I am working with a 1979 Flood Study for Shepherdstown WV. 3 bench marks are listed as "Binding bolt of fire hydrant". F.S. elevations are NGVD 1929; -0.62' approx. correection to NVD 88. Google shows sidewalk elevs. about 3' lower that FEMA BMs; So, are "binding bolts" what I call bonnet bolts, near the top of the hydrant, about 2.5' higher than the sidewalk?
Good question. Another reason (perhaps) they quit putting BM's on the newer maps.
As soon as you assume something it will be wrong. They could be the bolts at the base flange, or they could be the bonnet bolts.
Be careful with fire hydrant benchmarks; there's good chance the hydrant has been replaced.
Good luck......
What does Google have to do with it?
Are you talking about a street view photo?
I too would be careful about those types of BM's
I would tie the three BM's together and see if they agree with each other.
Whee did you get the info on the Bench Mark?
The FEMA map I am looking at has several BM's shown on the map, but there is no data to tell what, where, or elevation.
How do I get this data?
thanx,
geezer
On the older maps the benchmarks were labeled RM## and the description and elevation, if not shown on either the panel or the index panel, can be found in the FIS (flood insurance study). Go to the Map Service Center - Product Catalog and select Effective FIS.
On the newer maps the benchmarks were labeled with their National Spatial Reference System (NSRS)Point Identifier (PID). You can look up the data sheets from the NGS site. Note that only First and Second Class Vertical monuments with a stability of at least C are shown and their recovery status was not researched.
DDSM:beer:
A word of advice....never use only one of these BM's.......find another one to check into.
