Decisions about whether to build, remove, or modify dams involve complex trade-offs that are often accompanied by social and political conflict. A group of researchers from the natural and social sciences, engineering, arts and humanities, including an environmental economist at the University of Rhode Island, has joined forces to show how, where, and when it may be possible to achieve a more efficient balance among stakeholders.

Their research, a collaborative National Science Foundation project, was published this month in the Proceedings of the National Academy of Sciences.

“We have lots of dams and aging infrastructure and a growing demand for river restoration,” said Emi Uchida, URI professor of natural resource economics. “But there is also a growing need for renewable energy, including hydropower. When it comes to dam removal or improvement, there are a lot of complex trade-offs, and navigating those trade-offs is a huge societal challenge.”

In some parts of the world, there are proposals to build thousands of massive new dams for hydroelectricity, flood control, and irrigation. In other regions, such as the United States, there is a growing movement to restore rivers by removing dams that are obsolete, pose safety risks, or have large negative impacts on ecosystems. In both instances, difficult trade-offs and divergent stakeholder preferences can greatly complicate decision-making.

For example, conservation groups and resource agencies seeking to restore sea-run fish often favor the removal of dams that prevent these species from reaching their spawning grounds. But other stakeholders may value the diverse services that dams can provide, including water supply, hydroelectricity, and reservoir-related recreation.

“In Rhode Island, we just passed a ballot measure for the green economy, and part of it will be spent on dam removals,” Uchida said. “We want to make smart decisions about which to remove, and we found there are smarter ways to make dam decisions to get the biggest bang for the buck with minimal consequences to other ecosystem services that we would have only with intact dams.”

The research team built a database of more than 7,500 dams in New England as a model system to search for decisions that provide efficient outcomes for multiple criteria valued by stakeholders. These criteria include habitat availability for migratory fish, hydroelectric power production, water storage, drinking-water supply, water quality, recreational use, dam breach risks, waterfront property impacts, and decision costs.

Using an economic concept known as the production possibility frontier, combined with a scenario-ranking technique, the researchers identified potential dam decisions that maximize the combined ecological and economic benefits, for individual watersheds and the entire New England region.

They found that better decisions are made when coordination occurs among parties linked to multiple dams in a region, rather than making separate decisions about individual dams.

“Making decisions at larger scales would open up opportunities for better outcomes,” Uchida said. “Instead of each state or each watershed council making decisions on their own, it makes more sense for the region to collaborate and work beyond its boundaries.

“There will be some distributional consequences to doing that, however. Not all watersheds will necessarily end up with all of the ecosystem services they desire. Some dams are more cost effective at providing hydropower, whereas others might be more productive at providing fish habitat by removing the dams. So there might be regional disparities as a consequence. But we still would make better decisions by looking at this problem regionally.”

In addition to Uchida, the research team included URI professor Art Gold and graduate student Ben Blachly, along with colleagues from the Rhode Island School of Design, the University of Maine, the University of Southern Maine, and the University of New Hampshire.