Introduction

Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator.Less common variations make use of water's kinetic energy or undammed sources such as tidal power.Hydroelectricity is a renewable energy source..
For more information about the topic Hydroelectricity, see the following related articles:

Power station — A power station or power plant is a facility for the generation of electric power. At the centre of nearly all power stations is a generator.

Water turbine — A water turbine is a rotary engine that takes energy from moving water. Water turbines were developed in the nineteenth century and were widely used.

Distributed generation — Distributed generation is a new trend in the generation of heat and electrical power. The concept permits the "consumer", who is generating heat.

Electric power — Electric power is the amount of work done by an electric current in a unit time. When a current flows in a circuit with resistance, it does work.

Hydro energy is a Renewable source of energy that can be replenished on a time scale appropriate to human use. Solar energy for growing plants for food is renewable because light flows continuously from the sun, and plants can be reproduced on a time scale suitable for human needs. Coal is produced continually in some geologic formations, but the time scale is on the order of hundreds of thousands of years. Accordingly, coal is considered a nonrenewable energy.

The Department of Energy categorizes sources of nonrenewable energy production as fossil fuels, nuclear electric, and pumped hydroelectric. Sources of renewable energy are delineated as conventional hydroelectric, geothermal, biofuel, solar, and wind. Conventional hydroelectricity and energy from biofuels are considered mature sources of renewable energy; the remaining types are thought of as emerging.

More electric energy is invested in pumping water for pumped storage hydroelectricity than is produced by the electric generators. Therefore, the net production of electricity from pumped hydro sources is slightly negative and does not appear on the chart inFigure 1. A breakdown of the 9.57 percent contribution from renewable sources is shown in Figure 2. The great bulk of the energy produced from renewable sources is from biofuels and conventional hydroelectric systems, both of which are considered mature.

Nonrenewable energy such as coal, petroleum, and natural gas are vast but not inexhaustible. A nonrenewable resource can be preserved if it can be replaced with a renewable one. This is the prime attraction of renewable energy. Sometimes a renewable resource offers an environmental advantage. If a house heated by burning fuel oil could instead use a solar heating system, then products from burning that might contribute to environmental problems would not be released into the atmosphere. On the other hand, damming a river to make a reservoir for a hydroelectric power plant might inflict damage to the environs by destroying plant and animal habitat.

Most use of renewable energy involves the sun. Solar energy is converted to thermal energy for space heating, heating hot water for domestic use and, to some extent, for generating electricity. A photovoltaic cell, which functions like a battery, converts solar energy directly to electric energy. Biomass energy has its origin in plants grown with the help of solar radiation. Wind energy is due to unequal heating of Earth's surface by the sun. A hydroelectric plant converts the gravitational energy of water into electricity, but the mechanism that replenishes the water is powered by the sun. Roughly, 95 percent of all renewable energy is solar in origin. The remainder is from geothermal energy. Tidal energy, having its origin mainly in the gravitational force between Earth and Earth's moon, is used in some parts of the world (France, for example), but is yet to be exploited in the United States.

Famous Hydro project - James Bay Project

The James Bay Project, located in the Canadian province of Quebec, is testimony to the engineering skills of Hydro Quebec. Taken up in 1972, the phase I of the project consisting of three generating stations added more than 10000 MW of installed capacity to Quebec's power grid by 1985. The second phase of the project, which involves construction of six more generating stations, is to add another 5000 MW of capacity. Of this, four have already been commissioned. (The fifth, Laforge-2 is scheduled to be completed next year while the sixth, Eastmain 1, is on hold.) The La Grande 2 generating station, completed under phase I, is one of the World's largest power stations in terms of installed capacity (5328 MW).

The project makes use of the 548-metre drop between the source and mouth of the La Grande River and the average flow of 1700 cubic metres per second. The flow was doubled by diverting the waters of two adjacent rivers, Eastmain and Opinaca, into La Grande.

