In the given figure, the site of the Tehri dam has been labelled as

1. Overview of Himalayan River Systems (basic)

Welcome to our journey through Indian Geography! To understand India's landscape, we must first look at its lifelines: the rivers. The drainage system of India is primarily shaped by the country's broad relief features, leading to a fundamental division between the Himalayan rivers and the Peninsular rivers CONTEMPORARY INDIA-I, Geography, Class IX, p.17. While Peninsular rivers are older and have reached a state of maturity with shallow valleys, Himalayan rivers are relatively young, energetic, and still actively carving through the world's highest mountain range INDIA PHYSICAL ENVIRONMENT, Geography Class XI, p.23.

The most defining characteristic of Himalayan rivers is that they are perennial. Unlike many rivers that dry up during the summer, these rivers flow throughout the year. This is because they have a dual source of water: snow-melt from the glaciers during the hot summer months and heavy rainfall during the monsoon season. In geographical terms, we say their regime (the seasonal pattern of water flow) is both glacial and monsoonal Geography of India, Majid Husain, p.22. This makes them vital for irrigation and hydropower across Northern India.

The Himalayan drainage is dominated by three mighty international systems: the Indus, the Ganga, and the Brahmaputra. These rivers are not just Indian; they are truly international, traversing through Tibet (China), India, Pakistan, Nepal, Bhutan, and Bangladesh Geography of India, Majid Husain, p.5. Interestingly, while we categorize them separately, some rivers originating in the northern Peninsula—like the Chambal, Betwa, and Son—actually flow northwards to join the Ganga system, showing how these drainage basins can interconnect INDIA PHYSICAL ENVIRONMENT, Geography Class XI, p.23.

Feature	Himalayan Rivers	Peninsular Rivers
Nature of Flow	Perennial (all year)	Seasonal (mostly rain-fed)
Source of Water	Glaciers and Rainfall	Rainfall only
Geological Age	Young and youthful	Old and mature

Sources: CONTEMPORARY INDIA-I, Geography, Class IX, Drainage, p.17; Geography of India, Majid Husain, The Drainage System of India, p.22; INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Drainage System, p.23; Geography of India, Majid Husain, The Drainage System of India, p.5

2. The Ganga Basin: Origin and Upper Course (basic)

The journey of the Ganga begins not as a single stream, but as a series of Himalayan torrents. The primary headwater, known as the Bhagirathi, originates from the Gaumukh cave at the base of the Gangotri Glacier in the Uttarkashi district of Uttarakhand, at an elevation of approximately 3,900 meters INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Drainage System, p.21. This glacier is one of the largest in the Indian Himalayas and holds immense cultural and sacred significance Exploring Society: India and Beyond, Social Science-Class VII, Geographical Diversity of India, p.4. As the Bhagirathi flows south, it meets its first major tributary, the Bhilangana, at the site where the Tehri Dam—one of the highest dams in the world—now stands.

While the Bhagirathi is the traditional source, the Alaknanda river carries a larger volume of water. The Alaknanda rises from the Satopanth Glacier above Badrinath Geography of India, Majid Husain (9th ed.), The Drainage System of India, p.11. Before it meets the Bhagirathi, the Alaknanda undergoes a series of transformative confluences known as the Panch Prayag (Five Holy Confluences). Each meeting adds a new tributary to the Alaknanda, increasing its strength as it carves through the narrow gorges of the Central and Lesser Himalayas.

Confluence (Prayag)	River A	River B (Tributary)
Vishnu Prayag	Alaknanda	Dhauli Ganga (at Joshimath)
Nand Prayag	Alaknanda	Nandakini
Karna Prayag	Alaknanda	Pindar River
Rudra Prayag	Alaknanda	Mandakini (or Kali Ganga)
Devprayag	Alaknanda	Bhagirathi

It is only after the final confluence at Devprayag that the combined flow is officially called the Ganga CONTEMPORARY INDIA-I, Geography, Class IX, Drainage, p.18. The river then continues its mountain journey for nearly 290 km before finally debouching (emerging) from the Shivalik hills onto the North Indian Plains at Haridwar Geography of India, Majid Husain (9th ed.), The Drainage System of India, p.12.

