Undamming rivers is a rising trend. In the US, this has become a widespread movement, called a river restoration movement. Up to date, 1,185 dams have been removed and hundreds more are on the way. There are a couple of reasons listed: some dams have been there for more than 100 years, they are too old and facing major safety problems, some others are filled up by huge amount of sediments and turn out not very useful as designed, though their lifespans could be 100 years more. The Glen Canyon dam is just one example. However, the most intriguing reason is that people are having higher awareness on the value of ecosystem. They wish to somewhat recover the natural state of the rivers’ habitat, such as the Elwha’s. A good new, there has been some nice results.
I agree with this movement. I hope it will spread wider to developing countries, so dam removals would be considered even before they are built. Because, as I mentioned elsewhere, the option value, the value of the option to maintain future use, and the quasi-option value, which arising from expected new information from avoiding irreversible losses, are often higher than we think. So let us be cautious about changing the nature.