On which river in the Himalayas has the large Tehri Dam been constructed in Uttarakhand?

Introduction / Context:
Tehri Dam is one of the highest dams in India and an important multipurpose project providing hydroelectric power, irrigation water, and flood control. It is located in the Himalayan state of Uttarakhand. Many exam questions ask on which river this massive dam has been constructed to test knowledge of India's major river valley projects and their locations.

Given Data / Assumptions:

• The project in question is Tehri Dam in Uttarakhand.
• The options are Alakananda, Bhagirathi, Ganga main stem, and Hooghly.
• We assume the learner knows that several headstreams combine to form the Ganga.

Concept / Approach:
The Ganga in the Himalayas is formed by the confluence of different headstreams, mainly the Bhagirathi and the Alakananda. Tehri Dam is built on the Bhagirathi river near the town of New Tehri in Uttarakhand. While both Bhagirathi and Alakananda are important, it is specifically the Bhagirathi that is impounded by Tehri Dam. The Hooghly is a distributary of the Ganga in West Bengal, far from Uttarakhand. Referring simply to the Ganga main stem would be less precise than naming the correct headstream.

Step-by-Step Solution:
Step 1: Recall that Tehri Dam is located in the Garhwal region of Uttarakhand. Step 2: Remember that the major Himalayan headstreams of the Ganga include the Bhagirathi and the Alakananda rivers. Step 3: Identify that Tehri town lies on the Bhagirathi river, and the dam created a large reservoir by blocking this river. Step 4: Note that Alakananda has other projects, such as those near Srinagar and other hydel schemes, but not the Tehri Dam itself. Step 5: Recognise that the Hooghly flows in West Bengal and cannot be correct for a Himalayan project. Step 6: Conclude that the Bhagirathi river is the correct answer.

Verification / Alternative check:
Descriptions of Tehri Dam in geography texts and official project documents always specify that it is built on the Bhagirathi river. Maps of the project area show the dam site on this river, upstream of the eventual confluence with the Alakananda at Devprayag, where the Ganga in its main name begins. This clear mapping confirms that Bhagirathi is the correct river.

Why Other Options Are Wrong:

• Alakananda: An important headstream of the Ganga with several hydel projects, but Tehri Dam is not one of them.
• Ganga main stem: While the Bhagirathi is a headstream of the Ganga, the dam is specifically on the Bhagirathi segment before the confluence at Devprayag.
• Hooghly: A distributary of the Ganga in the plains of West Bengal, far from the Himalayan location of Tehri Dam.

Common Pitfalls:
A common mistake is to choose Alakananda simply because it is a well known Ganga headstream, or to select the generic term Ganga without realising that the question expects a precise headstream. To avoid this confusion, remember the key association: Tehri Dam plus Uttarakhand plus Bhagirathi equals the correct combination.

Final Answer:
Tehri Dam has been constructed on the Bhagirathi river in Uttarakhand.