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Drainage System, p.21; Exploring Society: India and Beyond, Social Science-Class VII, Geographical Diversity of India, p.4; Geography of India, Majid Husain (9th ed.), The Drainage System of India, p.11-12; CONTEMPORARY INDIA-I, Geography, Class IX, Drainage, p.18

3. The Panch Prayag of Uttarakhand (intermediate)

To understand the origins of the Ganga River, we must look at the high Himalayas of Uttarakhand, where a series of sacred confluences known as the Panch Prayag (Five Confluences) take place. Think of the Alaknanda River as the main 'spine' of this system. Originating from the Satopanth Glacier, it travels downstream, meeting several major tributaries at specific points before finally joining the Bhagirathi to form the Ganga Majid Husain, Geography of India, p.11.

The sequence of these confluences is vital for both geography and culture. Following the Alaknanda from its source toward the plains, we encounter the confluences in this specific order:

• Vishnu Prayag: The first meeting point where the Dhauli Ganga joins the Alaknanda.
• Nanda Prayag: Here, the Alaknanda meets the Nandakini River, which flows from the glaciers of the Trishul massif Majid Husain, Geography of India, p.12.
• Karna Prayag: The Pindari River (from the Pindari Glacier) joins the Alaknanda here.
• Rudra Prayag: This is a major confluence where the Alaknanda meets the Mandakini River (also known as Kali-Ganga), which originates near Kedarnath from the Chorabari Glacier.
• Dev Prayag: The final and most famous confluence. The Alaknanda meets the Bhagirathi (which flows from Gaumukh/Gangotri Glacier). From this point onward, the combined flow is officially known as the Ganga NCERT Class XI, India Physical Environment, p.25.

Confluence (Prayag)	River 1 (The Spine)	River 2 (Tributary)
Vishnu Prayag	Alaknanda	Dhauli Ganga
Nanda Prayag	Alaknanda	Nandakini
Karna Prayag	Alaknanda	Pindari
Rudra Prayag	Alaknanda	Mandakini
Dev Prayag	Alaknanda	Bhagirathi

Sources: Geography of India, The Drainage System of India, p.11-12; India Physical Environment, Geography Class XI, Drainage System, p.25

4. Multipurpose River Valley Projects in North India (intermediate)

In the lexicon of Indian development, Multipurpose River Valley Projects (MRVPs) were famously termed the "Temples of Modern India" by Jawaharlal Nehru. These projects are designed to serve multiple objectives simultaneously: irrigation, hydro-electric power generation, flood control, navigation, and fisheries. In North India, these projects leverage the perennial nature of Himalayan rivers, which are fed by both glaciers and rainfall, maintaining a steady flow throughout the year Majid Husain, Geography of India, The Drainage System of India, p.6.

The Tehri Dam stands as the most prominent example of engineering in the high-seismic zones of the Himalayas. Located in the Tehri district of Uttarakhand, it is the tallest dam in India. A critical geographical detail to master is its exact location: it is constructed across the Bhagirathi River, specifically just below its confluence with the Bhilangana River Majid Husain, Geography of India, Energy Resources, p.23. While it provides massive benefits like 1000 MW of power and irrigation to lakhs of hectares, it remains a subject of environmental debate due to its location in a highly earthquake-prone "young folded mountain" region, which can disturb the isostatic equilibrium of the range Majid Husain, Geography of India, Contemporary Issues, p.33.

