I wonder if a disclaimer would be ignored, like the disclaimers on GISs. I think better education of planning departments could help some, and that's something we could help with.?ÿ
@aliquot If FEMA had a disclaimer on their FIRM maps it would certainly be something I could use as evidence to use in explaining things to a Planner. Someone is giving them training. They were taught to mark divisions on a rubber and and stretch between FIRM map's BFE lines to determine BFEs to a tenth of a foot between BFEs.
I think we should eliminate any government involvement in flood insurance or paying for flood damage.?ÿ Let the people who choose to take the risk of flooding personally pay for that risk.?ÿ I see no need to protect a fool who chooses to live below sea level.
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Some levels of ignorance can be hard to overcome, but you work with them or the client suffers.
Pull the FIS profile and walk them through doing it right. Show them around the public portal at thr FEMA map service center.
If there is a serious problem with the data it will be easiest to find on the profile. It is also easy to obtain a BFE with repeatability of a tenth or so in most cases. Interpolating from the FIRM panel is almost never the right method...
As others have indicated, FEMA isn't in the floodplain modeling business, it's in the business of risk and political expectation management.?ÿ (Floodplain modeling is one of the tools it uses, knowing that it's an imperfect tool.)?ÿ It is an insurer of last resort, a role created and maintained for it by elected officials.?ÿ Whether or not that's a good thing is a political discussion not suitable for this forum, but flood insurance and all the bureaucracy and engineering flaws and unintended inequities inherent in the process are facts we have to deal with.
Complaining about FEMA might feel good, but it's unlikely to change anything.
They do show Benchmarks on most of our NAVD88 maps, but not all.?ÿ
It's important to know the process that generated the FIRM maps.
How did they cross-section the valleys, what was the elevation control at the time for that.?ÿ
What topo was used and how was it generated.
I've found Zone AE maps to be quite accurate, but Zone A maps were not professionally produced. An engineer needs to determine the real BFE in a Zone A area and when the engineer does that the surveyor following the engineer needs to be on the same elevation control. I've not had the experience you have had. I suspect there is some type of elevation control shift that put the log house into the flood plain.
The benchmarks you talk about in error. ?ÿWhat are they? ?ÿWhat is the stability? ?ÿWe??re they on the same level runs originally? ?ÿI personally have never found a problem with a benchmark unless the stability was an issue. ?ÿ
That said County Planning Department shouldn't be telling people they have to tear down structures that are a foot below the fantasy BFE.
The stability of the benchmarks is beyond reproach. It's the Determination of it's elevation that's in question. The data sheets associated with the benchmarks do not indicate the accuracy to which they were set. There's probably some records somewhere that show that. Me and several others on this Forum have observed some inconsistencies with the published elevations. Perhaps the inconsistencies are within the error ellipses they were set under. Those are unknown to me. OPUS is discovering some flaws in the NGS benchmarks. That's what I'm talking about.
I think the Government should protect us from money grabbing insurance companies. That's what the FIRM maps were meant to do. Not give Local governments a tool to harass property owners.
Several years ago many farmers were complaining that the cost of crop insurance was exorbitantly high since compliance with Government payments for certain approved practices dictated the acquisition of said crop insurance.?ÿ Guess what happened.?ÿ The Government attempted to bailout the farmers by agreeing to pay a certain percentage of the insurance cost.?ÿ Guess what happened next.?ÿ The cost of crop insurance shot up such that the net amount the farmer pays is now higher than what they were paying in the first place.?ÿ All of those tax dollars went to the insurance companies at no benefit to the farmers.
FIRM map elevations weren't an issue until Katrina in New Orleans cost the government flood insurance program huge amounts of money. The Federal government issued an edict, I don't know to who, to start enforcing Flood Plain Regulations. The Local government did exactly that when threatened with losing Federal funding. In my opinion they have become overzealous in doing that beyond the accuracy of the FIRM maps they were supplied with.
FEMA does state what they used. 20 foot contour maps and vertical accuracy ranges from 47 CMS (0.8 feet) to 147 cm (4.8 feet). The problem is someone has told Local governments to enforce the FIRM flood plain BFEs to a 0.1 feet.
There are a number of issues in play here. You state that the data sheet doesn't indicate an accuracy. That is a huge red flat. I only use first order bench marks to control FIRM map BFE's.
Although, I suppose I'm lucky to have so many of them.
There were older (by that I mean pre-NGVD29) bench marks run. Some of those are still around but it's not at all surprising to find one of them to be feet "off". Doesn't mean they weren't legitimate at the time they were set. If the data sheet doesn't give an accuracy then I wouldn't use it for anything.?ÿ
You mentioned a BFE for the log house. If the engineer used this bench mark to run cross sections then it should be used to figure out the BFE. Typically in a Zone A BFE determination there is a report filed by the engineer. I would get with the engineer, explain what you found and it may well be that the log house isn't really in the flood zone after all. I would not tell anyone anything until I figured out what's going on with the elevation control. Whenever you take on a Zone A or even a Zone AE flood zone job all the issues with map making, elevation control, BFE determination is placed on you. This isn't really about OPUS or NGS bench marks.?ÿ
The NFIP was undergoing modernization long before Katrina. If anything the biggest changes stalled due to social cost.?ÿ
Those of us who stay out of flood hazard areas pay the bulk of the costs associated with those who don't. I wish all flood plain development required premiums high enough to offset losses. We wouldn't see many precon e-certs...
The log house is on property that has a higher elevation than property than property nearby that is in Zone X. Neither FEMA or the County will accept that to remove it from the Zone A.
The Landowner told me the Local Official is pretty steadfast. If it's below the BFE it has to be removed. What were talking about here is significant figures related to data used. Im saying the data used does not warrant a BFE determination of tenths of a foot.
The Local emphasis on Floodplain manage occured here after Katrina. I suspect it was probably initiated by the Federal government by a threat to with hold money if it wasn't done. I'd never heard of an Elevation Certificate until after Katrina. The Federal Insurance program took a bath in claims then. They needed to generate more funds to sustain their program, thus the emphasis on Elevation Certificate.
That's my theory anyway on that subject. Which is off track to what were trying to discuss, but it is background to why we are discussing NGS benchmark and FEMA FIRM map accuracies.
I don't believe profile data is available in a Zone A.