At each site chosen for generating stations, the dam raised the water level immediately upstream of the powerhouse. The profile of the La Grande River is thus transformed into a very long multi level waterfall. The scale of the dams is monumental. The phase I of the project alone involved construction of 215 dams and dikes-- the longest stretches 4.3 km and the highest reaches 162 metres. The eight reservoirs of both the phases together cover 15873 square km. The land surface flooded by the reservoirs (excluding the areas of water bodies that originally existed) was 11505 square km. The impact of creating such large reservoirs on the water regime and land is obviously tremendous. Some environmental impacts of the project like the destruction of the shorelines could be predicted while those like mercury pollution could not be anticipated. Since the project area is relatively flat, damming the rivers draining those lands was sure to flood extensive areas of river, lake and forest habitat. The type of forests submerged by the James Bay Project is entirely different from tropical forests submerged by some of the reservoirs in India. The taiga is only 5000 to 9000 years old and its biodiversity is very limited compared to tropical forests. Yet it supports at least 39 mammals. The area is also habitat for more than a dozen species of birds and ten to 20 species of fishes.

Of the submerged area, the most biologically productive and diverse were the narrow strips of shrub vegetation along the banks of the rivers. These supported a number of species such as the ptarmigan, rabbits, birds, beaver, muskrat and moose. The La Grande dams inundated thousands of kilometres of such shoreline habitat. These habitats would not be reestablished owing to unnatural fluctuations of water level in the reservoirs that make it difficult for plants to colonise the banks.

These fluctuations are of a wide range and they reverse the natural patterns. The natural lakes and rivers would be at their highest levels during the spring thaw. On the other hand, reservoirs would be at their lowest level in spring owing to higher generation during winter to meet the demand for heating of interiors of houses and other buildings. These unnatural fluctuations could sound the death knell for species like beaver, which builds its underground shelter on the riverbanks. (The beaver's shelter has an exit into the river below the water level. When the top layers of the river are frozen, it can still reach the waters below for seeking food. If the water level goes down, its exit will be blocked with frozen ice. If the level goes up, its hole would be flooded.)

Another impact of the reservoirs is the truncation of trees by the action of lake ice. The water freezes around partially submerged trees. When the water level drops, the ice sticks to the trunks. The trunks eventually break because of the weight of the ice. This produces huge quantities of debris which are blown by the winds to the shores. These ruin spawning beds, hinder plant growth and block passage for both fish and people.

The James Bay Project involved diversion of two rivers-- the Caniapiscau and Opinaca, into La Grande River. This reduced the water flows down stream of the diversion points. At the same time, the diversions increased the flow through the lakes and rivers of the Caniapiscau Laforge route and the Opinaca Boyd Sakami route through which water is transferred to La Grande. Flow also increased on the lower stretches of the La Grande River. This speeded up the natural process of erosion. As the increased flow was sure to erode the island of Fort George at the mouth of the river, the Cree living there had to be shifted to a new settlement.

The project affected the Crees in a variety of ways. Apart from the loss of their island home, they lost trap lines and fishing zones and faced difficulties in navigating the rivers and obtaining drinking water supplies. While shortage of water in rivers whose flows had been diverted caused difficulties in moving boats up the river, floating wood debris made navigation risky in the reservoirs. Difficulties arose in fishing downstream of the La Grande River because of increased flows and the instability and unnaturally early break up of ice in spring.

The high way built to facilitate the movement of construction materials had profound impact on the Cree community besides the settlement of the Fort George band in permanent houses at Chisasibi. (The high way was initially considered a route that would open Quebec mid north territory for the development of resources, particularly mining, forestry and tourism. The Quebec Government had even set up a separate Corporation for the development of the region. However, with changes in mining produce prices and the difficulty in making forestry operations profitable in the territory, hydroelectric developments soon became the only priority.) The project also accelerated the cross-cultural transplant of life styles and consumption patterns of whites among the Crees. Their life became sedentary.

Hydro Quebec undertook certain mitigative measures to offset the negative impacts of its project on the environment and people. Weirs were built on Eastmain and Opinaca rivers to maintain water levels close to those observed under natural conditions. Most of the quarries, sand pits and construction sites and camps were constructed in areas to be flooded by the reservoirs. Once the work was finished, the contractors took up a major clean up of the location, banked overly steep slopes and loosened the soil to encourage regrowth of vegetation. This was followed by reforestation with trees suited for the territory.

The developers provided compensations running into more than $500 millions to the Crees and Inuits affected by the project under the James Bay and Northern Quebec Agreement and its complimentary agreements. These included compensation paid by the Federal Government for the extinguishment of aboriginal title on the land and royalties.