160

Low-tech climate control: the waterfalls fill the air with spray, which evaporates off and cools the populace. The Romans used to achieve a similar effect with fountains.


121

Still water is heaven for proliferating algae, bacteria and annoying insects like mosquitoes. A large city with large bodies of still water is a recipe for plague spreading. Having water on the move keeps the water clean and, as a consequence, the city healtier. Also, waterfalls help enriching the water with oxygen, helping bacteria to decompose organic ...


70

They can used for underground power and communication lines, as a replacement for overhead lines. The reason why overhead lines are still prevalent in America is due to the initial cost of installing the lines underground and the sheer number of lines needed for the sparse rural areas covering most of the US. However, if the power companies had available ...


68

Energy storage. You use a form of energy generation with unreliable or periodic output. As a form of energy storage you pump water up into a nice big reservoir when you have surplus, then power turbines by letting the water spill back down to a lower reservoir to create a more steady power supply. It might be more efficient in an enclosed system of pipes, ...


59

I would suggest composting. Design the waste water routing (trenches or plumbing) so that they can feed into one of several cesspits, then change which pit is fed on an annual basis. After each pit's year of service, add wood shavings and leaves, then allow it to season for a few years until it comes up again in rotation. Just before you change the waste ...


57

You're looking at it backwards. Nobody added artificial waterways to a city. They did what they had to do to support building a city on top of existing waterways. Human settlements naturally spring up near water sources for a number of different reasons. An annoying drawback of these water sources is that they limit the settlement's ability to expand. ...


55

A (local) population of about ten thousand people should be enough. In my opinion there are three factors here. Is there enough need for a restaurant? There seem to be around 14.000 McDonalds restaurants in the US, which is roughly one per 23.000 inhabitants. Assuming that the first one on Mars will be on the smaller size and have less competition, 10.000 ...


49

The Fast and the Furiously Crazy Since you've eliminated the sensible solution (bypasses or double tracks), let's go with an insane one! All your trains have rail tracks running on top of them and extra wagons with ramps at the front and back. When a priority train approaches, they lower the ramps onto the rails and the priority train drives straight over ...


44

Restriction for religious and political reasons No building should be higher than the local religious, historical, political or symbolic buildings. Such restrictions existed in the past, be it for religious, political or esthetic reasons, and there are still examples in today's cities. And it doesn't prevent you from a high density. A good example is ...


43

It is actually a trick question, in a fully renewable energy economy natural gas pipelines will continue to transfer natural gas produced from renewable sources. Natural gas normally comes from fossil fuel sources, but at its most basic it is methane which can be renewably generated from the decomposition of organic material (such as food wastes or other ...


41

Two trains become one. On the track there is a train heading in one direction at 100 km/h and a second train heading towards it at 200 km/h. You do not specify the distance between them. If there is some distance there is time for this maneuver. Slow train slows down, stops, goes into reverse. Previously slow train accelerates, in reverse, until it is ...


41

what challenges beside engineering and cost would make such a machine impossible to realise? The same reason for which you have noise cancelling earphones but not noise cancelling speakers. Earthquakes produce different types of seismic waves, like P-wave, S-wave and many more, each traveling with a different velocity. If you want to nullify the ...


41

Change the ground I once heard it said that skyscrapers represented the mountain beneath your feet. What that meant was that skyscrapers require rock-hard bedrock in order to be built, or at the very least, requires a foundation hundreds of feet deep. Basically, the deeper and more solid the bedrock, the easier it is to build skyscrapers. Consequently, ...


39

Apart from the high speeds, I think this might be possible. Diolkos was "a trackway paved with hard limestone with parallel grooves running about 1.60 metres (63 in) apart" near Corinth, in Ancient Greece to quote Wikipedia. It operated from ~600BC to 100AD and seems to have been used for moving goods and entire ships overland. It only ran for somewhere ...


38

Let's take a look at Kowloon Walled City - closest real world analog of what you're asking. Government There used to be somewhat competing gangs. There was, generally, a truce between them, and people who didn't belong to any gang was generally left alone. No taxes, no police. Small troubles were your troubles, big troubles were dealt with by the gang. Was ...


