So we got a project for an elevation certificate on a project. I ran OPUS on two points. While it was running, I assumed cords and elevations on nl #1 and backed one in on 2 so I could start shooting with a total station.
Located bldg., and adjacent grades, machinery. It had a garage attached at a lower level. etc.
When we got done, I localized my gps on my assumed coordinates and datum so that I could tie to an NGS monument and some key intersection locations to help me orient the flood map.
OPUS checked vertically for 0.14, NGS mon checked for less than .2
It seems the building is about three feet lower than the base flood elevation which is determined by the flood map, squiggly black lines with elevations on them. Legend says they are base flood maps.
I double checked datums...they are OPUS and NGS and Flood map all the same NAD 83 and NAVD88.
It seems the buyer of the property is being quoted a $25k per yr premium which seems outrageous. I'm just wondering if I made a mistake. If you have time to help me, please shoot me your email and I'll send the drawing, points etc.
THX
Base flood elevations have been revised since Katrina. I know of 3 subdivisions that were not in flood plains prior, but now have 40% or more of the lots lying in the flood plain.
You might do a little research on what the designated flood elevations were in recent history.
I would be happy to help you out and review your data if you need some help. My email address is attached to my profile.
I do 8 or 10 of these a year, but my area is blessed with a County Flood Control Dept that is extremely helpful, and they are the administrator for FEMA's debacle approach to EC's. Not to mention that we have a pretty well structured NGVD 29 BM system all over. I use VERTCON over OPUS, and they are happy.
Perhaps you don't have benefit of such a data source, but my suggestion would be to just turn it in with what you found and go cash the check. 2 OPUS solution's within a couple tenths is pretty reliable IMO. Sounds like the house is too low, and 3 ft is a lot. It's not like you're chasing a tenth or 2, but 3 feet - yikes. You could double check your building diagram number, that can be a big factor too.
Don't forget that you are just the messenger, not the savior.
If you want to send me your form I can bounce it off my friends at Flood Control. They're a pretty good bunch
I think that if the flood source is riverine, which I suspect, since you describe the base flood elev. lines on the FIRM as "squiggly", then you should make sure there is no FIS for the stream. If there IS an FIS, then you need to use the 1.0% line on the flood profiles in that FIS to determine BFE to the nearest 0.1' at the most upstream edge of your structure and/or attached deck/stairs.
SS
Three feet isn't a crazy amount to be in the flood zone, depending of course on the area and when the house was constructed. I had a call this morning from an attorney I do a lot of work with whose area was just revised. She's going from a shaded X zone to about 6' under the flood zone.
If you have squiggly lines it sounds like you have an area with a detailed study, make sure you look at the cross sections and scale accurately.
Procedure sounds pretty solid. Could it be the building was built while a different zone was in effect?
As others have said, check the FIS profile. Usually the FIRM and the FIS are close as far as the BFE is concerned. If the house was built pre-firm, then its not surprising at all that it would be three feet below BFE. Definitely check the diagram # as well...it can throw off the rates.
I heard today the US senate passed the house rolling back rates to get rid of the $25,000 type bills, so maybe the can get some relief.
Your procedures seem sound to me though.
I've got to agree with Andy on this one. Around here, any building built before 1982 was not built in compliance with any FIRM map, and they are often very low. After 1982, in some areas, the BFE has been raised since the initial map, so you'll find houses built in compliance with older maps that are now considered too low. Your dates will vary, but it's important to know your cut offs for PreFIRM and major map revision dates for these types of questions.
Try to figure out when the building was built and then look at your FIRM to see if it was before the "initial identification date" (or whatever they call it), if that's the case, it's PreFIRM and you can't expect it to comply with any map. If it was built more recently, go the MSC.FEMA.GOV, product catalog, historic maps, and try to find the map that was in effect at the time of construction. Often, that will answer the client's questions.
Yes, a Biggert Waters Fix was passed recently by both houses and will go to the Pres. for signature. Not sure if he's signed it yet.
The FIRM map is rounded to the nearest foot; so use the FIS data when it is available.
So how do I get the FIS information?