Further west, the Bhakra-Nangal Project on the Satluj River serves as the lifeline for Punjab, Haryana, and Rajasthan. It is essential to distinguish between the two: the Bhakra Dam is the primary storage dam, while the Nangal Dam, situated about 13 km downstream, acts as a balancing reservoir to regulate water supply for the canal system and generate additional electricity Majid Husain, Geography of India, Energy Resources, p.21. In the eastern part of the North-Central belt, the Damodar Valley Corporation (DVC), established in 1948, was India's first major multipurpose project, comprising several dams like Tilaiya (on the Barakar river) and Konar (on the Konar river) Majid Husain, Geography of India, Energy Resources, p.20.

Sources: Geography of India (Majid Husain), The Drainage System of India, p.6; Geography of India (Majid Husain), Energy Resources, p.20, 21, 23; Geography of India (Majid Husain), Contemporary Issues, p.33

5. Seismic Vulnerability and Environmental Impact (exam-level)

To understand India's seismic vulnerability, we must first look at the country's tectonic foundation. India is not a single, solid block; rather, it is a mosaic of different geological units with varying levels of stability. According to the latest seismic zone maps, nearly 59% of India's land area is prone to moderate or severe earthquakes Physical Geography by PMF IAS, Earthquakes, p.187. The National Disaster Management Authority (NDMA) and the Bureau of Indian Standards (BIS) divide the country into four distinct Seismic Zones (II, III, IV, and V) based on the intensity of historical tremors and geological features. While the Peninsular plateau is relatively more stable, the Himalayan region and the Rann of Kutch fall into the highest risk category, Zone V, where earthquakes of magnitude 8 or higher on the Richter Scale are a real possibility Geography of India, Majid Husain, Contemporary Issues, p.10.

The Himalayas represent a unique environmental challenge because they are young fold mountains that are still in the process of rising due to the ongoing collision between the Indian and Eurasian tectonic plates. This makes the entire range inherently unstable. When we introduce large-scale infrastructure projects—such as the Tehri Dam, located at the critical confluence of the Bhagirathi and Bhilangana rivers—the environmental impact is magnified Geography of India, Majid Husain, Physiography, p.29. Human interventions like blasting for tunnels, road cutting, and building heavy multi-storied structures can loosen earth and rocks. During heavy rains, this destabilized debris can transform into humongous slush and debris flows, destroying everything in its path Geography of India, Majid Husain, Contemporary Issues, p.33.

Moreover, the construction of massive reservoirs in high-seismic zones introduces the risk of Reservoir-Induced Seismicity (RIS). The weight of billions of cubic meters of water can exert immense pressure on the underlying fault lines, potentially triggering tremors. Therefore, experts emphasize that any development in these fragile ecosystems—whether it be hotels, factories, or hydel projects like Bhakra-Nangal or Tehri—must be preceded by a rigorous Environmental Impact Assessment (EIA) to ensure they align with ecological principles Geography of India, Majid Husain, Contemporary Issues, p.33.

Seismic Zone	Risk Level	Key Regions
Zone V	Very High Damage Risk	Himalayas, NE India, Rann of Kutch, Andaman & Nicobar
Zone IV	High Damage Risk	Delhi, Indo-Gangetic Basin, Parts of Gujarat and Maharashtra
Zone III	Moderate Damage Risk	Kerala, Lakshadweep, remaining parts of Uttar Pradesh and Punjab
Zone II	Low Damage Risk	Most of the Peninsular Plateau

Sources: Physical Geography by PMF IAS, Earthquakes, p.187; Geography of India by Majid Husain, Contemporary Issues, p.10, 33; Geography of India by Majid Husain, Physiography, p.29, 71

