美国有很多的大坝_科普读物

    the purpose of all dams is to reduce or prevent flooding by controlling the water in a river.
    the united states society on dams lists many reasons why dams are important. it says they provide clean water to drink. they also provide water for industry and farming. they create lakes for fishing and other kinds of fun activities. dams also provide water to produce hydroelectric power (水力发出的电).
    naming the biggest dam in the united states is not easy. is it the tallest dam? the one that contains the most concrete material? or the one that produces the most electricity?
    if you ask an american to name the most famous dam in the country, he or she would probably say hoover dam. it is on the colorado river near las vegas, nevada. hoover dam was the tallest dam in the world when it was finished in 1936. until 1948, it was also the largest producer of hydroelectric power.
    but this is no longer true. the united states society on dams says the highest dam in the united states is the one on the feather river near oroville, california. the oroville dam is two hundred thirty-five meters high. it was completed in 1968 to provide electric power, drinking water and water for agriculture in central and southern california.
    the dam that produces the most hydroelectric power in the united states is the grand coulee dam in the state of washington. it controls flooding on the columbia river and is said to be the largest single producer of electricity in the country. it is the main source of electric power to the northwestern states. the grand coulee dam was completed in 1942. it is one of the largest concrete structures in the world.
    hoover dam is still at the top of the list of dams in one way. the building of the dam created lake mead, the largest man-made lake in america. people use lake mead for boating, swimming and other activities that would not be possible in that desert area.