Page 423 - Environment: The Science Behind the Stories

hundreds of sewage treatment and waste disposal facilities. On
top of all these worries, earthquakes in southern China in 2008
and again in 2012 raised fears that a future quake could dam-
age the dam, perhaps even leading to a catastrophic collapse.

Some dams are being removed
People who feel that the costs of some dams outweigh
their benefits are pushing for such dams to be dismantled
(Figure 15.18). By removing dams and letting rivers flow free,
they say, we can restore riparian ecosystems, reestablish eco-
nomically valuable fisheries, and revive river recreation such
as fly-fishing and rafting. Increasingly, private dam owners
and the Federal Energy Regulatory Commission (FERC), the
U.S. government agency charged with renewing licenses for
dams, have agreed. Many aging dams are in need of costly
repairs or have outlived their economic usefulness, and
roughly 400 dams have been removed in the United States in
the past decade.
The drive to remove dams first gathered steam in 1999 with
(a) The Three Gorges Dam in Yichang, China the dismantling of the Edwards Dam on Maine’s Kennebec
River. FERC had determined that the environmental benefits
of removing the dam outweighed the economic benefits of
relicensing it. Within a year after the 7.3-m (24-ft) high, 279-m
(917-ft) long dam was removed, large numbers of 10 species of
migratory fish, including salmon, sturgeon, shad, herring, ale-
wife, and bass, ventured upstream and began using the 27-km
(17-mi) stretch of river above the dam site. Some property
owners along the former reservoir who had opposed the dam’s
removal had a change of heart once they saw the healthy and
vibrant river that now ran past their property. More dams will
come down as over 500 FERC licenses come up for renewal in
the next decade.

Wetlands are affected by human
manipulations of waterways

(b) Displaced people in Sichuan Province, China From the Mississippi River Delta to the Aral Sea, wetlands
are being lost as we divert and withdraw water, channelize
Figure 15.17 China’s Three Gorges Dam (a), completed in rivers, build dams, and otherwise engineer natural waterways.
2008, is the world’s largest dam. Over 1.2 million people were
displaced and whole cities were leveled for its construction, as
shown here (b) in Sichuan Province.

Figure 15.18 The Great Works Dam on the Penobscot River
However, the Three Gorges Dam cost $39 billion to in Maine was removed in 2012. Its removal will provide endan-
build, and its reservoir flooded 22 cities and the homes of 1.24 gered Atlantic salmon and other fish species improved access to
million people, requiring the largest resettlement project in around 1000 miles of waterways for their inland spawning runs.
China’s history (Figure 15.17b). The rising water submerged
10,000-year-old archaeological sites, productive farmlands,
and wildlife habitat. The reservoir slows the river’s flow so
that suspended sediment settles behind the dam. Because the
river downstream is deprived of sediment, the tidal marshes
at the Yangtze’s mouth are eroding away, like those in coastal
Louisiana. This has left the city of Shanghai with a degraded
coastal environment and less coastal land to develop. Many
scientists worry that the Yangtze’s many pollutants will also
be trapped in the reservoir, making the water undrinkable.
422 The Chinese government plans to spend $5 billion building

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