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Arizona's solar-over-canal project will tackle its major drought issue
(interestingengineering.com)
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this post was submitted on 26 Nov 2023
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As someone who knows nothing about canals (or what they are even used for), anyone want to explain why they are used, why they are dumb, and what we should do instead?
Evaporation. You lose a phenomenal amount of water moving it by canal over large distances in an arid climate. Ideally you'd enclose the whole system to reduce loss but sticking a roof over the top helps to some degree and is less complicated.
An irrigation canal like this is a big ditch to move water from a river to near farm fields. Without the extra water taken from the river, there wouldn't be enough water in the soil for crops to grow in the area.
Being a big ditch open to the sky, the hot sun and dry air make a bunch of the irrigation water evaporate before it even gets to the field. So we went to all the effort of taking water out of the river just to waste it humidifying the nearby air.
Why did we do it in the first place? Because it's way easier and cheaper to dig a ditch than to lay a big pipe, and I don't know if the US had any other water-delivery tech at the right scale when these were built.
Are there not enough areas of the US that get rainfall suitable for growing the needed food?
There probably are, but Saudi Arabia owns a bunch of land in Arizona and decided it was the perfect place to grow alfalfa, a very water intensive crop. That said, some farming does make some sense even in the desert, since it is almost certainly cheaper to have local produce than to need to import everything from places that have an abundance of water, even if that means building canals to water them.
The US has lots of land that doesn't require irrigation, but also lots of land that can grow crops if irrigated. Some of that land in California is some of the best farmland in the whole country, growing things that prefer California's Mediterranean climate (similar to parts of Australia's southwest coast).
We have the technology and have had it for a while. But we don't have the laws and habits of dry countries so US water laws are a wasteful mess.
Almost everything West of the Colorado Rocky mountains is very arid and requires extensive irrigation.
Everything except for the Pacific Northwest, and only the area west of the Cascade mountain range in Oregon and Washington.
Imagine a canal which is 3 feet wide at the minimum. It contains a constant volume of water. This canal ultimately waters farm land. By way of example, California has the imperial valley which contains these canal systems. They feed desert farm land. The problem is these canals are often:
Water rights have perverted water usage. People take cheap water which was grandfathered in by old laws and agreements and they waste it to evaporation. If you think "well the water isn't lost, just evaporated, right?" You'd be close, but slightly off the mark. The water is evaporated but it's transported often hundreds or thousands of miles from its original source. We are basically bleeding rivers to feed a desert. And deserts might as well be an infinite sink for water.
We should not have farm land in deserts. But if we do, we should at least conserve the water we are using. Just because it's cheap doesn't mean it's good (not that you're implying that, just saying).
This guy has never been to the Phoenix area :P we even have rivers with no water, too! Bring the whole family, camp out and have imaginary marco / polo by the hill infested with scorpions, only a half-mile from the city dump! Bring your RV so you can feel like a complete moron with the other people who thought it was a great idea to buy a mini house on wheels that gets 6 miles to the gallon. And if you are early to rise, you can make Laughlin a day-trip to lose all your social security check by dusk, before sauntering back to the depression-rut of a life you have carved out for yourself. Because living in a desert with a large elderly population, just-barely-enough power during the summer even though there is a fucking nuclear power plant 20 miles out of town, and has been in a drought for my entire life while everyone waters their lawn 3 times a week, never felt so good!
Oh sorry I got mixed up with my "fuck off and stop moving here" speech. Give me 10 minutes.
I've been to Phoenix and I agree. I don't understand why they waste so much water.
Wouldn't that make it an aqueduct?
Hundreds of miles of shallow canals in the middle of the desert, where regular exceeds 120° f. The water evaporates very quickly.