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Thread: Route Around Removed Pemi Wld. Bridge?

  1. #31
    Senior Member MichaelJ's Avatar
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    Because UTM is a Mercator Projection, perhaps?

    Note that if you look on the bottom-left corner of the USGS Crawford Notch quad, it states:

    Horizontal Datum ……………… 1927 North American Datum
    To place on the predicted North American Datum of 1983, move the project lines as shown by dashed corner ticks (3 meters south and 39 meters west).
    So:
    a) It appears the 30-40m is the correct one for on-the-ground distance.

    2) Ahh … THAT's what those little tick marks on the map are!
    May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view. May your mountains rise into and above the clouds. - Edward Abbey

  2. #32
    Senior Member DougPaul's Avatar
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    Quote Originally Posted by MichaelJ View Post
    Because UTM is a Mercator Projection, perhaps?
    Don't know--I'm no expert on projections from a spheroidal earth to flat pieces of paper.

    Lat and Lon are well matched to locating positions on a spheroidal earth so I regard them as the "best"* means of specifying locations.

    In contrast, UTM is a collection of 60 local projections of zones from the spheroid to flat maps. Perhaps the difference is due to errors in these projections. Or perhaps the projection from lat-lon to UTM is sensitive to the datum.

    * While either method can specify a location to any accuracy, lat-lon allows one to calculate the relationships (eg distance and direction) between two points accurately whereas any projection to a flat representation contains distortions which will introduce errors in the relationships.


    Horizontal Datum ……………… 1927 North American Datum
    To place on the predicted North American Datum of 1983, move the project lines as shown by dashed corner ticks (3 meters south and 39 meters west).
    So:
    a) It appears the 30-40m is the correct one for on-the-ground distance.
    Agreed for a lat-lon representation, but my evidence suggests that it is not true for a UTM representation.

    <comment>
    My initial assumption was that the change due to the datums should be the same for either position representation (my 226m figure was computed in UTM based upon this assumption), however the evidence is suggesting that it is not the same.
    </comment>


    I think it is worthwhile to be aware that position errors due to using the wrong datum are much greater (at least in the Crawford Notch area) using UTM than when using lat-lon. However, I've spent enough time on this issue and will be happy to wait for someone adequately knowledgeable about map projections and datums to explain why.

    My basic point remains: one should specify the datum with the coordinates.

    Time to get back to the Pemi Wilderness?

    Doug
    Last edited by DougPaul; 10-26-2011 at 09:53 PM.

  3. #33
    Senior Member forestgnome's Avatar
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    Quote Originally Posted by Stan View Post
    Any speculation on the best crossing with xc skis? By this I mean an area where the snow might drift deep enough to form a secure bridge, the water generally shallow enough not to drop you in to your hips if it isn't secure and the banks low enough to scamper up without removing the skis.
    I've been thinking about this as well. I've been wanting to try xc skiing and this was the route everyone described as the best in the Whites for easy skiing Too bad I never got to enjoy it before it was taken from the public. I'm hoping that at some point a natural bridge will form at some point if you go far enough upstream. I would be nervous to be over water with planks attached to me feet. Anyone?

  4. #34
    Senior Member Becca M's Avatar
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    Quote Originally Posted by forestgnome View Post
    I've been thinking about this as well. I've been wanting to try xc skiing and this was the route everyone described as the best in the Whites for easy skiing Too bad I never got to enjoy it before it was taken from the public. I'm hoping that at some point a natural bridge will form at some point if you go far enough upstream. I would be nervous to be over water with planks attached to me feet. Anyone?
    End of Feb last year, it was common to see ski tracks crossing the Pemi River where the old suspension bridge was. Snow bridging looked good, but, I would be scared to cross the Pemi River there because once ya sink a ski there, you might as well have a boat anchor around your neck :0 Near the Thoreau Falls Trail Bridge, the water was moving too fast and deep to create a snow bridge, so, hopefully *that* bridge will be there for a while!!!!!
    Yay for winter!!!!!

  5. #35
    Senior Member DougPaul's Avatar
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    Quote Originally Posted by Becca M View Post
    End of Feb last year, it was common to see ski tracks crossing the Pemi River where the old suspension bridge was. Snow bridging looked good, but, I would be scared to cross the Pemi River there because once ya sink a ski there, you might as well have a boat anchor around your neck :0
    The crossing didn't look too bad... (there are ski tracks visible over on the right)

    There were also ski tracks on portions of the N Branch. (FWIW, Goodman suggests skiing on the river in his guidebook.) We probably could have crossed without difficulty at the location of the old crossing that I mentioned earlier in the thread--I did it out and back in 2002.

