On which one of the following rivers is the Tehri Hydropower Complex located?

1. Classification of Indian Drainage Systems (basic)

To understand the geography of India, we must first look at how its water moves. A drainage system is essentially the geometric arrangement of a main river and its tributaries, shaped by the land's slope, rock structure, and climate Geography of India, The Drainage System of India, p.1. In India, the drainage is primarily divided into two broad categories based on their origin and physical characteristics: the Himalayan Drainage and the Peninsular Drainage. While the Himalayan rivers are relatively young and still actively carving deep Gorges, the Peninsular rivers flow through broad, shallow valleys, indicating they are much older and have reached a stage of 'maturity' INDIA PHYSICAL ENVIRONMENT, Drainage System, p.23. One of the most critical differences between these two systems lies in their regime—the seasonal pattern of water flow. Himalayan rivers like the Indus, Ganga, and Brahmaputra are perennial, meaning they flow year-round because they receive water from both monsoon rainfall and the melting of Himalayan glaciers CONTEMPORARY INDIA-I, Drainage, p.17. In contrast, Peninsular rivers are mostly seasonal; their flow is almost entirely dependent on rainfall, making them prone to significant fluctuations during the dry season Geography of India, The Drainage System of India, p.22.

Feature	Himalayan Rivers	Peninsular Rivers
Nature of Flow	Perennial (Rain + Snowmelt)	Seasonal (Mainly Monsoon Rain)
Geological Age	Young and active	Old and stable
Drainage Pattern	Anticedent and Dendritic	Mostly Trellis, Radial, and Rectangular

Beyond just origin, we classify these rivers by the patterns they form on the landscape. For instance, a Radial Pattern occurs when rivers flow outward in different directions from a central high point, like spokes on a wheel. A classic example is the Amarkantak Hills, where the Narmada, Son, and Mahanadi rivers originate and flow in diverging directions Geography of India, The Drainage System of India, p.3. Understanding these patterns helps us predict how water will behave across different terrains of the Indian subcontinent.

Sources: Geography of India (Majid Husain), The Drainage System of India, p.1, 3, 22; INDIA PHYSICAL ENVIRONMENT (NCERT Class XI), Drainage System, p.23; CONTEMPORARY INDIA-I (NCERT Class IX), Drainage, p.17

2. The Ganga River System: Sources and Mainstream (basic)

Welcome back! Today we are tracing the birth of the Ganga, India's most significant river both geographically and culturally. The Ganga does not simply emerge from a single point; it is the result of a spectacular network of glacial streams in the high Himalayas of Uttarakhand. To understand its origin, we must look at two primary mother-streams: the Bhagirathi and the Alaknanda.

The Bhagirathi is traditionally considered the source-stream of the Ganga. It originates at an elevation of about 3,892 meters from the Gaumukh (the snout of the Gangotri Glacier) in the Uttarkashi district NCERT Class XI, Drainage System, p.21. As it flows downstream, it meets its first major tributary, the Bhilaganga. Just below this confluence lies the Tehri Dam, India's highest dam and a massive hydropower complex Majid Husain, Geography of India, p.441. Meanwhile, the Alaknanda rises from the Satopanth Glacier above Badrinath. The Alaknanda is actually the "workhorse" of the system, collecting several other rivers at sacred junctions known as the Panch Prayag.

As the Alaknanda flows south, it meets various tributaries at specific confluences that every UPSC aspirant must memorize:

Prayag (Confluence)	River 1	River 2 (Joining Stream)
Vishnu Prayag	Alaknanda	Dhauli Ganga (or Vishnu Ganga)
Nand Prayag	Alaknanda	Nandakini
Karna Prayag	Alaknanda	Pindar
Rudra Prayag	Alaknanda	Mandakini (or Kali Ganga)
Devprayag	Alaknanda	Bhagirathi

The river is officially called the Ganga only after the final confluence at Devprayag NCERT Class XI, Drainage System, p.21. From here, the river cuts through the Lesser Himalayas in narrow, deep gorges. After a journey of about 289 km through the mountains, the Ganga finally reaches Haridwar, where it debouch (emerges) from the hills and begins its long journey across the vast Northern Plains Majid Husain, Geography of India, p.12.

