In the late 1980's we did a subdivision near a creek. FEMA had no BFE's for this location and only a Zone A was determined. An engineer was hired and he determined the flood plain which was put on the plat. That flood plain was shown with bearings and distance ties to lot lines so it could be reproduced. After many complaints Zone As were removed from county mapping and life went on. An owner wanted to build near the flood plain and it was staked out and the house was constructed uphill from the staked line.
Then in the 2010's after much back and forth FEMA released new mapping. Today that owner wants to re-finance and can't get a loan because the new Zone A in the county mapping GIS shows the house into the flood plain.
Now the option is to locate the flood plain from the plat, get a new 88 elevation BFE from that and do an elevation cert from the platted flood plain. Or, hire a new engineer, redo the entire process and get the new BFE that way. From our experience the first engineer who did the flood mapping is quite good at it. Floods we have seen where he did mapping are spot on. Of course the new Zone A is a joke, much like the previous one, some of the water course isn't even covered by the Zone A very near the house.
So my question is: will FEMA accept the original flood plain if stated as platted, or does a new study need to be completed. This is a mountain stream, not subject to accretion or avulsion, it's remained in place since the 80's since the huge rocky bed isn't going anywhere, or at least we haven't had the 1000 year flood that might move something.
If it makes sense to surveyors, it is nonsense as viewed by government employees who may lose their title after any election cycle.