[ExI] fermi flood was: RE: California storms

[spike at rainier66.com]

-----Original Message-----
From: spike at rainier66.com <spike at rainier66.com> 
...

>...Consequently... plenty of people come to the USA and choose homeless
here rather than homeful wherever they come from.  If one is going to live
outdoors, an overpass or under a bridge makes perfect sense...The masses
want freedom and capitalism, even if it means they must camp out here to get
there.  spike


I have been all over the map on this one, so I decided to post something
over on a yet-uncommented part of the thought-map.

The high schools play a game named for Enrico Fermi who was really good at
this: estimating the order of magnitude.  An example of a fermi question
would be: How many neutrons are in a fig newton?

A good player would estimate its mass at about 10 to 20 grams, mostly
carbon, a mole of carbon is about 12 grams, so about a mole times six
neutrons per carbon atom, so 3.6E24 neutrons approximately, and depending on
how you estimate mass, the answer might be either 24 or 25.

Local flooding: there is a footbridge across the local waterway.  I was over
there during last year's rains and noticed that the water is the color of
chocolate milk.  I found a cup and scooped out a water sample, let it settle
and observed that you aren't far off if you estimate the water is 10%
sediment by mass, perhaps 5% by volume.  There really is that much silt and
soil washing down that channel.

I was over there yesterday and estimated, Fermi style, the average depth
across there, about a meter, and its width, about ten meters.  When the
water is that color, as it is now, the flow rate is likely higher than a
meter a second, but a meter per second as a Fermi-ey estimate will get you
there.  So... after a hard rain, as we have been having all week, about ten
cubic meters per second flow rate down that channel, at about 10% silt.

Fermi question: in kg, the mass of silt carried by the Penitentia Creek
after a hard rain per second.  Answer: 3.  10^3 kg per second.  A ton of
silt per second.  This process can go on for hours, or days.

Second question: where does all that silt go?  

It gives one a new sense of how deltas form, and what happens when we need
the space to build homes, so we defeat nature's course and build a single
narrow channel where a vast river delta used to be.  

Prediction: eventually that channel will silt up and restrict flow rate,
causing water to rise along the course of that river.  Consequence: the
homeless living under those bridges will get washed out more regularly.

spike