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0 pointscarlob5y ago0 comments

hydro is really not that green: salmons are losing their spawning runs for an example in your area. Also not renewable, because dams get filled with sediment and lose capacity over time.

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belval5y ago

Hydro has a big upfront cost because you submerge a lot of land which usually was covered with trees. It also adds a bunch of mercury to the water. However over the lifespan of the dam this is not a real concern especially compared to gas/oil. Furthermore if you need to account for energy stockage with batteries for wind/solar as they are conditional to the weather the environmental cost analysis becomes much closer as you have to account for all the manufacturing externalities. Hydro on the other hand can increase and reduce production by drawing from its reservoir which makes it at least as green as other renewables that we have right now.

BelenusMordred5y ago

> dams get filled with sediment and lose capacity over time

I'm struggling to believe this. Can you name one dam on Earth that has lost over 10% capacity due to sediment?

abdullahkhalids5y ago

> Because the source of the Indus River is glacial meltwater from the Himalayas, the river carries huge amounts of sediment, with an annual suspended sediment load of 200 million tons.[15] Live storage capacity of Tarbela reservoir had declined more than 33.5 per cent to 6.434 million acre feet (MAF) against its original capacity of 9.679 MAF because of sedimentation over the past 38 years.

https://en.wikipedia.org/wiki/Tarbela_Dam#Lifespan

jmkd5y ago

Dams all over the world capture sediment. This not only reduces their capacity, it deprives downstream areas of sediment needed for natural habitat, to fertilise wetlands and to buffer against oceanic incursion.

The Sanmenxia Dam in China lost 17% of its capacity in the first 18 months of its operation due to sediment accumulation [1]

Countless other dams have already been dismantled due to sediment build up, and many more will follow, considering that around 19000 large dams worldwide are over 50 years old [2]

[1] https://en.wikipedia.org/wiki/Sanmenxia_Dam [2] https://e360.yale.edu/features/water-warning-the-looming-thr...

belval5y ago

Honestly this sounds like mostly poor engineering planification and analysis. If you look at the dams with a lot of sediment it's mostly in South-East Asia and Africa while Europe/North America have little of it.

jmkd5y ago

Asia's rivers have by far the highest level of sediment of any continent [1] meanwhile the US has quietly destroyed over 1000 dysfunctional dams in the post war period [2]

[1] https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/WR0...

[2] https://www.pbs.org/wgbh/nova/article/dam-removals/

rualca5y ago

> I'm struggling to believe this.

If seems you didn't even did the most basic cursory search on the issue.

Here's literally the first hit on a google search for "dam sediment".

https://www.hydroreview.com/world-regions/dealing-with-sedim...

And think about it: what's a dam reservoir other than a big old sedimentation basin.

https://en.wikipedia.org/wiki/Sediment_basin

Also, think about it: hydro power is not the only use for a dam. They are also typically used for things such as flood control, water supply, and energy storage. All of those usecases rely on the sam's ability to hold water (and it's sediments) and lower discharge, if not totally block it.

nimbleal5y ago

Depending on the impounded area they can (in some cases) be worse than fossil fuels for greenhouse gases.

https://www.scientificamerican.com/podcast/episode/not-all-h...

stanmancan5y ago

I wish that went into more detail! I have no clue how it could be worse than fossil fuels. I get that trees are a store of carbon and if they get submerged they will break down and release it all, but surely over the lifespan of the dam that’s significantly lower than burning coal non-stop? Wouldn’t it be equivalent to a forest fire clearing the area?

I always assumed they would clear the area of trees first anyways. Why let the wood rot when you can cut it down and use it?

nimbleal5y ago

> I always assumed they would clear the area of trees first anyways. Why let the wood rot when you can cut it down and use it?

The spaces are often so vast that chopping down the wood could delay a project by impractical lengths of time.

> I get that trees are a store of carbon and if they get submerged they will break down and release it all, but surely over the lifespan of the dam that’s significantly lower than burning coal non-stop? Wouldn’t it be equivalent to a forest fire clearing the area?

My understanding is that microbial breakdown means a lot more carbon is released as methane vs. CO2 from fires — methane being a much more potent greenhouse gas.

Here’s one related paper I found

https://academic.oup.com/bioscience/article/66/11/949/275427...

(I work for a hydro developer but I’m not an expert).

stanmancan5y ago

While it’s not perfect it’s significantly better than burning coal.

Geographically we can’t rely on solar; I’m not sure why we don’t have more wind turbines!

j / k navigate · click thread line to collapse

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belval5y ago

BelenusMordred5y ago

> dams get filled with sediment and lose capacity over time

I'm struggling to believe this. Can you name one dam on Earth that has lost over 10% capacity due to sediment?

abdullahkhalids5y ago

https://en.wikipedia.org/wiki/Tarbela_Dam#Lifespan

jmkd5y ago

The Sanmenxia Dam in China lost 17% of its capacity in the first 18 months of its operation due to sediment accumulation [1]

Countless other dams have already been dismantled due to sediment build up, and many more will follow, considering that around 19000 large dams worldwide are over 50 years old [2]

[1] https://en.wikipedia.org/wiki/Sanmenxia_Dam [2] https://e360.yale.edu/features/water-warning-the-looming-thr...

belval5y ago

jmkd5y ago

Asia's rivers have by far the highest level of sediment of any continent [1] meanwhile the US has quietly destroyed over 1000 dysfunctional dams in the post war period [2]

[1] https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/WR0...

[2] https://www.pbs.org/wgbh/nova/article/dam-removals/

rualca5y ago

> I'm struggling to believe this.

If seems you didn't even did the most basic cursory search on the issue.

Here's literally the first hit on a google search for "dam sediment".

https://www.hydroreview.com/world-regions/dealing-with-sedim...

And think about it: what's a dam reservoir other than a big old sedimentation basin.

https://en.wikipedia.org/wiki/Sediment_basin

nimbleal5y ago

Depending on the impounded area they can (in some cases) be worse than fossil fuels for greenhouse gases.

https://www.scientificamerican.com/podcast/episode/not-all-h...

stanmancan5y ago

I always assumed they would clear the area of trees first anyways. Why let the wood rot when you can cut it down and use it?

nimbleal5y ago

> I always assumed they would clear the area of trees first anyways. Why let the wood rot when you can cut it down and use it?

The spaces are often so vast that chopping down the wood could delay a project by impractical lengths of time.

My understanding is that microbial breakdown means a lot more carbon is released as methane vs. CO2 from fires — methane being a much more potent greenhouse gas.

Here’s one related paper I found

https://academic.oup.com/bioscience/article/66/11/949/275427...

(I work for a hydro developer but I’m not an expert).

stanmancan5y ago

While it’s not perfect it’s significantly better than burning coal.

Geographically we can’t rely on solar; I’m not sure why we don’t have more wind turbines!

j / k navigate · click thread line to collapse