Environmental

Researchers say new hydropower dams and plants need to be placed ‘more strategically’

Researchers say new hydropower dams and plants need to be placed ‘more strategically’

Hydropower plants do not need to be disastrous for fishermen and nature if new dams are placed more strategically and some existing ones are modified or even removed, according to researchers at the Leiden Institute of Environmental Sciences and Stanford University.

Valerio Barbarossa and Rafael Schmitt said a conflict between sustainable development goals of affordable and clean energy on one hand and life below water, and no poverty and hunger on the other is evident in and around the Mekong River, which originates in Tibet and flows into the South China Sea after 4,900 km. “This river basin hosts one of the most productive freshwater fisheries on Earth. It is home to more than 1,000 fish species, and this fish forms the primary income for many families,” Barbarossa said.

Over the past 30 years, the fish and fisherfolks in the Mekong Basin have increasingly faced problems due to large dams for hydropower generation. “These have been placed ad hoc, without considering the consequences for fish and the livelihoods of many depending on them,” Barbarossa said.

Barbarossa and Schmitt explored how to optimally organize hydropower generation while preserving fish populations. They published their work in One Earth. The two researchers created a computer model of the lower Mekong Basin, meaning that the part occupied by China is excluded. The model initially assumed a situation without dams and searched for an optimal distribution of dams across the Mekong River basin. Optimal for the model meant maximum hydropower generation and minimal impact on fish populations. Thus, the model placed dams by minimizing the cascading effects that barriers have on fish habitats. The model also retrofitted dams with, for instance, fish ladders where possible.

“Fish ladders are not an optimal solution for many fish,” Barbossa said. “They usually target fish like salmon with specific swimming characteristics.” Other solutions, like nature-like bypasses, could further improve the longitudinal connectivity more than ladders, allowing more fish species to pass around the barrier. “Particularly some of the basin’s ‘megafauna’ like the Giant Mekong catfish that can reach 3 meters in length and weigh up to 350 kg. However, these fish passage solutions only work for relatively small dams, lower than 50 meters, so they should not be seen as a silver bullet,” he said.

The researchers compared the best scenario with one that closely resembled the current distribution of dams. They outlined three scenarios for policymakers: with low, medium and high ambition levels. At the lowest ambition level, all existing dams remain and only future dams are strategically positioned for optimal hydropower and fish populations. At the medium ambition level, the eight dams with the greatest impact on fish and less than 50 meters high are enhanced with fish passage, allowing some fish to partially migrate upstream or downstream again. From this starting point, the computer model proposed other new, strategic dams with fish passages.

In the highest ambition scenario, 10 dams are removed and replaced with dams in different locations. This brings about the highest benefits for fish and total hydropower revenues.

The two scientists conducted their research with the Mekong River Commission in mind. “All Mekong countries except China work together within this international commission to generate – preferably sustainable – hydropower for the Mekong region,” Barbarossa said. “If policies to protect freshwater biodiversity in such an international basin are possible, this commission could facilitate them.”

The researchers believe their model is also relevant to other parts of the world. “It has been projected that by 2050, there might be 70% more hydropower than now,” they write. “Especially along the tropical belts, hosting high fish diversity and highly productive freshwater ecosystems, hydropower is booming. The Amazon region is a clear example of this.”