We have preliminary flood maps. Woo hoo. Coastal flood zones.
They ran LiDar to determine and I have been downloading GeoTiffs made from the LiDar data. They compare well to the aerial topos we have. The aerials usually compare well to the surveys we perform.
What does not compare well are the limits of the zones. I have seen an AE el 11 extend about 100 feet up to a 15 contour. I have seen another AE 11 bisect a garage whose slab is at elevation 10.
So I plan to trim the first AE 11 back to the 11 contour. Sounds good to me.
I would also plan to extend the second AE 11 to the 11 contour. The client does not think this is a good idea though as it would put his house into the A zone. The map does not show that, so how could I consider it?
Neither of these A zones back up to a B (shaded X) zone. They are both terminating.
Thoughts, opinions, jokes?
GIStastic!
You're not attempting to compare FEMA mapping with reality are you?
It's not like I'm planning to visit a site during a 1% storm.
or GIS... Flood Map Interpretation> spldeus
Why wouldn't you run the 11' contour in the subject area?
On a different note, are you going to the convention?
I don't know what your local floodplain administrator would have to say about either plan but I know the local one here would have a fit. The line is "EXACTLY" as shown on the map until such time that a Letter of Map Revision (LOMR) is issued.
Still preliminary maps... I am just trying to gather data to know where LOMAs and LOMRs will be practical.
I also have some pro-development political clients who would love to delay the implementation of the FIRMs. Flood zones that grossly mismatch the underlying data could be as bad for FEMA as using the Pacific Wave models in the Northeast.
or GIS... Flood Map Interpretation> spledeus
I think I will be there Friday. Going skiing Saturday.
or GIS... Flood Map Interpretation-rejection
Is there a process for a town or county to get FIRM maps rejected that are way out of bounds?
I've got at least two new 2012 maps that are so wrong that they are causing all kinds of issues, and everyone can't redo the flood plain for FEMA.
In one case an AE zone is in complete disagreement with a new flood plain done for a subdivision, the FIRM clearly isn't following any contour information.
In another case an A zone is clearly not conforming with topo features climbing a hill and not covering lowlands. It would be better just to pull them and use the old ones.
At least one town's engineer is looking into doing just that.
or GIS... Flood Map Interpretation-rejection
Three weeks ago I heard that FEMA is delaying the effective date for Plymouth County, Massachusetts because all those pilgrim loving folks complained. They complained to FEMA, NFIP, Politicians, Bartenders and any one else who would be foolish enough to listen.
My interest in this revolves around the third party use of the flood maps. Wetlands Protection Act defines flood plain or Land Subject to Coastal Storm Flowage (LSCSF) as a resource area (wetland) with minimal performance standards. 2 Towns I work in have defined LSCSF as a full resource area with a 50' 'No-Disturb Zone' and 50-100' heavily regulated buffer.
You want to go in and tell a Cons Comm that the line is exactly where the line is when it clearly is not where the line should be? The Agents have been fed raw kool-aid (no water to help wash it down) that these maps are better then what a surveyor can produce.
or GIS... Flood Map Interpretation-rejection
Many of these maps are clearly drawn without cross-section data or topo information.
Then they get plotted on photos and houses are in the A zone. It looks like someone drawing the line for the flood plain looked at tree lines and went around them.
Of course in this arid land people plant trees around their houses so the houses get included even when they are on a high bluff 500' feet from the stream, while on the low side where there are hay fields and low country, but no trees, the flood plain is much lower, and this happened over and over.
Getting lots of calls, we can't redo whole valleys. Better to just reject the maps. If they are clearly wrong what's the point of them anyway.
or GIS... Flood Map Interpretation-rejection
There is one new map here that actually now has a portion of a lake out of the floodplain.
or GIS... Flood Map Interpretation-rejection
Well, I'm really disappointed with the new ones. I thought more care would be taken, and one town engineer was showing me an area where the stream was east of the flood plain, so you can build in the stream but not the high hill to the west.:-$
or GIS... Flood Map Interpretation-rejection
Ummm, my maps were all based on lidar. There are GeoTiffs available through the GIS site. Metadata claims 7cm/17 cm vertical error on the raw data (open / covered).
So if they mapped flood plain based on GeoTiff, why wouldn't the flood plain match the elevations on the Geotiff?
or GIS... Flood Map Interpretation-rejection
Well out here there are two different food plains, one done with topo and cross sections and the other ones drawn somehow (who knows how they do it). I haven't had any problem with ones using data so far, until this one in the small town showed up. If the town engineer wants me to I'll track down just what info they used, but it's not official yet so you don't have the typical data, and he is new so wasn't involved with the process
The town engineer is not happy.
Wants to scrap it all; I said take the printout showing the stream outside the flood plain to the county and demand they remove it.
He called FEMA and they got annoyed with him and told him to: "do your own study then." The problem with telling him that is that the major subdivision creating most of the problems did have a flood study and he gave it to FEMA and it was ignored.
Now; outside any area with new topo it's a real mess. I thought the old stuff was bad and now I get this, looks like they decided to put every house near a stream in to force them to take themselves out and without any BFE's it forces the property owner to spend thousands doing a real study or pay some crazy number for insurance they don't need. Almost like some evil plan.
