One day London will flood. Geologically speaking London floods quiteregularly, although our lifetime is brief enough that most people rarely notice. The Thames Barrier is meant to reduce the probability of a catastrophic tidal surge inundating the centre of town, but one day it won't be enough. The river's walls will overtop and water will start to spill into areas where people live, travel and work. And it'll carry on overspilling until it reaches higher ground, which in some cases may be a surprising distance away. When the Big One comes, London will be a hell of a mess.
So all this rain we've been having lately has made me wonder. Where, exactly, is the River Thames's flood plain? Which London neighbourhoods will one day realise they've been built on the equivalent of a water meadow, but only when it's too late and all the insurance documents are soaking wet? It's possible to find this out by logging on to the Environment Agency's Flood map, on which areas at risk of flooding are shaded blue. You can either enter your own postcode on the homepage, or else leap directly to the overall map for London. To check the approximate risk at street-by-street level, zoom in. Or you can take a look at my (extremely approximate) handy summary map, which shows the extent of the Thames and Lea valley floodplains. Click to view it larger. If you live in a low-lying blue bit, prepare (one day) to evacuate.
London's flood risk zone is divided up into "embayments", which are separate and distinct floodable basins of land. If water breaches the barriers around an embayment, be they artificial or natural, then the entire embayment is at risk. Meanwhile the embayment nextdoor could still stay dry - it's all a matter of precisely where the river gets through. If North Greenwich goes under, Bermondsey might not. Or vice versa. So below I've knocked up a rough list of London's Thames embayments, ordered from east to west. Be warned that it's only approximate, but there may be some surprising "at risk" places therein.
Dartford embayment: Slade Green Barking embayment: Rainham Marshes, Ford at Dagenham, Creekmouth, Barking (roughly south of the A13). Thamesmead embayment: Crossness, Thamesmead, Abbey Wood, Belmarsh, Woolwich Arsenal Roding embayment: Beckton Sewage Works Isle of Dogs & Royal Docks embayment: Beckton, North Woolwich, Silvertown, City Airport, Custom House, Plaistow, West Ham, Canning Town (all in an area roughly south of the Greenway); Stratford (south); Poplar, the entire Isle of Dogs Greenwich embayment: Maritime Greenwich, The entire North Greenwich peninsula, New Charlton (all roughly north of the A206) Bermondsey embayment: Deptford, Rotherhithe, Canada Water, Bermondsey, London Bridge, Camberwell (roughly north of the Peckham Road), Walworth, Elephant & Castle, Waterloo, Lambeth, Kennington, Vauxhall, Nine Elms, Battersea City embayment: A tiny bit of the City riverside, Wapping. Westminster embayment: Victoria Embankment, Whitehall, Westminster, Houses of Parliament, St James's Park, Victoria, Pimlico Hammersmith embayment: Chelsea Harbour, Sands End, Parsons Green, Fulham, West Kensington, Brook Green, Shepherd's Bush (roughly south of the Uxbridge Road), Hammersmith, Turnham Green Other (smaller) western embayments: Wandsworth, Barnes, Chiswick, Mortlake, Kew Gardens, Syon Park, Isleworth
There are, to me, three unexpectedly large potential flood zones in this list. The bottom half of Newham is one, the northern chunk of Southwark is another, and then there are the well-to-do neighbourhoods of Hammersmith and Fulham where residents might have hoped to be far enough upriver to be safe. Not so. Meanwhile most of the Lea Valley's flood plain remains free from housing, but do think twice before buying a ground floor flat in the new Olympic Park.
For more details, and to discover more about emergencyplanning, you might want to flick through the London Flood Response Strategic Plan (a thick and meaty 53-page pdf). You'll find a map of the flood plain on page 45, a map of the various embayments on page 46, and a detailed close up of East London on page 50. A very approximate flood map of central London can be found here (Buckingham Palace safe, 10 Downing Street drowned). If you'd prefer tales of a fictional London inundation, here's the website for Richard Doyle's not-bad book "Flood", and here's the website for the ridiculously laughable film that was based on it. Watch the skies. But, more importantly, watch that gap under your front door, just in case.