Is this the correct way to log a benchmark that is no longer there/destroyed?

[+jeff35080]

I logged this benchmark:

 

http://www.geocaching.com/mark/details.asp?PID=DH1586

 

and took a picture of what I was trying to describe. Is this the correct method for logging something like this?

 

Jeff

http://www.StarsFellOnAlabama.com

http://www.NotAChance.com

[+embra]

I would have done it the same way...no find, but describing the rather interesting situation you *did* find.

 

I wonder why they did it that way. Would it have been done to help those searching for the disk figure out what had happened? Does it still have any surveying value?

 

Don't get even - get odd

[+Kewaneh & Shark]

That is definately a suprising find, Jeff. I think that I would have logged it just as you have done too.

 

To quickly answer Embra's questions, I would have to say 'Yes' to both. To the first question: It probably was done to help others to find the location of the benchmark, but I don't know if it would really help to figure out what happened. In the picture, on the top of the concrete, there is a painted arrow and some numbers that look like a '73'. The description of the mark designates it as 'D173' and that would probably be found if some of the rocks were moved. As far as the spike having a surveying value: provided that it's not loose, it could have value as something called a 'turning point', used when surveyors perform level runs to determine elevations of one or more points. Railroad spikes, driven into the base of power poles, large fence posts, and into the cracks of boulders, are commonly used in the area where I work to perform such tasks. I would have to say, however, that the spike in Jeff's photo has little or no value as the benchmark itself. It was probably put into the hole in the slab as it was just a convenient place to put it, and not meant to be the original place for the real benchmark. (The data sheet says the benchmark was placed in a drill hole - believe me when I say that no surveyor is going to drill all of those holes.)

 

If I had the opportunity, I would look closely (if possible) into the crevase between the 1st & 2nd layers of concrete. The 1944 description describes that it (the disk portion) was set horizontally, indicating that it was set in the top of the concrete. (Here's an example of a vertical benchmark: GT1428) I would think that it may still exist between the two slabs, (but you may not get to see it without the use of a big crane). Intrestingly enough, the original data sheet says that 'The orthometric height was determined by differential leveling and adjusted by the National Geodetic Survey in June 1991', and that it's Vertical Order is First Order/Second Class - a fairly precise level run performed by an NGS surveyor. I can only assume that the data sheet was not ammended because it was found in the condition described in 1944. I think if the surveyor would have found a spike in a hole in the side of the concrete and no actual benchmark, he would have noted it.

 

Hope this helps.

 

Keep on Caching!

- Kewaneh

[+jeff35080]

Thanks for the great answers guys! Not only is benchmark hunting fun, it's quite educational also!

 

Jeff

http://www.StarsFellOnAlabama.com

http://www.NotAChance.com

[pdumas]

Jeff, I would have done it the same way. Also a very good picture.

[Z15]

I have a different take on this.

 

While the adjusment was made in 1991, this does not mean is was leveled accross again. This is probalby the 1988 NAVD adjustment.

 

What you found could be anything and you can't assume the survey disk and the rr spike have anything in common. Someone could have looked for that mark, found where they thought is was and roughly transferred an elevation over to the spike to use and that was it. As a matter of fact I have done that very thing in the past when working for the DOT. There was a BM is the top of a culvert headwall and the headwall was raised higher, burying the disk. You could see the seam in the concrete. Our hydraulics engineers needed the river/new bridge survey to be based on the NAVD88 so ww had to come close to this elevation because there was no other BM in miles to use, besides being told to do so by the Survey Chief (PS)!

[survey tech]

El Camino is correct, the spike is unrelated to the NGS disk. Its a typical example of a new point being set near an old point by a local surveyor when he dscovers that the old one is no longer useful. By the way, since the old point is almost certainly still intact and merely covered up, it cannot be verified that it is destroyed, so the appropriate description would be not found with an explanation of the circumstances.

[+embra]

I think we've covered this ground before, but I gets confused after short-term memory fades away.

 

Today I found the remnant of a disk in the location described. The disk had been removed;all that was left was the shaft that anchored it to the concrete bridge abutment. From the description and the appearance of the concrete, I felt confident of what I thought I saw. You can see photos at JV1828.

 

We seemed to have something like a consensus that here we would call this destroyed (yes?), but I'm confused about how the NGS would regard this. Is that shaft considered a part of the disk, in which case a report of destroyed would be appropriate? If it is not a part of the disk proper, than I would presume that "not found" is the call (with a description of the current scene).

 

Don't get even - get odd

[Z15]

One thing to note. Not all those that use the marks are surveyors in the true sense of the word. My former employer had construction engineering techs that would always set BM' for road work. Very few of them cared or new much about the NGS marks. (fyiwe had 1 sruvey tech and about 25 engr techs in our region). They would drive a RR spike into anything, assume some bogus elevation and go from there. We constantly had problems with the way some these guys would do things. Most all of these techs had 2 yr civil technology degree's and new enough about surveying to be dangerous. We constantly were having to explain to people that what they did only served thier purpose on a single project and should not be taken as gospel. We even had occasions when we ran levels for the project only to have the engineering techs still asign some assumed elevation to our marks. Constant battle between the P. Surveyors and the Civil Engineers (Project Engineers) who only cared about getting the job done, no matter what. They often never protected or saved valuable points like, sections corners, plats, BMS and USGS marks etc. We had to always be one step of ahead of them and were GPS'ing all control into the Mi Coord System. Contractors were another problem and often wiped out the marks.

[survey tech]

Embra

Deb Brown at NGS has previously pronounced others like V 12 destroyed, so technically that is the appropriate description in your case, but as I have mentioned before, the fact that the shaft remains, positively identifying the spot, means that the spot is still potentially useful for some purposes, and many surveyors would not consider it destroyed. The NGS treats the disk, or other object, itself, as the whole object of the description, largely discounting the continued presence or condition of its setting or mounting, while most surveyors, motivated more by practicality, are more willing to accept the spot, sans disk, provided it can be positively identified and there is no reason to believe it has moved. The important principle to remember is that the destroyed description is not appropriate in any case where speculation about the actual presence of the marker is employed, such as the one above, which may or may not remain in place beneath the concrete slab.

[+embra]

Thanks, Surveytech, I think that sunk in this time. I make no promises for my comprehension a week from now, though...

 

Don't get even - get odd

[+jeff35080]

Survey tech is a wealth of knowledge. I really enjoy reading his posts. Although I will never be a surveyor, I really enjoy learning about it. Thanks for being willing to educate me survey tech, it is appreciated!

 

Jeff

http://www.StarsFellOnAlabama.com

http://www.NotAChance.com

[+happycycler]

Today I logged No Find for JC1223 & for JC1224. I could not say that I found them since no disks were found, they are very close together, have scaled coordinates and none of the landmarks from the description have survived.

A third one in the area JC1222 still has a disk that is mostly readable. I guess that they could be used for some purposes IF one could be sure which was which. However JC1222 may be all that is needed in that area now that the navigation lock has moved down river?