Aral
Sea
One example of catastrophic
surface water drawdown is the Aral Sea, located in Central Asia
between Kazakhstan and Uzbekistan. The Aral Sea is fed by the Amu
Darya and the Syr Darya rivers. In the past 40 years, large amounts
of water have been taken from these rivers for irrigation of millions
of acres of cotton and rice crops in Soviet Central Asia. This water
withdrawal has caused the Aral Sea to shrink in size and water amount
by more than half. The level of the sea was lowered by 17 meters.
The Aral Sea went from being the fourth largest inland body of water
to being the eighth largest. More than 27,000 square kilometers
that were once covered with water became exposed.
source:
http://www.grida.no/aral/aralsea/english/arsea/arsea.htm
With the reduction in
the amount of water the salinity of the sea increased from 10% to
23% and higher. This salinity has had devastating effects on the
local fishing industry whose boats are now stranded miles inland
from the coast. In the areas where the water receded, dust made
of salt and chemicals from fertilizers and pesticides was left.
This toxic dust blew away and was scattered over hundreds of square
miles. In the areas where the sea once existed a new desert has
appeared.
Surce:
http://www.uni-bielefeld.de/biologie/Oekologie/aralsee.html
The
Yellow River
The Yellow River (also
called the Huang He) originates in the Qinghai Province and makes
its way more than 3,000 miles across China to the Yellow Sea. The
fertile area around the Yellow River is the cradle of Chinese civilization.
Millions of people rely on the river for agricultural, industrial,
and domestic uses. During the winter the river is small and silt-laden,
but during the summer it becomes swift and cause serious flooding.
Many areas in the arid western parts of China rely heavily on the
river to irrigate their crops. The river has many dams, to provide
water to people, for hydroelectric power, and also to prevent catastrophic
flooding.
Source:
http://www.kented.org.uk/ngfl/rivers/Feature%20Articles/huanghe.htm
Because
of dams and diversions of the river, in 1972 for the first time
in history the Yellow River failed to reach the sea. The problem
continues to grow worse as use continues to increase and more dams
are built upriver. In 1997 the mouth of the river was dry for over
200 days. Many of the river’s tributaries are now dry.
Source:
http://www.sfgate.com/cgi-bin/article.cgi?f=/chronicle/archive/2002/03/04/MN50621.DTL
The Yellow
River is not the only river in China that has this problem. Many
dams are built or are planned to be built on other major rivers
such as the Yangtze (or Chang). In 2000, China announced tht it
would build canals to divert water from the Yangtze to the Yellow
River. As water use continues to increase the amount of water in
these rivers will decrease.
The
Colorado River
In the
arid Southwest of the United States several large cities such as
Las Vegas and Phoenix have grown beyond the capacity of groundwater
resources to support them. Despite the arid climate there is enough
water for the growing populations, and you can find swimming pools,
green lawns, and decorative water fountains. The reason these cities
have had an adequate supply of water in the desert is the Colorado
River. The Colorado River provides water to nearly 25 million people
in Arizona, California, Colorado, Wyoming, Nevada, New Mexico and
Utah.
Uses
of Water in Colorado
Water
Use |
%
of total used |
Municipal |
4.4 |
Industrial |
1.0 |
Irrigation |
91.6 |
Livestock |
0.4 |
Other |
2.6 |
data
from: http://waterknowledge.colostate.edu/withdrawals.htm
The Colorado River originates in the mountains of Colorado and makes
it way across the Southwest U.S. and through Mexico to the Pacific
Ocean. Because of the large amounts of water drawn from the river
however, little water finds its way to the ocean. a treaty signed
in 1944 requires the U.S. to allow a certain amount of water to
reach Mexico, but almost all of this is used before it reaches the
ocean.
Source: http://www.kaibab.org/misc/gc_coriv.htm
The Colorado
River is the location of the largest dam in the United States, the
Hoover Dam, which was built in 1935. The river also has many other
dams, including the controversial Glen Canyon Dam which was completed
in 1963. These dams have altered the ecology of the Colorado River,
causing many fish species to die off. With the creation of these
dams large reservoirs are created, such as Lake Powell which is
behind the Glen Canyon Dam. The water in these reservoirs evaporates
more quickly than it would normally, causing reduced water levels
and high levels of salinity in the downstream river. Due to recent
dry conditions, Lake Powell is the lowest it has been in 30 years,
making the salinity problems worse.
Source: http://www.kaibab.org/misc/gc_coriv.htm