For the last century or so, governments have been keen on building dams. Nowadays, about half the world’s rivers have at least one large dam, which is often an emblem of national pride. No doubt, it is fruitful to store water in order to produce energy, to irrigate land, to reserve running water. However, is building dams a greener way to generate energy than burning coal, oil or gas? In my opinion, that is a controversial point, because the overall costs of dams for both people and nature have never been considered fully. I personally think that at present dams exercise mostly a negative effect on the ecosystem.
The building of dams is often destructive. Usually, it is necessary to cut down forests in areas to be flooded. That is sure to increase the emissions of greenhouse gases to the atmosphere. Furthermore, water in dams is covered with vegetation. As it rots, it emits carbon dioxide and methane, contributing to the greenhouse effect. For example, in 1998 in Brazil the study of the hydropower project was performed. The findings have shown that Turcurui dam (2,600 km²) emitted 76 tones of methane per km² and 3,808 tones of CO2 each year.
There are other problems too. Some large dams pollute rivers, change the water temperature, thus endangering the survival of plants, fish and animals. Besides, dams may serve as a place to live for mosquitoes and diseases that they spread. Blocked rivers break up the migration and breeding of fish. This leads to the fact that some species are likely to become extinct.
Nevertheless, dams make some contributions: environment friendly electricity, reservoirs of running water, irrigation of the land. But on the other hand projects of building dams have often proved unprofitable. They are expensive to build and to keep, occur to be slow to deliver energy or water. To crown it all, sometimes the decision to build a dam is made for political reasons – to create jobs, or to benefit a particular group.
Obviously, those advantages and disadvantages vary from one dam to another. I conceive that we need to improve the way dams are built and it depends on us whether they will become a future failure or a future great benefit for humanity.