I am writing a story about London flooding for an English project.

What would the most likely cause be for this huge city to be completely flooded about 10 meters above street level?

  • $\begingroup$ Welcome to Worldbuilding! The tagging says natural-disaster. Is that a requirement or is a powerful technological/magical effect ok? $\endgroup$
    – PatJ
    Feb 14, 2017 at 10:43
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    $\begingroup$ Problem is: London itself is elevated 35 meters above sea level, so you'd need at least 45 meters of tidal wave :/ $\endgroup$ Feb 14, 2017 at 10:44
  • $\begingroup$ You may be interested in the 2007 movie Flood, which deals partly with the scenario you are envisioning. IIRC in the case of London they opted for a storm surge overwhelming the Thames barrier and flooding the estuary, leading to massive flooding. To what extent the filmmakers took poetic license I don't know. $\endgroup$
    – user
    Feb 14, 2017 at 10:58
  • $\begingroup$ @AlexandervonWernherr, it ranges from sea level to 245 meters. I'm not sure where would be at 35m but it seems an arbitrary value. $\endgroup$
    – Separatrix
    Feb 14, 2017 at 11:45
  • $\begingroup$ Elevation: 35 m (115 ft) according to en.wikipedia.org/wiki/London $\endgroup$ Feb 14, 2017 at 11:48

5 Answers 5


London covers ~1000 square miles (according to my old A-Z). Standard definition of Greater London: Everything inside the M25 London Orbital Motorway. Shown a a yellow ring on the map below.

Elevation ranges from sea level by the river to 245m (804ft), but that's Bromley which isn't really London anyway. Take it to 150m to cover almost everything of interest with a couple of little islands. You're still going to have a lot of the taller towers peaking out of the top of this as they range up to 300m.

This sea level rise tool only goes up to 60m, but that shows that when around half of London is flooded you've already completely lost Denmark, the Netherlands, half of Belgium including Brussels, and places like Berlin, Dublin and half of Paris.

Even if you considered a minimal level of localised flooding to this level you're still going to lose the Netherlands and Belgium. Flooding map, NW Europe, 60m

I'd suggest playing with a tool like this one to work out how much of London you want to flood and tone down your requirements and remember that no matter what you choose, there are going to be entire cities wiped out before London gets hit.

Remember that London is defended, the Thames Barrier will prevent any "normal" storm surge reaching the city. It doesn't look like much in most photos, but when you kayak through it you realise quite how big it is. There will be major flooding in other places before London gets hit at all.

An effect coming off the North Sea will knock out Amsterdam and The Hague first. Something coming off the Atlantic will take out Southampton and Brighton on the way through.


The most likely scenario would be a Storm Surge, however boring it might be as Pete suggest in his answer meaning no critism. The North Sea has regularly suffered such surges and a recent (in historical terms) one in 1953 was the worse peacetime disaster in recorded British history.

On the 31 st of January 1953 a storm surge hit the Eastern Coast of Britain and the Western one of the Netherlands, Belgium etc. In Britain 307 people were killed in major flooding and large amounts of infrastructure were destroyed. It also lead to major loss of life in the other countries affected by the flooding. Parts of London were flooded by this event which lead to the planning and construction of the Thames Barrier.

This is the British Metrological Offices page on the disaster.East Coast Disaster.

Edit I have just though of another possible cause of a flood that could affect London, the wreck of the S.S. Richard Montgomery, a US Liberty ship that sank in the Thames Estuary in WW2. On board the vessel are still around 1400 short tons of explosives that are unstable and could explode under the correct conditions. This could generate a tsunami which estimates vary in height of around 1-5 meters which would funnel up the Thames towards London.Although this flooding would not be a deep as Ben Poulter wishes it could be a source of disaster if a lower flood was desired, and have the advantage of being highly localised to the Thames River and its surrounds rather than a global event and as a sudden event the Thames Barrier might not be raised quickly enough to protect London particularly if it was under going maintenance at the time.SSRichard Montgomery


A pretty severe mid-atlantic sea-quake would do the job.

The English Channel would form a nice funnel, concentrating the Tsunami, which would flood the relatively shallow North Sea and flood the Thames Estuary.

enter image description here

A slightly more boring alternative would be a storm surge in the North Sea.

A storm surge is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low pressure weather systems (such as tropical cyclones and strong extratropical cyclones), the severity of which is affected by the shallowness and orientation of the water body relative to storm path, and the timing of tides. Most casualties during tropical cyclones occur as the result of storm surges.

