I don't really know what kind of rechanneling might take place during
a major flood, so I suppose a natural avulsion could have taken place
between 1862 and 1891.
I wish the USGS could tell us what information they used to construct
their map. I doubt that they just guessed. Hopefully the USACE map
did not simply propagate the guess. It is a much smaller scale map,
about 1:12000 and depicts the river and adjacent features in great
detail, hopefully with great accuracy.
So I guess I'll take my maps, questions, GPS, inner tube, and tape
measure out there for a look. Maybe some new information can be
gleaned during an extended field trip.
BJB
In
BoundaryPoint@yahoogroups.com, "acroorca2002" <orc@o...> wrote:
> --- In BoundaryPoint@yahoogroups.com, "bjbutlerus"
> <bjbutler@b...> wrote:
> > The "adjustment of 1912" appears to be a vertical datum
> correction
> > that affected benchmarks all over the country, not just in the
> greater
> > MN-ND-SD area, so I think there is nothing sacred about that
> year in
> > terms of boundary changes or the DAMN line.
> >
> > BJB
>
> ok right
> this is a misidentification of what i meant
> which as i say has been eluding rediscovery
>
> perhaps more to the point are the similarly elusive references to
> many rural wetlands drained in 1912 to provide more crop land
> such as occurs at the end of
> http://midwest.fws.gov/ecosys/hilights.htm
>
> but again for the reasons mentioned
> i myself have pretty much given up on 1912
> in favor of the period between 1869 & 1891
>
> the historic records at
> http://www.rrbdin.org/floodtables.htm
> indicate devastating floods in 1871 1873 1882 & 1883
>
> & i realize you dont believe natural avulsions are even possible
> on this river
> so i wont argue with you
> except to reiterate my perhaps naive belief that if a flood on any
> stream is powerful enough for the entire flood plain to get
> scoured then the channel might resettle in a new location
>
> & i do have to mention the problematic flip side of this coin
> which is that i find it hard to imagine what 19th century manmade
> avulsions might have looked like
>
> i mean what could a very few locals & their oxen or horses have
> done to reconstruct a scene like this
> http://www.oldprintshop.com/images/large/28107.jpg
>
>
> also your puzzled observation about the old & new channels on
> your usace map seeming to be in the reversed positions
> could be resolved by a return of the stream to its old bed
> in a subsequent avulsion
>
>
> but anyway with far more questions now than we can answer
> with any confidence
> we may well have reached an impasse in our speculations
> which will only be resolved by harder data than we now have