I just got a request from an engineer working on a site that I provided topographic survey of.
"Additionally, there is another issue with the survey regarding the flood line. The surveyor has mapped a floodline based on an elevation from his field run topo. Unfortunately, that is not the enforceable floodline from FEMA's perspective. Only a floodstudy with appropriate field run cross sections that are reviewed and approved by FEMA can change the location of the floodline. Please have him modify the survey to show the line that is available from the FEMA website. We need this done as soon as possible, as we are finalizing the plans"
Okay here are some details. AE flood elevation from FEMA Panel is 677' across entire property. There is a cross section north of property , on property, and south of property. My survey holds the 677' contour as the AE floodline. The line as scaled from the fema map differs quite a bit, due to pretty flat ground. The alignment between cross sections is usually drawn from Lidar, isnt it. They are losing probably 50' or so. The engineers statement that "only a flood study........location of the flood line is absolutely correct, I am not the one changing the 677' elevation, that would be him in requesting to use the scaled line which doesnt follow the 677' elevation.
Let me know what I am missing, please.
Do a search for FEMA Flood Mitigation Directorate on 'use of digital flood hazard data'. It will give you the accepted method of plotting the lines.
Most Surveyors are tempted to plot the conditions that quantify actual risk. The administrative boundaries determined by FEMA are for the purpose of providing an objective way to price insurance. Two different missions entirely...
thebionicman, post: 330219, member: 8136 wrote: Do a search for FEMA Flood Mitigation Directorate on 'use of digital flood hazard data'. It will give you the accepted method of plotting the lines.
Most Surveyors are tempted to plot the conditions that quantify actual risk. The administrative boundaries determined by FEMA are for the purpose of providing an objective way to price insurance. Two different missions entirely...
Adam, post: 330207, member: 8900 wrote: I just got a request from an engineer working on a site that I provided topographic survey of.
"Additionally, there is another issue with the survey regarding the flood line. The surveyor has mapped a floodline based on an elevation from his field run topo. Unfortunately, that is not the enforceable floodline from FEMA's perspective. Only a floodstudy with appropriate field run cross sections that are reviewed and approved by FEMA can change the location of the floodline. Please have him modify the survey to show the line that is available from the FEMA website. We need this done as soon as possible, as we are finalizing the plans"
Okay here are some details. AE flood elevation from FEMA Panel is 677' across entire property. There is a cross section north of property , on property, and south of property. My survey holds the 677' contour as the AE floodline. The line as scaled from the fema map differs quite a bit, due to pretty flat ground. The alignment between cross sections is usually drawn from Lidar, isnt it. They are losing probably 50' or so. The engineers statement that "only a flood study........location of the flood line is absolutely correct, I am not the one changing the 677' elevation, that would be him in requesting to use the scaled line which doesnt follow the 677' elevation.
Let me know what I am missing, please.
It would seem to me that if FEMA has determined that the AE line is at the elevation of 677, then where you determine that contour to be should be the AE line. I believe that FEMA will rely on your determination of that line.
NYLS, post: 330228, member: 1722 wrote: It would seem to me that if FEMA has determined that the AE line is at the elevation of 677, then where you determine that contour to be should be the AE line. I believe that FEMA will rely on your determination of that line.
The AE limit is controlled by a geographic (horizontal) line. The vertical information can be presented for an amendment where justified.
FEMA has to start with an objectively defined line, followed by a process that evaluates actual risk where justified.
This sounds like a perfect candidate for a LOMA with a m&b description of the area to be removed based on your topo. Mo money please.
http://www.fairfaxcounty.gov/dpwes/publications/lti/12_03_floodplain_boundaries.pdf&apos ;">BEST AVAILABLE DATA
With your application package, in addition to elevation information regarding the structure(s), provide a map showing the topographic data of the property and the immediate surrounding area, and the location of any structure(s) existing on the property (certified by a registered professional engineer or licensed land surveyor) to demonstrate that the above criteria have been met.
