What are Hydroelectric Dams?

Image source: Shutterstock / Constantineandrosoff

A dam is a support structure built over a river to stop or regulate its flow and raise the water level. Once a dam is built, water collects behind it to form a lake or reservoir. It therefore also includes retention structures for a large or small backwater body.

While dams are built to stop flooding and make shipping easier, they can also be used to generate electricity, and these are known as hydroelectric plants. Such a structure is an essential part of a hydropower project.


The construction of dams is a hard and skilled work that begins by temporarily diverting the flow of water. Then the area of ​​the river bed that will serve as the foundation for construction is prepared for construction, making sure that the rocky or sedimentary bed is strong enough to support the dam. The area on both sides can also be reinforced. Then a concrete block formation is built. Once it is high enough, the water is poured in under strict control and careful supervision. Finally, there are additional operational structures.

How it works

Dams are the highly visible part of a hydropower plant that stores water at great heights. When this water is released, it flows down by gravity and the potential energy is converted into kinetic energy. The height of the water level and the flow rate of the water determine the power output. The water flow is regulated by a gate or a blind, which in turn is determined by the electricity demand. The water flows through a series of channels or pressure pipes that guide and regulate the steepness of the fall to optimize the efficiency of the dam.

The water eventually flows through a hydraulic turbine and then into a drain or outlet stream at the bottom of the dam to flow back into the river.

Hydro power is generated by the controlled flow of water through the turbine, a device whose shaft is connected to a generator that contains metal coils surrounded by magnets. When the water rotates the turbine shaft, the magnets rotate around the metal coils, resulting in electromagnetic induction, a phenomenon that creates electrical energy. In this way, the potential energy of the stored water is converted into kinetic energy as it flows through the pressure pipe and then into mechanical energy in the rotating turbine shaft, which in turn is converted into electrical energy.

The energy requirement varies over the course of the day. One advantage of hydropower plants is that they can adapt their output to peak electricity demand for short periods of time by integrating pumped storage. The water flowing through the turbine is pumped to a storage basin higher up above the turbine using excess electricity generated during periods of low consumer demand. When there is a peak demand for electricity, it is released back into the undercurrent in order to generate more electricity. In this way the reservoir acts like a kind of battery.


Hydropower plants can be put into operation quickly. Its performance can be easily adjusted. Your operations will remain efficient for both short and long periods of time. The construction costs for small or medium-sized dams are low compared to other hydropower plants. A dam produces electricity without burning fossil fuels and is therefore considered a source of clean energy.


Hydropower plants come in different sizes:

  • Large – A dam with a capacity of over 30 MW is a large project.
  • Small – A hydroelectric plant with a capacity of 10 MW or less.
  • Micro – A micro hydroelectric power plant generates up to 100 KW of electricity, for example for a family house, a ranch or a village.


Dams have some negative effects on the environment. For example, many species of fish cannot migrate to spawn if their rivers are blocked by dams. In the USA alone, some salmon populations have fallen from over 15 million to a few million after the dam was built.

Dams and reservoirs also change the natural temperature, the chemical composition, the type of current and the silt loads in the river water, which affects life in the river and its banks.

Dams extend over hundreds or millions of hectares of agricultural land or land or archaeological sites populated by large and productive populations.

The human cost of dam construction includes these physical changes, relocations, and other far-reaching consequences.

Concrete and other materials used in dam construction come from fossil fuel burning, but these one-off environmental costs are believed to be offset by the availability of clean energy over a long period of 50 to 100 years.

Sometimes reservoirs serve as a source of greenhouse gases such as carbon dioxide and methane, which can have a significant impact due to the large amount produced. However, scientists have devised means to use this methane to generate more electricity, which can increase power output while minimizing environmental costs.


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