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 "China's 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
flood ever recorded occurred in 1887. Nearly a million people died in China after the river
overflowed its banks.
Three major rivers--the Brahmaputra, Ganges, and Meghna--flow through plains that cover most
of Bangladesh. These rivers overflow in periodic floods and deposit fertile soil along their banks.
But many of the floods cause great damage. In 1988, floodwaters covered most of Bangladesh,
killing about 1,600 people and leaving about 25 million temporarily homeless.
The Mississippi-Missouri river system and the rivers that flow into it, such as the Ohio, also
overflow at times. A greatly destructive flood occurred in 1937, when the Ohio and Mississippi
valleys were overrun by the rivers. This flood killed more than 135 people and left about a million
people homeless.
In 1993, heavy rains in the Midwest for about two months resulted in flooding along the upper
Mississippi and Missouri river systems. The floods caused about $15 billion worth of damage and
forced about 75,000 people from their homes. Heavy rain from a tropical storm caused rivers in
New York and Pennsylvania to overflow in 1972. The resulting floods destroyed or damaged
about $3 billion worth of property and left over 15,000 people without homes.
Seacoast floods. Most floods from the sea result from hurricanes or other powerful storms that
drive water against harbors and push waves far inland. In 1970, a cyclone and a large, destructive
wave called a tsunami in the Bay of Bengal, a part of the Indian Ocean, caused the greatest sea
flood disaster in history. Huge waves struck the coast of Bangladesh and killed about 266,000
people. The flood also destroyed the cattle, crops, and homes of millions of other victims.
In the Netherlands, the land lies partly below the level of the sea and faces the constant danger of
being flooded. The country is protected by its famous dikes, which wall off the sea. These dikes
have seldom failed in modern times.
In other places, there is danger from great tsunamis which come up suddenly and unexpectedly.
After the great flood of 1900, Galveston, Texas, built a sea wall. But the storms of 1913 went over
the wall. Earthquakes and volcanoes also produce tsunamis. During the Good Friday earthquake in
Alaska in 1964, tsunamis struck the Kodiak Islands and the southern coast of Alaska. The waves,
some as high as 35 feet (11 meters), killed 122 people, including 11 in California and 4 in Oregon.
Volcanic waves as high as 50 feet (15 meters) have struck Lisbon, Portugal; Messina, Sicily; and
the coast of Japan. In 1883, the volcano Krakatau in Sunda Strait, west of Java, erupted and raised
the surrounding water so high that one ship was carried 11/2 miles (2.4 kilometers) inland and was
left 39 feet (12 meters) above the sea. Some seacoast floods result from abnormally high tides.
Other floods. Storms and high winds also cause floods along lakeshores. Some floods occur when
the water of a lake moves suddenly from side to side in rhythm. Such a movement is called a
seiche.
The failure of artificial structures, such as dams, has caused a number of floods. In 1889, a dam
near Johnstown, Pennsylvania, burst. The resulting flood killed more than 2,000 people. At least
5,000 people died in India after a dam on the Machu River collapsed in 1979.
Flood control involves building dams to store water and channels to allow it to flow quickly to the
sea. It also involves building dikes, flood walls, hurricane barriers, and levees that help keep water
off the land.
Continuing floods in the Mississippi Valley and other river valleys caused Congress to adopt the
Flood Control Act of 1936. In 1938, Congress appropriated $376,700,000 for a five-year program
of building and keeping up reservoirs, levees, and flood walls. The engineering work along the
Mississippi by the U.S. Army Corps of Engineers stopped the floods of the upper Mississippi from
doing damage below Cairo, Illinois. Before then, the lower Mississippi had been one of the most
dangerous flood areas of the world.
In 1943, the rivers that flow into the Mississippi flooded badly. More than 12 million acres (5
million hectares) of farmland were covered by water, and more than 50,000 people had to leave
their homes. The Mississippi-Missouri river system has flooded several times since then. But the
flood-control system between Cairo and New Orleans has provided some protection against the
flooding.
Reducing flood losses. Engineers work not only to control floods, but also to reduce flood losses.
A program to decrease such losses includes regulations to control permanent construction on the
flood plain (land that gets flooded) and to make buildings waterproof. Other programs aim to help
flood victims by improving methods to warn and evacuate people from flood plains and to provide
better insurance and relief aid.
The U.S. Geological Survey and the army engineers identify and map flood hazard areas in the
United States. About 18,000 communities have used this information to set forth regulations for
flood plain management. Many of these regulations require that a small strip of land along a
waterway be left vacant. Such a strip of land is called a floodway. Numerous communities
establish a wider area along the floodway for use as farmland or parkland.
Permanent buildings can be located on a flood plain and withstand flood damage. The technique
of keeping water out of buildings is called flood-proofing. It involves raising buildings off the
ground or using waterproof construction materials.
The U.S. government and the Red Cross provide relief for flood victims. Flood insurance is
available in about 18,000 communities in a program administered by the U.S. government.
The National Weather Service has a network of 13 river forecast centers and 50 hydrologic service
areas that provide flood warnings. Meteorologists measure the height of rivers and the amount of
rain and snow to decide whether a flood may occur. They use radar to estimate how much rain or
snow will fall in the near future. The National Weather Service can provide enough warning to
greatly reduce loss of life and to lower property damage by as much as 15 percent.
New technologies have improved our ability to handle floods. For example, artificial satellites in
space carry instruments that can record where flooding is worst and help authorities determine
where relief work should be concentrated.