Benchmarking Reliability Queston

[ThugDragon]

I haven't done any benchmarking yet, but I plan too

 

My question is:

 

Since most structures settle over time, or due to erosion/weather/earthquake/etc. have shifted..... how can any benchmark really be trusted by surveyors?

 

Thanks for any clarification you can offer!

[+frex3wv]

TD: I am in no way saying I have a technical answer to your question - but.... I found a benchmark high in the WV hills in a MASSIVE rock outcropping that I bet very few human beings even know is there. With little threat of WV having any earth shifting problems .... my bet is this would be a reliable mark for a very long time.

Edited September 20, 2007 by frex3wv

[+Klemmer]

Welcome ThugDragon!

(like that name - sound very serious!)

 

Like frex3wv, IANAS (I Am Not A Surveyor), but part of the periodic adjustments of certain types of benchmarks compensate for known continental drift (especially out here in California). That should say something about their stability and accuracy. Not ALL benchmarks, mind you.

 

In your handheld consumer grade GPS terms, it will be handy for you to remember that "SCALED" benchmarks will NOT be accurate. Follow the written description for the last 600 feet or so. On the other hand, "Adjusted" benchmarks will be MORE accurate than your GPS.

 

For a newcomer, you might want to browse the "Me First" topic at the top of the forum, and there is also some good info on the Geocachng website.

[Bill93]

Most settings which extend significantly below the frost line will be pretty stable, barring movement associated with continental drift and earthquakes. A small minority of the old marks were in concrete poured into a post hole that wasn't deep enough to prevent the frozen ground from moving them a bit, and erosion has exposed others, but most are pretty good.

 

In the last few decades a lot of benchmarks have been deeply driven rods with or without a disk on top. If you go down to bedrock and sleeve the top few feet so frost won't grab it, then that mark is going to be very stable vertically.