I know all the information has to match the datum used.
My question is: what is the best way to handle the BFE that are given in NGVD 29 elevation:
1) Convert the BFE that is on NGVD 29 Datum to a BFE NAVD 88 Datum and put in the notes that the conversion was made?
2) Convert the bench mark NAVD 88 elevation to NGVD 29 Datum and use the NGVD 29 BFE elevation in B9?
If the bm has an NGS data sheet there is probably an NGVD29 value listed under SUPERCEDED down in the middle of the sheet.
Bill93, post: 397556, member: 87 wrote: If the bm has an NGS data sheet there is probably an NGVD29 value listed under SUPERCEDED down in the middle of the sheet.
It does, I was also wondering if we should report everything now in NAVD 88 if it was available.
Thanks,
Ed
I use what the FIRM and FIS maps state because that is what it used for flood insurance or building permits, and then make a note in Section D stating my process
New FIRMs are in NAVD 88 so you need to match that. Either by using a fairly new benchmark or by converting from an old one. Old FIRMs that are still valid are in NGVD 29. Either use an older benchmark or prepare to convert a fairly new one to NGVD 29.
Holy Cow, post: 397578, member: 50 wrote: New FIRMs are in NAVD 88 so you need to match that. Either by using a fairly new benchmark or by converting from an old one. Old FIRMs that are still valid are in NGVD 29. Either use an older benchmark or prepare to convert a fairly new one to NGVD 29.
The FIRM is an older one with the BFE in NGVD 29, so I used the superseded elevation from the Datasheet and kept everything on NGVD 29 datum.
Thanks,
Ed
Good job.
I come across that quite often. One way is to look in the FIS where they state what the conversion is. Sometimes it isn't the same value when I use VERTCON. If this is the case, I note the conversion used and the page on the FIS where I found it. If not, I state that I used VERTCON. Unfortunately, the newer maps don't show RM so I go to the archives, find the closest RM from the old FIRM, state what was used and what the conversion factor is.
I have spent hours on the phone and thru emails on this one with FEMA. We are in a subsidence area where BM's have been updated twice in the last few years but our maps are in the 29 datum. What we do us use the most current published NAVD 88 elev. on a BM and then convert it to the 29 datum and use it to fill out section C .
Lamon Miller, post: 397626, member: 553 wrote: I have spent hours on the phone and thru emails on this one with FEMA. We are in a subsidence area where BM's have been updated twice in the last few years but our maps are in the 29 datum. What we do us use the most current published NAVD 88 elev. on a BM and then convert it to the 29 datum and use it to fill out section C .
Make lemonade. Prepare an SOQ for a community wide flood study.
