Zone A BFE determination

There is a free version of Hex ras(sp) on FEMA's site. I'm not sure of your situation but in many instances FEMA will require the output from the program to be submitted along with the MT-EZ form (or others). If you are along a ravine then you can download the cross sections from the FIS to help show your work and how you interpolated you BFE.

I highly recommend that you do not attempt to use hec-ras to determine the 100-year flood plain level. Request the information from your county flood plain coordinator. HEC-RAS is far more complex than one might imagine, and input of the data without a full understanding of how it all works, and what the pitfalls are can be disastrous.

Contact your local ACE office. You have to pay for it, but they will supply you with a letter of determination.

Yes ... Do what Frank Willis said, and if the flood plain manager refuses to provide a BFE, then put N/A in the BFE box ...

BTW ... coutour interpolation is specificially mentioned on some FEMA docs as a method NOT APPROVED for determining a BFE for use in elevation certificates.

For me, it's either flood plain manager, or nothing.

"Contour interpolation" is considered one of the "simplified methods" of determining a BFE, and you can't use a simplified method for an MT-EZ. Psuedo cut and pasted that info here a while back and I've seen it in the TB-? document.

I am dealing with a lacustrine area in a Zone A, and the county flood plain coordinator is more or less expecting me to determine the BFE, or said that it ranges from 65' to 70', for example. I have explored the Contour Interpolation Method outlined by FEMA, and it doesn't meet the requirement for accepted accuracy anyways.

Also, I am not doing this for MT-EZ or insurance. This is for Elev. Cert purposes for the placement of a mobile home on a lot.

You're in a tough position. Frankly, I don't think many surveyors are qualified to determine a base flood elevation suitable for construction or insurance. The proceedures of determining a base flood elevation are outlined in this FEMA doc.

http://www.fema.gov/library/viewRecord.do?id=2215

When I spoke to a county engineer, who is designated by the county flood plane manager as the person qualified to make the BFE determinations, I was informed that he uses a lidar model of the county, and takes into consideration:

-how much water falls in a 100 year storm
-the maximum flow rate of outfall canals
-drainage structures along highways
-soil absorbtion rates
-areas of water pooling and barriers such as highways and railroads

... and still considered it an educated guess.

I think it's something that's beyond a normal surveyor's qualifications, and liability can be high considering that a BFE determination too low can flood and/or result in higher insurance rates for the life of the building. And a BFE determined too high can result in unnessasary constructions costs, and cause a homeowner to overpay for flood insurance.

The only real purpose of an elevation certificate is for rating insurance. I'm aware that some counties misuse elevation certificates and require them construction as a proof of elevation / county code compliance.

There is no way I'd fill out an elevation certificate based for a Zone A unless the BFE was provided by a county official. I might, perhaps, provide a "guess" on a company letterhead with the proper disclaimers.

Darrell,

Is there really enuf money in this job for you to on take the liability of saying that the bldg is OUT of the flood zone?

I know we want to be nice, but is this little fee worth putting a possible millstone around your neck? Is it really?

The entire lot and most of the block is completely in Flood Zone A. No building exists yet, but one is expected.

That's the FEMA document I have been referring to for the Contour Interpolation Method. Does it say anywhere what to do if that method doesn't meet the intended accuracy? All it says is the method should not be used. It doesn't come out and say fall back to another idea. Typical FEMA ambiguity.

At this point, I am going to determine the mean annual flood line and see how that elevation works out, if nothing else, treat it as a lower bound. I will make a comparison to an existing structure that sits on the other side of the pond as well. As for my submittal, I am going to note the hell out of it. The county flood plain manager still has the option to accept or reject the elevation I determine.

I agree, this is beyond the normal duties of a typical surveyor.

I just completed an elevation certificate for a mobile home located in a Zone A with no BFE determined. I did not specify a BFE, and only showed the real world elevations based upon OPUS observations, and Section E.

Is your County requiring you to detrmine the BFE?