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    $\begingroup$ Came to my mind too. But how? The continents are drifting apart, so there's no friction. $\endgroup$ Feb 14, 2017 at 10:51
  • $\begingroup$ @AlexandervonWernherr - True. Possibly the sudden collapse of the sea floor resulting in a rather instant sub-sea volcano and possible lowering of the continental shelf. Storm surge is probably the most realistic answer, boring as it is.... $\endgroup$
    – user10945
    Feb 14, 2017 at 10:54
  • $\begingroup$ Volcano sounds interesting. What about sub-sea volcanic eruption and the pressure from the ocean collapses the magma chambers. $\endgroup$ Feb 14, 2017 at 10:59

Why not a meteor?

Your meteor strikes the Southern Bight portion of the North Sea and sends a devastating wave of water and sediment in all directions. Keep in mind that the sediment part;

enter image description here

The narrowing of shape of the outflow region of the Thames could suggest that the positioning of the meteor would cause more damage to London while a tiny bit less damage to everyone in countries like Norway (I cannot save the Netherlands for you, they're effed no matter which plausible answer you choose);

enter image description here


As suggested in the comments, I've moved your meteor to deeper water. This should also reduce the amount of sediment you get in general.

enter image description here

Why not a meteor.

  • This would not be a flood that you're requesting, but an incredibly devastating surge of water and material.
  • A lot of math is required to get your desired result, but if you're not focused on this, then it is entirely plausible within science.
  • People would likely be well-notified of this, so I'm not sure the amount of 'surprise' you want from this flood event.
  • $\begingroup$ This is theoretically the only way to get enough water moving. Only one little problem, would you believe in your second image you've dropped your meteor in only a couple of meters of water. It looks like you're pretty much bang on long sand there, but there's not much more than 20-30m in the whole outer estuary. $\endgroup$
    – Separatrix
    Feb 15, 2017 at 9:56
  • $\begingroup$ @Separatrix - good suggestion. I moved the meteor to 40m depth in an edit. $\endgroup$
    – Mikey
    Feb 15, 2017 at 21:15

As others have suggested the best plausible solution is a storm surge up the Thames estuary.

Thames barrier storm surge according to Wikipedia:

London is vulnerable to flooding and from heavy tides closing in. A storm surge generated by low pressure in the Atlantic Ocean sometimes tracks eastwards past the north of Scotland and may then be driven into the shallow waters of the North Sea. The surge tide is funnelled down the North Sea which narrows towards the English Channel and the Thames Estuary. If the storm surge coincides with a spring tide, dangerously high water levels can occur in the Thames Estuary.

This sort of disaster would only create flooding of 1 or 2 metres above street level (and a lot of London is below street level) BUT the initial surge could probably be several times larger than that.

Several contributing factors to make it full blown disaster:

  • Make it a very low pressure atmospheric storm system maybe feed by an arctic low pressure system. So it will be very cold.
  • coupled with a high spring tide in conjunction with a supermoon or alignments of the planets and the position of the earth relative to the sun (apogee/perigree).
  • have heavy rains/snowmelt flooding the rivers/canals to the west and north of London.
  • have heavy rains over London and the Thames as well.
  • have some additional structural damage/lack of maintenance/100 year flood cause the Thames Barrier to collapse or be rendered useless.
  • have either clogged up storm drains or major infrastructure engineering works on the drains to force water into the streets.
  • collapse a tube tunnel or too due to old age/ interrupted maintenance/ terrorist activity
  • have the flooding occur during a major festival/event when there are millions extra people visiting the city.
  • have the police and emergency services facing budget cuts so that their resources are over strained... oh wait, that's already happening.

Just a few affects on buildings/infrastructure:

  • flooding will saturate the soil and foundations of many London features, buildings/tubes tunnels/ canal works etc. Collapses of structural integrity could lead to several knock-on Collapses and flooding.
  • basement level will be flooded (at least). Some of the older houses have no concrete foundations. They were built straight into the clay. Flooding them will lead to substantial structural damage if not collapse.
  • silt from the river and surrounding flooded plains with be washed up onto the flooded streets. When it settles it will settle down into the drains and block them up further, preventing rapid drainage when the flooding subsides.
  • Will have lots of standing water. Pray that none of the sewage pipes break. Unlikely not to happen. Expect lots of stinky water. In some places the water will be very acidic/alkaline from various chemicals/sewage and could eat away at foundations/brickwork if left too long.

Pretty much, think of all the things that can go wrong and put together the 1 in a 100 year perfect storm and you have a natural disaster like nothing you have seen before... oh wait, that's already happened with Hurricane Katrina in New Orleans, USA.


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