36

It is pretty simple, and this is actually how it was done until about 50 years ago in the region where I come from, where most of the houses had no sewer at all, but only a small cesspit. The method is surprisingly similar to the one used to clean barns... The access to the cesspit was granted via a large manhole. Once in a while through the manhole straw ...


35

This technology, called "Tuned Mass Dampers", is in practical use for decades, see the corresponding Wikipedia article. In skyscrapers, they do exactly what is asked for: changing the resonant frequency of a building (by means of a pendulum, for example) in a way that it never resonates to the frequency typical for an earthquake. In regard to earthquakes, ...


31

The way that preindustrial / early industrial people achieved what you want is with canals. Depicted: Barton aqueduct taking the canal across a river. England had hundreds of miles of canals, and there were canals serving most major European and American cities. You can build and use a canal with Roman technology and the Romans did so, using them to ...


30

Sewers still work the way they always did The DWV (drain-waste-vent) system in a high-rise building is actually quite similar to that found in a house -- it's simply bigger! The principles (gravity flow, mostly) that make a building's DWV system work scale quite beautifully with the size of the building. As to the sewers under the streets, you'll have ...


29

How do we make the impossible, possible? We begin by explaining why it's impossible. WB sees a lot of questions of the form, "how do I stop X from ever happening?" X can be a technology, or an historical event, or a lot of other things. When it comes to a technology like tall buildings, there's a critical issue you really need to understand. Technology ...


27

Mid Spring Around late April the last freezes will have passed through the U.S.. It will be possible to remain outdoors with little protection for seven months from this time. Farmers will have already prepared their fields (which would have required the heavy equipment) and planted the first crops of the year. Setting up manual irrigation will not be an ...


27

Pumped Storage If your family has significant resources, and access to two water reservoirs (One at a high altitude up the mountain, the other lower down), then they could have a custom pumped storage system installed. When they are running an electricity surplus, they pump water from the lower reservoir to the upper reservoir. When they have an electricity ...


25

Catastrophic Failure In the early 20th century, airships as a means of travel were on the rise. That is, until the fateful crash of the Hindenburg shocked the world. This marked the abrupt end to the airship era, and is why you rarely see blimps at all anymore beyond small ones for advertising at sporting events. Imagine if something similar happened in ...


24

Actually, cleaning of cesspits and latrines was a well rewarded, if not we'll respected job since Medieval times to 19 century, you might want to consult this article: https://en.m.wikipedia.org/wiki/Gong_farmer Up to 19 century many houses in Europe had cesspool in basement, sometimes it caused wooden beams to rot and floor to collapse, as in the case of ...


23

There's a difference between the trendy places that make an apartment building out of shipping containers (which is what you have as your picture) and actual slums. While there were patents for shipping container living as far back as the 1960s, the first place to do it where it was widely documented was Armenia in the 1980s after an earthquake. many of ...


22

So we have a duchy of some 5,000 square miles, or 14,000 square kilometers, some 120 km by 120 km, which makes it about one third the size of the medieval Duchy of Bavaria or about one fifth of the modern Free State of Bavaria. Wikipedia has a great list of 627 castles in Bavaria (by which they mean the modern state); pro rata this results in some 100 to 110 ...


22

It's unlikely that they would be repurposed. Since natural gas is the least carbon-emitting of the fossil fuels, it's likely to continue to be used for longer than coal, and its use is likely to tail off over a period of fifty years or more. The key thing here is that pipelines don't stay in good shape without maintenance and as natural gas usage ramps down ...


22

I have an idea which I'll try to put into writing but it might not be obvious what I'm driving at. I actually had a couple of thoughts on this but one may be more sensible than the other. Up and Over My initial thought was that one of the trains, probably the 200 km/h one as it would already likely be a streamliner, would be designed in such a way that it'...


22

Jackscrews The slow train will come to a complete stop. At both ends of each of its cars, two outrigger hydraulic- or screw jacks (each as tall as the train) are extended outwards to beyond the fast train's width, and after this downwards to beyond the height of the fast train, lifting up the entire slow train. Effectively, this forms a tunnel underneath ...


21

You can't Well you can, but it's going to take a few days. First you're going to need to get the infrastructure in place. A train weighs between 1500 and 6000tons. I'm assuming this is a passenger train rather than a cargo train which could weigh nearly 100,000 tons. We're going to need cranes in place able to lift at least 250tons just to move the ...


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