Two-thirds of world's longest rivers throttled by mankind: study

Just one-third of the world's longest rivers remain free-flowing
Aerial view of where the Araguaia River splits into the Coco River (to the left) in Brazil. Credit: Day's Edge Productions / WWF-US

Almost two in three of Earth's longest rivers have been severed by dams, reservoirs or other manmade constructions, severely damaging some of the most important ecosystems on the planet, researchers said Wednesday.

Using the latest satellite data and computer modelling software, the international team looked at the connectivity of 12 million kilometres of rivers worldwide, providing the first global assessment of human impact on the planet's waterways.

They found that out of the 91 rivers longer than 1,000 kilometres (600 miles) in length, just 21 retained a direct connection between source and sea.

Just a little over a third (37 percent) of the 242 longest rivers had retained their free flow, something experts said was having a profound effect on Earth's biodiversity.

"The world's rivers form an intricate network with vital links to land, groundwater and the atmosphere," said Gunther Grill from McGill University's Department of Geography and lead author.

"Free-flowing rivers are important for humans and the environment alike, yet economic development around the world is making them increasingly rare."

Most of the remaining free-flowing rivers were confined to remote parts of the Arctic, the Amazon and the Congo basins, the study found.

This week the UN's panel on biodiversity released a summary of its devastating assessment on the state of Nature.

The underlying report, which will be made public in the coming weeks, found that 50 percent of rivers "manifest severe impacts of degradation" from human activity.

Wednesday's study, published in the journal Nature, laid bare in intricate detail just how drastically manmade activity is impacting our waterways.

It estimated there was now a total of 60,000 large dams at least 15 metres tall severing rivers, out of a total of 2.8 million worldwide.

The blocking or damming of rivers disrupts the flow of nutrients vital to replace those lost through agriculture, and diminishes the amount of river-bourne species that can complete their life-cycles.

3,700 hydropower projects

It also lessens the sediment flows river deltas provide coastal regions with, which currently help to protect millions of people against sea level rises.

Less than a quarter of free-flowing rivers now connect to oceans, depriving estuary environment from vital nutrients and sediments.

The team warned that dams had already led to a significant fall in river fish, which provide nearly all the animal protein eaten by close to 160 million people.

A separate assessment last year from conservation group WWF said freshwater species had experienced the most pronounced decline of all vertebrates over the past century, falling on average 83 percent since 1970.

The study also identified more than 3,700 hydropower projects either planned our currently under construction, including some on rivers offering vital life support for the human populations who live along them.

While hydroelectric power are significantly cleaner in terms of emissions than oil, gas or coal, the team stressed that mega power projects involving dams and reservoirs could have unforeseen negative effects.

"Hydropower certainly has more complex environmental impacts than the often-cited positive effects of avoiding fossil fuels," Bernhard Lehner, a professor at McGill, told AFP.

"While hydropower inevitably has a role to play... countries should focus on sustainable options like solar and wind which can have less detrimental impacts on rivers and the communities, cities and biodiversity that rely on them."

The health of Earth's rivers will also be impacted as climate change accelerates, affecting flow patterns and water quality, as well as bringing more invasive species, the authors said.


Explore further

Undervaluing hidden benefits of rivers undermines economies and sustainable development

More information: Mapping the world's free-flowing rivers, Nature (2019). DOI: 10.1038/s41586-019-1111-9 , https://www.nature.com/articles/s41586-019-1111-9
Journal information: Nature

© 2019 AFP

Citation: Two-thirds of world's longest rivers throttled by mankind: study (2019, May 8) retrieved 19 August 2019 from https://phys.org/news/2019-05-one-third-world-longest-rivers-free-flowing.html
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May 08, 2019
Damming a river for flood control and power generation is a terrible thing. We should tear them down and accept the deaths of thousands and destruction of land from seasonal floods each year as an acceptable sacrifice to appease the gods of the church of environmentalism. Because humans suck. But nature doesn't. Or something.

May 08, 2019
A very unbalanced article IMHO. Humans wouldn't be damming rivers if it weren't for HUGE benefits to mankind. How many does the article mention? Hardly any. Just keeps reiterating some negatives. A balanced discussion is needed. Otherwise these kind of articles should be put in the "OPINION" section.

May 09, 2019
Thick as bricks you two.
Don't understand science. Can't face reality. Confuse facts and opinions.
"Because humans suck. But nature doesn't. Or something."
You could so easily find the answers and explanations if you wanted to. What are humans doing that suck and why does it suck? If only there was a place where science articles on the subject were published. If only. It could help to get you up to speed with the latest science and facts.
"Humans wouldn't be damming rivers if it weren't for HUGE benefits to mankind"
How removed from reality do you have to be to not realize the whole reason the planet is getting screwed up is because there are consequences to having "HUGE benefits to mankind"?
Those HUGE benefits have had even HUGER detrimental effects on the rest of the biosphere.
You have to be seriously stupid to not be concerned that we have managed to half the total biological carrying capacity of the planet since the start of civilization.

May 09, 2019
A very unbalanced article IMHO. Humans wouldn't be damming rivers if it weren't for HUGE benefits to scammers and profiteers
No bart it's like religion - short term thrill, long term consequences. Dams eventually become silted up and unprofitable to fix. And the only solution is to remove them.

