The Chinese used waterwheels to begin a chain of cogs turning, which eventually moved a huge block of wood up and down to pulverise grain. Simpler water wheels placed in flowing rivers and streams were used to move water through pipes into fields. Hydroelectricity has been used since the late 1800s, and its technology was implemented on a grand scale during the Great Depression, when Franklin D. Roosevelt commissioned the Grand Coulee Dam on the Columbia River. This was hailed as one of the greatest achievements of the time, and the plant generated more than enough electricity to power its surrounding population and send more to power-hungry California far to the south. Hydroelectric power plants require the creation of huge dams along waterways.
Water flows into the dams and is only released over ledges or spillways.
The concentrated flow of rushing waters travels through turbines, usually more than once, and electricity is thus generated. Many conservationists warn that this apparently clean power source is in fact not at all environmentally sound. Damming rivers can cause a lot of harm to river ecosystems, not to mention the displacement of people living near the river. The negative impact of the co-called clean and renewable energy sources will be discussed in later articles. The purpose of the dam was both to control flooding, which had already killed over 300,000 people since 1900, and to help meet the country's huge demand for electricity.