Proposals to build more than 150 hydroelectric dams on Andean tributaries of the Amazon River could have catastrophic ecological impacts, causing the first major breaks between the tributaries and the Amazon and leading to widespread forest loss, according to a study published today in the scientific journal PLoS ONE.

The study by researchers at the environmental advocacy group Save America’s Forests, the Center for International Environmental Law, and North Carolina State University found that 47 percent of dams planned for Amazon tributaries in Bolivia, Colombia, Ecuador and Peru would have a high environmental impact, suggesting the need for additional evaluation and increased regional planning.

(Related Photos:  “A River People Awaits an Amazon Dam“)

Examples of high-impact dams, according to the study, include the Andaquí dam in Colombia, which would cause the first major break in connectivity for the Caqueta River and would flood a national park; and the Coca Codo Sinclair in Ecuador, which would disrupt downstream sediment flow for a major tributary of the Napo River and would require extensive construction in primary forest for roads and transmission lines. (See a map with impact assessments from the study).

“If there is continued business as usual, 20 years from now we could be looking at a catastrophic scenario where he have cut off the Andes from the Amazon,” said lead author Matt Finer, a staff ecologist at Save America’s Forests, who received a National Geographic Society grant to gather data on proposed dams and other environmental threats to the region. “The current lack of strategic planning has become an important issue.”

Proposals for hydropower dams are rapidly increasing in the region in response to intense and rising local demand for energy and the abundant untapped potential that fast-moving open tributaries present. Peru, for example, faces a projected 7 percent annual increase in domestic energy demand. In 2010, Peru signed a deal to provide additional energy to Brazil. The three other countries also face dire energy needs.

Regional governments have made dams the centerpiece of long-term plans to meet this demand. If built, the 151 planned dams the researchers studied would be a 300 percent increase over the number of existing dams in the region. Over half would be large dams over 100 megawatts, and 40 percent are already in the advanced planning stages.

Hydropower is often sold as a cleaner alternative to thermoelectric power, but Finer said dams would have their own ecological consequences in one of the most diverse ecosystems on the planet.

Rain and melted snow flows from the Andes Mountains foothills to the Amazon through six major tributaries—the Caqueta, Madeira, Napo, Marañon, Putumay, and Ucayali Rivers. The rivers wash into the Amazon, providing the vast majority of sediment, nutrients and organic matter important for the survival of birds, fish and other organisms. Many Amazonian fish species spawn in the tributaries, including a number that migrate all the way to the foothills of the Andes.

Any break in water flow would alter this dynamic. The study, however, found that 60 percent of dams planned across the six major tributaries would cause breaks in connectivity. More than 80 percent would lead to deforestation from flooding, road building, and power transmission lines, a consequence Finer said often escapes consideration by planners. “There is this whole other world of impact that few people are talking about because they are focused on the impacts to the river,” he said.

Beyond the environmental concerns, the study says the high impact dams would directly affect indigenous communities. People living upstream from new dams could be displaced by flooding, while those living downstream may suffer from disruption of the river’s flow.

The study is the first to consider the ecological impacts of proposed dam projects for all major rivers connecting the Andes to the Amazon, and offers a contrary assessment to previous published accounts. Most of the data the researchers used came from government sources. “We dug in,” said Finer, who spent four months in Ecuador, Peru and Bolivia gathering data. The researchers hired help to gather data on dams proposed in Columbia.

Currently, almost two-thirds of the world’s largest rivers are dammed, leaving few major free-flowing river systems, many of which are in South America. With their natural decline in elevation and deep canyon walls, the rivers of the Andean Amazon are ideal for building dams, Finer said. That combined with the explosive need for energy has made it the frontier for the technology.

“There really aren’t a number of other options,” said Finer, who stressed that the study was not designed to show that dams should or should not be built, but rather was meant to be a tool policy makers can use to better understand the consequences of projects. “A lot of these dams are going to happen and they are happening,” he said. “The idea is how can we use more strategic planning to minimize the impacts?”

Among the proposed dams the researches studied, the largest number, 79, were in Peru, which currently has 26 dams, the most among the countries in the study. Ecuador has the second highest number of dams planned at 60, followed by Bolivia with 10, and Colombia with one.