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Drainage System, p.21; Geography of India, Majid Husain (McGrawHill 9th ed.), The Drainage System of India, p.12; Geography of India, Majid Husain (McGrawHill 9th ed.), Energy Resources, p.441

3. Multipurpose River Valley Projects in India (intermediate)

Hello! To understand the physical and economic geography of India, we must look at what Pt. Jawaharlal Nehru famously called the "Temples of Modern India": the Multipurpose River Valley Projects. At their core, these are large-scale engineering marvels designed not just for a single use, but to address a suite of regional needs simultaneously. While a simple dam might only store water, a multipurpose project integrates irrigation, hydro-electric power (HEP) generation, flood control, navigation, and even fisheries (pisciculture).

The Damodar Valley Corporation (DVC), modeled after the Tennessee Valley Authority (TVA) in the USA, serves as the gold standard for this integrated approach. It doesn't just provide water; it acts as a regional catalyst by controlling devastating floods in West Bengal and Jharkhand, reclaiming land for agriculture, and even promoting public health by managing water flow to reduce malaria breeding grounds Geography of India, Regional Development and Planning, p.66.

India’s river systems host several critical projects, each tailored to the unique topography of its basin:

• Northern Giants: The Tehri Dam, located on the Bhagirathi River in Uttarakhand, is a powerhouse of energy (1,000 MW) and a vital water source for North India. Similarly, the Salal Project on the Chenab River in Jammu & Kashmir provides crucial electricity to the northern grid Geography of India, Energy Resources, p.22.
• Central & Western Lifelines: The Mahi Project (Mahi River) and the Tawa Project (a tributary of the Narmada) are essential for turning the semi-arid stretches of Madhya Pradesh and Gujarat into fertile belts Geography of India, Energy Resources, p.23.
• Southern Pioneers: The Shivasamudram Project (1902) on the Kaveri River is historically significant as one of Asia's first major HEP projects, originally built to power the Kolar Gold Mines Geography of India, Energy Resources, p.23.

Project	River	Primary Benefits
Tehri	Bhagirathi	Hydropower (1,000 MW), Irrigation, Drinking Water
Mayurakshi	Mayurakshi (Hugli tributary)	Irrigation (3 lakh hectares), Electricity for West Bengal/Jharkhand
Rihand	Rihand (Son tributary)	Flood control in Son valley, Tourism, Soil erosion control

Sources: Geography of India, Regional Development and Planning, p.66; Geography of India, Energy Resources, p.22; Geography of India, Energy Resources, p.23

4. Hydropower Potential and Energy Security (intermediate)

To understand India's energy security, we must look toward the 'water towers' of the north. Hydropower is a critical pillar of energy security because, unlike thermal power, it is renewable, produces no direct carbon emissions, and can be switched on or off almost instantly to meet peak demand. India’s hydropower potential is disproportionately concentrated in the Himalayan region due to its unique drainage system. The Himalayan rivers, categorized into the Indus, Ganga, and Brahmaputra systems, are mostly perennial—fed by both monsoon rains and glacier melt—ensuring a steady flow of water year-round Geography of India, Majid Husain, The Drainage System of India, p.8.

The true 'secret' to this potential lies in a concept called antecedent drainage. Major rivers like the Indus, Satluj, and Alaknanda are older than the mountains themselves. As the Himalayas rose, these rivers maintained their paths by cutting deep, narrow gorges across the mountain ranges Geography of India, Majid Husain, The Drainage System of India, p.6. These deep V-shaped valleys provide the perfect natural architecture for high-head dams. For instance, the Tehri Hydropower Complex, one of India's most significant energy projects, is strategically located on the Bhagirathi River in Uttarakhand. By harnessing the confluence of the Bhagirathi and Bhilaganga, this project provides 1,000 MW of capacity, reinforcing the grid's stability Geography of India, Majid Husain, Energy Resources, p.8.9.

