Consider the following statements 1. Tista river flows through Arunachal Pradesh. 2. Tista river falls into the Brahmaputra. Which of the statements givern above is/are correct ?

1. Evolution of the Himalayan Drainage System (basic)

Welcome to your first step in mastering the Himalayan river systems! To understand how these mighty rivers flow today, we must first look back at their fascinating birth. Unlike the Peninsular drainage system, which is older, stable, and has reached a state of maturity with broad shallow valleys, the Himalayan drainage system is relatively young and still evolving INDIA PHYSICAL ENVIRONMENT, Chapter 3, p.23. This youthful nature is why Himalayan rivers are energetic, forming deep V-shaped valleys and spectacular gorges.

The most unique feature of this system is that some of its rivers, like the Indus, Sutlej, and Brahmaputra, are actually older than the Himalayas themselves! This is known as antecedent drainage. Imagine a river flowing on a flat plain; as the Earth's crust slowly buckled and pushed up to form the Himalayan ranges, these rivers didn't change their path. Instead, they acted like a saw, cutting vertically into the rising land at the same rate the mountains were lifting Physical Geography by PMF IAS, Fluvial Landforms and Cycle of Erosion, p.211. This persistent cutting created the massive, deep gorges we see today.

Geologists suggest that in the distant past (the Miocene period), there was a single, massive river called the Indo-Brahma or the Siwalik river. This giant river supposedly flowed along the entire longitudinal span of the Himalayas from Assam in the east to Punjab in the west, eventually discharging into the Arabian Sea. However, over time, major geological shifts—specifically the uplift of the Potwar Plateau (Delhi Ridge) and the subsidence of the Rajmahal-Garo gap—fragmented this single river into the three distinct systems we study today: the Indus, the Ganga, and the Brahmaputra.

To help you visualize the fundamental differences between the two major drainage systems in India, let’s look at this comparison:

Feature	Himalayan Rivers	Peninsular Rivers
Nature of Flow	Perennial (water from rain and snowmelt) CONTEMPORARY INDIA-I, Chapter 3, p.17	Seasonal (dependent mainly on rainfall)
Geological Age	Young and active	Old and stable INDIA PHYSICAL ENVIRONMENT, Chapter 3, p.23
Valleys	Deep Gorges and V-shaped valleys	Broad, graded, and shallow valleys

Sources: INDIA PHYSICAL ENVIRONMENT, Drainage System, p.23; CONTEMPORARY INDIA-I, Drainage, p.17; Physical Geography by PMF IAS, Fluvial Landforms and Cycle of Erosion, p.211

2. The Brahmaputra: From Tibet to the Bay of Bengal (basic)

The Brahmaputra is a river of many names and a truly international character, traversing nearly 2,900 km through Tibet (China), India, and Bangladesh. It begins its journey in the Chemayungdung glacier of the Kailash range near Mansarovar Lake INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Drainage System, p.22. In its initial 1,200 km stretch through the high, dry, and flat plateau of Southern Tibet, it is known as the Tsangpo, which beautifully translates to 'the purifier' CONTEMPORARY INDIA-I, Geography, Class IX (NCERT 2025 ed.), Drainage, p.20. Unlike the turbulent river we see in India, the Tsangpo in Tibet carries a smaller volume of water and less silt due to the cold and dry climate of the region.

The river's entry into India is one of the most dramatic geographical shifts in the world. On reaching the Namcha Barwa peak (7,757 m), the river takes a sharp 'U' turn and carves out a deep gorge — the Dihang-Gorge — to enter Arunachal Pradesh Geography of India, Majid Husain (McGrawHill 9th ed.), The Drainage System of India, p.17. At this stage, it is known as the Siang or Dihang. It is only after the Dihang is joined by its major left-bank tributaries, the Dibang and the Lohit, near Sadiya in Assam, that the mighty river finally earns the name Brahmaputra.

As it flows through the 750 km long Assam valley, the Brahmaputra becomes a braided channel with several riverine islands (like Majuli). It receives an enormous volume of water and silt from high-rainfall areas, making it prone to massive seasonal flooding. Its journey ends in Bangladesh, where it is joined by the Tista (Teesta) and takes the name Jamuna, eventually merging with the Padma (Ganga) to reach the Bay of Bengal INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Drainage System, p.23.

