At which one of the following places do two important rivers of India originate; while one of them flows towards north and merges with another important river flowing towards Bay of Bengal, the other one flows towards Arabian Sea ?

1. Evolution of Indian Drainage Systems (basic)

To understand the Indian drainage system, we must first look at its two distinct families: the Himalayan rivers and the Peninsular rivers. This classification is primarily based on their mode of origin and geological history INDIA PHYSICAL ENVIRONMENT, Chapter 3, p.19. While the Himalayan rivers like the Indus, Ganga, and Brahmaputra are geologically 'young' and perennial (fed by both melting glaciers and rain), the Peninsular rivers are much older, characterized by broad, shallow valleys and seasonal regimes dependent entirely on monsoon rainfall Geography of India, Chapter 3, p.22.

The present-day Peninsular drainage was shaped by three monumental geological events. First, during the early Tertiary period, the subsidence of the western flank of the Peninsula caused it to submerge below the sea, disrupting the original symmetrical river patterns. Second, the upheaval of the Himalayas caused the northern flank of the Peninsular block to sink, creating trough faults (rift valleys). This explains why the Narmada and Tapi flow through deep troughs rather than traditional alluvial valleys INDIA PHYSICAL ENVIRONMENT, Chapter 3, p.23. Finally, a slight tilting of the entire Peninsular block from the northwest toward the southeast forced major rivers like the Godavari and Krishna to flow toward the Bay of Bengal.

An interesting exception to these broad regional rules is found at the Amarkantak Plateau. This high ground acts as a unique watershed where two major rivers originate: the Narmada, which follows a westward course through a rift valley into the Arabian Sea, and the Son, which flows northeast to join the Ganga. This illustrates that while the systems are distinct, the older Peninsular block provides essential tributaries (like the Son, Chambal, and Betwa) to the younger Himalayan Ganga system INDIA PHYSICAL ENVIRONMENT, Chapter 3, p.23.

Feature	Himalayan Rivers	Peninsular Rivers
Nature of Flow	Perennial (Glacier + Rain)	Seasonal (Rain only)
Geological Age	Young and Active	Old and Mature
Valleys	V-shaped, deep gorges	Broad, largely-graded shallow valleys

Sources: INDIA PHYSICAL ENVIRONMENT, Drainage System, p.19; INDIA PHYSICAL ENVIRONMENT, Drainage System, p.23; Geography of India, The Drainage System of India, p.22

2. The Great Indian Water Divide (basic)

Imagine a giant ridge running across the map of India, acting like the roof of a house. When rain falls on one side, it flows to the Bay of Bengal; on the other, it heads toward the Arabian Sea. This is the Great Indian Water Divide. It isn't a single mountain range, but a series of highlands—the Delhi Ridge, the Aravalli Range, the Vindhyas, and the Sahyadris (Western Ghats)—that dictate the destination of every river in the country. INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 3, p.19. Historically and geographically, this divide creates a massive imbalance in where India’s water goes. About 77% of India’s drainage area (including the Ganga, Brahmaputra, and Mahanadi) is oriented toward the Bay of Bengal, while only 23% (including the Indus, Narmada, and Tapi) discharges into the Arabian Sea. INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 3, p.19.

Feature	Bay of Bengal Drainage	Arabian Sea Drainage
Major Rivers	Ganga, Brahmaputra, Godavari, Krishna, Kaveri	Indus, Narmada, Tapi, Mahi, Periyar
Share of Area	~77%	~23%
Character	Mostly long rivers forming large deltas	Shorter rivers (except Narmada/Tapi); often form estuaries

One of the most fascinating points on this divide is the Amarkantak Plateau. This region acts as a radial drainage center where the divide is incredibly sharp. From here, the Son river flows northeast to join the Ganga (eventually reaching the Bay of Bengal), while the Narmada river flows west through a rift valley to reach the Arabian Sea. Geography of India, Majid Husain (9th ed.), Chapter 3, p.16, 20. While the Western Ghats form the main divide in the South, running close to the western coast, the Narmada and Tapi are the two major 'rebels' that flow west against the general eastward tilt of the peninsula. CONTEMPORARY INDIA-I, Geography, Class IX, Drainage, p.21.

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 3: Drainage System, p.19, 22; CONTEMPORARY INDIA-I, Geography, Class IX (NCERT 2025 ed.), Drainage, p.21; Geography of India, Majid Husain (9th ed.), Chapter 3: The Drainage System of India, p.16, 20

3. West-flowing Rivers & Rift Valley Geomorphology (intermediate)

To understand why certain Indian rivers defy the general eastward tilt of the Peninsula, we must look at the unique geomorphology of Central India. Most Peninsular rivers flow toward the Bay of Bengal because the Deccan plateau is tilted from West to East. However, the Narmada and Tapi are exceptions. These rivers flow westward because they occupy rift valleys (fault zones) created by deep structural fractures in the earth's crust. Interestingly, these rift valleys were not formed by traditional seafloor spreading, but are believed to have formed due to the subsidence or bending of the northern part of the Indian plate during the intense pressure of the Himalayan mountain-building process PMF IAS, Physical Geography, Divergent Boundary, p.128.

