Hydropower first started as early back as 100 B.C. when the Greeks and Romans used a waterwheel, which was vertical and placed a long a stream or river, for grinding corn with its gears. Running water in the stream would turn the wheel, therefore operating the mill. Milling was the main task performed with hydropower back then, and soon it traveled through Asia and the rest of Europe by 4 A.D.
As the waterwheel spread to different parts of the world, people began to try ideas to improve on it. Change in wheel orientation was one important development. The horizontal wheel laid on its side and the wheel turned from left to right. The vertical wheel stood up, turning from top to bottom. In the beginning, "millers mounted the wheel so that the center was above the water surface and the running water would turn the bottom of the wheel. Later, they would dip the wheel below water level in an "overshot" orientation." In the 18th century, John Smeaton tested both orientations and found that the overshot worked more efficiently. "In the next century, engineers perfected the waterwheel and found two improvements: curved paddles worked better and that the breasted position (where the center of the wheel lies on the water surface) made the wheel more efficient (Brit. p.334)." These developments helped people apply the waterwheel to more tasks, such as a mill where gears, shafts, and conveyors would not only grind grain but also transport the grain up, down, and sideways within a mill. In the 19th century, the water turbine slowly replaced the waterwheel due to its higher efficiency. However, waterwheels still exist throughout the world to this day.
Following the waterwheel came the water turbine, which used gravity to turn the wheel. James Francis perfected Samuel Howd's turbine by curving its blades, and today it is known as the Francis turbine. This was used for a long time in mills, but eventually steam engines took the turbines place as it's source of power. However, the Francis turbine would make a comeback as a different source of energy; hydropower.
In effort to control streams and rivers, people began to create dams much like those that a beaver makes. These structures were used to divert the water flow, or obstruct it. To store water in a reservoir, engineers constructed a gravity dam, whose weight would stop the river flow. They made these dams initially with soil and rock, but as time progressed, concrete and brick became more popular. This is because of to their ability to trap water without allowing any flow within them. At first, dams were made straight, but later they became curved to transfer the force of the water pressure to the land it gripped. The Hoover Dam is an example of this arched dam. Bracing the land on each side, it can withstand the tremendous force of the Colorado River"
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When the idea of creating electric energy from water arose, the turbine was back. In 1882, the world's first hydropower station in Wisconsin produced 12.5 kilowatts of power. In the 1930's, these stations developed dramatically. A hydropower plant was established at the Hoover Dam on the Colorado River in 1936, and it contained multiple Francis turbines (which were taken over by steam engines in mills) that produced 130,000 kilowatts of power. These stations provided electricity to major cities through high-voltage power lines. Countries all over the world have followed the lead of the United States by building stations and supplying their citizens with electricity.
As one can see, the transition of hydropower as a source of mechanical energy to electric took some time, but in the end has been worth it. With hydropower expanding throughout the world, governments and environmental organizations have been trying to find common ground on the pros and cons of using hydropower.
Information provided by http://web.mit.edu/STS001/www/Team16/history.html
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