For example , the Three Gorges Dam on the Yangtze River in China is more than five times the size of the Hoover Dam ( U.S. ) , and creates a reservoir long to be used for flood control and hydro-power generation . Its construction required the loss of over a million people 's homes and their mass relocation , the loss of many valuable archaeological and cultural sites , as well as significant ecological change . During the 2010 China floods , the dam held back a what would have been a disastrous flood and the huge reservoir rose by 4 m ( 13 ft ) overnight
2010 China floods
2010 China floods
Dam