diamond geezer

 Thursday, January 28, 2021

Thanks for the frankly astonishing number of responses to yesterday's post.

After which the only sensible follow-up question is What's the lowest I've ever been?

Again I'm going to consider 2021 first and then my entire lifetime. And apologies, because although this sounds like a much more interesting question than yesterday's it's actually riddled with caveats and probably less satisfying.

We don't normally venture below ground level and when we do it tends to be not very far, for example to go down into a basement or to walk through a subway. In certain parts of the country, say Norfolk, there's very little opportunity to go down any further. For most of us going deeper underground is something we only do when travelling, for example riding on the tube or driving through a tunnel underneath something, or when visiting a subterranean attraction. And we've not been travelling or touristing much this year, so asking how far underground we've been in 2021 risks being exceptionally mundane.

It'd be more practical instead to consider depth in relation to sea level. What's the lowest I've been, contourwise, on my perambulations over the last four weeks? And the problem here is that I think it's a positive number because I haven't been on the tube, let alone for a walk through the Greenwich Foot Tunnel. 2021 is an astonishing year thus far, depth-wise, because most Londoners who'd normally expect to have been significantly underground at some point probably haven't.

I have therefore been scouring the streets of east London to see where the lowest point I've been is. In this quest I've been aided by a post I wrote in 2019 where I scanned the Ordnance Survey map of London for the lowest spot heights. The only places with a 1m spot height are too far east, on the borders with Thurrock and Kent, but 2m spot heights are a bit more commonplace in Newham with a scattering between the District line and the Thames.

What I did yesterday is go for a walk round the relevant area using the altimeter on my iPhone as a check. The walkways along the edge of the Thames, which you might expect to be the lowest, registered 5m. But stepping back inland, say from Thames Barrier Park to the road at Silvertown Way, saw a drop to 3m. A heck of a lot of southwest Newham turned out to be 3m above sea level, including most of Custom House, a lot of Canning Town and a fair chunk of Plaistow. It's just as well that the riverside is higher, for reasons of flood defence, but a substantial area of low-lying land lies just beyond.

I registered 2m around West Ham station, Memorial Recreation Ground, Grange Road and Cundy Park, and on a couple of occasions my app flickered down to 1m. One of these was alongside Star Lane DLR station, specifically within Sycamore Close, and the other was at the southern end of Sheppard Street to the south of Hermit Road Rec. This residential depression is one mile from the Thames and half a mile from the Lea, so absolutely not where you'd expect a low point to be. It's also the lowest place I've been in 2021.

If only it hadn't been high tide I could have got lower, climbing down some steps somewhere onto a muddy beach beside the Thames. The river's tidal and typically has a 7m range... and that got me wondering how all this fits in with the official definition of sea level. The UK's Ordnance Datum is based on measurements at Newlyn in Cornwall, so it'll come as no surprise to hear that the midpoint between high and low tides is generally how the zero point for altitude is defined. The highest spring tides at North Woolwich reach 3½m above sea level whereas the very lowest get down to 3m below. It's not exactly the same all along the estuary but '3m below sea level' is fairly typical for low tides between Tilbury and Westminster.

So What's the lowest you've been this year? turns out to be a bad question. People who've stayed inland in 2021 will be beaten by people who've been to the seaside. People who've been to the seaside and walked to the water's edge will have been above sea level if it was high tide and a few metres below if it was low tide. Nobody's going to have been more than 5m below sea level unless they've been diving, or burrowed underground somewhere else. So better to consider the long term and ask...

What's the lowest you've ever been?

Londoners may be wondering how low the Underground takes them. I can answer this courtesy of an FoI request ten years ago which revealed how far below sea level and how far below ground all the platforms on the tube are. Here are the lowest stations on each line (tracks inbetween may of course be lower).

 below groundbelow sea level
Bakerloo25m Piccadilly Circus20m Elephant & Castle  
Central30m Notting Hill Gate10m Shepherd's Bush
Jubilee31m Bond Street/Green Park  26m Waterloo
Northern59m Hampstead20m London Bridge
Piccadilly  41m Holborn (w/bound)14m Covent Garden
Victoria32m Euston16m Pimlico
W & City20m Bank  6m Bank

» The Circle, District, Hammersmith & City and Metropolitan lines never go more than 9m beneath ground level and never go below sea level.
» The DLR at Bank is, I believe, a metre or two further below sea level than the Jubilee Line at Waterloo.
» Crossrail, Londonist reckons, will reach 42m below ground level.

To summarise, if you've travelled a bit on the tube during your lifetime you'll have been 40m, maybe 60m, below ground level at some point and 26m below sea level. That's pretty good going for starters. But it's easily beatable.

 below ground  below sea level  
Channel Tunnel   75m 115m  

If you've been through the Channel Tunnel you have at one point, on the English side, been 75m below ground level. But you've also been 115m below sea level and this is quite possibly the lowest you have ever been. The Hvalfjörður Tunnel in Iceland gets down to 165m below sea level, the Seikan Tunnel between Honshu and Hokkaido in Japan 240m and the new Ryfylke Tunnel in Norway 292m, but only a few of you will have passed through those. All are easily beaten by a visit to the Dead Sea, which is an amazing 430m below sea level, but I've never floated there.

The other thing about tunnels is that they can go a very long way below ground level if they pass through a hill or a mountain. The Standedge Canal tunnel, for example, may be 196m above sea level but still manages to be 194m below ground. Anyone who's travelled between Manchester and Sheffield on the Hope Valley line, myself included, has gone much deeper. The air shafts above the Totley Tunnel are 200m deep, while the Cowburn Tunnel (just west of Edale) is England's deepest railway tunnel at 277m below the surface.

One European monster is the Simplon Tunnel between Switzerland and Italy where trains pass beneath 2150m of rock. The Gotthard Base Tunnel in Switzerland is now the world's deepest, passing an astonishing 2450m beneath the Alps. Tunnels overseas wipe the floor with our paltry British specimens (although you may never know how deep because websites are often silent on the precise figure).

Which is why I'm not 100% sure how low I've been below ground level. I hoped it'd be my cage ride at the National Coal Mining Museum which our guide told us descended further than the height of St Paul's Cathedral. 140m below ground level is pretty impressive... except I've also been through the Cowburn rail tunnel and that tediously beats it. Also the top of the mineshaft at the museum is 133m above sea level which means the bottom is only 7m below sea level, a depth I can easily beat by travelling on the Underground.

All I know for certain is that the furthest I've been below sea level was 115m in the Channel Tunnel, and a lot of you can probably say the same. So the following aren't very good questions - too hard to research, too many similar answers and too riddled with uncertainty - sorry.

What's the lowest you've been this year? comments
(measure from sea level, if you can)
Sprout Eater's been on the Jubilee line through Waterloo - nobody else has! (-26m)

What's the lowest you've ever been below ground level? comments
(could be a mine, cave or tunnel)
Five of you have been through the 5-year-old Gotthard Base Tunnel (-2450m)

What's the lowest you've ever been below sea level? comments
(if it's not the Dead Sea it's probably a tunnel)
Eleven of you have been down to the Dead Sea (-430m)

If you're not sure, or if you have any other deep comments, please use the normal comments box below.

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