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Benchmark smokestack destroyed. How much documentation to report?


amazar

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My first two benchmarks I tried, PO0741 and PO0737, appear to have both been destroyed icon_frown.gif. I've looked through a local archives and have posted historical aerial photographs depicting PO0741 before it was destroyed. Can I/should I report it destroyed?

 

(I did find my third one PO0742. icon_smile.gif )

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You don't want to log a benchmark as destroyed unless you're absolutely sure that it is. Many times a brasscap may not be found, and assumed to be destroyed, just because it was not found. This happens often when the surrounding area conditions have changed a great deal, even though the mark may only be covered and/or hidden from view and still be in a usable condition.

 

A smokestack, on the other hand, used for triangulations are a bit easier to determine if they are destroyed or not. They're not as easy to hide. They were used as triangulation marks because they could be seen from a great distance. Even if the surrounding area conditions have changed, or the coordinates are off a few hundred feet, if you can't see it anymore, it's probably not there.

 

Just be absolutely sure that it's gone if you decide to log it as destroyed. I still may be hidden right behind that tree...

 

Keep on Caching!

- Kewaneh

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OK, well, for PO0741, since the benchmark IS the stack and I have aerial photographs clearly showing where it was and is no longer, I guess it is safe to say it is gone.

 

But what about something like PO737, where the benchmarke is a pipe cap at the top of a knoll. Again, I have aerial photographs showing where the knoll was and the parking lot and building that replaced it. I'm not so sure that this proves that the pipe cap is gone. Could it still be there - now on the roof of the building? Unfortunately, the angle of the aerial photographs is not identical, so I can't tell where in the building or parking lot the pipe cap would end up.

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If the structure or land on which a disk (or nail, or similar device) had previously been installed is no longer present, the mark might be replaced, but it would probably be designated a "reset." For example, if the old designation was HILL, and the hill where it was located was graded for new construction, a new station may be placed with the designation HILL RESET, which would have a new PID.

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The designation RESET is applied to geodetic control monuments in one of two ways. A typical bench mark (vertical control point only) was not established with either an underground or nearby reference marks. Should such a mark be in danger or being disturbed or destroyed, the National Geodetic Survey (formerly the Coast and Geodetic Survey) would attempt to establish a new monument nearby with a direct vertical survey connection between the two monuments. The new mark would be given the designation of the old mark (e.g. B 173) plus the work RESET stamped on the disk.

 

In the case of horizontal control points (also referred to as Bench Marks on this board), the vast majority were established with either or both an underground mark centered directly below the surface mark, and/or two or more nearby reference marks (disks with arrows) usually set within 100 ft. In the surface mark were disturbed or destroyed it could be RESET by using the information from the reference marks, assuming they had not also been disturbed or destroyed, and/or centered over the underground mark it if could be located. In these cases the surface mark would be stamped with the name of the original station with the original date it was established and the date of the reset added. Should a horizontal station be moved from is original position, a new mark would be set with the name of the original station and a number 2, 3 etc. added (e.g. WHITE 2).

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