please empty your brain below
Fascinating,the things you find to fill your time,DG. That's an awful lot of the wet stuff.

Jo W | 14.02.21 - 7:27 a.m. | #

I'm disappointed. You have written about large dimensions and not mentioned the standard units 'the size of Wales' and 'number of London buses'.

mikeS | 14.02.21 - 7:28 a.m. | #

Fascinating. But the width of the Thames between high and low tide is a factor as well - which would slightly lower the total figure.

davews | 14.02.21 - 8:29 a.m. | #

Love the smell of casual maths on a Sunday morning.

Ignore all the pedants who say "But you forgot..." and bask in your magnificence.

Jon Jones | 14.02.21 - 8:59 a.m. | #

Have you ever thought about applying for a job on BBC4's More or Less?

Mike | 14.02.21 - 9:13 a.m. | #

Splendid achievement.
My minor quibble is that you cannot really ignore the part above Teddington. Although this is non-tidal in the sense that water never flows upstream, it still has a tidal variation in depth. However, the river is so small there, that correcting this would likely have no perceptible effect on your conclusion.

Malcolm of Kent | 14.02.21 - 9:15 a.m. | #

I had a brutal reminder of high spring tide last month when the road on the river bank in Mortlake was flooded.

The rise and fall of the river was distinctly different in the big floods a few years ago.

Sprout Eater | 14.02.21 - 10:05 a.m. | #

In your description of tidal time differences you've got low tide and high tide the wrong way round. High tide at Teddington is an hour after high tide at London Bridge. At low tide the time difference is almost 3 hours.

dg writes: Dammit yes. Never rewrite a paragraph after midnight! All fixed now, thanks, including an updated map.

Mudlark | 14.02.21 - 10:06 a.m. | #

Top work DG!

Hadders | 14.02.21 - 10:41 a.m. | #

The river Severn has a tidal difference of up to 15m

scrumpy | 14.02.21 - 10:45 a.m. | #

I must admit, any questions which pop into my brain that involve maths tend to get kicked back out again just as quickly - so thanks for doing the difficult bits for me! Fascinating stuff.

Cornish Cockney | 14.02.21 - 10:47 a.m. | #

Great post DG. I was wondering if the flow of water in the Thames affects the levels in the tidal part.

Last week the Thames was flowing very fast through Berkshire and flooding water meadows. Would this water running into London offset to any extent the outflow of the tide and cause low tide to be slightly higher than expected? Possibly the effect would be trivial but DG's the man to offer an opinion (and possibly calculations!).

Martin | 14.02.21 - 10:53 a.m. | #

The Thames is usually considered a freshwater river down to Battersea, brackish to Gravesend then seawater. This may provide a measure of the impact of inflowing water on river levels.

Malcolm of Kent | 14.02.21 - 12:24 p.m. | #

And magically, 100 billion litres comes sloshing back twice a day.

Autolycus | Homepage | 14.02.21 - 12:42 p.m. | #

By my (rough) calculations, 50% of the change in river volume occurs below Woolwich, and only 10% above Chelsea.

diamond geezer | Homepage | 14.02.21 - 12:46 p.m. | #

How many upturned Millennium Domes?

R2 | 14.02.21 - 2:31 p.m. | #

Hmm..ballpark figure. Etymology of that is the game of baseball, and that makes the usage problematic, in many cases including this one.

Baseball fields, although sizeable, are finite and not really that large, certainly not in the sense of an error bar of an order of magnitude. If I was dropping a stone from 50,000 ft I would be quite pleased to land within a ballpark.

Also, Baseball, like many games, is statistically quite precise (and perhaps more obsessed with stats than, say, cricket).

MilesT | 14.02.21 - 3:21 p.m. | #

Do I like the eau de nil/light duck egg temporary(?) icy revamp? Maybe...

Blue Witch | Homepage | 14.02.21 - 4:19 p.m. | #

The high spring tides frequently overtop Teddington weir, with the river encroaching onto the Lower Ham Road in Kingston.

timbo | 14.02.21 - 5:20 p.m. | #

All that water sounds like it could be persuaded to generate electricity - but Private Eye seem to think that proposals for a Severn tidal barrage are a scam. I (genuinely) wonder why it doesn't work in practice.

mark addy | 14.02.21 - 7:10 p.m. | #

I've been sat on the boat at Brentford, waiting to go up to Teddington on the tide. And I've been up from Limehouse to Brentford - but never tried it in the other direction.

Sarah | Homepage | 14.02.21 - 8:31 p.m. | #

worth knowing that the tide tables aren't always very accurate

I was at the Thames Barrier a couple of years ago to watch a planned closure ... and it was delayed by about half an hour ... because it turned out that the tide table was wrong !

ADS | Homepage | 14.02.21 - 10:33 p.m. | #

The Severn barrage has been put off and on and off again because of the ecology and coping with the second highest tidal range on earth.

All that Thames water, well imagine trying to snatch forty winks when there's a high tide and the barrier's been shut for a while and the boat you're on is bashing and bouncing around on the mooring ropes.

Pauvre moi, I know.

JP | 14.02.21 - 10:49 p.m. | #

There's a tidal power station on the Rance in Brittany. It has a storage volume of 184 million cubic metres and an average tidal range of around 8 m and generates 500 GWh per year. Unless there have been any major technical advances since Rance opened in the 1960s, I'd think that with a bit more than half of both the drop and the volume, the Thames could generate about a quarter of the power, say 125 GWh per year or about 14 MW on average. That's useful but peanuts compared to the big thermal power stations.

Michael | 15.02.21 - 11:35 a.m. | #











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