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Comment by superkuh | Hacker News Reader

Unless the US embraces nuclear fission (or renewables at a scale not yet seen) for ocean water desalination the arid deserts of the southwest (and they have always been arid, that's not new) might have to return to their natural state instead of the artificial state they've been irrigated to the last century.

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According to the graph in the article, the Colorado River is about 5 million acre-feet (per year, i assume) below its benchmark. That's ~6.17 billion cubic metres.

If that shortfall was made up by desalination, using 3 kWh/m3 (the low end of the range [1]), that's ~18.5 million MWh per year. California's only operating nuclear power plant produced 18.9 million MWh in 2016 [2].

So this would be a big job, but not an unthinkably big one.

Unless i've dropped some orders of magnitude somewhere in there.

[1] https://en.wikipedia.org/wiki/Desalination

[2] https://en.wikipedia.org/wiki/Diablo_Canyon_Power_Plant

Also interesting to think that, on a global scale, we could put a dent in rising sea levels by desalinating and pumping water inland.

The oceans have an area of ~89.2 billion acres [0]. Abstracting those 5 million acre-feet would lower sea level by 17 microns. Sea level is rising by ~3.6 mm per year [1], so you would need 211 of these setups to counteract that. Scaling up Diablo Canyon's nameplate capacity of 2256 MW, that is 475 GW. There is currently 390 GW of nuclear power in the world [2].

So, again, not unthinkable, but really quite a lot of work.

And i'm not sure what you do with the water.

[0] https://en.wikipedia.org/wiki/Ocean

[1] https://royalsociety.org/topics-policy/projects/climate-chan...

[2] https://en.wikipedia.org/wiki/List_of_commercial_nuclear_rea...

I'm thinking bigger than the Colorado river. I also think scaling up nuclear power is a good idea--the economics of managing nuclear waste imply that the cost of managing a little bit of nuclear waste is not much lower than the cost of managing a whole lot of nuclear waste, so we're already committed to most of that cost.

> And i'm not sure what you do with the water.

Use it for agriculture (presently a whole lot of agriculture depends on unsustainable access to water) and desert greening. To be clear lowering the ocean levels is a nice byproduct of producing more water, not the other way around.

Nuclear takes a long time to scale up so this certainly isn't feasible in the next 50 years even if we had the political will. It's more of an interesting long term idea.

Are you aware that desalination plants are a huge threat to marine life?

Thias can't be the solution.

Do you have a source? I was not aware and would like to learn more.

"Brine, water comprising about five percent salt, often includes toxins such as chlorine and copper used in desalination, it said. By contrast, global sea water is about 3.5 percent salt."

"Brine can cut levels of oxygen in seawater near desalination plants"

https://www.reuters.com/article/us-environment-brine-idUSKCN...

Can we lay those huge tubes underwater to disperse it drip irrigation style? It's not like it's a lot of salt once diffused, especially with those glaciers melting.

We're already assuming far more electricity, so I'm not too concerned about the energy required to pump the brine many miles out, just worried about capital and repair costs.

>often includes toxins such as chlorine and copper used in desalination

This is very avoidable. Most extant desalination plants are in the Middle East and subject to relatively little environmental oversight. While desalination will always produce brine, introducing extra chemicals is something that can be solved at the technology level.

I wonder if the salt can be converted into a useful byproduct? Or else if it can be disposed of in an environmentally-friendly way?

It's not pure salt. It's just water with abnormally high salinity. It would require a fair bit of additional processing to make it useful.

Evaporation pools?

Entirely possible (and occurring already in the south bay), but they scale poorly - they require very large tracts of land since the pools need to be fairly shallow. They're also fairly labor intensive, between harvesting, purifying, and transporting the resulting salt.

The salt has to be transported in any case (whether salt comes from a mine or from evaporation pools). Even if we don't make it into a byproduct but just put it in a big pit of salt adjacent the evaporation pools it would probably be fine (somewhere that we don't need to worry too much about it leeching into the environment, which is already a concern for evaporation pools). Not sure what applications of salt there are or how pure it needs to be (presumably there are other applications besides table salt)? Since we're already positing very cheap energy, we can probably also posit more efficient desalinization plants (resulting brine is even more concentrated, taking the load off of evaporation pools) since I'm assuming that the energy cost is the bottleneck in desalinization efficiency.

Here's an article about the problems with brine from desalination plants https://www.scientificamerican.com/article/slaking-the-world...

The brine is too salty for marine life causing dead zones.

This can be a solution - perhaps it's not a good solution, but if the other options are worse, people will gladly trade a dead zone in the ocean to prevent a dead zone around where they live and grow their food.

Desalination might be more appropriately located in the Gulf of California. There is extreme tidal variation (about 4 meters!) in the upper part of the Gulf, which means that released brine will be mixed with seawater more rapidly than in most coastal areas.

>Sea-to-Sea plans would augment the declining volume of water flowing into the Salton Sea by importing water from either the Gulf of California or the Pacific Ocean. Because such ocean water will bring tens of millions of tons of new salts into the Salton Sea, such plans also need to either pump a lot of water out of the Salton Sea to export the millions of tons of salt, desalinate the water before it enters the Salton Sea, or run multiple desalination plants at the Salton Sea itself.

https://pacinst.org/salton-sea-import-export-plans/

Yeah, you're not going to do that without a ton of pumps. I ran the numbers once for a pipeline to the Salton Sea and it looks bad. However, if you built a canal (about ten meters wide and the same deep) and flooded the whole Imperial Valley (this isn't popular!), tidal variation would exchange all of the water on average about three times per year. There's an equation for pipe flow rate given a diameter and a pressure difference; the pipe you would need for the Salton is either unrealistically huge or has a really big pump. Hence, canal. I doubt it ever happens, of course, due to all the lost farmland/towns (and the "why bother?" factor).

What I was referring to is entirely different: the desalination occurs in Mexico and fresh water is piped around.

The canal has economic advantages as well.

There are some proposals suggesting (I don't how practical this is) to use geothermal plants in the Salton area to power the desalination.

As to the pumps, isn't the valley below sea level? Therefore power could be generated from the flow?

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