The Amarkantak Plateau serves as a fascinating geographical pivot. It is the source of both the Narmada and the Son rivers. While they share a common origin, they follow drastically different paths: the Narmada flows west into the Arabian Sea, while the Son flows northeast to join the Ganga Majid Husain, Geography of India, Chapter 3, p.16. This represents a classic example of radial drainage, where rivers radiate out from a central highland in different directions NCERT Class XI, India Physical Environment, Chapter 3, p.22.

South of the Narmada lies the Satpura Range, which acts as a divide between the Narmada and the Tapi. The Tapi also flows through a rift valley, though it is significantly shorter and more constricted than the Narmada's trough Majid Husain, Geography of India, Chapter 3, p.20. Beyond these two giants, other west-flowing rivers like the Sabarmati, Mahi, and the rivers of the Western Ghats (like the Periyar) are much shorter because the coastal plain between the mountains and the Arabian Sea is extremely narrow NCERT Class IX, Contemporary India-I, Drainage, p.21.

Feature	Narmada River	Tapi River
Source	Amarkantak Plateau (MP)	Betul District, Satpura Range (MP)
Geomorphology	Flows in a wide rift valley between Vindhyas & Satpuras	Flows in a constricted rift valley south of Satpuras
End Point	Gulf of Khambhat (Arabian Sea)	Gulf of Khambhat (Arabian Sea)

Sources: PMF IAS, Physical Geography, Divergent Boundary, p.128; Majid Husain, Geography of India, Chapter 3, The Drainage System of India, p.16, 20; NCERT Class XI, India Physical Environment, Chapter 3, Drainage System, p.22; NCERT Class IX, Contemporary India-I, Drainage, p.21

4. The Ganga Basin: Tributaries from the South (intermediate)

Welcome to Hop 4! While we often visualize the Ganga as a purely Himalayan river, it is actually a grand meeting point for two different geological worlds. To understand the Ganga Basin fully, we must look south toward the Peninsular Plateau. The rivers joining the Ganga from the south are known as its Right Bank Tributaries. These rivers are generally non-perennial, meaning their flow depends heavily on monsoon rains, unlike the glacier-fed rivers of the north INDIA PHYSICAL ENVIRONMENT, Geography Class XI (2025 ed.), Chapter 3: Drainage System, p.22.

The most significant of these is the Yamuna. It is the westernmost and the longest tributary of the Ganga, stretching 1,380 km. It originates from the Yamunotri glacier on the western slopes of the Banderpunch range Geography of India, Majid Husain (9th ed.), Chapter 3: The Drainage System of India, p.13. Interestingly, while the Yamuna itself is a Himalayan river, it acts as a "collector" for many Peninsular rivers like the Chambal, Sind, Betwa, and Ken. These rivers originate from the Vindhyan Range and the Malwa Plateau, flowing north to join the Yamuna before it finally merges with the Ganga at the holy confluence of Prayag (Allahabad).

The second major southern tributary is the Son. The Son is unique because it originates from the Amarkantak Plateau in Madhya Pradesh. This plateau is a remarkable geographical feature—a water divide where two great rivers part ways. While the Narmada flows west through a rift valley toward the Arabian Sea, the Son flows north-east across the Kaimur hills to join the Ganga in Bihar INDIA PHYSICAL ENVIRONMENT, Geography Class XI (2025 ed.), Chapter 3: Drainage System, p.22, 25. This makes the Son the most important direct link between the Peninsular drainage system and the Ganga-Bay of Bengal system.

Feature	Yamuna River	Son River
Source	Yamunotri Glacier (Banderpunch)	Amarkantak Plateau
Type	Perennial (Himalayan)	Non-perennial (Peninsular)
Confluence	Prayag (Uttar Pradesh)	Near Patna (Bihar)

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (2025 ed.), Chapter 3: Drainage System, p.22; Geography of India, Majid Husain (9th ed.), Chapter 3: The Drainage System of India, p.13; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (2025 ed.), Chapter 3: Drainage System, p.25

5. Drainage Patterns: Radial and Dendritic (intermediate)

When we look at a map of a river and its tributaries, we aren't just looking at random lines; we are looking at a drainage pattern. This is the geometric arrangement of streams determined by the slope of the land, the hardness of the rocks, and the tectonic history of the region Geography of India, Majid Husain, Chapter 3, p.1. Two of the most fundamental patterns you must master for the UPSC are the Dendritic and Radial patterns.

