Guest no schist Sherlock by David Middleton

From the AGU’s “bleeding obvious” files…

Where Did All the Free-Flowing Rivers Go?

A map of the world’s free-flowing rivers shows a shrinking number can still meander as they please. New plans for hydropower will further constrain flow.

By Jenessa Duncombe

Giant catfish once swam in the golden-brown waters of the Mekong River near the Thai village of Sob Ruak. But since the Chinese government built hydropower dams upstream, the waters now drop too low for the catfish to lay their eggs. The loss of habitat for the catfish is just one of many stressors the increasingly developed river faces.

A new study released 8 May in the journal Nature suggests that the Mekong’s plight is not unique: Humans have significantly impacted the majority of the world’s 242 longest rivers. Just one third of long rivers still flow freely throughout their entire length, and the most untouched rivers exist far from population hubs in the Arctic, the Amazon River Basin, and the Congo River Basin.

[…]

“This study is not meant to be a study that says ‘stop any kind of development,’” Bernhard Lehner, an associate professor in the Department of Geography at McGill University in Montreal, Canada, and one of the first authors on the study, told Eos. “But it’s meant to find smart solutions.”

[…]

The analysis revealed not only that most of the world’s longest rivers are no longer free-flowing but also that dams are the overwhelming cause.

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“We always come back to dams as being the main culprit in all this,” Lehner said.

Dams stop species from migrating upstream, and they also trap sediment, preventing it from flowing down the river.

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Murky Waters

Although dams fragment a river and cause a litany of downstream damages, they also provide a source of renewable energy. There are increasingly urgent calls worldwide for lowering greenhouse gas emissions, and hydropower dams are one answer.

Climate change driven by greenhouse gas emissions harms rivers as well: Hotter air temperatures warm river waters and decrease the amount of dissolved oxygen they can hold. Restricting the free flow of rivers by installing hydropower dams will hurt the ecosystem further, according to the new study.

“While we try to counter climate change, it makes the situation in rivers worse for ecology,” Lehner noted. “This is the conundrum in this whole story.”

Lehner hopes that the new data set, which is available with its source code for free, will give planners a resource to scrutinize the full effects of river management infrastructure.

[…]

Eos

“This study is not meant to be a study that says ‘stop any kind of development… But it’s meant to find smart solutions… We always come back to dams as being the main culprit in all this… While we try to counter climate change, it makes the situation in rivers worse for ecology… This is the conundrum in this whole story.”

Ummm yeah, have you thought about just going with natural gas and nuclear power for new power plants? And… Maybe trying to capture as much CO₂ as possible from coal-fired plants and using it for enhanced oil recovery?

I think we can defeat the Green Mafia the same way Captain James T. Kirk defeated Harry Mudd’s androids…

The Eos article did feature a really neat map…

Citation: Duncombe, J. (2019), Where did all the free-flowing rivers go?, Eos, 100,https://doi.org/10.1029/2019EO123209. Published on 08 May 2019.