大学英语-习题及答案-大学英语Ⅰ-Unit 7 floodamp;amp;Fire prevention.docVIP

PAGE  PAGE 7 Flood Albert Rango Flood is a body of water that covers normally dry land. Most floods are harmful. They may destroy homes and other property and even carry off the topsoil, leaving the land barren. Sudden and violent floods, which leave people little time to prepare, may bring huge losses. Rivers, lakes, or seas may flood the land. River floods are more common, though lake and seacoast floods can be more serious. However, sometimes floods may be helpful. For example, the yearly floods of the Nile River built up the plains of Egypt and made the Nile Valley one of the most fertile regions in the world. These floods brought fertile soil from lands far to the south and deposited the soil on the Egyptian plains. River floods. Most rivers overflow their normal channels about once every two years. When a river overflows land where people live, it causes a flood. When a river overflows land where people do not live, it is said to be in flood. Common causes of river floods include too much rain at one time and the sudden melting of snow and ice. Under such conditions, rivers may receive more than 10 times as much water as their beds can hold. Heavy rains, sometimes from thunderstorms, can produce flash floods if small rivers or streams rise suddenly and overflow. Flash floods occur chiefly in mountainous areas and do not allow much time for people to be warned of danger. A flash flood at Rapid City, South Dakota, in 1972 killed 238 people along Rapid Creek. Minor causes of flooding include bridges, piers, filled land, sand bars, and other obstacles to river waters. The Huang He (Yellow River) in China is known for its tendency to overflow its banks. This river has been called Chinas sorrow because its floods cause such great destruction. Soil carried by the Huang He has been deposited in large amounts at the bottom of the river. As a result of the soil deposits, the riverbed has been raised, increasing the chances of flooding. The worst Huang He flo