The Dendritic pattern is the most common and derives its name from the Greek word 'dendron', meaning tree. Just like the branching of a tree or the veins of a leaf, the tributaries join the main river at acute angles. This pattern typically develops in regions where the underlying rock is homogeneous (uniform in texture and resistance), such as the vast, flat Indo-Gangetic Plains Geography of India, Majid Husain, Chapter 3, p.3. Because the rock offers equal resistance everywhere, the river simply follows the gentle slope of the land, branching out naturally.

In contrast, a Radial pattern looks like the spokes of a bicycle wheel. It occurs when streams flow outward and downward from a central high point, such as a volcanic cone or a dome-shaped mountain Geography of India, Majid Husain, Chapter 3, p.3. The most famous Indian example of this is the Amarkantak Plateau. Here, the topography forces rivers to move in entirely different directions: the Narmada flows west toward the Arabian Sea, while the Son flows north-east to join the Ganga, eventually reaching the Bay of Bengal INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 3, p.22. Other notable radial examples include the Girnar Hills in Gujarat and the Mikir Hills in Assam.

Feature	Dendritic Pattern	Radial Pattern
Visual Shape	Tree-like branching	Spokes of a wheel
Geological Driver	Uniform rock resistance and gentle slopes	Central uplift, dome, or volcanic peak
Key Indian Example	Rivers of the Indo-Gangetic Plains	Amarkantak (Narmada and Son rivers)

Sources: Geography of India, Majid Husain, Chapter 3: The Drainage System of India, p.1, 3; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 3: Drainage System, p.22

6. Key River Source Nodes (Nasik, Mahabaleshwar, Amarkantak) (exam-level)

To master Indian geography, we must look at the Source Nodes—specific high-altitude points that act as the 'cradles' of our great rivers. One of the most fascinating nodes is the Amarkantak Plateau in Madhya Pradesh. It is a unique geographical feature because it gives rise to two major rivers that flow in opposite directions: the Narmada and the Son. While the Narmada carves a path westward through a rift valley to reach the Arabian Sea, the Son flows northeast to join the Ganga, eventually draining into the Bay of Bengal Geography of India, The Drainage System of India, p.16, 20. This creates a radial-like drainage pattern where a single highland serves two completely different maritime destinations. Moving to the Western Ghats, we find two other critical nodes in Maharashtra: Nasik and Mahabaleshwar. Nasik is the birthplace of the Godavari, the largest of the peninsular rivers, often called the 'Dakshin Ganga' Contemporary India-I, Drainage, p.21. About 200 km south lies Mahabaleshwar, the source of the Krishna river. While both the Godavari and Krishna originate on the eastern slopes of the Western Ghats and flow toward the Bay of Bengal, their characteristics differ significantly. For instance, the Krishna is known for forming a distinct bird-foot delta (similar to the Mississippi) near the Srisailam hills Geography of India, The Drainage System of India, p.21. Understanding these nodes helps you visualize the 'slopes' of the Indian plateau. The fact that Nasik and Mahabaleshwar rivers flow East despite being so close to the West coast tells us that the Deccan Plateau has a pronounced eastward tilt.

Source Node	Primary River(s)	Drainage Direction
Amarkantak	Narmada & Son	West (Narmada) & East (Son via Ganga)
Nasik	Godavari	East (Bay of Bengal)
Mahabaleshwar	Krishna	East (Bay of Bengal)

Sources: Geography of India, The Drainage System of India, p.16, 20, 21; Contemporary India-I, Drainage, p.21, 22

7. Solving the Original PYQ (exam-level)

Now that you have mastered the radial drainage patterns and the distinct paths of Peninsular rivers, this question serves as the perfect synthesis of those building blocks. The core of the puzzle lies in identifying a geographical "water divide" where rivers flow in diametrically opposite directions. The correct answer, (A) Amarkantak, acts as this unique hub. As we explored in INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT), the Narmada originates here and follows a westward course through a rift valley to the Arabian Sea, while the Son River flows northward to join the Ganga, eventually reaching the Bay of Bengal.

UPSC often uses prominent pilgrimage sites to test your precise mapping skills; do not be distracted by the other options just because they are major river sources. For instance, Mahabaleshwar and Nasik (specifically Trimbakeshwar) are the sources of the Krishna and Godavari rivers respectively, but both these systems flow exclusively eastward toward the Bay of Bengal. Similarly, Badrinath is associated with the Alaknanda, a Himalayan river that does not satisfy the criteria of flowing toward the Arabian Sea. By systematically applying your knowledge of river orientations and drainage basins, you can avoid these common traps and confidently identify Amarkantak as the singular point of divergence described in the question.