FEMA issue has raised it's ugly head.

What were your RMS values and peak' to peak solutions?
I would say for a 2 hour 'courtesy OPUS session that may fall in the 0.2'+/- range.
Have you tried to just download a CORS data at Hammond and do a vector solution for the comparison.
If you are not tieng into a geodetic network that has been develop and only relying on th minimal OPUS solution to to establish a BM than I think ....Never mind.
Since you have one receiver, I assume you can't simultaneously occupy a blessed point of NGS also to form a net with the CORS.

Those marks are also blessed to about 0.1 -0.2'

Geoid 09?

This is why the Dfirms haven't been accepted here. There are errors on the maps. Some of the adjoining parishes just opened the letter from FEMA telling them the maps are ready and blindly adopted them.
They are finally going to adopt them here early next year (I was told by the local FPA) but after revisions.
For instance, I did a cert in Mandeville last week or so for a nice family and they are in an A5 on the old effective FIRM. On the Dfirm they will be in a C. The whole street has been LOMAed and FEMA reversed the zones. I assume because of the prior LOMAs.
Ironically, they were 0.2' above the BFE.
But having lost everything in Katrina, they told me that they will always have insurance.
So next year, there are going to be quite a few confued homeowners . I alresdy have gotten a lot of requests for LOMAs. TG for Elomas
But getting back to your situation...It is your professional judgment to realize that the 0.2' is wandering around out there in various variables of your solution.Elevations are not bedrock here unless tyou go the distance on getting a good solution. i.e vertical geodetic network, multiple ties to NGS stuf and lond=g durions on the sessions.
What I am saying is..with a 2 hour OPUS solution that I could sleep weel if I had them at the BFE. There are too many variables to the solution on the numbers.
remeber this is Louisiana.

I hear you.

Don't know if you've seen this, but it's a link with info about FEMA's "Grandfather Rule" and a flow chart to help figure out where your client's property falls.

Grandfather Rule Link

If the property was in a B, C, or X zone when the home was built, it would be grandfathered into that zone, and rates should be based as if you're trying to get flood insurance for a home that's NOT in a flood zone (very low rates).

Thanks, that link was very helpful.

A 4-hour OPUS solution was originally intended to be a "check" after one had made a local geoid slope determination with dual frequency receivers on at least four reliable benchmarks - as if there are any in South Louisiana. Even though they now allow OPUS to solve with a 2-hour solution, NGS specifications still call for equal morning and afternoon observations on two different days for a meaningful determination.

Considering what an annual insurance premium would cost, each and every year, why isn't it economical to do a kosher GPS survey for such a client? Since a boundary survey is rarely done on a firm, fixed price, why should a flood elevation survey in South Louisiana be done on a firm, fixed price basis?

My 2¢.

Alternate solution

Could you run a level loop from the nearest RM? You'd be absolutely sure that way.

Alternate solution

Problem is that the closest BM might have been dropped from the NGS datasheets because it has subsided out of tolerance ... many BMs in South Louisiana already have been dropped, and we now go by epochs, based on recent NGS/LSU GPS campaigns.

The likely last of the NGS GPS campaigns is starting up soon, and it's looking like the only way in the future to get elevations in Louisiana will be the LSU GULFNet system.

Think of a state moving down the same rate as the Addicks Reservoir in West Houston.

> Considering what an annual insurance premium would cost, each and every year, why isn't it economical to do a kosher GPS survey for such a client? Since a boundary survey is rarely done on a firm, fixed price, why should a flood elevation survey in South Louisiana be done on a firm, fixed price basis?
>
> My 2¢.

Competition.
Here there are 'Across the Lake" surveyors who are doing them at 1980 prices. Don't ask me how?
I was fortunate enough to get a contract to do a boatload of ECs a year so after Katrina.
for a Parish entity. I got a little network that I can keep going back to and occupying plus download local CORS.
OPUS is basically a QC for me as basically it has always been.
I don't like some of the 'new' blessed marks because they are in the median of the Interstate. Another is a 'gone pecan' already from construction.
and there ain't too many here to begin with. 🙁

Clients are price shopping also. They need a piece of paper and that is all there focus.

I don't do that many now. I don't do any across the Lake anymore.
I had someone who wanted me to go to St. Bernard last week.
He probaly could get someone to do it there for my 'ride time'.
I just refer them to the N.O surveyors.

I get a fair price for mine and I tend to do them solo and schedule them during other jobs or weekends.
Just set them up and let them cook.

I agree with Cliff. If you are going to use OPUS you need two days of observation. I would leave the L1-L2 unit at the site (if it is a safe site) for two days of observations.

I have used 4 hours of OPUS observations for elevations, but if the results indicate that the house is anywhere near the BFE I will not use the data and and try something else. The way I see it the liability is just too great.

Also, I share your anger at FEMA's screwing up people's lives. In many of these cases all one has to do is do the math and you can see what a gigantic ripoff flood insurance is for most home owners.

I would really like to see someone do an impartial study on the relationship between the major insurance companies and the Federal Government. Also, I would like to know just how much money the insurance companies make.