brahmaputra · Chenab · Ganga · Himachal Pradesh · Himalayas

How do dams affect a river?

That sounds like a rather innocent question and I was asked to write an article, addressing it. But before we go into that, let us try and understand a few things. Firstly, what is a River? Let us first try and understand that.

There is no single definition of this complex entity. For every definition, there is something more a river does.

Take the example of the one of the most complex rivers of all, the Ganga that we think we know. Before being a religious entity cultural icon, etc Ganga is, first & foremost, a River. A perennially flowing river like Ganga flows all the time. But that flow is not constant. It changes from day to night, from one day to another, from one season to another, one year to another, from one place to another.

And then, the Ganga that we know is not only a single river but a collection of rivers. So Yamuna, Bhagirathi, Alaknanda, Mandakini, Dhauliganga, Pinder, Ramganga, Kali, Tons, Gomti, Ghaghra, Sone, Gandak, Budhi Gandak, Kosi & Mahananda are some of the major tributaries that directly meet Ganga. Each of them is a river in its own right.

The Ganga Brahmaputra Basin Photo from: Wikimedia Commons
The Ganga Brahmaputra Basin Photo from: Wikimedia Commons

Take Yamuna for example. Some of its major direct tributaries include: Tons, Giri, Som, Sahibi, Hindon, Chambal, Sind, Betwa & Ken, each of them are again significantly big rivers.

Take Chambal, some of the major direct tributaries of Chambal include: Parbati, Kali Sindh (Lakhundar, Ahu, Parwan are some of the tributaries of Kali Sindh, Newaj is one of the tributaries of Parwan, Dudhi is one of the tributaries of Newaj), Banas, Ider, Retam, Sau, Kshipra, Chhoti Kali Sindh, Cham, Siwana, Kural: each of which is a river by its own right.

Take Parbati: some of the major tributaries of Parbati include: Papnaus Ajnal, Sewan Paru, Utawali, Paraparwa, Mawal, Tem, Bhader, Gochi, Gaumukh, Sunk, Negri, Chopan, Uproni, Duhral, Andheri, Beram, Kosam, Ahelil and Sukni. These are all rivers too!

We can go on like this much longer. But such is a vast network of rivers that we call Ganga.


Secondly what flows in a river is not just water, though most governments, official agencies & engineers see the rivers as channels of water. Flowing water is surely a major visible defining component of a river. But even a canal or a pipeline can claim that. But unlike a canal or pipeline, a river carries dissolved matter, suspended matter, bed load, microorganisms, many levels of aquatic flora and fauna.

Thirdly, a river is a connected entity. It is connected with upstream and downstream river, biodiversity & landmass, the terrestrial land & life, underground geology and groundwater aquifers and is also connected with the floodplain. Perennial rivers like Ganga meet the sea forming a delta and this connection is vital for the river and as well as the sea. The connections are so strong that a river provides a report card about what is happening upstream and downstream, if read carefully.

From: The River continuum Concept. Species in India will be different, but this represents how biological entitites in a river are linked to each other through a number of processes including nutrient spiralling
From: The River continuum Concept. Species in India will be different, but this represents how biological entitites in a river are linked to each other through a number of processes including nutrient spiralling

This is admittedly a partial description of a river, limited by the constraints of an article or blog. This is also a bit simplistic description of how humans deal with rivers, since there are exceptions. But this provides a broad direction of our journey with the rivers.

from :
from :

Apart from its many functions like ecological, hydrological, geomorphological ones, a river is also connected with the human society along the banks. The connection with human societies has been as long as the humans have existed. This connection is not really necessary for the river to survive, but we cannot say the same about human survival. Humans cannot survive without the rivers, though is doubtful if the human society understands or even acknowledges that reality.

More importantly, till about a century ago, our interaction with the rivers did not endanger the existence of the rivers themselves. But what we have been doing in last century has created existential threat for rivers. This threat comes in the form of big dams, diversions, chemical pollution from agriculture and industries, large dose of sewage pollution at major urban centers, encroachment on floodplains, deforestation, unsustainable groundwater use, riverfront developments, embankments, and climate change.

