The objective here should not be trying to determine what is the most correct, true, accurate or precise NAVD88 elevation. The objective should be trying to MATCH THE DATA THAT WAS USED TO BUILD THE MODEL that established the flood elevation reported on the FIRM map.
This.
The objective here should not be trying to determine what is the most correct, true, accurate or precise NAVD88 elevation. The objective should be trying to MATCH THE DATA THAT WAS USED TO BUILD THE MODEL that established the flood elevation reported on the FIRM map.
This.
Double this ^^^^.
While FEMA has updated the mapping of the flood plain lines, the model used to define those lines could still be based on surveys run before GPS elevations were available.
I worked on a flood plain study for FEMA in 1990 after a major flood event in Maine. We only measured cross-sections at the bridges and culverts that had been destroyed and replaced in the prior flood. All the cross-sections at the "undamaged" constriction points were re-used for the new flood model.
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NC Flood Inundation Mapping (FIMAN)
Quality mapping saves lives, saves money, draws businesses, and in general make it easier to make good decisions.?ÿ This entire thread is another indictment of our inability as a country to make wise and long term decisions.?ÿ The tools needed to generate the real time map linked above also provide free statewide orthometric imagery, free LiDAR that can be immensely useful for planning, and over time provide snapshots of the past.?ÿ
FIMAN has predictive capabilities, the accuracy of which is astounding and have been verified numerous times by expert geodesists as well as anecdotally by PLSs and visual observance of high water marks.?ÿ
It took back to back hurricanes to prompt North Carolina into action, but we quickly realized that its value far exceeded the cost.?ÿ What will it take in your state?
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That's some pretty fancy stuff.
It would be nice if all federal, state, and local gov't were at that level of accessibility and usefulness, etc.
I try to have my elevations match the RM(s) on the FIRM.?ÿ Put it back on FEMA.
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I think it??s only fitting that we have vertical pincushions if we have horizontal pincushions. ?ÿI would base my elevations on the recovered NGS Benchmarks.
Shown below are the input file for Phase 1, Output for two points in previous post, and header information for output file showing corrections applied. In this run all possible corrections were applied. Corrections are listed in the header section.?ÿ
BTW, there is another NGS tool for transforming published NAVD88 orthometric height differences into the leveled height difference by removing the orthometric correction.
Extracted from the tool's documentation:
I received a PM asking me to provide information about a number of monuments. While willing to point to resources and provide examples of the tools available, I do not provide additional free services. Nor am I interested in taking on fee-based services.
To expand and elaborate on information I provide the following.
To find a PID given only a designation, one uses the following link. You enter the designation, select the state in which its located and submit. Note that the date is not generally part of the designation.
https://geodesy.noaa.gov/cgi-bin/ds_desig.prl
Once you know a PID, use this tool to find projects associated with it: https://www.ngs.noaa.gov/cgi-bin/SURV_ID/mark_sources.prl
L 435 is PID SS1269 the only level project in which it appears is L24479/6 (the /6 means that it is part 6 of L24479).
K 455 is PID RX0124 there are two level projects associated with this BM. A line observed in 1936 is L7684/5; the BM also appears in a 1961/2 level line L18718/3.
Using the Leveling Project Page https://beta.ngs.noaa.gov/datasheets/leveling-projects/index.html you can display and retrieve a multitude of information after entering the level project designation.
See previous posts for screen captures of the Phase 1 output for L18721. See previous posts for a link to the Phase1 tool. The complete output file is shown below:
Note that this is output where all corrections were applied.?ÿ
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@kevin-hines I was gonna say, the instructions are rather plain on using OPUS derived elevations.
FEMA accepted the OPUS Elevations and issued a LOMA taking the area out of Zone A and making it Zone X. The County Flood Plain Administrator dug up the sewer line topography, compared them. They differed by a little over a foot. No benchmark used indicated on the Engineer's topography. The County objected to FEMA, and they rescinded the LOMA.
FEMA agrees with OPUS, it's the County Flood Plain Manager that's the problem. FEMA replied it's the local officials call. But FEMA audits the hell out of the local governments checking their Flood Plain decision, but it appears to me doesn't give them any training. Appears to me the Counties should be required to have a reviewing professional.
Making accusation of fraud over a foot difference in Flood Plain arguments is utterly ridiculous in my opinion.
5 different Engineering firms, plus FEMA did Flood Studies and none of the BFE's were the same. FEMA's BFE differed by 5 feet. How do you make anything match existing data.
I feel OPUS gives some credibility to the Elevations stated. Comparing Flood Plain elevations to property surveys is ridiculous. They are totally not related, but the pin cushion theory is definitely related.
