Re: Why is New Orleans sinking?


anothername@xxxxxxxxxxxxxxx wrote:
> I have read New Orleans is sinking (anyone know how much in the last
> 100 years or so?). If so, why? Is it becuase the soil is drying out? Or
> is it from the pounding by cars and construction and such? Or some
> other reason? Why would land at New Orleans sink and not, the land
> under Lake Ponchatrane? Or nearby other land?

John Lansford explains subsidence in a flood plain quite well. Land
that is formed by rivers has a lot of organic material (peat). Microbes
digest the organic material as well as any metals. As long as the land
is wet, the digestion is anaerobic and relatively slow. What is
digested is replaced by silt layed down by the next flood cycle. Think
about Egypt before the Aswan dam.

If the land dries out, the digestion is aerobic. Aerobic digestion
produces carbon dioxide as a by product and is relatively faster than
anaerobic digestion. About every ten years or so, a village or
ecosystem in a valley will be destroyed by the land "belching" out a
bubble of carbon dioxide under an atmospheric inversion. The last
carbon dioxide bubble that killed people was somewhere in Africa. How
would you plan to counter that naturla disaster?

The Coachella Valley (Indio, Salton Sea) in California has subsided
about 35 feet since the 1910s. About the same that New Orleans has
subsided since the 1880s, as I remember. Todays' research project is to
find documents on subsidence. USGS records is a start.

Where the land does stay wet, the digestion is anaerobic. One byproduct
gas is methane (swamp gas). In addition to smelling bad, swampy areas
grow mosquitoes. People don't do well in swampy areas. So they don't
live in swamps. Anaerobic digestion of metals produces some very nasty
things. One being methyl mercury which gets into the food chain and
concentrates in fat. Old (large) fish will have high levels of methyl
mercury. As the people die off, the medicine men warn of evil spirits
and zoning people discourage construction.

Landfills harvest methane and have "impervious" membranes to trap evil
spirits.

In years past, medicine men have kept people out of dangerous areas by
invoking evil spirits. Today, keeping people out is the job of the
zoning board and the health department.

Another factor of subsidence is expansive soils. When clays get wet
they expand and hinder any additional movement of water. This is the
basis of the slurry wall. When sandy soils get wet, the water fills in
the spaces between grains. The angle of repose of a sand dune may
change depending on moisture presence or the sharpness of the sand.
Besides shrinking, clayey soils lose their strength when they dry out.
Clay also hydrates.

Road builders, as far as I can tell, use California Load Bearing Ratios
as the test to determine whether fill or compaction is needed to keep
the road from settling. Some of these tests use a radioactive source to
determine the amount of water and as a predictor of expansive soil.
Those tests are more in John Lansford's field.

What may be a larger disaster than a New Orleans flood is the death of
the Mississippi delta. A river will naturally meander. One year going
here, the next year going there. When the river gets channeled, the
same area remains wet and the same areas remain dry. Eventually
selectively killing microbes and such that live there. When the natural
system does return, either from drought or flood, the area does not
have the ability to recover in a short time. Some rivers in Ohio and
West Virgina, for example. The entire area may die off for twenty to
fifty years.

Pumping ground water from aquifers is producing subsidence in Texas,
Arizona and dry areas. Problem is, when the ground subsides, it can no
longer absorb as much water. Think of a sponge that is squeezed dry and
then compacted. When it does rain, flash flooding is even more likely.
In the Coachella Valley some wells are pumping water from a thousand
feet in areas where water could once be found at twenty feet.

Nevada and California go to great pains to settle out organic material
from the road drains before it gets into Lake Tahoe. The same measures
would be useful in other areas if the factions would stop this "global
warming" fighting. Like two kids in the back seat. Touched me. Did not,
Did too. Costs too much money. Does not. Does too. No return on
investment. Does not, does too. Don't even ask.

Squirting duck dung through your teeth may begin at this time.

.

Loading