From the specific to the general...
Normally, when there is accretion, that deposited land
becomes part of the territory to which it is
deposited. If significant accretion causes a change
in the riverbed, then the border will move, following
either the median line or the thalweg. If there is an
avulsion, the border will not change and remains where
the old channel was.
I am getting this from:
http://www.mhhe.com/earthsci/geology/mcconnell/streams/channel.htm
http://www.nebraskasurveyor.com/rip-bnd.html
So borders will generally move by accretion, but not
by avulsion. Any other exceptions worldwide?

--- "Lowell G. McManus" <mcmanus71496@...> wrote:

> Michael,
>
> The 1970 treaty provided for several artificial
> channel relocations and the
> placement of the boundary into their specified
> middle lines upon their
> completion. It also says that the boundary moves
> with the middle of the
> accreting main channel in the natural segments, each
> state being entitled to
> efforts to stabilize its banks. If the river moves
> by avulsion, the boundary
> also moves, subject to a three-year delay for the
> losing state to exercise the
> option or restoring the boundary to the original
> channel at its expense. If the
> land lost is more than 250 hectares or has more than
> 100 residents, the boundary
> stays put permanently, and it is the duty of both
> governments to restore the
> river to the former channel at their joint expense.
> Prior to the 1970 treaty,
> changes by accretion and avulsion were handled quite
> differently, although the
> pertinent documents are not on-line.
>
> Only the USGS can explain why it maps the way it
> maps. As to the map in
> question, I suspect that they show the most recent
> river locations and have
> applied the specified boundary in the new artificial
> channel. They appear not
> to have revised the boundary shown in the
> neighboring natural channel, even on
> the new portion of the map. Note that neither have
> they revised their contours.
> In the natural channel just upstream from the large
> arc, they show the boundary
> touching the Mexican bank and the 100-foot contour
> is in the middle of the
> river! Apparently, they have revised the river
> throughout and the boundary in
> the artificial channel, but not the boundary in the
> natural channels nor the
> contours.
>
> The IBWC makes a fresh map of the evolving boundary
> at least every ten years
> (drawn onto aerial photos). I suspect that their
> schedule is out of sync with
> the USGS's map revision schedule, and the USGS is
> loathe to move its depiction
> of a boundary without authority on paper from the
> IBWC, even though their own
> aerial photos show that the river has evolved.
>
> Lowell G. McManus
> Leesville, Louisiana, USA
>
>
> ----- Original Message -----
> From: "Michael Kaufman" <mikekaufman79@...>
> To: <BoundaryPoint@yahoogroups.com>
> Sent: Friday, July 16, 2004 12:33 AM
> Subject: Re: [BoundaryPoint] world class border arc
> census was Re: real bjneng
> try afoot
>
>
> > Ok thanks.
> > In http://tinyurl.com/5ppgp how come the border
> hits
> > both river banks? Isn't it supposed to be the
> median
> > line in the river?
> > Also in the same map, if you pan NE you can see an
> old
> > map with the 2 meanders (and the border running
> > through them). Here also the border is not in the
> > middle of the river. In fact there it ran on land
> in
> > one part. I CAN understand this (avulsions,
> > accretions would NOT affect the border normally,
> > right?).
> > But this brings me back to my first question -
> where
> > the current border hits the banks - didn't the
> 1970
> > treaty make it so it was the median line even if
> the
> > river moved? (Or am I not understanding this
> > correctly?)
> > -Mike
> >
> >
> > --- "Lowell G. McManus" <mcmanus71496@...>
> wrote:
> > > Michael,
> > >
> > > See my insertions below.
> > >
> > > Lowell G. McManus
> > > Leesville, Louisiana, USA
> > >
> > >
> > > ----- Original Message -----
> > > From: "Michael Kaufman"
> <mikekaufman79@...>
> > > To: <BoundaryPoint@yahoogroups.com>
> > > Sent: Wednesday, July 14, 2004 10:55 PM
> > > Subject: Re: [BoundaryPoint] world class border
> arc
> > > census was Re: real bjneng
> > > try afoot
> > >
> > >
> > > > Thanks for these maps:
> > > > For 1. Is the arc the one which faces north
> with
> > > the
> > > > "HUA" of CHIHUAHUA under it and the "S" of
> TEXAS
> > > above
> > > > it? Or the tighter one facing south just to
> the
> > > right
> > > > of it? Or the real wide one facing northeast
> to
> > > the
> > > > right of that?
> > >
> > > The arc in this map ( http://tinyurl.com/6msfp )
> is
> > > the really wide curve. The
> > > others are bends in the natural channel above
> the
> > > beginning of the artificial
> > > channel. There is a short tangent stitch in the
> > > artificial channel connecting
> > > the natural channel to the beginning of the wide
> > > arc. After making the arc, the
> > > artificial channel enters a very long tangent
> for
> > > over five miles. The former
> > > natural channel is represented on this map by
> the
> > > line that wanders away to the
> > > lower left.
