Hydropower Presents a Host of Tough Choices

Wednesday, May 18, 2011

hydro dam There’s a lot of agreement that the world has to move more quickly toward renewable energy sources, but there’s an equal amount of controversy about each one – solar (too expensive), wind (too intrusive), geothermal (too expensive), biofuels (damaging food production) and ocean energy (not ready for prime time). But hydropower – the energy released by dammed water — is another matter; it’s been around for a long time. The trouble is, the ecological, economic, geologic and cultural damage dams can do can often end up outweighing their benefits.

First there is the land that is innundated. In China, the great Three Gorges dam displaced 1.3 million people; entire districts, towns and villages with millenia of history, farms that were in families for countless generations – all wiped away, with many of the people still displaced, still unable to make a new life. Huge controversies surround dam proposals in many areas, like India and Brazil, where entire tribes of indigenous people will be affected, their way of life literally obliterated. In Chile’s Patagonia, three of the country’s most distinct scenic valleys may disappear behind a new proposed dam.

Then there’s the problem of sedimentation, both behind the dam and below it. The Three Gorges dam will hold back sediment that once provided both land and nutrition along the Yangtze’s path and to its estuary, where Shanghai has depended upon the continued replenishment of the sedimentary plain on which it sits. It will be a huge long-term problem for this major city. Still, for huge projects like Three Gorges, sedimentation is a relatively slow. But for small-and medium-sized dams, sedimentation has become the primary problem. Many dams throughout the United States are so filled with sediment that they only await the money to take them down.

In the tropics, the sedimentation problem is worse because most of the dams are built in areas that have been deforested. In Haiti, the Peligre Dam on the Artibonite River was completed in 1956. Only 30 years later, it was ready to be decommissioned. In China, the Sanmenxia Reservoir, completed in 1960, had to be decommissioned only four years later due to premature siltation. And the effect of dam siltation is long-lasting. As the silt is deposited, it compacts, so that when the land is uncovered, very little can grow on the soil.

In the U.S., more dams are currently being decommissioned than built, but the energy impact so far is minimal. Of the 80,000 dams in the country, only 24oo generate electricity. Most of the dams were built to create reservoirs for water supplies, recreation and crop irrigation.

The ultimate arbiter for many dam projects will be climate change. Norway has determined that as more of its snows turn to rain, its hydroelectric projects will yield more electricity. But the reverse could be true for Three Gorges. Most of the water that feeds the tributaries of the Yangtze comes from glacial melt. Chinese scientists have found that the more than 46,000 glaciers on the Qinghai-Tibet Plateau are shrinking by an average of 7 percent annually. At that rate, the power gained from the vast hydro project might fall increasingly short.

But aside from generating energy with relatively little greenhouse gases as a byproduct, many dams, like the Three Gorges, provides needed protection from disastrous floods. In 1954 the Yangtze flooded some 75,000 sq mi, killing 33,000 people and forcing 18,884,000 people to move. The flood covered Wuhan, a city of eight million people (the population of New York City) for over three months. Control of the Yangtze is not a choice for China: it’s a necessity.

While solar and geothermal approaches promise clean energy over the long term, many countries see hydropower as the shorter-term alternative to coal-fired plants and the pollution they bring. There are nothing but difficult choices, and the coal and oil habits of the 20th century continue to die hard.

 

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