Toward friendlier dams

Despite the adverse impacts of large-dam construction on ecosystems and human settlements, dams are here to stay. And more most likely will be built in the 21st century wherever there is a need to store water for irrigation, provide urban water supplies, and generate power. But societies and governments worldwide would do well to evaluate the consequences of dam construction as an integral part of the planning process, a leading Caltech authority writes in a new book.

The reason? Because hundreds of millions of people have been adversely affected by dams in the last century, says Caltech anthropologist Thayer Scudder in his new book, The Future of Large Dams (Earthscan, February 2005). Somewhere between 40 and 80 million people have been forcibly relocated by the flooding of land to create the reservoirs above the dams. Furthermore, even larger numbers of people have had their lives and livelihoods disrupted by the change of the river flow below dams.

According to Scudder, large dams are a “flawed yet still necessary development option.” Flaws include both the shortcomings of the dam itself as well as ecological and social impacts. In terms of the former, Scudder says that dams on average become clogged with sediment at a rate of about 0.5 to 1 percent per year. And in terms of the latter, changing habitat caused by the flooding of land behind and below dams is certain to change the habits of nearby humans and animals alike—if not devastate both.
“Although dams have their problems, they’re unfortunately still necessary because of the growing needs of humans for water storage,” says Scudder. “That’s the dilemma.”

Still, he says, many people in the world are dependent on the natural flow of rivers, and the consequences can be the sort of things you might not normally take into account. “For example,” he says, “a settlement that depends on an annual flooding of agricultural land when the river rises can be wiped out if the regulated flow of the dam causes the annual flooding to cease.”

But the book argues that despite these adverse impacts there are modern ways of addressing them. “For example, if local populations downstream have been depending on an annual inundation of an agricultural flood plain,” he says, “then the authorities in charge should consider a controlled release of water that recreates the flooding conditions.” Experiments have been done, he notes, with coordinating hydropower generation and flooding for irrigation needs with the release of “environmental flows”—”that is,” notes Scudder, “releases of water to protect habitats and communities. This approach has been tried in several African countries, and research has shown in other cases that managed floods would be a ‘win-win’ option.”

In general, the way to make dams work for humans everywhere, Scudder suggests, is to address the social and environmental impacts before a dam is even built and, further, to evaluate the situations in river basins where dams have already been constructed. The political considerations of dam construction should be addressed as well, says Scudder. Too often, a dam project is built at a specific locale because of its political expedience, not because it is the best way to minimize the negative human and ecological impact.

“We should all be able to benefit from the dams that are to be built in the future rather than suffer from them,” he concludes.
•