Let's say in a post-apocalyptic flooded Earth, the land is becoming more crowded and more scarce as the sea levels rise.

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So a countries government decides to build a floating city that expands overtime when the population rises.

The city is assembled by parts that look like this. enter image description here

So is it a good idea to invest money and resources in a city like this?

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    $\begingroup$ What are the boundary conditions? We can't tell good from bad without knowing them. $\endgroup$
    – L.Dutch
    Feb 16, 2020 at 4:59
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    $\begingroup$ I didn't think about that. Probably shallower waters in a bay-like area. Basically the city would be floating on former land. $\endgroup$
    – Borbman
    Feb 16, 2020 at 5:03
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    $\begingroup$ Ever heard of tectonic plates? Those are large masses of rock floating in a "sea" of magma. And as earthquakes and other phenomenons can show, they don't have a tendency to stay stationary. Expect the risk of your structures floating apart from one another, into each other and sliding across one another. $\endgroup$ Jun 2, 2020 at 11:05

2 Answers 2


Not really, no.

You'd be far better off calling in the Dutch and having some dykes put in and drying out an area of shallow water or building like Venice on piles in shallow water.

Floating is a problem

Even when single floating habitat is reasonably practical multiple floating habitats become a problem. Two vessels alongside each other cause damage at the contact points, the larger the movement the more damage.

Compound mobile structures are a problem

Consider the movement of a compound pendulum, it's chaotic. You're linking masses together either close enough that they constantly do direct damage or far enough apart that you're building a complex compound pendulum system.

Anchored objects move

Have you ever stood near a large tower block in a wind? The wind around any large structure is changed, normally amplified as it flows round the structure. Anchored ships (and other structures) move around in the wind. And in the waves, and the current, and with the tide. An ocean world will have significant waves, currents, winds, and tides, your structures are going to have significant movement caused by all of these things. The wind could cause serious issues as you have created structures large enough to significantly affect airflow and hence objects downwind differently from the initial objects.

Add this to the previous two factors and you have a city that will shred itself in short order.


You could potentially build on shallow water oil rig platforms that are effectively set on piles into the ocean floor, this is still a temporary option as you're fundamentally isolated from natural resources. You'd be far better off building dykes and pumping up the seabed to expand the available dry land. See Netherlands, Hong Kong, Dubai (though they do it for other reasons) for practical examples.



It’s Already Been Done

Venice is a extremely similar to what you’re asking. It’s a city built on pilings in a lagoon that has been continuously maintained and added to for centuries.

So if the water is shallow and calm like the Venetian Lagoon than you can easily have the platform construction and floating buildings.

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    $\begingroup$ Venice is not floating. It is standing, supported by pilings driven into the lagoon bed. $\endgroup$ Feb 16, 2020 at 18:44
  • $\begingroup$ @M.A. Golding Yes I know it’s built on pilings, it’s even in my answer $\endgroup$
    – user71781
    Feb 16, 2020 at 20:20
  • $\begingroup$ I'm afraid you can't directly compare building on piles to floating in that way. Being afloat has a whole barrage of complications that building on piles completely neutralises. $\endgroup$
    – Separatrix
    Jun 2, 2020 at 10:35

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