No need to be mystified. Just put two drops of water on the counter, and then
use your finger to pick one up, and then drag the whole shebang around. Your
finger would be gravity, the droplets demonstrate the affinity water has to
itself in space.
You do make a good point... I was making a very dangerous assumption and
picturing this all from what I normally see, let alone cover a couple chapters
of text in 4 paragraphs.
With what I'm used to dealing with... The compaction was already created by
unsorted material off a glacier and then a glacial lake laying a very thick
and very fine layer of clays on top of of that material to create a nearly
impervious soil. This will happen on any alluvial plain or historic costal
area. Some it's more graphic than others, which pre-Euro history, or over
geologic time in different climate, were most likely swamps or marshes.
Anyway, if there's no connectivity between droplets, water isn't going
anywhere. The streams have enough energy from watershed wide impervious or
lack of vegetation to downcut so that base flow is no longer connected to the
floodplain. There's nothing to pull water through those fine materials
besides gravity (lost the affinity effect), as they're now basically two
separate systems.
This is totally different on larger grained soils, which most of the world is
fortunate in having, and is why you were like "huh?" :)
Todd
The Muddy Maumee Madness, Toledo, OH
It's never too late to have a happy childhood.
http://www.farmertodd.com
----- Original Message -----
From: "Gerald Pottern" <gbpottern-in-yahoo.com>
To: "NANFA-List" <nanfa-l-digest-in-nanfa.org>
Sent: Friday, July 14, 2006 4:40 PM
Subject: NANFA-L-- Todd's Floodplain Physics Lesson
> Hi Todd -- can you please explain further the physics
> behind your statement below, why pools on a floodplain
> drain away SLOWER after a channel has become incised ?
> I dont understand how/why this would occur, unless
> there's also some soil compaction going on as a result
> of channel incision. The capillary action/ water
> continuum thing is especially mystifying. Does
> channel incision cause air voids in the soil that
> inhibit water percolation or something like that ?
>
> --Gerald, hangin on the Neuse
>
>>> Todd Crail wrote:
>
> What it sounds like (if it were here in OH, MI, IN) is
> that you had hydrologically connected wetland features
> on the historic floodplain, but the high to peak
> discharge of the stream has downcut material from the
> river channel so that the base flow channel of the
> stream is _far_ below the watertable. This forces the
> water to drip off the old floodplain (and sit fetid
> with'skeeters that everyone whines about), rather than
> pull via capillary action through the soils back into
> the river (water is a continuum when connected, and
> this water would "disappear" much more quickly if the
> channel wasn't whacked, ...
> http://mail.yahoo.com
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