Environmental Engineering Reference
In-Depth Information
Pumping out more groundwater is not the an-
swer—groundwater is already being withdrawn faster
than it is replenished throughout much of California.
Quicker and cheaper solutions would be to improve
irrigation efficiency, stop growing water-thirsty crops
in a desert climate, and allow farmers to sell cities their
legal rights to withdraw certain amounts of water
from rivers.
CALIFORNIA
NEVADA
Shasta Lake
Oroville Dam and
Reservoir
Feather
R
iver
UTAH
Sacramento
River
Lake Tahoe
North Bay
Aqueduct
Sacramento
San Francisco
South Bay
Aqueduct
Hoover Dam
and Reservoir
(Lake Mead)
Fresno
San Luis Dam
and Reservoir
Colorado
River
Los Angeles
Aqueduct
Colorado River
Aqueduct
California Aqueduct
Science Case Study: The Aral Sea Disaster
Diverting water from the Aral Sea and its two feeder
rivers mostly for irrigation has created a major
ecological, economic, and health disaster.
The shrinking of the Aral Sea (Figure 11-11) is a result
of a large-scale water transfer project in an area of the
former Soviet Union with the driest climate in central
Asia. Since 1960, enormous amounts of irrigation wa-
ter have been diverted from the inland Aral Sea and its
two feeder rivers to create one of the world's largest
irrigated areas, mostly for raising cotton and rice. The
irrigation canal, the world's longest, stretches more
than 1,300 kilometers (800 miles).
This large-scale water diversion project, coupled
with droughts and high evaporation rates due to the
area's hot and dry climate, has caused a regional eco-
logical, economic, and health disaster. Since 1960, the
sea's salinity has tripled, its surface area has decreased
by 58%, and it has lost 83% of its volume of water. Wa-
ter withdrawal for agriculture has reduced the sea's
two supply rivers to mere trickles.
About 85% of the area's wetlands have been elimi-
nated and roughly half the local bird and mammal
species have disappeared. In addition, a huge area of
former lake bottom has been converted to a human-
made desert covered with glistening white salt. The
increased salt concentration caused the presumed ex-
tinction of 20 of the area's 24 native fish species. This
has devastated the area's fishing industry, which once
provided work for more than 60,000 people. Fishing
villages and boats once located on the sea's coastline
now sit abandoned in the middle of a salt desert (Fig-
ure 11-12).
Winds pick up the salty dust that encrusts the
lake's now-exposed bed and blow it onto fields as far
as 300 kilometers (190 miles) away. As the salt spreads,
it pollutes water and kills wildlife, crops, and other
vegetation. Aral Sea dust settling on glaciers in the
Himalayas is causing them to melt at a faster than nor-
mal rate—another example of connections and unin-
tended consequences.
To raise yields, farmers have increased their in-
puts of herbicides, insecticides, fertilizers, and irriga-
tion water on some crops. Many of these chemicals
have percolated downward and accumulated to dan-
ARIZONA
Santa Barbara
Los Angeles
Central Arizona
Project
Phoenix
Salton Sea
San Diego
Tucson
MEXICO
Figure 11-10
Solutions:
California Water Project and the Cen-
tral Arizona Project. These projects involve large-scale water
transfers from one watershed to another. Arrows show the gen-
eral direction of water flow.
heavily populated, arid and semiarid agricultural re-
gions and cities. In effect, this project supplies massive
amounts of water to areas that without such water
would be mostly desert.
For decades, northern and southern Californians
have feuded over how the state's water should be allo-
cated under this project. Southern Californians want
more water from the north to grow more crops and to
support Los Angeles, San Diego, and other growing
urban areas. Agriculture consumes three-fourths of the
water withdrawn in California, much of it used ineffi-
ciently for water-thirsty crops growing in desert-like
conditions.
Northern Californians counter that sending more
water south would degrade the Sacramento River,
threaten fisheries, and reduce the flushing action that
helps clean San Francisco Bay of pollutants. They also
argue that much of the water sent south is wasted.
They point to studies showing that making irrigation
just 10% more efficient would provide enough water
for domestic and industrial uses in southern California.
According to a 2002 joint study by a group of
scientists and engineers, projected global warming
will sharply reduce water availability in California
(especially southern California) and other water-short
states in the western United States even under the
best-case scenario. Some analysts project that some-
time during this century, many of the people living in
arid southern California cities (such as Los Angeles
and San Diego), as well as farmers in this area, will
have to move somewhere else because of a lack of
water.
