Blog : Posts tagged with 'flooding'

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It’s all in the timing

In which we are not as wet as we might have been


Last weekend, feeling like we needed a holiday, we went away and pitched the tent. And it rained. The tent, fortunately, didn’t leak, but we ended up with great puddles round the door, a wading trip whenever we wanted to go in or out. Our last morning, we looked out to see ducks sitting and paddling in the water.

Still, it could have been worse. For no particular reason, we’d decided to visit Somerset. If we’d gone a week or even half a week, we’d still be there now, camping by a river. And we’d be rather deeper in the water.

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Statistics and probability

In which we think about flooding and chance


In the summer, we had big floods up here, worse floods than anyone in this village could remember. It was, apparently, a once in fifty years event.

Now: we’ve got floods again, six months later. Maybe not a once in fifty years event, true, but let’s say (for the sake of argument) that this is a once-in-twenty-five year flood.

Maths time: in any 6 months, your chance of having a 1-in-50 year flood is 1/100. 1/50 for the more likely 25-year flood. The chance of having both, though, is those numbers multiplied together. 1 in 5000. Which doesn’t, at face value, look like a particularly big number; but that’s because we’re not great at judging magnitude. Something that has that chance of happening within 6 months should, on average, have happened once in the last 2,500 years. That’s once, since the start of the Iron Age.*

The problem with probability, though, is that you can’t say: this will definitely only happen once. It could happen three times within a week,** and still be within the bounds of probability. It could still happen, within the rules of our simple model; it is just highly unlikely to happen. If it does, you’ve just seen something amazing, but it doesn’t necessarily mean that your starting figures are off. On the other hand: if something happens that, according to your figures, is highly unlikely, it does make more sense sometimes to decide that the numbers you’re basing your statistics on are out of date. Suddenly, big floods aren’t rare any more.

* slightly more than once, to be honest, because the Iron Age started about 2,700 years ago.

** Hull was flooded twice, 14 days apart, in summer 2007. Some of the floodwaters in unimportant places, such as verges and parks, still hadn’t drained from the first flood when the second (and worse) flood came. That, though, means that normal “multiply the two numbers together” probabilities don’t work. The two floods weren’t independent of each other, because of all that water lying about, so the probability of the second was rather lower than it would have been.

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Memories of the year

In which we remember things we’ve done


Last year, I spread my favourite memories over a series of posts, and wrote each one up properly. This year, I’m still feeling rather woozy and fuzzy-headed; but, nonetheless, these are the things I remember most clearly about the year.

The sight of Devon in January. Driving down the M5 in the dark, and wondering what it would look like in the daylight; then the next morning seeing everything clearly.

Getting on a plane for the first time, and feeling it throw me back in my seat on take-off. I didn’t realise, beforehand, just how forceful it feels. I tried to identify towns, roads, railways from the window, but didn’t do very well. From what I did recognise, we took a very sinuous course around southern England before heading out over the Channel.

Driving around town in the middle of summer, trying to find my way to work, via a route that wasn’t closed by flooding. The estates and marshland east of town were being pumped out by the army; not many routes were passable. Thinking: it’s a bit silly making the sea defences bigger and louder, only to get swamped by the rain.

And, finally: at the end of summer, on a Sunday afternoon, sitting on a stile listening to church bells, and all the other noises one hears at such times.

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Juxtaposition

In which sometimes things can be too successful


News story of the week (as of Wednesday)

News story of the week (as of today), including the Cerne Abbas local area.

Does anyone else think: sometimes an idea can work too well?

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Just for once…

In which the world spins around us


…I am going to write a post without a one-word title.

The news is full of utterly incompetent terrorists; politics is all changing;* and the floodwaters are finally dropping.** And, I’ve been all quiet. Because I’ve been feeling absolutely terrible – as if I’m going to be sick any minute, without ever actually being sick.

Oh, and there was a wedding party, too; and the usual turning world.

On Doctor Who: I have a long post planned, about the similarities between the series finale and the books of Pratchett. It can wait, though, until I have more energy. And until Ian is back from his holidays, so I don’t accidentally spoil anything. I wonder what he might be getting up to.***

* this may be an exaggeration

** unless you live near Doncaster

*** and if there will be photos.

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Floods

In which the waters rise again


Everyone has a flood story at the moment. Lots of people who couldn’t drive home, who had to abandon their cars in the street. People whose houses were cut off, who had to wade home. Phone photos of water, water, everywhere. Some rivers burst their banks last night, and have expended themselves, run out of effort. Other rivers are still rising – our branch office was evacuated late this afternoon, and the escaping staff saw rescue officers tying motorboats up in the dry streets, ready for the flood water expected to come.

I’ve stayed dry myself, although at some points last night we were cut off, if we’d tried to go out. I slept fitfully, wondering if it would rise more, creep over the front step and into the hallway. And the clouds outside are dark again; still more rain to come.

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Alarming

In which there is a flood, and the flood sirens stay silent as per specification


A few months back now, the Local Council decided to spend lots and lots of money on flood warning. They picked the most advanced flood warning system they could find, and erected enormous, giant-scale towers around the town, with large banks of speakers on top. They published maps of the town, with circles spattered over them, looking rather like those 1980s maps of nuclear blast radius,* so everyone knew which areas would be able to hear the flood sirens.

And now, with the worst rainfall for years, and roads closed or barely passable all over town, what have the flood sirens done? Absolutely bugger all, of course. Because that’s not the sort of flood they’re designed for. They’re to warn us against floods from the river defences failing, or the New Haven** bursting its banks. Neither have happened, although the New Haven looked to be within a few inches of a breach yesterday. Instead, we have flooding here because the Council don’t bother cleaning the drains out, so all the rainwater puddles on the roads.

* Talking of nuclear blast radius, who was the “psychic” who “predicted” that Hull would be destroyed by a nuclear attack in 1981? I really must look him up some time.

** It’s the “New” bit of the sluggish stream running through town, because it was cut in the sixteenth century.

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