Comment by saalweachter
8 years ago
Also too, of course you should build your "prevent floods from wrecking our shit" system to handle floods "beyond anything we've seen before". Building it to handle less than what you've seen before would be stupid.
> Building it to handle less than what you've seen before would be stupid.
Let me tell a second hand anecdote of a Burmese village.
It was a rather small collection of huts raised on tall poles. But it was a village none the less.
All paths in the village were laid out with a connected mass of wood. Along the path were sticks, rising pretty high up in the air. Somewhere along the top of the sticks were a lot of cuts made out in the wood, at various heights. By a knife or so.
In the dry season, this path laid on the ground to be walked on. You didn't have to walk on it of course, since the surrounding dirt was dry.
In the wet season however, floods often came. And so, they raised the path up along the sticks so that it became a water bridge for when floods came. They raised it to the level of the highest cuts that were made in the sticks. A very reasonable thing to do, in order to connect the village in times of crisis, without using boats.
Interestingly, however was the background of the cuts. Each cut represented a water height that had some time ago been the highest the flood had become. So each season, they only raised the water bridge to the level of the worst flood they had experienced.
They did not have a margin.
While they didn't prepare for less than what they had previously seen, they only prepared for the worst flood in history, and not the worst flood in history + a margin.
Probably going over the margin would be a matter of wet feet and moving some bamboo which wouldn't be as big a deal as flooding Tokyo.
Were the flood waters raging? Or placid?
Did they have room on the uprights to tie the cross members higher? Maybe the flood water held the wood up (buoyancy) and the uprights were there as anchors.
How did they raise the wood? I imagine it weighed a lot.
Interesting story. Never knew that and I am a Burmese.
That isn't entirely true. How much is it worth to upgrade from a "once every 500 years" system to a "once every 5000 years" system? If it's more than the expected damages...
Well if my country floods its all over, considering we're under sea level the water may never leave.
And I can imagine Japan doesn't want to risk Tokio.
When you start talking truly cataclysmic events, the value of the physical infrastructure at risk will be dwarfed by the human lives. In 2016, the assessed value of all real estate in Manhattan crossed the $1 trillion threshold (which of course leaves out the bridges, the subways, the personal property...) At a value of $9.1 million / life, there are $77.7 trillion worth of humans in New York City.
If there's a natural disaster which would wipe out the population of New York once every 5000 years, we should be willing to spend $15 billion per year to prevent it.