While the potential is vast, energy security must be balanced with ecological security. The very features that make the Himalayas ideal for power—steep gradients and young, fragile geology—also make them prone to landslides and seismic activity. This is why projects like the Tanakpur Hydroelectric Project on the Sharda (Kali) river are managed by specialized entities like the NHPC to ensure technical and environmental viability Geography of India, Majid Husain, The Drainage System of India, p.15. Comparing the two major river zones helps us see why the North is so vital for power:

Feature	Himalayan Rivers	Peninsular Rivers
Flow Regime	Perennial (Glacier + Rain)	Seasonal (Rain-fed)
Topography	Deep gorges (High Head)	Broad valleys (Lower Head)
Energy Role	Baseload and Peaking power	Mostly seasonal/irrigation focus

Sources: Geography of India ,Majid Husain, (McGrawHill 9th ed.), The Drainage System of India, p.6, 8, 15; Geography of India ,Majid Husain, (McGrawHill 9th ed.), Energy Resources, p.Table 8.9

5. Environmental Impact and Seismicity of Himalayan Dams (exam-level)

The Himalayas, as Young Fold Mountains, represent one of the most tectonically volatile regions on Earth. Building mega-structures like the Tehri Dam—the highest and tallest dam in India—presents a unique set of challenges. Located on the Bhagirathi River just below its confluence with the Bhilaganga, the Tehri project generates 1,000 MW of hydroelectricity, yet it sits within a high-risk seismic zone Geography of India, Energy Resources, p.23. The primary geological concern is the disturbance of isostatic equilibrium. Because these mountains are still rising and moving due to the collision of the Indian and Eurasian plates, the massive weight of water stored in large reservoirs can exert downward pressure that triggers Reservoir Induced Seismicity (RIS), potentially leading to earthquakes in an already fragile landscape Geography of India, Contemporary Issues, p.33.

Beyond the immediate weight of the water, geologists are deeply concerned about the Central Himalayan seismic gap. This refers to a 500 km stretch in the northwest Himalayas that hasn't experienced a major earthquake in over 200–500 years Physical Geography by PMF IAS, Earthquakes, p.188. In seismology, a 'gap' is not a safe zone; rather, it is a region where tectonic strain is building up and could eventually be released in one massive, catastrophic event. Constructing large dams in or near such gaps is a subject of intense environmental and safety debate.

The environmental impact extends beyond seismicity. These projects often lead to the submergence of pristine forests and the displacement of local communities, sparking significant social movements. While the Narmada Bachao Andolan is perhaps the most famous anti-dam movement in India, the Tehri project also faced long-standing opposition due to its potential impact on the ecology of the Ganga's headwaters Contemporary World Politics, Environment and Natural Resources, p.92. Today, India is divided into five seismic damage risk zones, with much of the Himalayan belt falling into the highest-risk categories (Zones IV and V), making the engineering and environmental clearance of these dams a critical national priority Environment and Ecology, Natural Hazards and Disaster Management, p.23.

Sources: Geography of India, Energy Resources, p.23; Geography of India, Contemporary Issues, p.33; Physical Geography by PMF IAS, Earthquakes, p.188; Contemporary World Politics, Environment and Natural Resources, p.92; Environment and Ecology, Natural Hazards and Disaster Management, p.23

6. Geography of Uttarakhand Rivers: The Panch Prayag (intermediate)

In the high-altitude landscape of Uttarakhand, the Alaknanda River serves as a master stream, originating from the Satopanth Glacier. As it descends toward the plains, it meets five distinct tributaries at sacred confluences known as the Panch Prayag. Understanding these confluences is vital because they define the spiritual and physical geography of the Ganga's headwaters. The Alaknanda is the constant factor in all five meetings, growing in volume and power at each step Geography of India, Majid Husain, Chapter 3, p.12.

The journey begins at Vishnu Prayag, where the Alaknanda meets the Dhauli Ganga (sourced from the Mana Glacier). Moving downstream, we reach Nand Prayag, where the Nandakini (from Trishul Glacier) joins the flow. The third confluence is Karan Prayag, where the Pindari River, flowing from the Pindari Glacier, merges with the Alaknanda. These first three confluences occur along the eastern and northern stretches of the Garhwal region.

The final two confluences are perhaps the most famous. At Rudra Prayag, the Alaknanda meets the Mandakini (also known as Kali-Ganga), which descends from the Chorabari Glacier near Kedarnath. Finally, the journey culminates at Dev Prayag. Here, the Alaknanda meets the Bhagirathi, which originates from the Gaumukh of the Gangotri Glacier INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT), Chapter 3, p.25. It is only after this final confluence at Dev Prayag that the river officially takes the name Ganga before descending to the plains at Haridwar.

