Geography Reference
In-Depth Information
Figure 7-3:
Rivers may flow
through different
landscapes on
their journey to
the ocean.
When rivers empty into the sea, they disgorge eroded sediments that have been carried along. Where
coastal waters are fairly calm, these particles may be deposited at the rivers' mouths, and progress-
ively accumulate and form a delta, as shown in Figure 7-4. This landform is so-named because many
of them — most notably that of the Nile River — assume a roughly triangular shape reminiscent of
the Greek letter delta (∆).
Figure 7-4:
Deltas are
formed from sed-
iments deposited
at river mouths.
The floodplain: Land of promise and pitfalls
Floodplain
refers to flat lands beside rivers that are prone to flood when the waters over-
flow their banks. Their extent may vary from a few feet to many miles on either side of
the watercourse. The latter is common in the case of large rivers flowing through coastal
plains.
Floodplains often are characterized by rich, fertile soils (
alluvium
) that have been depos-
ited by past floods. For thousands of years, people have been attracted to these areas
due to their favorable prospects for good harvests. Indeed, the attraction is so great that
several alluvial regions — including the lower Nile, Ganges, Huang, and Yangtze (Chang)
Rivers — have long supported very high human-population densities. And therein lies
a major predicament: The alluvial lands that attract and nourish so many, may also be
the scenes of terrible flooding and uncountable drownings. For that reason, the Huang
(Yellow) River, which provides irrigation for millions of acres of cropland, is also called
“China's Sorrow.”
In modern times, engineering has sought to control (and ideally eliminate) flooding by
building high artificial levees (banks) intended to make rivers stay put. While these
