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The Three Gorges Dam in China cost USD37 billion to build. It created a
reservoir hundreds of feet deep and nearly 400 miles long. To achieve this, 13
cities, 140 towns and more than 1600 villages had to be evacuated and then
inundated. The dam generates 11 times as much power as the Hoover Dam in the
United States. The Three Gorges Dam, built across three gorges in the Yangtze
River, was supposed to control flooding on that river. Yet, 2010 saw the worst
flood in years. There is now a USD 62 billion project to divert water to China's
scorched Northern region. Northern China has half the population of the country
but only 15 % of its freshwater.
The ambitious Three Gorges Dam was first envisioned in 1919. Much of the
approach to the project did not take into account the warnings of various
scientific groups and activists. More often than not, it was in direct
contradiction to scientific recommendations. The massive quantity of water
dammed up is said to slow Earth's rotation. This may sound far-fetched. But is
must be noted that the detonation of the largest bomb by Russia is said to have
produced a sonic wave that went round the Earth twice. Our region has been
suffering the haze for more than twenty years due to massive fires in a
neighbouring country. The point to be noted is that man is capable of projects
and activity massive enough to have a tangible effect on the planet as a whole.
The environmental consequences of large dam include direct impacts to the
biological, chemical and physical properties of rivers and the stream-side
environments. Fish that migrate upstream to spawn can lose access to their
spawning grounds when rivers are dammed up. In some parts of the world, small
side streams connect the upper and lower parts of the dammed river to create a
path for the fish to move upstream and find their natural spawning grounds.
Dams trap sediments that are an integral part of physical processes and
habitats downstream, including productive deltas, barrier islands, fertile
floodplains and coastal wetlands. Damming slows the water flow. From a
free-flowing river the body of water becomes an artificial slack-water
reservoir. This completely changes the environment of the river as a body of
water. Aquatic plants and animals suffer to adapt to the change in temperature,
chemical composition, dissolved oxygen levels and physical properties of the
river that becomes a reservoir. Non-native and invasive species move in to the
detriment of the river's natural communities of plants and animals.
The greatest sustained environmental impacts of dams are the alteration in
the river's flow and transportation of sediment downriver. Areas of the river's
reaches, the natural seepage of water to the sides are disrupted. This
dewatering severely affects the life forms contained in these areas. The
ecological web of the river system is adversely altered.
Some sediment naturally replenish downstream ecosystems. Riverbeds downstream of
dams are typically eroded by several meters within the first decade itself. This
damage can extend for hundreds of kilometres below a dam. This deepening of the
riverbed will lower groundwater tables along the river. Plants will lose their
supply of groundwater as will human communities who draw from wells.
Invertebrates and fish lose this riverbed environment for natural spawning.
Dams also have a significant effect on the atmosphere. Most reservoirs in the
tropics show a significant increase to greenhouse gas emissions. Large dams have
led to the extinction of many fish and other aquatic species, the disappearance
of birds in floodplains, huge losses of forest, wetland and farmland, erosion of
coastal deltas and many other negative impacts that cannot be reversed. |