Bank	Key Tributaries
Right Bank	Subansiri (antecedent), Kameng, Manas, Sankosh, Tista
Left Bank	Dibang (Sikang), Lohit, Burhi Dihing, Dhansari (South)

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 3: Drainage System, p.22-23; CONTEMPORARY INDIA-I, Geography, Class IX (NCERT 2025 ed.), Chapter 3: Drainage, p.20; Geography of India, Majid Husain (McGrawHill 9th ed.), Chapter 3: The Drainage System of India, p.17

3. Tributaries of the Brahmaputra River (intermediate)

The Brahmaputra, one of the world's largest rivers, undergoes a dramatic transformation as it enters India. After cutting a deep gorge through the Himalayas near Namcha Barwa, it emerges in Arunachal Pradesh as the Siang or Dihang. It officially becomes the Brahmaputra only after it is joined by its major left-bank tributaries, the Dibang (or Sikang) and the Lohit, near Sadiya in Assam INDIA PHYSICAL ENVIRONMENT, Geography Class XI, p.23. Understanding its tributaries is best done by dividing them into those joining from the North (Right Bank) and those from the South (Left Bank).

The Right Bank Tributaries originate in the high Himalayas and are known for their massive water discharge and sediment load. Key rivers include the Subansiri, Kameng (also known as Jiabharali in Assam), Manas, and Sankosh. Notably, the Subansiri is an antecedent river, meaning it existed before the Himalayas reached their current height and has maintained its course by cutting through the rising mountains INDIA PHYSICAL ENVIRONMENT, Geography Class XI, p.23. Another vital right-bank tributary is the Tista (Teesta). It originates from the Tso Lhamo lake (or Teesta Khangse glacier) in North Sikkim and flows through West Bengal before entering Bangladesh to join the Brahmaputra Geography of India, Majid Husain, p.16.

The Left Bank Tributaries primarily drain the regions south of the Brahmaputra, such as the Patkai and Naga Hills. Aside from the Dibang and Lohit, major contributors include the Burhi Dihing, Dhansari (South), and the Kopili Geography of India, Majid Husain, p.18. A fascinating historical fact about this system involves the Tista: until the great flood of 1787, it was actually a tributary of the Ganga. Following that catastrophic event, it diverted its course eastward to become a tributary of the Brahmaputra Geography of India, Majid Husain, p.16.

Bank	Major Tributaries	Key Characteristics
Right Bank	Subansiri, Kameng, Manas, Sankosh, Tista	Himalayan origin, high sediment, antecedent (Subansiri).
Left Bank	Dibang, Lohit, Burhi Dihing, Dhansari, Kopili	Drains southern hills; Lohit is known as the 'River of Blood'.

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 3: Drainage System, p.23; Geography of India, Majid Husain, Chapter 3: The Drainage System of India, p.16-18

4. Trans-boundary Rivers and Inter-State Water Sharing (intermediate)

When we talk about the Himalayan river systems, we aren't just discussing physical geography; we are discussing the lifeblood of nations. Trans-boundary rivers are those that cross international borders (like the Indus, Ganga, and Brahmaputra), while inter-state rivers flow across different states within India. Managing these waters requires a delicate balance of geopolitics, engineering, and environmental conservation.

A fascinating example is the Tista (or Teesta) River. Originating from the Tso Lhamo lake or Teesta Khangse glacier in North Sikkim, it flows through Sikkim and West Bengal before entering Bangladesh Geography of India, Majid Husain, The Drainage System of India, p. 16. Interestingly, the Tista hasn't always been where it is today. Historically, it was a tributary of the Ganga, but following a massive flood in 1787, it shifted its course eastward. Today, it is a major right-bank tributary of the Brahmaputra (known as the Jamuna in Bangladesh), joining it at Fulchori INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 3: Drainage System, p. 23.

Sharing these waters is often a source of diplomatic tension. For instance, India and Bangladesh signed a 30-year treaty in 1996 for sharing Ganga waters during the lean season Geography of India, Majid Husain, The Drainage System of India, p. 39. There are also ambitious proposals like the Brahmaputra-Ganga Link Canal, which aims to divert water from the Brahmaputra at Dhubri (Assam) to the Farakka Barrage to augment the Ganga's flow. However, such projects require international concurrence and massive funding Geography of India, Majid Husain, The Drainage System of India, p. 43.

Domestically, India faces several inter-state disputes where states contest their share of river water. These are often resolved through specialized tribunals or technical cooperation.

River System	States Involved in Dispute
Ravi and Beas	Punjab, Haryana, Rajasthan
Narmada	Madhya Pradesh, Gujarat, Maharashtra, Rajasthan
Krishna	Maharashtra, Andhra Pradesh, Karnataka
Godavari	Maharashtra, Telangana, Andhra Pradesh, Karnataka, Madhya Pradesh
Periyar	Tamil Nadu, Kerala

Source: Geography of India, Majid Husain, The Drainage System of India, p. 38

Sources: Geography of India, Majid Husain (McGrawHill 9th ed.), The Drainage System of India, p.8, 16, 38, 39, 43; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 3: Drainage System, p.23