Prayag (Confluence)	Master River	Joining Tributary	Source of Tributary
Vishnu Prayag	Alaknanda	Dhauli Ganga	Mana Glacier
Nand Prayag	Alaknanda	Nandakini	Trishul Glacier
Karan Prayag	Alaknanda	Pindari River	Pindari Glacier
Rudra Prayag	Alaknanda	Mandakini	Chorabari Glacier
Dev Prayag	Alaknanda	Bhagirathi	Gaumukh (Gangotri)

Sources: Geography of India, Majid Husain, Chapter 3: The Drainage System of India, p.12; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT), Chapter 3: Drainage System, p.25

7. The Tehri Hydropower Complex: Specifics (exam-level)

The Tehri Hydropower Complex is a marvel of modern engineering and a focal point of India's energy infrastructure. Located in the Tehri Garhwal district of Uttarakhand, this multipurpose project is primarily situated on the Bhagirathi River, which is one of the two main headstreams of the Ganga. Specifically, the dam was constructed just downstream of the confluence of the Bhagirathi and the Bhilaganga rivers Geography of India, Energy Resources, p.23. It is significant to remember that while the Ganga is formed at Devprayag (where the Alaknanda meets the Bhagirathi), the Tehri project sits further upstream on the Bhagirathi branch Geography of India, The Drainage System of India, p.11. Technically, the Tehri Dam holds the distinction of being the highest and tallest dam in India. The project was originally conceived in 1972 and began construction in 1975 with significant Soviet (Russian) technical and economic assistance Geography of India, Energy Resources, p.23. It serves a dual purpose: generating a massive 1,000 MW of hydroelectricity and providing irrigation to approximately 2.74 lakh hectares of land across Uttarakhand and Western Uttar Pradesh Environment and Ecology, Distribution of World Natural Resources, p.22. However, the project has been a subject of intense geographic and environmental debate. Because it is located in the Central Himalayan Seismic Gap, a highly earthquake-prone region, experts have raised serious concerns about its structural safety and the potential ecological impact on the fragile Himalayan ecosystem Geography of India, Energy Resources, p.23. For your UPSC preparation, it is vital to view Tehri not just as a power plant, but as a case study in the trade-off between developmental needs and environmental conservation.

Sources: Geography of India, Energy Resources, p.23; Environment and Ecology, Distribution of World Natural Resources, p.22; Geography of India, The Drainage System of India, p.11

8. Solving the Original PYQ (exam-level)

Now that you have mastered the Himalayan River Systems and the Ganga's drainage basin, this question tests your ability to pinpoint major infrastructure projects within those networks. The Tehri Hydropower Complex is a landmark project that serves as a prime example of a multipurpose river valley project. To solve this, you must recall the specific headstream of the Ganga where this record-breaking dam is situated. As you learned, the Ganga begins its journey as the Bhagirathi, and it is precisely on this high-velocity, glacier-fed stream that the dam was constructed, specifically just below its confluence with the Bhilaganga river.

To arrive at the correct answer, think like a geographer: the Tehri project is located in the Tehri Garhwal district of Uttarakhand. Among the options provided, Bhagirathi (B) is the primary river channel that hosts this 1,000 MW facility. When navigating such questions, always look for the principal stream associated with the project's basin. As noted in Geography of India by Majid Husain, this siting is strategic, utilizing the steep gradient of the Bhagirathi for maximum hydroelectric potential before it reaches the plains.

UPSC often uses geographical proximity as a trap. Options (A), (C), and (D)—the Alakananda, Dhauliganga, and Mandakini—are all vital tributaries within the same greater Ganga system in Uttarakhand. While these rivers host their own hydroelectric projects (such as the Tapovan Vishnugad on the Dhauliganga), they flow through different valleys and meet at various Prayags (confluences). Distinguishing between these specific tributaries is essential; remember that the Tehri Dam is exclusively linked to the Bhagirathi river before it joins the Alakananda at the famous Devprayag confluence.