> > >
> > > > 2. Arc is the wide curve facing WSW where the
> > > other
> > > > stream comes in?
> > >
> > > Yes. In this map ( http://tinyurl.com/6u56h ),
> the
> > > arc comes at the end of the
> > > very long tangent mentioned above. The other
> stream
> > > coming in is the old
> > > channel. Notice how it formerly crossed the
> middle
> > > of the arc. After the arc,
> > > there is another short tangent before this
> segment
> > > of the relocation ends as the
> > > river resumes its natural channel.
> > >
> > > > 3. Arc faces NNE to the right of "CO" of
> PRESIDIO
> > > CO?
> > > > Or facing S/SSW just below BM 252?
> > >
> > > The former. Between arcs 2 and 3, the river has
> > > occupied its natural channel
> > > between the cities of Presidio and Ojinaga.
> Just
> > > below the highway bridge, it
> > > enters a tangent artificial channel of
> approximately
> > > 1.25 miles without any
> > > transitional arc. Then, in this map (
> > > http://tinyurl.com/6qgrl ), that tangent
> > > ends with a transitional arc back to the natural
> > > channel just above the railroad
> > > bridge. The curve near the benchmark is a
> natural
> > > bend. There are two more
> > > tangent artificial channels in the area below
> the
> > > railroad bridge, but they are
> > > without transitional arcs.
> > >
> > > > 4. I remember seeing this before - the 1/4
> circle
> > > > facing SE.
> > >
> > > Yes. At http://tinyurl.com/5ppgp , you can see
> the
> > > natural channel making a
> > > large meander off to the northwest of this arc.
> It
> > > makes another large meander
> > > to the north of the artificial tangent just
> below
> > > the arc. The relocation here
> > > eliminated both meanders in the river and
> boundary.
> > >
> > > > Also - Is Beaver Island somewhere in this
> > > vicinity?
> > > > Is this still an island (if it is in the area,
> did
> > > > rechannelization have an effect?)?
> > >
> > > The "Beaver Island" tract that was transferred
> to
> > > Mexico in the 1970 treaty was
> > > located near Roma-Los Saenz, Texas (about 48 air
> > > miles upriver from the fourth
> > > arc above). It was where the word "Tamaulipas"
> now
> > > appears on the map at
> > > http://tinyurl.com/54zcp . It was a rather
> squarish
> > > piece of the USA had been
> > > been orphaned high-and-dry on the southern side
> of
> > > the river by a much earlier
> > > avulsion. This tract and the more contentious
> > > Horc�n tract, on which part of
> > > the town of R�o Rico had unwittingly developed
> > > (about 26 air miles downriver
> > > from the fourth arc above) were transferred to
> > > Mexico in exchange for the two
> > > meanders gained by the USA at the artificial
> fourth
> > > arc. No channel relocations
> > > were necessary for the transfer of the Beaver
> Island
> > > and Horc�n tracts because
> > > both were already on the southern side of the
> > > existing river. The island within
> > > the river that is visible on the map belongs to
> the
> > > USA.
> > >
> > > > -Mike
> > > >
> > > >
> > > > --- "Lowell G. McManus" <mcmanus71496@...>
> > > wrote:
> > > > > The maps from the MXUS Treaty of 1970
> showing
> > > four
> > > > > arcs are at a scale of
> > > > > 1:20,000 on three long sheets, each about
> one
> > > foot
> > > > > by three feet. They are
> > > > > black-and-white aerial photos with the
> > > boundaries
> > > > > through both the old channels
> > > > > (shown by lines between numbered traverse
> > > points)
> > > > > and the projected relocated
> > > > > channels plotted onto them.
> > > > >
> > > > > I can scan pertinent portions of these maps
> for
> > > you
> > > > > on request. Meanwhile, here
> > > > > are links to view the arcs on USGS topo maps
> > > showing
> > > > > the arcs in the relocated
> > > > > channels.
> > > > >
> > > > > There are three arcs in the Presidio/Ojinaga
> > > area:
> > > > > Curve No. 1: http://tinyurl.com/6msfp
> > > > > Curve No. 2: http://tinyurl.com/6u56h
> > > > > Curve No. 3: http://tinyurl.com/6qgrl
> > > > >
> > > > > The fourth is above Hidalgo/Reynosa:
> > > > > http://tinyurl.com/5ppgp
> > >
> > > > >
> > > > > Lowell G. McManus
> > > > > Leesville, Louisiana, USA
> > >
> >
> >
> >
> >
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