Botkin Environmental Science Earth as Living Planet 8th txtbk

18.7 Dams and the Environment 391
FIGURE 18.19 Three Gorges on the Yangtze River is a
landscape of high scenic value. Shown here is the Wu Gorge, near
Wushan, one of the gorges flooded by the water in the reservoir.
Chinese princess who symbolizes peace, prosperity, and
love) are functionally extinct. A few may still exist, but scientists
believe recovery is not possible. On land, habitats
were fragmented and isolated as mountaintops became
islands in the reservoir.
The dam, which is approximately 185 m high and
more than 1.6 km wide, produces a reservoir nearly
600 km long. Raw sewage and industrial pollutants that
are discharged into the river are deposited in the reservoir,
and there is concern that the reservoir will become
seriously polluted. Since the reservoir has been filling for
several years, the banks are becoming saturated, increasing
the landslide hazard. Large ships make matters worse
by generating waves that increase shoreline erosion and
cause the rock slopes and shoreline homes to vibrate and
shake. Some older homes are thought to be unsafe due
to the landslide hazard that has evidently increased since
the reservoir began filling. In addition, the Yangtze River
has a high sediment load, and it is feared that damage to
deepwater shipping harbors will eventually occur at the
upstream end of the reservoir, where sediments now being
deposited are producing shallower water.
The dam may also give people living downstream a
false sense of security. Should the dam fail, downstream
cities, such as Wushan, with a population of several million
people, might be submerged, with catastrophic loss
of life. 24 The dam may also encourage further develop-
ment in flood-prone areas, which will be damaged or lost
if the dam and reservoir are unable to hold back floods in
the future. If this happens, loss of property and life from
flooding may be greater than if the dam had not been
built. Contributing to this problem is the dam’s location
in a seismically active region where earthquakes and large
landslides have been common in the past.
A positive attribute of the giant dam and reservoir is
the capacity to produce about 18,000 MW of electricity,
the equivalent of about 18 large coal-burning power
plants. As pointed out in earlier discussions, pollution
from coal burning is a serious problem in China. Some
of the dam’s opponents have pointed out, however, that
a series of dams on tributaries to the Yangtze River could
have produced similar electric power without causing
environmental damage to the main river. 25
The Glen Canyon Dam on the Colorado River was
completed in 1963. From a hydrologic viewpoint, the
Colorado River has been changed by the dam. The river
has been tamed. The higher flows have been reduced, the
average flow has increased, and the flow changes often
because of fluctuating needs to generate electrical power.
Changing the hydrology of the river has also changed
other aspects, including the rapids, the distribution of
sediments that form sandbars (called beaches by rafters;
Figure 18.20), and the vegetation near the water’s edge. 26
FIGURE 18.20 A sandbar in the Colorado River below Glen
Canyon Dam in the Grand Canyon. Releases of relatively large flows
in recent years are designed to help maintain the sandbar.