.

The Islands

India has two island groups. The Andaman and Nicobar Islands in the Bay of Bengal are larger and of volcanic and tectonic origin — Barren Island is India's only active volcano. The Lakshadweep Islands in the Arabian Sea are small coral islands.

Drainage: The Two Great River Systems

Drainage means the river system of an area. Indian rivers fall into two broad families that differ in almost every way — this contrast is the single most tested idea in the drainage portion.

Himalayan Rivers

The Indus, Ganga and Brahmaputra and their tributaries. They are mostly perennial (flow all year) because they are fed by both monsoon rain and melting Himalayan snow. In their youthful stage they cut deep gorges, perform intense erosion, and in the plains form large meanders, ox-bow lakes and deltas.

Peninsular Rivers

The Mahanadi, Godavari, Krishna, Kaveri, Narmada and Tapi. They are largely seasonal, depending on monsoon rain alone, so they shrink in the dry season. They flow in shallow, fixed valleys with little erosive power, having reached a mature stage long ago.

Key Rivers and Their Tributaries

NDA loves questions on "which river is a tributary of which." Group them and they become easy.

The Ganga System

The Ganga rises from the Gangotri glacier (as the Bhagirathi). Its major left-bank tributaries are the Ghaghara, Gandak and Kosi (the Kosi is the "Sorrow of Bihar"); its main right-bank tributaries are the Yamuna, Son and the peninsular Chambal and Betwa (which join the Yamuna).

The Indus System

The Indus rises near Lake Mansarovar in Tibet. Its five Punjab tributaries are the Jhelum, Chenab, Ravi, Beas and Sutlej ("Punjab" means land of five waters).

West-Flowing Peninsular Rivers

The Narmada and Tapi are unusual: they flow west into the Arabian Sea through rift valleys and form estuaries, not deltas. Most other peninsular rivers flow east into the Bay of Bengal and build deltas.

Worked Example: Reading a Drainage Question

NDA questions often describe a feature and ask you to name the river or division. Here is how to reason it out step by step.

Notice the method: collect each clue, eliminate options, and the answer falls out. The same logic works for landform and division questions — match the description to the fact-pairs you memorised.

Common Mistakes to Avoid

A few confusions cost students easy marks every year. Fix them now.

• Swapping Bhangar (old) and Khadar (new) alluvium — remember Khadar is fresher and more fertile.
• Calling the Eastern Ghats continuous — only the Western Ghats are continuous and higher.
• Thinking Lakshadweep is volcanic — it is coral; Andaman-Nicobar are volcanic/tectonic.
• Assuming all peninsular rivers flow east — the Narmada and Tapi flow west.
• Mixing up the Himalayan ranges — Himadri is highest, Shiwalik is lowest.

Previous-Year Style Question

Try this in exam conditions, then check the reasoning below.

The trick is to recall the single contrast — continuous-and-high versus broken-and-low — and the answer is immediate.

Quick Recap and Revision

Run through this checklist the night before the exam — it covers the highest-yield facts of the whole topic.