    Near the Thoreau Falls Trail Bridge, the water was moving too fast and deep to create a snow bridge, so, hopefully *that* bridge will be there for a while!!!!!
    Keeping my fingers (and ski tips) crossed...

    Courtesy of my pics (their memory is better than mine...) it looked crossable above the bridge but not below. Pics at http://mysite.verizon.net/dbpwebjunk...-22/index.html

    Doug
    Last edited by DougPaul; 11-01-2011 at 11:17 AM.

  6. #36
    Senior Member Becca M's Avatar
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    another question

    Another question:

    Do people who have been to the mouth of the North Fork into the Pemi River think a river crossing of the North Fork would be easier to find coming from the north side of the Pemi (from the Lincoln Woods Trail) or from the East side of the North Fork (just after the Thoreau Falls Trail Bridge)?
    Yay for winter!!!!!

  7. #37
    Senior Member Becca M's Avatar
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    Today I roughly followed the North Fork crossing location - at the mouth of the North Fork into the Pemi. The crossing right at the mouth definitely looked the most favorable compared to upstream. It was pretty wide and semi-shallow, but, a LOT of rock hopping as a result of the width.

    Although I continued north (rather than west along the pemi to the Black Brook/molly monument area), the woods in general seemed reasonably open.
    Yay for winter!!!!!

  8. #38
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    Quote Originally Posted by Becca M View Post
    The crossing right at the mouth definitely looked the most favorable compared to upstream. It was pretty wide and semi-shallow, but, a LOT of rock hopping as a result of the width.
    We found that spot wide and slow, but with several yards pretty deep compared to upstream a little bit. One described it as requiring "swimming" through that short stretch of the crossing, but I'll certainly take another look.

    Quote Originally Posted by Becca M View Post
    Although I continued north (rather than west along the pemi to the Black Brook/molly monument area), the woods in general seemed reasonably open.
    Yes, that's a major issue here. You go high up and it seems it may be easy *, or keep low to the East branch and it's easy, with some interruptions. It's that mid-level, 20-150 yards or so up the East Branch bank that has some horrors.

    * and there's that old rail bed up high as you get closer to the monuments. My attraction to staying low to the East Branch bank is that it's such a pretty walk (not that open woods high up isn't nice too).

  9. #39
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    I just did the Molly Route from the foot of the Bondcliff Trail to the Thoreau Falls Trail for the first time in years, with a newer GPS to check old data, and things are pretty much as I reported and the data points accurate. Amazingly, cheap consumer GPS gadgets are apparently a lot more accurate than a lot of maps! I was again walking at times in the middle of the River or even on the other side, according to the maps.

    The abandoned section of the Wilderness Trail is clearer than it was: the NFS seems to have given up hiding it from us. Most of the saplings are gone and the debris kicked to the side. It’s a trail. The path from the top of the removed bridge down to the river is less clear, that’s puzzling, but it’s still there. Lots of footprints in the sand along the river moving towards the Thoreau Falls Trail.

    I stayed on the River’s edge for all but maybe 5-6 very short sections where I had to go only a few yards in, twice about 20 yards in but never deeper into the woods. There lie monsters. The first detour was right at the beginning, but very quickly back out to the “easy ledges” I had described. I’m sure there are good paths way further up the bank but I enjoy walking along the River as long as the flow level allows it. Sometimes you temporarily rock step out into the river to keep going, counter-intuitive, just look ahead for your easiest steps. Better stepping on low flatish rocks out into the river than scrambling over boulders right at the shore.

    When I got to the island I talked about, I decided to just walk the island itself. Very nice. End to end. Easy walking and some nice resting spots.

    Crossing the N branch of the E Pemi was much easier than it was as I remembered. I did it much lower ( just a short way N of the fork) and dry booted across. My convoluted route from there to N of the the needlessly-destroyed Thoreau Falls Bridge and the Trail is still there. I’m sure there is easier, but what I reported works. The two campsites I mentioned show disuse, also puzzling; I guess the destruction of the three bridges in this area has drastically reduced visitation, I guess that was the Plan. The Thoreau Falls Trail itself seems much less travelled, I really felt alone.

    A thoroughly enjoyable trip, Been away from it too long.

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