What humans have done to the rivers in last century can possibly be described as Terraforming (one of the grandest concepts in science fiction in which “advanced” societies reshape entire planets to suit their needs). Or what some geologists describe as Anthropocene, meaning a new geological age of humans to suggest that humans are now a planet transforming force.

It seems humans have stopped valuing the rivers as they exist in nature and decided that they can stop, bend, tunnel, channelise, divert, encroach, pollute the rivers. So when we build a dam, we do not put any value to the destruction of river & destruction of the services provided by a river that entails in the process of building the dam.

But let us get back to Rivers & what dams do to them. A river, by definition, must flow freely. A dam stops the free flow of river, and impacts the river in the most fundamental ways. In India when we construct a dam (e.g. Tehri), a hydropower project (e.g. 400 MW Vishnuprayag project on Alaknanda in Chamoli district in Uttarakhand) or diversion (Lower Ganga – Bhim Goda at Haridwar, Middle Ganga – Bijnor and Upper Ganga-Narora barrages), we do not have to leave any water for the downstream stretch of river. So complete drying up of the rivers for most of the dry months by these structures is the first direct impact of these structures on the river. To put it mildly, that action practically kills the river. Upstream of the dam too, the river gets killed, for immediate upstream there is stagnant water and further upstream, the river has lost its connections with the downstream river!

Dry Baspa River downstream Baspa II Dam, Himachal Pradesh
Dry Baspa River downstream Baspa II Dam, Himachal Pradesh Photo: SANDRP Partners

This is because these structures not only stop the flow of water to the downstream areas, they also stop flow of everything else that was flowing in the river: the silt, the nutrients, the sand, the organisms, the flora, fauna, and severe every one of the connections of rivers we described earlier

And imagine when a river has to face such death every few kilometers in its journey!

Density of dams in the Upper Ganga Basin Map by SANDRP
Density of dams in the Upper Ganga Basin Map by SANDRP


That is not all. As the river continues its journey, if the tributaries are flowing reasonably freely, there is some chance for the river to recover some of its defining characteristics. But we have dammed most major tributaries too.

To top it, we also have other elements that help kill the river, like pollution, encroachment, abstraction, etc, as described earlier.

And remember just about a century back Ganga and other rivers were not in such a bad shape. This is an achievement of less than 100 years.

Chandra Basin in Himachal Pradesh depicted by Nicholas Roerich in 1932. The same Chenab Basin now witnesses one of the highest dam densities in Himalayas. From: WikiArt
Chandra Basin in Himachal Pradesh depicted by Nicholas Roerich in 1932. The same Chenab Basin now witnesses one of the highest dam densities in Himalayas. From: WikiArt

Some people will read in this a plea to go back by those 100 years. That is not possible, and we all know that. But there are other ways to deal with the rivers. Human society can take what is needed for the society, without destroying the river.

This is true of Ganga, as any other River!

Himanshu Thakkar (,


This is 200th post from SANDRP! We always look forward to your suggestions and comments for improvement.

Our 100th Blog on River Conversations:



7 thoughts on “How do dams affect a river?

  1. Thank you for this post. Far from being simplistic, it reveals just how fundamentally important rivers are to humanity and how we have set about wreaking havoc in the name of development. I am reminded of Justice Oliver Wendell Holmes’ judgment in New Jersey v. New York, 283 U.S. 336, 343 (1931): “A river is not just an amenity, it is a treasure.”

    Liked by 1 person

    1. Dear Ahmad Rafay Alam Saab,

      Many thanks for your very encouraging words. Yes, Justice Oliver Wendell Holmes has famously said this about rivers. Your comment and post on twitter will greatly help spread the word about this blog post. Do let us know if you have other comments.

      Himanshu Thakkar


  2. Excellent piece.
    Every river and water body should be preserved as national heritage.
    It is extraordinary that only built structures are considered national heritage.


  3. It is said that after construction of Hirakud dam across Mahanadi, the flood devastation has rather increased than to control flood.The nos of flood & its devastation are more after construction of Hirakud dam .


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