Adam, post: 330207, member: 8900 wrote: I just got a request from an engineer working on a site that I provided topographic survey of.
"Additionally, there is another issue with the survey regarding the flood line. The surveyor has mapped a floodline based on an elevation from his field run topo. Unfortunately, that is not the enforceable floodline from FEMA's perspective. Only a floodstudy with appropriate field run cross sections that are reviewed and approved by FEMA can change the location of the floodline. Please have him modify the survey to show the line that is available from the FEMA website. We need this done as soon as possible, as we are finalizing the plans"
Okay here are some details. AE flood elevation from FEMA Panel is 677' across entire property. There is a cross section north of property , on property, and south of property. My survey holds the 677' contour as the AE floodline. The line as scaled from the fema map differs quite a bit, due to pretty flat ground. The alignment between cross sections is usually drawn from Lidar, isnt it. They are losing probably 50' or so. The engineers statement that "only a flood study........location of the flood line is absolutely correct, I am not the one changing the 677' elevation, that would be him in requesting to use the scaled line which doesnt follow the 677' elevation.
Let me know what I am missing, please.
You determined the location of the 677' contour line. If that is the elevation FEMA is holding, then you have done your job. FEMA maps are wrong all the time in respects to horizontal location. Maybe show both with a detailed explanation of what the scaled line represents?
Adam, post: 330207, member: 8900 wrote: I just got a request from an engineer working on a site that I provided topographic survey of.
"Additionally, there is another issue with the survey regarding the flood line. The surveyor has mapped a floodline based on an elevation from his field run topo. Unfortunately, that is not the enforceable floodline from FEMA's perspective. Only a floodstudy with appropriate field run cross sections that are reviewed and approved by FEMA can change the location of the floodline. Please have him modify the survey to show the line that is available from the FEMA website. We need this done as soon as possible, as we are finalizing the plans"
Okay here are some details. AE flood elevation from FEMA Panel is 677' across entire property. There is a cross section north of property , on property, and south of property. My survey holds the 677' contour as the AE floodline. The line as scaled from the fema map differs quite a bit, due to pretty flat ground. The alignment between cross sections is usually drawn from Lidar, isnt it. They are losing probably 50' or so. The engineers statement that "only a flood study........location of the flood line is absolutely correct, I am not the one changing the 677' elevation, that would be him in requesting to use the scaled line which doesnt follow the 677' elevation.
Let me know what I am missing, please.
One additional tip...
The BFE shown on FIRM panels is usually not the same as one taken from the FIS. The FIS number should be used.
WA-ID Surveyor, post: 330246, member: 6294 wrote: You determined the location of the 677' contour line. If that is the elevation FEMA is holding, then you have done your job. FEMA maps are wrong all the time in respects to horizontal location. Maybe show both with a detailed explanation of what the scaled line represents?
Sorry but no, he hasn't. The AE line is not the contour unless and until the amendment is done. The AE line is an administrative line delineating insurance rates. The line may not relate to the actual risk but that's a different story...
Adam, post: 330207, member: 8900 wrote: I just got a request from an engineer working on a site that I provided topographic survey of.
"Additionally, there is another issue with the survey regarding the flood line. The surveyor has mapped a floodline based on an elevation from his field run topo. Unfortunately, that is not the enforceable floodline from FEMA's perspective. Only a floodstudy with appropriate field run cross sections that are reviewed and approved by FEMA can change the location of the floodline. Please have him modify the survey to show the line that is available from the FEMA website. We need this done as soon as possible, as we are finalizing the plans"
Okay here are some details. AE flood elevation from FEMA Panel is 677' across entire property. There is a cross section north of property , on property, and south of property. My survey holds the 677' contour as the AE floodline. The line as scaled from the fema map differs quite a bit, due to pretty flat ground. The alignment between cross sections is usually drawn from Lidar, isnt it. They are losing probably 50' or so. The engineers statement that "only a flood study........location of the flood line is absolutely correct, I am not the one changing the 677' elevation, that would be him in requesting to use the scaled line which doesnt follow the 677' elevation.
