While the concept of a thalweg is simple enough, its practical application can
be as fraught with as many problems as its alter ego, the ridge line. In fact,
the ridge line makes a perfect analogy in reverse for the thalweg.
Early diplomats, with inexact and/or overly simplified notions of the lay of the
land, often resorted to ridge lines as convenient landforms on which to hang a
paper boundary. These ridge lines, however, were often more complex than they
imagined, resulting in conflicting claims and requiring renegotiation a
generation or so later. The northern boundary of Maine is a case in point,
where the original treaty said "along the highlands..." Reality is seldom that
simple. Mountain ranges are not the "woolly worms" that early cartographers
used to depict them.
Think of the following problematical ridge lines and invert them to visualize
some thalweg problems:
1. What if a drainage divide follows a relatively low range of hills in front of
a higher ridge, the land between them draining around one end of the higher
ridge? (If this landscape were inverted to form a waterbottom, the deepest
point in a given cross section would not necessarily be the channel through
which the current would flow continuously at low water.)
2. What if the drainage divide splits into two ridges with a non-draining basin
between? (In the inverted example of the thalweg, the basin would be a shoal or
island, but what if the channels on either side of it both had their deep and
shallow sections? This can become very complex in deltas.)
3. What if the drainage divide flattens out into a plain where drainage is not
easily discerned? (The inverse would be the thalweg of a wide, flat-bottomed
river.)
I could go on, but I think you can see the point.
While the determination of a thalweg is usually easy, very difficult situations
can arise.
Lowell G. McManus
Leesville, Louisiana, USA
----- Original Message -----
From: "acroorca2002" <orc@...>
To: <BoundaryPoint@yahoogroups.com>
Sent: Friday, August 01, 2003 9:36 AM
Subject: [BoundaryPoint] Re: eelvru - > thalweg
jesper
a thalweg has nothing to do with the size of a stream
& is not arbitrary nor any mere matter of opinion
but is a fact of physics & of natural geography
exactly in the same way as a watershed or ridge line is a fact
regardless of the elevation or mass of the heights it divides
or plainer still
a thalweg is just the absolute bottom line of a valley
regardless of the dimensions of that valley or of its water flow
so why complicate this utterly simple reality with interpretations
rationalizations exceptions excuses etc
& if you are still with me here
for purposes of any earnestly punctilious try
a thalweg junction tripoint is far from an occasion for shrugging
ones shoulders or throwing up ones hands
but is actually just as flagrantly obvious & real
& just as much an occasion for dancing
as a summit tripoint
indeed
think of it as a summit tripoint in reverse & you cant miss it
you know
as in highpointing or lowpointing
only wetter
also a thalweg is definitely not an effect of navigation
on the contrary
navigation if any seeks & follows the thalweg
there doesnt need to be navigability for there to be a thalweg
there only needs to be running water
in this regard the definition quoted from gideons bible below is
incomplete & misleading
& i am just as sure as you are of the opposite
that if the treaties specify the thalwegs
as they usually do in europe & most probably do in these cases
then the thalwegs are the boundary lines
& the thalweg junctions mark the tripoints
so maybe we should look for the treaties before settling this
but as for how to know where the thalweg is
if you still cant tell from the above description
or jans fantastic picture of you pointing straight at a tri thalweg
please see also my recent answer to jan when he first asked
--- In BoundaryPoint@yahoogroups.com, "Jesper Nielsen"
<jesniel@i...> wrote:
> I would think using the thalweg-principle is only for wide rivers
where navigation is possible and normal. Probably more often
outside Europe where small rivers would be used for navigation
as well. This makes navigation possible for both countries.
>
> For smaller water courses I am sure the middle line is the
general rule.
>
> And how to know where the thalweg is? I guess people
navigation know. Otherwise onless the countries have problems
with one another it's not an issue untill something happens. Just
like land borders with poor demarcation: Nobody really cares
(only freaks) untill it is necessary to find out, with the help of
surveyors etc.
>
> Jesper
>
>
>
> > THALWEG
> > 1. «A German term, literally "downstream," with reference to
> river
> > navigation. Here referring to the deepest channel in a river,
> genereally the
> > most suitable channel for navigation at the normal lowest
> water level.»
> > (Biger, p. 522)
> >
> > (How to find the deepest channel in a 5 metre broad river?!?)
>
>
>
>
>
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