Pump seawater to Nevada and cover it in desalination greenhouses. http://www.seawatergreenhouse.com/
For irrigation all that is necessary is to soak the rainwater in as soon as possible to prevent evaporation and runoff, since potability is not a requirement. This is even cheaper than rooftop catchment.
Of course you may need to re-green the upwind deserts first (since ~80% of terrestrial rainfall comes from plants, not evaporation), but we already have that technology. http://www.youtube.com/watch?v=K1rKDXuZ8C0
This is hardly unprecedented. The CCC installed thousands of miles of swales during the Depression (that function to this day), but nowadays most people don't even know what a swale is.
It works when there is no rain without needing a tank big enough to last a several year long drought.
The architecture of the greenhouse acts as a solar desalinator that in testing creates more water than is needed to irrigate the plants, so it not only grows plants, but also can provide clean water in the desert.
That's not to say I'm against conservation. I think conservation is a necessity that few appreciate (having lived in a desert all my life, I have a certain appreciation for scarce resources), but comments like the one you replied to are exactly the kind we don't need. That is, dismissal of alternate solutions isn't going to help the problem get any better.
Out here, there's a large, untapped reservoir of brine that would be ample water to supply the neighboring communities for decades or more. The local government continues to humor bonds to build a desalinization plant every 10 years with conditions that the money will be redirected after 3 years if the plant isn't built, and unsurprisingly, the plant is never built. These greenhouses, if they work, would be a worthwhile experiment and probably substantially cheaper considering the wider variety of crops that could be grown and sold. Not to mention local growers could continue growing their crops without ruining the freshwater wells of their neighbors by running them dry. I just doubt it'll happen until the cost of pumping fresh water becomes too expensive or the wells are run completely dry.
GP here. :)
I'm 100% in favor of using technology "to offset much of what we've done, largely as a fault of technological advancement." After all, rainwater collection is technology! But desalination isn't that kind of technology — it's the destructive kind.
My question was genuine. What advantage does plastic greenhouse desalination have over rooftop rainwater harvesting? It uses less land. It costs less. It produces less pollution. No piped distribution to tear up the streets for every 50 years. No energy needed to pump water long distances.
The only advantage I can see is that under desalination, someone gets to control your access to water. Advantageous for them I mean.
But is it really? You're effectively doing what occurs in nature. Clearing land and building a distribution infrastructure is destructive, but certainly no more than what is already going to happen regardless of whether or not desalinization is used. Pumping from salt water aquifers might qualify as well.
> My question was genuine.
It was, but your comment seemed dismissive of alternatives. I don't think that objectively adds anything to the conversation. I apologize if that wasn't your intent.
I can see a solar desalinization system in place in areas where much of the water you encounter underground is brine or otherwise non-potable, and it's particularly useful in areas where other methods of collection won't work. Yes, it has the potential drawback of kicking the can farther down the road in terms of potentially extracting water faster than it's replaced. But that said, in much of the west, the topography lends itself well to draining much of the run off into large basins and water ingress likely far outpaces whatever could be pumped out of the ground. Perhaps a hybrid (rainfall collection + solar desalinization) would be ideal.
I think you're focusing exclusively on the advertised "seawater greenhouse" and may not be aware of the benefits such a design would have in areas where there certainly is plentiful salt water, just not from a sea.
Remember, the alternative I'm comparing it to is restoring the land to a forested state (specifically one with much higher food production).
>draining much of the run off into large basins
…from which it evaporates, leaving the salt. Not a great plan.
You have to design for the desert: evaporation > rainfall. That means getting the water shaded asap. Further, run-off is not a given. It's better to design for in-place infiltration instead of run-off by remediating hardpan, imprinting, contour earthworks, etc.
>water ingress likely far outpaces whatever could be pumped out of the ground
The Ogallala aquifer is currently pumped 6x faster than it's being recharged, and that's not even a desert yet. http://www.upi.com/Science_News/Blog/2013/08/28/Ogallala-Aqu...
You do both, the two activities feed into each other, the greenhouses increase air moisture down wind and help you get plants growing, which feeds back into getting more rainfall once you get a large enough area going.
You have to design for the desert: evaporation > rainfall. That means getting the water shaded asap.
That's what the fucking greenhouse is for.
I'm puzzled. If the land is forested, it's no longer usable for crops in the sense that land occupied by trees cannot simultaneously be occupied with something else. So, even if you interspersed crops among the trees somehow, you're not going to have higher food production than fields that consist of nothing but food crops.
> …from which it evaporates, leaving the salt. Not a great plan.
I see you're cherry picking my comments without full context. Although I can't remember specifically why I mentioned drainage basins. I suspect it was because of run-off storage. See below.
Anyway, the point of solar desalinization (or rather, any desalinization) is to, well, evaporate or separate the water to separate salt and other unwanted things in solution, so unless you're willing to accept that desalinization is going to yield dissolved salts, then there's no point in doing it, is there? The salt doesn't magically disappear.
I also suspect that you may not live in a climate like I do, which is largely classified as a high desert, mountainous region. You don't have to design for run-off. Run-off is a given. An inch or less of rain leads to heavy flooding of lower areas simply because the soil isn't conducive to drainage or absorption of precipitation, and the steep canyons upstream serve to collect and concentrate rainfall. So, you wind up with low-lying areas that fill up with brine collected upstream from various salts and minerals, and eventually settle in subterranean aquifers that are entirely non-potable without desalinization. The drainage basins already exist. Oftentimes, salt lakes appear and persist for weeks following a rain because the atmospheric humidity is too high to allow for quick evaporation. The upshot is that if you were using a solar greenhouse, you wouldn't have to pump the water particularly far. Or you could pump it out of the ground.
> The Ogallala aquifer is currently pumped 6x faster than it's being recharged,
I wasn't talking about potable water. I was humoring the "seawater greenhouse" as a method of treating non-potable water, pumped from underground briny aquifers. I think you have this idea in mind that all subterranean water deposits are fresh water. They're not.
Desalination does not intefere with rainwater harvesting. Rainwater harvesting is an entirely parallel enterprise, mostly involving accumulating very large bodies of freshwater.
Currently desalination is very energy intensive and so tends to do harm due the pollution generated from producing that energy.
These greenhouses desalinate water with a fraction of the energy requirements (pumping sea water inland takes energy, but nowhere near as much energy as you might imagine, as long as the inland end is not too far above sea level), while producing food, increasing the amount of moisture in the local area so greening that area of desert, and also increasing the amount of water available to the local municipal supply, at a rate that can be offset by the main farming business.
This is only control of water in the way that a pipe is control of water. It is continuous production of clean water in areas where that is often a problem.
You're way overestimating the size needed. Even in drought years there is substantial precipitation, but generally it happens at the wrong time of year.
Often you'll have flooding in the same year as drought! See this recent example: http://news.nationalgeographic.com/news/2013/09/130913-color...
That flooding is made worse by hardware (meaning roofs, concrete, etc) that prevents infiltration and overwhelms surrounding areas.
It's often cheaper to oversize your catchment area and direct tank overflow to a nearby garden. Generally the available roof area isn't the limiting factor, but I encourage you to verify this by looking up annual rainfall numbers for areas you're interested in. Do you know how much rain falls on your roof each year?
crusso raises his hand then goes off to google.
They are very interesting technology and if I wasn't working on the organization I am working on now I would probably be working with a large scale Seawater Greenhouse installation somewhere today.
edit - I just had a look at what you are doing through your username, akvo looks pretty cool.