Due to absence of smokestacks or radioactive waste, hydropower is often considered a clean source of power. But is it really? Lets find out.
First the environmental impacts
1) Habitat loss: The reservoir behind the dam submerges thousands of square kilometres of land which in most cases is undisturbed habitat for thousands of species.
2) Ecological disruption: Apart from the habitat loss, dams (both large scale and small scale ones) alter the ecology of the river. This includes obstructing the path of aquatic species who travel the course of the river (like salmon who travel upstream to lay eggs). Dams also lead to siltation behind them, which means that the river downstream is not as rich in nutrients as the river upstream, and this seriously affects the ecology of its delta.
3) Greenhouse gas emissions: Although its true that hydropower doesn't involve and direct greenhouse gas emissions, but they still contribute greenhouse gases to the atmosphere indirectly.
An article from New Scientist lays it out:
This is because large amounts of carbon tied up in trees and other plants are released when the reservoir is initially flooded and the plants rot. Then after this first pulse of decay, plant matter settling on the reservoir's bottom decomposes without oxygen, resulting in a build-up of dissolved methane. This is released into the atmosphere when water passes through the dam's turbines.
Seasonal changes in water depth mean there is a continuous supply of decaying material. In the dry season plants colonise the banks of the reservoir only to be engulfed when the water level rises. For shallow-shelving reservoirs these "drawdown" regions can account for several thousand square kilometres. In effect man-made reservoirs convert carbon dioxide in the atmosphere into methane.
And methane, dear friends, is 20 times more potent than carbon dioxide as a greenhouse gas!
In addition to this, the reservoir also submerges forest areas which over time would have absorbed carbon dioxide from the atmosphere, and this amount should be considered as emissions by the project.
Social impact
Everytime a large dam is constructed, it not only wildlife which loses its home, people too are displaced. An estimated 40-80 million people have been displaced from ancestral homes because of hydropower projects. Even if adequately compensated for the physical relocation, there unquantifiable disruptions to cultural patterns and traditions which can occur to the people all along the watercourse around the hydropower project. All of which is made worse when the power generated by the project is carried by transmission lines to places far away, with only a small amount of the electricity used locally.
As with the problems with habitat disruption and potential greenhouse gas emissions, the amount of the disruption to communities around the project goes up dramatically as the size of the project increases. This is why environmentalists and social rights activists advocate the construction of many small hydroprojects instead of one big one.
So do you still consider large scale hydropower projects a clean source of power? Take the poll below and/or let your opinion be known in the comments :)
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