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In
the last section, we saw that the degree of flooding is determined by
the amount of water that accumulates in an area, as well as the nature
of the land surface. As civilization has expanded, human beings have
altered the landscape in a number of ways. In the Western World, one of
the most significant changes has been covering the ground in asphalt and
concrete. Obviously, these surfaces are not the best sponges around:
Almost all rain that accumulates becomes runoff. In an industrialized
area without a good drainage system, it may not take much rain to cause
significant flooding.
People
haven't had much success with controlling flooding along coastlines.
Excessive water in these areas is particularly destructive to man-made
structures because of the erosion it causes. One method of controlling
this erosion is to build fences and walls where the water meets the
land. This keeps the power of the waves at bay, so they don't wear down
the beach. But the structures also interfere with the process of beach
formation. When you block the water from moving against the coast, the
ocean can't distribute sand and you don't get beautiful beaches.
The
same can be said for many inland areas. While a river may appear to us
to be a stable, unmovable feature of the landscape, it is really a
vibrant, dynamic entity. This is particularly true of big rivers, such
as the Mississippi in the United States and the Yangtze and Huang He in
China. Over time, these waterways expand, shift their path dramatically
and may even change the direction of flow. For this reason, the land
around the banks of a river is highly susceptible to flooding. Source: http://science.howstuffworks.com |
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