FEMA FIRM map fraud
I’ve got two separate clients in different Counties dealing with the two County Planning Departments. They’ve both gotten notice to remove a log house and one to remove a garage. The log house got verbal approval from the then County Flood Plain coordinator to construct the building. No written permit. The Flood Plain coordinator has since moved on to a better paying job bagging groceries. The garage was built without any County approval. I did Elevation Certificates for both. One is 0.4 feet below the BFE. The other 1.3 feet below. I used OPUS to establish my elevation. The neighbor downstream got LOMA’d out of the Floodway. His property is obviously lower than my client’s property. I contacted the FIRM that did the LOMA and he told me they used a NGS benchmark. I checked into that benchmark and guess what? It’s 3.9 feet higher than what my OPUS solution was. I checked into another NGS benchmark and it’s 0.3 lower. I researched FEMA’s website. There’s a chart that displays the Vertical Accuracy of FIRM maps. 24.5 cm (0.8 ft.) the highest specification level to 147 cm (4.8 ft).
How the hell can a County Official tell some one to tear down their house or garage when the NGS benchmarks are bogus and FEMA’s FIRM maps are the same quality?
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This is not clear. Are you saying you got OPUS on a bench mark and it differs from its data sheet by that amount?
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No, I established a benchmark using OPUS. Then checked into two different NGS published benchmarks using a Trimble R10.
The Log House I used the Published Benchmark Elevation. Checked into another nearby NGS Published Benchmark. The elevation differs by 1.55 feet higher. I’ve not checked these elevations with OPUS yet.
What is the base flood elevation control?
NAVD88 or NGVD29?
Are these zone AE’s?
NAVD88. They are in Floodway zoned A for the Log house and Zone AE for the garage. The Log Cabin owner had a Flood Plain Analysis done to the tune of $10,000. Using that BFE the Analysis came up with is how we determined the Log House was 1.3 feet below.
Flood Plain Studies are another scam.
Don’t use OPUS for elevations. The only accurate way to determine vertical elevations with GPS (and the only way NGS recognizes GPS vertical elevation determinations) is to read simultaneous static observations at both points. Others here will disagree, but I have found OPUS to be unreliably for vertical heights.
I have found OPUS to be unreliably for vertical heights.
Depends on what your tolerances are. Under good conditions 2-hour OPUS should usually be within a tenth ft vertically.
But an OPUS value, no matter how accurate it is, is not as good for this purpose as a comparison to the BMs used to create the BFE, compared either by optical leveling or by simultaneous GNSS receivers processed together.
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This reminds me of a few years back when a survey tech for some firm I had never heard of called to report my elevations were off something like three feet. I had done the initial survey work and topo for a hotel site. Multiple DOT benchmarks and city benchmarks were available within a half mile in any direction. We had checked into several and had excellent agreement. I have no idea how he was arriving at his clearly wrong conclusion. Told him to check into the same several we had used and then tell DOT to change all of their roads/bridges/culverts/etc. by that amount.
I only use benchmarks shown on the FIRM. If wrong, it’s on them.
How the hell can a County Official tell some one to tear down their house or garage when the NGS benchmarks are bogus and FEMA’s FIRM maps are the same quality?
Because they saw a presentation at a conference.
Seriously. I brought a planning department meeting to a halt when I questioned the statement that they would just pass a policy based upon 500 yr flood maps.
I said, “You’re going to need to get get every single property surveyed, and you can’t just use a Fema map and tell people that’s the way it is”
They looked at me like I said I was going to behead the pope at the next Rotary Meeting.
Planners and their departments need to be watched with deep suspicion in lots of cases.
My $0.02
They don’t show benchmarks on the FIRM maps anymore. They did on the old NAD27 based maps, bu5t not on the relatively new NAVD88 FIRM maps.
Why is NGS begging Surveyors to GPS the NGS benchmarks and submit OPUS results for the new datum. Is OPUS another NGS scam? OPUS solutions report error estimates in the order of .034 m (0.09 feet). I was told at an OPUS training seminar. “It doesn’t get better than OPUS”. The old FIRM maps had Benchmarks on the maps which were set by a Contractor on questionably stable items. Those benchmarks when converted to NAVD88 using NGS’s conversion program are totally bogus.
My argument isn’t with NGS. NGS knows they have a problem with their benchmarks. Its with County Planning Departments that think FIRM map BFE elevations are accurate to a tenth of a foot. I think an OPUS elevation is more than accurate for a FEMA Elevation Certificate. It’s not logical to tell someone they have to tear down their structure because its 0.4 below FEMA’s BFE. Why would you require less than a foot accuracy to compare to a elevation that was computed by statistical methods using 20 foot contour maps as a base, questionable flood flow data, and reporting their accuracy estimates to be between 0.8 and 4.8 feet? Makes no sense to me, but I learn something new everyday.
DOT benchmarks are way worse than NGS benchmarks. From what I know now I would never question anybody else’s elevations. It depends on what you based them on and there appears to be a problem with what they are based on. NGS changes their elevations, which happens to be something like 3 feet. Average NAD27 to NAVD88 elevation conversion is 3.26 feet in my location, which is a curious coincidence in your example.
Only done a few years ago. If someone experiences flooding whatever you charged won’t be worth the hassle. I’d rather stake a bridge and base the elevations on the project benchmarks.
0.42, or thereabouts, is a long way from three feet, and these were 88 elevations
The County is requiring Elevation Certificate on property shown in the Flood areas by the FEMA FIRM maps. If your below the BFE you can’t get a building permit. If you build without the permit and they find out you did. You get a letter demanding you remove the structure. My example is a property is 0.4 feet below the BFE. I’m saying NGS benchmarks are not accurate enough to make a 0.4 foot decision.
We were tasked with staking the local airport runway to 1/4 inch tolerance. The Project benchmarks didn’t agree with each other by that much. We established our own.
My thinking: It has to be assumed that when the Base Flood contours, or initial determination of the flood zone was created, it was most likely created using aerial surveys based off of NGS benchmarks. Not OPUS. Therefore when I do Certs, I compare apples to apples. If your OPUS doesn’t fit an NGS mark, it’s irrelevant. You have to use the datum that made the determinations not matter how correct or incorrect it may be.
The FIRM maps don’t reference what basis was used for their elevations. To use the benchmarks they would have had to identify the NGS benchmarks somehow on the imagery they used to develop the Flood areas. I’m fairly certain precise photogrammetry wasn’t used. What bothers me is the flood boundaries don’t follow contour lines either. There appears to be to be no logic to how somebody created those boundaries. The FIRM maps do state the accuracy is to their standards, which are 24.5 cm (0.8 Feet) to 147 cm (4.8 Feet). NGS doesn’t state what their accuracy standards are on the Data Sheets. Maybe its somewhere else. When I get an OPUS report back it tells me what the 1-sigma RMS values are. I’m ignorant as to exactly how they are creating Ortho Heights using GEOID18, but the geiod information has been pretty reliable to me in the past.
Again my argument is Government Agencies should not be interpolating FEMA FIRM map elevations to 0.1 foot. I’m not even sure it should be 1.0 feet.
Fraud is a serious accusation. You raise some points worth discussing, but nothing you have described sounds like fraud to me.
I personally wouldn??t use OPUS to do a flood certificate. It might be a good check.
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