China ponders: Are a few big hydropower projects better than many small ones?

of intermittent renewable energy sources, such as wind and solar. “Xiluodu [Dam] could be used to stabilize against wind and solar to a very large degree because of its size and because it’s got another reservoir downstream that can dampen out any fluctuations,” Harrison notes. “How many kilowatts of other renewables can you enable if you develop smartly? Building small dams in small places doesn’t help you with that.”
Flood control
Of course, there is also the specter of floods. Inundations in 1931 and 1954 killed hundreds of thousands along the lower Yangtze and a similar flood in 1998 displaced at least 1.8 million people. Therefore, one of the primary reasons to build Three Gorges Dam, in addition to hydropower and improved shipping channels, was to restrain the periodic, devastating flooding of the Yangtze.

A river basin regime that also restores some of the natural floodplains — without displacing the rich rice paddies and vegetable fields that provide 60 percent of the country’s food supply — could also generate more power. After all, preparing for floods means lowering water levels in the reservoir to allow for extra water, resulting in reduced hydropower output. Allowing the Three Gorges reservoir to remain at a higher water level, for example, by opening some flood storage downstream could “generate $1 billion more in hydropower revenue,” Richter argues.

The key would be to inundate several hundred thousand hectares of the agricultural lands periodically during times of flood to provide as much as 15 billion cubic meters of floodwater storage  — three-quarters of the 20 billion cubic meters of flood control offered by the Three Gorges reservoir itself.

It would, however, also involve temporarily relocating the inhabitants of these lands through early warning and compensating them for lost harvest-something China already does, such as during the 1998 flood. Some of the $1 billion in extra hydropower revenues could go into a proposed compensation fund for such displacement and lost crops, Richter argues, a plan for which Goldman Sachs is preparing a feasibility study. “Using floodplains to store floods is more reliable, safer and more economical,” Richter says.

Such a plan would also more closely mimic the natural flow of the river, which is naturally high during spring and summer and low in winter, the opposite of the flow pattern imposed by dams such as Three Gorges that attempt to reserve room for floodwaters. “Fish reproduction in the Yangtze and other rivers depends on the maintenance of natural flow patterns, because it is these that set the cues for breeding and stimulate breeding migrations,” Hong Kong’s Dudgeon notes.

Such river basin regimes could prove vital in other areas of the world undergoing a hydropower boom, as well, Richter says. In Central America there are more than 300 dams of varying sizes planned or under construction. “What we’re seeing is a very rapid proliferation of hydropower development in these countries,” he says. “It’s a race to build dams and get them hooked up as quickly as possible, because the first in line are the first to be rewarded in terms of revenue.”

It might also help ameliorate or avoid some of the other impacts from dam construction now coming to the surface. “More than 100 miles of [Three Gorges] reservoir banks are at risk of collapsing. More than 50 percent of the reservoir area is affected by erosion and an additional 500,000 people will need to be relocated,” says Peter Bosshard, policy director at International Rivers, a dam watchdog group. Further downstream there is also erosion in the Yangtze’s delta as well as seawater intrusion. “Shanghai is subsiding. All these factors need to be taken into account.”

Despite these concerns, dam construction continues. Coffer dams — a temporary barrier that allows work on a permanent dam to proceed — are already in place for many projects, such as the Ahai Dam on the Jinsha River, closing off yet more sections of the waterway.

“It’s not just dams versus no dams,” Harrison adds. “It’s about elegant dams — and if we can’t do that, we shouldn’t build them. The proliferation of small- and middle-size ones is chewing up the whole place.”