"Every year the dam removal movement continues to grow stronger. In 2018, 82 dams in total were removed from across the country... with most removals (1,355) occurring over the past 30 years. Pennsylvania has the highest number of removal projects so far (337 total recorded), while other states nationwide are also stepping up to the challenge (this year's leader, California, has 148 total removals, followed closely by Michigan with 139). From 1912 through 2018, 1,578 dams have been removed in the U.S."

May 09, 2019
Surprise! Another example of man improving his life and the lives of others by damming rivers to prevent floods and devastation caused by them, for using water to grow crops and feed the population. With people like these authors and their ''progressive agenda'' we'd still be swinging from the branches of trees in the jungle or fighting the predators on the Savannah. We'd be more diverse because the Neanderthals and our other ancestors would be dirtying up all the caves. Alas, there would be no one to pay the Tax Based Salaries of these researchers and they'd be sitting in a tree picking bugs off their mate. I think I will sell my home and build a thatch hut without a hearth, of course, to further prevent ''Climate Change".

May 09, 2019
man improving his life and the lives of others by damming rivers to prevent floods and devastation caused by them, for using water to grow crops and feed the population
"Hydroelectricity and irrigation are far more expensive when we count down-the-line costs of blocking forest regrowth, aquifer recharge, and topsoil renewal. Instead, dams encourage unsustainable growth, such as the mirage-metropolises of Phoenix and Las Vegas. Out-of-place agriculture makes deserts bloom briefly, but then leaves fields salted, palms wilting..."
cont>

"Huge reservoir surfaces mean terrible annual evaporation losses. Even the largest reservoirs silt up; Hoover Dam's reservoir has less than 100 years left."

May 09, 2019
"The Imperial Valley in California, formerly productive agricultural lands in South America, China, India, Iraq, and many other regions throughout the world are all facing the threat of losing fertile land because of salinization. After the building of the Aswan Dam in Egypt, the Nile River and the surrounding fields that had been irrigated successfully for over 5,000 years became threatened by high salinity in the water."
I think I will sell my home and build a thatch hut without a hearth
-Because of ill-conceived tech like dam-based irrigation, which ruins cropland, you may have to.

"Doug Cox manages the dam for the Imperial Irrigation District. "This is the only source of water for the Imperial Valley," Cox says. "All the drinking water, all the agricultural water — this is it." Imperial Dam shunts water from the Colorado River 82 miles through a canal, across the desert to Imperial Valley Farms."

May 09, 2019
Pssst, ghostofblotto. All those dam removals that you're excited about? Virtually all of them are short (5 to 20 feet high), inconsequential dams built in the 18th and 19th century that have long outlived their original purpose: creating mill ponds, water supply and recreational ponds. Sure, lets remove them. The big ones with major hydroelectric power plants that also provide flood control and irrigation? They aren't going anywhere. As Bart_A and Joker23 point out, their benefits far outweigh any environmental impacts.

May 10, 2019
Pssst, ghostofblotto. All those dam removals that you're excited about? Virtually all of them are short (5 to 20 feet high), inconsequential dams built in the 18th and 19th century that have long outlived their original purpose: creating mill ponds, water supply and recreational ponds
Your attention span apparently is only 1 post long so let me repeat...

"Hydroelectricity and irrigation are far more expensive when we count down-the-line costs of blocking forest regrowth, aquifer recharge, and topsoil renewal. Instead, dams encourage unsustainable growth, such as the mirage-metropolises of Phoenix and Las Vegas. Out-of-place agriculture makes deserts bloom briefly, but then leaves fields salted, palms wilting..."

"Huge reservoir surfaces mean terrible annual evaporation losses. Even the largest reservoirs silt up; Hoover Dam's reservoir has less than 100 years left."

May 10, 2019
They aren't going anywhere
BIG DAMS
"Klamath River in California and Oregon. It's the first time four dams will be removed simultaneously, making it an even bigger endeavor than those on the Elwha."

"the Bloede Dam on the Patapsco River in Maryland. Crews have been working to remove the rest of the structure and restoration efforts are expected to continue into next year."

"a dam removal on the Middle Fork Nooksack River is the "next biggest important restoration project in Puget Sound,"

"removal of Edwards Dam on the Kennebec was a pivotal moment"

"Condit Dam removal. After decades of court battles and grassroots action by river advocates, 700 pounds of dynamite blew Washington State's Condit Dam"

"10-story concrete dam in the wooded canyons of the Carmel River, between the Big Sur hills and the beach front town of Carmel... The destruction of the San Clemente Dam..."

May 10, 2019
Heres a biggie

"The Colorado River can no longer sustain two huge reservoirs," Balken says. "There isn't enough water."

"That's one reason the Glen Canyon Institute is pushing an audacious proposal called "Fill Mead First," which calls for the U.S. Bureau of Reclamation to drain Lake Powell and send the water downstream to Lake Mead."

"Over its 50-year life, Glen Canyon Dam has blocked hundreds of millions of tons of sediment from being carried downstream. That sediment now sits at the bottom of Lake Powell, much of it contaminated by agricultural runoff, mining waste and even uranium. Some people believe a drained reservoir could be eligible for Superfund status..."

-And yes, it will come down.

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