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There is a nuclear war. It lasts for 4 hours and most cities are destroyed. How long could a sewer last without maintenance?

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    $\begingroup$ By "last", are you referring to survival of the physical structure (e.g. until collapse / cave-in), or the time period over which it continues to provide drainage of wastewater (e.g. until it becomes blocked)? The two time periods are probably quite different, with the former on the order of 100+ years, while the latter may be more on the order of 100+ weeks. You may also want to distinguish between sewer systems relying on gravity only, vs those that also include active components like pumps. $\endgroup$ – njuffa May 26 '18 at 21:29
  • $\begingroup$ I understand what is the question about, but it's poorly written $\endgroup$ – Mranderson May 26 '18 at 21:36
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    $\begingroup$ I don't know much about nuclear war, but if there is some kind of attack which leads to sewers not being maintained anymore, what exactly remains intact? Or what exactly got destroyed that led to them being abandoned but someone is still trying to flush a toilet and all the pipes are undamaged? I don't get the premise. Could you perhaps describe what you are trying to do exactly? $\endgroup$ – Raditz_35 May 26 '18 at 21:47
  • $\begingroup$ @njuffa: The Former $\endgroup$ – DT Cooper May 26 '18 at 21:48
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    $\begingroup$ The Cloaca Maxima (the main sewer of ancient Rome) was built in the late 7th or early 6th century before the common era and it still exists and is operational today, 2600 years later. Some maintenance work was done during this time, but there were long periods of time when it was not maintained in any way. It helps that when it was built it was grossly oversized and relies on gravity only. $\endgroup$ – AlexP May 26 '18 at 22:49
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Unfortunately not more than 48 hours in many cases

Gone are the days where sewer systems in cities were simple tunnels or underwater rivers, flowing out to sea.

Modern cities are large, complex and cover undulating and complex topography. Population demands are also large - the sheer quantity of effluent requiring disposal is a major factor in a modern city. Gravity fed sewers work to a point, however in most modern cities sewerage is pumped to treatment plants located away from populated areas, in particular in sloping sites, hilly terrain or cities in basin-like areas.

Some cities, in particular those in complex terrain, even use 'vacuum pipes' to assist in drawing effluent through pipes.

A sewer system in a city is one of the most expensive infrastructure costs in modern cities - with new developers often having to contribute large amounts to improve the system when they develop property. Constant maintenance is required, they are constantly being cleaned out, upgraded and worked on - everyday large parts of cities are affected in this manner. Without this the sewer system will quickly fail.

Although treatment itself is varied, with hundreds of utilised techniques to treat waste water, in the end a nuclear attack will likely disable all electrical systems, including water and sewerage pumps and plants.

It would only be a small matter of time for the dormant pipes fill with waste (keep in mind not just blackwater is disposed of in sewerage systems, but grey water and on some occasions stormwater too), without normal operation they would be filled to capacity or clog within a short amount of time, likely within a day or two of disposal entering the pipes.

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