Let me know what I am missing, please.
Have you discussed this with you local flood plain administrator?
Jim in AZ, post: 330256, member: 249 wrote: Have you discussed this with you local flood plain administrator?
I am awaiting a reply
thebionicman, post: 330247, member: 8136 wrote: One additional tip...
The BFE shown on FIRM panels is usually not the same as one taken from the FIS. The FIS number should be used.
What if something gets built in the area between the 677 contour and the floodline from the panel?
Adam, post: 330262, member: 8900 wrote: What if something gets built in the area between the 677 contour and the floodline from the panel?
The owner will have 2 potential problems. First, if the map is amended he may find himself in a Special Flood Hazard Zone. Second, he may find out that unless printed on sand bags, FIRM Panels, FIS Profiles and Elevation Certs don't stop water.
The point of all my posts is the same. Navigating Flood Hazard regulations and advising on wise construction practice are 2 different animals. If you mix them up you are creating a liability bomb for yourself and your clients..
So FEMA wants a surveyor to use a scaled line from the map instead of actual survey data and the listed elevation? By the way the area is very rural and not many defined points to scale from. Thanks for the help, ya'll
Adam, post: 330278, member: 8900 wrote: So FEMA wants a surveyor to use a scaled line from the map instead of actual survey data and the listed elevation? By the way the area is very rural and not many defined points to scale from. Thanks for the help, ya'll
The directorate letter explains how they want the line plotted. They require the use of the geographic coordinates and grid ticks on the map or in the drawing/shapefile. Local improvements are specifically listed as not to be used...
Adam, post: 330278, member: 8900 wrote: So FEMA wants a surveyor to use a scaled line from the map instead of actual survey data and the listed elevation? By the way the area is very rural and not many defined points to scale from. Thanks for the help, ya'll
ABSOLUTELY! The graphical line on the map controls everything - elevations are essentially (but not always) irrelevant. It has been this way from day 1 - that's why you see so many of us stating over and over again what an absolute joke the whole process is.
thebionicman, post: 330251, member: 8136 wrote: Sorry but no, he hasn't. The AE line is not the contour unless and until the amendment is done. The AE line is an administrative line delineating insurance rates. The line may not relate to the actual risk but that's a different story...
This could be considered a highjack; although, not intended to take away from the OP.
I took a quick break from phone calls and this thread caught my eye (note: that was probably 2 hours ago and, after thinking/ doing some reading, I still have this bouncing around my head).
The following is a little hypothetical but, I've got a potential job that appears to be right on the AE line per the current map.
If I agree that the AE line is a "correct" line on the map, and, after locating that correct line on the ground, I determine the structure is "outside" of the AE zone, doesn't item B8 effectively not have an answer (or, an answer of "none")?
In other words, you stop the cert and tell the client, "you are outside of the SFHA".
However, that could mean the HAG, or even the FFE, is not above the immediately adjacent, published BFE. So, where does that leave you (from a professional standpoint)?
Does reporting to the client (in a sealed report) the "facts" (outside of AE/ below adjacent BFE), do it? I know it wouldn't exactly feel right. But, is the role of the surveyor to advise a client to consider insurance in any case? Am I increasing professional exposure by not saying the structure is in the flood plain?
Your post is on point IMO.
It is not unusual to report a structure is in the SFHA but above the BFE. While not as common, outside the SFHA but below does happen. The choice to purchase flood insurance rests with the client. The job of educating them so that choice is informed rests with us. We need to separate the insurance part from the actual risk and explain the difference.
It would seem that the surveyor's duty is to let the client know both the legal line and physical contour, so they can consider both factors to make an informed decision on where to build.
Follow up on this matter. I spoke with our state director of our states flood mapping agency. He advised me to show the AE line from the panel as well as the contour of the Base flood elevation. I did this and labeled as AE flood line drawn from FEMA panel and Base flood elevation contour from field run topography. The engineer has responded back and told me to remove the contour and note about the Base flood elevation. What now?