Really clean energy?

Hydroelectric power suggests, in our mind, the idea of a clean source of energy, that is eco-compatible and especially a source of energy that is renewable.  Actually, a large power plant  has  problems  in connection with the environmental impact, problems of an aesthetical nature, electromagnetic pollution and  overload of the ground.
Water intake decreases the amount of water in the streams and rivers downstream from the power plant and provokes disorders in the river ecosystems with severe damage for the fish- and naturalistic heritage. According to the law,   water intake must not exceed a percentage of the natural flow, and what is called the “ minimum vital flow” must be guaranteed, in order to protect  life and the ecosystems of the river or stream. Actually during the periods of draught, long stretches of the waterways become quite dry, with consequent damages to the environment. The negative effects are not only limited to parts of the river downstream of the power plants, but may be noted in the entire water supply network, a decrease in the flow rate of the waterways consequently leads to a greater concentration of the pollutants in the water and also in the underground water table that they supply water to.
With regard to the future development of hydroelectric power, in Italy, as in most of Europe, this type of resource has been almost completely exploited, i.e. the hydroelectric power plants have been built in almost all the locations where  there were ideal conditions to exploit the kinetic energy of water precipitating towards the valleys from the mountains. It is therefore difficult to increase the number and the power of the  existing park of hydroelectric power plants.  In other large regions of the world, this form of energy is available in large amounts,  and still has not been exploited.
It is the case of Africa, where as a result of the low consumption of energy per person and the low level of wellbeing,  this type of energy can become precious and important  to support the economic development of these populations .
A second limit of the hydroelectric power plants are the vast areas of territory that are often occupied and flooded  by very large dams,  which are built for the purpose of accumulating the water that is necessary to move the turbines constantly. It is therefore necessary to modify the original plan of the territory and the natural flow rate of the rivers and streams, which, in some cases, causes environmental impacts on the ecosystems and economic impacts on other agricultural or industrial activities.
Therefore  large hydroelectric plants with a reservoir require  opportune assessments with regard to the impact on the environment, in order to guarantee the absence of  interference with the natural environment. Underground hydroelectric power plants partly eliminate the aesthetical problem, however there is the problem of the disposal of the excavation materials, and these plants can influence underground water circulation.

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    Dam on the Sacramento River

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    Dam on the Colorado River

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