5. Physiography of the Eastern Himalayas (intermediate)

The Eastern Himalayas represent a dramatic and distinct segment of the Himalayan arc, stretching from the **Kali River** in the west to the **Tista River** and beyond into Arunachal Pradesh Geography of India, Majid Husain, p.16. Unlike the Western Himalayas, which are characterized by broad valleys and gradual slopes, the Eastern Himalayas rise abruptly from the North Indian plains. This rapid rise contributes to higher rainfall and a much denser forest cover. One of the most fascinating aspects is the change in the mountains' direction: while the ranges in **Sikkim and Darjeeling** generally run in an **east-west direction**, they pivot toward a **southwest to northeast** direction as they enter **Arunachal Pradesh** INDIA PHYSICAL ENVIRONMENT, Geography Class XI, p.11. In the Sikkim region, the landscape is dominated by the majestic **Kanchenjunga massif** (8,598 m), the third-highest peak in the world. This high-altitude terrain is home to the **Zemu Glacier**, which is the largest glacier in the Eastern Himalayas and the vital source of the **Teesta River** Geography of India, Majid Husain, p.24. The region is also strategically significant due to its high mountain passes; notably, **Nathu-La** and **Jelep-La** serve as ancient gateways connecting Gangtok in Sikkim to Lhasa in Tibet Geography of India, Majid Husain, p.16.

Feature	Sikkim/Darjeeling Himalayas	Arunachal Himalayas
General Orientation	East to West	Southwest to Northeast
Key Peaks	Kanchenjunga	Namcha Barwa (near the border)
Major Rivers	Teesta	Dihang (Brahmaputra), Lohit, Dibang

Sources: Geography of India, Majid Husain, Physiography, p.16; INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Structure and Physiography, p.11; Geography of India, Majid Husain, Physiography, p.24

6. The Tista River: Geography and Historical Shift (exam-level)

The Tista (or Teesta) River is the lifeline of Sikkim and North Bengal, known for its turbulent flow and its remarkable history of course-changing. It originates at an altitude of over 5,000 meters in the Eastern Himalayas, specifically from the Tso Lhamo Lake and the Teesta Khangse glacier in North Sikkim. It is also significantly nourished by the Zemu Glacier, which is the largest glacier in the Eastern Himalayan region Majid Husain, Geography of India, p.24. The river carves through deep gorges in the Sikkim Himalayas and flows through the Darjeeling Hills of West Bengal before emerging onto the plains near Siliguri Majid Husain, Geography of India, p.16.

What makes the Tista a favorite topic for the UPSC is its historical shift. Before the late 18th century, the Tista did not flow into the Brahmaputra. Instead, it flowed south and was a major tributary of the Ganga. However, a catastrophic flood in 1787 caused the river to suddenly divert its course eastward. This process, known as avulsion, led the Tista to abandon its old path and join the Brahmaputra system instead. This shift fundamentally altered the hydrology of the Bengal Delta.

Currently, the Tista is categorized as a major right-bank tributary of the Brahmaputra (known as the Jamuna in Bangladesh) NCERT Class XI, India Physical Environment, p.23. It enters Bangladesh from West Bengal and eventually merges with the Jamuna at Fulchori. It is important to note that while the Brahmaputra enters India through Arunachal Pradesh, the Tista does not flow through Arunachal Pradesh; its Indian journey is restricted to Sikkim and West Bengal.

Sources: Geography of India, Physiography, p.24; Geography of India, The Drainage System of India, p.16; INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Drainage System, p.23

7. Solving the Original PYQ (exam-level)

In our recent sessions, we mapped the Himalayan Drainage Systems, focusing on how major rivers carve their paths across specific state boundaries. This question tests your ability to synthesize political geography with river morphology. You’ve learned that while the Brahmaputra enters India through Arunachal Pradesh (as the Dihang), the Tista (or Teesta) is the lifeline of Sikkim. By connecting these spatial building blocks, you can identify that Statement 1 is a geographical mismatch; the Tista's course is restricted to Sikkim and West Bengal before it enters Bangladesh, a fact highlighted in Geography of India by Majid Husain.

To evaluate the second statement, we recall the river's confluence history. While the Tista was historically a tributary of the Ganga, a catastrophic flood in 1787 forced it to change its course eastward to join the Brahmaputra (known as the Jamuna in Bangladesh). This historical shift is a classic example of river course diversion often discussed in NCERT Class XI: India Physical Environment. Since the Tista currently falls into the Brahmaputra at Fulchori, Statement 2 is factually correct. Walking through this logic, we arrive at the correct answer: (B) 2 only.

The trap in this question lies in regional proximity and historical vs. current flow. UPSC often uses Arunachal Pradesh as a distractor for North-Eastern rivers, banking on the student confusing the Tista with other Brahmaputra tributaries like the Lohit or Subansiri. Option (C) is a common pitfall for those who remember the river is in the "East" but fail to distinguish between the Eastern Himalayas (Sikkim) and the Arunachal hills. Always verify the state-wise trajectory and the modern-day drainage basin to avoid these precision-based errors.