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Geo-Joint: Three Gorges Dam

Posted on October 16 2014

Three Gorges Dam

Image: Laiwan Ng

For centuries, the Chinese people have lived with both the gift and the brutality of the Yangtze River.  It unfailingly provided water, fish, transportation and in places, scenic beauty.  But flooding that occurred every few years caused massive damage to infrastructure and farmland, and took enormous tolls on human life – around 300,000 during the 20th century’s worst floods.  With a mind toward this, as well as a need for the massive electrical energy to power an economic resurgence, China devised a way to tame the Yangtze.  In a narrow part of its course, where it would drown three famous gorges, a massive dam would rise – Three Gorges Dam.  Along with those gorges, the rising waters of the 410-mile-long reservoir submerged well over a thousand towns, villages and more than a dozen cities, once the homes of around 1.3 million people.  Needless to say, while some effort was made to deconstruct and recreate historical structures and move even whole villages to higher elevation, there was incalculable cultural loss.

Dreamed of for decades, construction started in 1994 after massive preparation, and the mile-and-a-half-long dam began to store water in 2003.  It has since held back floodwaters of considerable size, proving its ability to safeguard areas downstream from flooding.  But other consequences, many foretold by critics, have come to plague the Chinese.  Reservoirs are big, heavy things and they press hard on the land, saturating formerly dry soils.  Water levels behind the dam are lowered before the floods come, in order to create space for the anticipated volume.  These fluctuations massage the land, and landslides can result.  Several have destroyed buildings, highways and those unlucky enough to be in the way.  River gorges are sometimes formed along fault lines, and the flexing caused by the rising and falling waters can also cause earthquakes on those faults.  Three Gorges Dam is built on two major faults and is a prime candidate for this effect called reservoir-induced seismicity.  So far only small tremors have been noted there, though shakes near other dams are blamed on their reservoirs.

Of a less speculative nature are the problems caused by the alteration of water flow and timing.  This has affected everything from fish to farmlands to Chinese sturgeon and the baiji, the now-extinct Yangtze River dolphin.  The cycles of dry and wet that used to prevail in the channel and floodplain of the river no longer apply, as the water levels are carefully controlled and evened out at the floodgates.  Consequently, the lifecycles of countless organisms attuned to the river for hundreds of thousands of years are thrown into disarray.  Compounding the stress on these animals, and on humans as well, is the quality of the water itself.  Think for a moment about what became submerged as the water rose over whole towns.  It’s unlikely every garage was cleaned of its chemicals, and every tank drained of its contents.  Further, the simple drowning of all the brush and trees now under 400 square miles of water, created a huge store of methane as decomposition set in, thereby stoking the world’s supply of greenhouse gas.  It’s one powerful offsetting factor to the green advantage that China gained by developing this massive hydroelectric source.

The project has brought many other environmental and social problems to bear, too many to chronicle here, but the truly disturbing fact is that the Three Gorges Dam is but a small fraction of China’s dam building program.   Already the home of 22,000 dams of at least 15 meters built since 1950, China has plans for about 100 more dams on many major rivers that cross both its own territory and that of other countries.  In many cases these dams are to be built in staircase fashion, strung out along the length of a river course.  These dams are being built quickly, with little environmental review, and under development pressures that could affect construction quality. The possibility of one dam failure leading to the next downstream, etc, is sobering.  China is to be commended for seeking energy sources that can replace its current enormous dependence on coal-fired power plants, but hydropower is far from the silver bullet it once seemed to be.

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