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Hydroelectric dams grace bank notes in developing

countries, from Mozambique to Laos, Kyrgyzstan to Sri

Lanka, a place of honor reflecting their reputation as

harbingers of prosperity.

That esteem, now enhanced by hydropower’s presumed

low-carbon profile, continues to overrule concerns about

environmental consequences and displaced people, as

evidenced by a surge in dam-building in the developing

world.

The phenomenon is perhaps most intense in the Mekong

River Basin, in Southeast Asia, where 12 more dams are

planned for the main stem of the river and 78 on its

tributaries.

Because many of these projects seem inevitable,

institutions, nongovernmental organizations and academics

worldwide, from the World Bank to the German

Corporation for International Development to the Nature

Conservancy, are developing strategies for dams with

softer environmental footprints.

The Mekong is the richest inland fishery in the world, with

more than 60 million people who live along it surviving on

subsistence fishing.

The dams would have “catastrophic impacts” on fish

productivity and biodiversity, including species such as the

Irrawaddy dolphin, according to a 2012 paper in the

Proceedings of the National Academy of Sciences.

Sediment mobility is also a concern. Vietnam, despite its

own dams, is concerned that new upstream dams would

deprive its low-lying delta — the country’s rice basket and

home to millions — of critical sediment replenishment in

the face of sea-level increases and saltwater intrusion.

Nevertheless, the countries along the Mekong — China,

Myanmar, Thailand, Laos, Cambodia and Vietnam — are

eager to develop, and for now that means large dams.

Historically, dam builders sought to maximize

hydroelectricity and profits. Aquatic scientists came in at

the tail end of the planning process to assess the

environmental impacts and try to mitigate them to some

By ERICA GIES DEC. 8, 2015

ENERGY & ENVIRONMENT | SPECIAL REPORT: ENERGY FOR TOMORROW

Heading Off Negative Impacts of Dam Projects

The Xayaburi Dam under construction in Laos. It isan example of how public comment can lead tochanges that are intended to reduce the potentialharm of hydroelectric projects. In the Mekong RiverBasin, 12 dams are planned for the main stem ofthe river and 78 on its tributaries. Courtney Weatherby

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degree.

A recent paper in the journal Nature Climate Change

suggests a seemingly obvious yet novel approach: Bring in

aquatic scientists at the beginning so that engineers can

consider ecological principles first, not last.

The paper came out of meetings organized by the National

Socio-Environmental Synthesis Center in Annapolis, Md.,

in 2013. Engineers and aquatic scientists discussed their

core requirements for a hypothetical case study of the

Iowa River in the United States.

For the engineers, it was revolutionary to get quantitative

environmental variables at the beginning of the process

that they could put into a model to address ecosystem

issues. “I can work with that,” said Casey Brown, an engineering

professor at the University of Massachusetts Amherst and a co-author

of the paper.

John H. Matthews, an ecologist and secretariat coordinator for the

Alliance for Global Water Adaptation and a co-author of the paper, said:

“Engineers are native problem solvers. If you can define a problem

accurately and broadly, they will come up with a solution.”

Called ecological engineering decision scaling, the framework models

tradeoffs between power loss and environmental gain to find the sweet

spot. That approach can work especially well if planners consider the

entire river basin rather than just a single dam, a strategy that is also

atypical, Mr. Brown said.

For example, a 2012 study considered 26 dams proposed for the

Mekong’s tributaries and found that building them all would reduce

migratory fish by 20 percent. Forgoing just a few dams

could minimize fish losses to 3 percent, while still

producing 75 percent of the energy, according to the study.

Taking a holistic look at the river system is also

economically advisable because multiple dams have a

cumulative impact not just on the environment but also on

energy performance. “Projects can end up interfering with

each other,” said Jeff Opperman, senior freshwater

scientist with the Nature Conservancy.

Nevertheless, there are ways to reduce the impact of a

single dam by softening the barrier it creates to fish and

sediment moving through the river.

After the Xayaburi Dam in Laos came under heavy public criticism,

planners widened the fish passage channel, put switchbacks in the fish

ladder to make it easier to climb, and added several entry points at

different flow velocities to attract different species of fish, according to a

report from the Stimson Center, a public policy institute in Washington.

To allow sediment through the proposed Sambor Dam in Cambodia, the

Natural Heritage Institute in San Francisco advocates a bypass channel

for environmental releases of water to help river ecology and the full

opening of dam gates in certain seasons to flush sediment.

The way a dam is operated can also soften its impact. Typically, dam

operators respond to energy demand by moving a lot of water through,

then rapidly cutting off the flow when demand drops.

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“It’s a very unnatural stream flow that has many negative impacts to

the ecosystem,” said N. LeRoy Poff, professor of biology at Colorado

State University in Fort Collins and a co-author of the Nature Climate

Change paper. One remedy is “a second dam downstream that re-

regulates the river flows out of the dam, mimicking on the downstream

side the flow of water that’s coming in on the upstream side.”

Dam developers may be growing more receptive to some of these

strategies because water flows are becoming more unreliable as the

climate changes, said Mr. Matthews, the ecologist. That raises questions

about the risk of such large investments.

Increasingly organized social and environmental opposition to large dam

projects are also raising financial risks.

Reducing the risk of controversy by engaging stakeholders in early

planning and environmental impact studies can lower risk for investors,

reducing financing costs, said Mr. Opperman, at the Nature

Conservancy.

Nevertheless, even as hydropower booms, its days may be numbered

because of the rapidly decreasing price of more agile alternatives like

wind and solar.

A version of this special report appears in print on December 9, 2015, in The International New YorkTimes. Order Reprints | Today's Paper | Subscribe

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