6. Tributaries of the Bhagirathi River (intermediate)

The Bhagirathi River is traditionally and culturally considered the main source stream of the Ganga. It originates from the Gaumukh ice cave at the foot of the Gangotri Glacier in the Uttarkashi district of Uttarakhand, at an elevation of approximately 3,892 meters Majid Husain, Physiography, p.24. As a youthful Himalayan river, it carves through deep gorges and is fed by several high-altitude tributaries before it eventually unites with the Alaknanda River at Devprayag to formally become the Ganga Majid Husain, The Drainage System of India, p.12. Understanding its tributaries is crucial because they define the hydro-electric potential and the geography of the Garhwal region. Among its many mountain feeders, the most significant is the Bhilangana River. The Bhilangana originates from the Khatling Glacier and joins the Bhagirathi at a spot historically known as Ganesh Prayag (now submerged under the reservoir of the Tehri Dam). This confluence is of immense strategic and economic importance as it serves as the site for the Tehri Dam, India's highest dam. Other notable tributaries include the Jadh Ganga (also known as the Jahnavi), which joins the Bhagirathi at Bhaironghati, and the Asi Ganga, which meets it near Uttarkashi. These rivers are characterized by high velocity and steep gradients, typical of the transverse drainage pattern of the Himalayas.

Sources: Geography of India ,Majid Husain, (McGrawHill 9th ed.), Physiography, p.24; Geography of India ,Majid Husain, (McGrawHill 9th ed.), The Drainage System of India, p.12

7. The Tehri Dam: Features and Exact Location (exam-level)

The Tehri Dam is not only an engineering marvel but a vital geographical landmark in India's energy landscape. Located in the Tehri Garhwal district of Uttarakhand, it holds the distinction of being the highest, biggest, and tallest dam in India. While many major dams are built on a single primary river, the exact location of the Tehri Dam is highly specific: it is constructed across the Bhagirathi River, precisely at the confluence where the Bhilangana River (also spelled Bhilaganga) joins it Geography of India, Energy Resources, p.23. This placement allows the reservoir to harness the combined flow of these two Himalayan rivers before they continue downstream to eventually form the Ganga at Devprayag.

The project has a long history, having been conceived by the Planning Commission in 1972 and starting construction in 1975. A unique aspect of its development was the technical and economic aid provided by the Soviet Union (Russia). As a multipurpose project, its benefits are vast: it provides irrigation to approximately 2.74 lakh hectares of land in Uttarakhand and western Uttar Pradesh and has an installed capacity to generate 1000 MW of hydroelectricity Geography of India, Energy Resources, p.23.

Despite its utility, the dam's location is a subject of intense geographical and environmental debate. It is situated in the Central Himalayan Seismic Gap, a highly earthquake-prone region (Seismic Zone V). Critics have long argued that the weight of the massive reservoir and the geological instability of the terrain pose significant risks to the ecology and the safety of downstream populations. This makes the Tehri Dam a classic case study in Indian geography for balancing developmental needs with environmental conservation.

Sources: Geography of India, Energy Resources, p.23

8. Solving the Original PYQ (exam-level)

To solve this question, you must synthesize your knowledge of Himalayan drainage patterns with the specific geography of Uttarakhand. You have already mastered the sequence of the Panch Prayag and the individual paths of the Bhagirathi and Alaknanda rivers. This question tests your ability to pinpoint the Tehri Dam, which is not just situated on the Bhagirathi but specifically at its confluence with the Bhilangana River. This precise geographical "anchor point" is the key to identifying the site on a physical map rather than just memorizing a state name.

When analyzing the map, first identify the main stem of the Bhagirathi River flowing from the north. Then, look for the specific tributary joining it from the east; this is the Bhilangana. The intersection of these two lines marks the site of the dam. Since Point C is positioned exactly at this junction within the upper reaches of the Garhwal Himalayas, it corresponds to the actual site of the Tehri reservoir. This demonstrates why knowing confluence points is a high-yield strategy for UPSC geography, as discussed in NCERT Class 11 India: Physical Environment.

Be careful not to fall for common UPSC traps! Options like A or B often represent the glacial sources (like Gaumukh) or higher-altitude religious sites which lack the wide river valley required for a major rock-fill dam. Option D is a classic trap; it likely represents Devprayag, the famous confluence where the Bhagirathi meets the Alaknanda to form the Ganga. If you chose D, you identified the end of the Bhagirathi rather than the mid-stream location of the Tehri project. Always look for that secondary tributary to confirm the specific site of the Tehri Dam.