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fema LOMA's  

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Posts: 2684
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I get calls to do loma's.  I haven't done them.  My county has FIRM's with Zone A but there has not been any BFE established.  I have a lot of hydrology experience in the past (designed flood control dams).

So how would you do a LOMA.  I've looked at some that have been granted but it doesn't say much other than granted but some of the property still remains in the flood zone.

So what would you do? Record an elevation and lat-long and send it to FEMA with your finger crossed?

The last call I got was for a house (Zone A with no BFE) at least 40 feet above the creek bottom, 5% sloped channel.  a 20 foot depth flow would about be Noah's flood here.  Half mile downstream the map shows the flood contained in the channel through town, channel is about 10 feet deep and 20 feet wide at the most, flatter slope.

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holy cow
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In Kansas these days we can contact the Kansas Division of Water Resources  (under Dept of Ag.) to obtain a BFA, which is apparently close enough to a BFE, to satisfy FEMA.  Lat/Long or street address for town lots is the primary input plus a little digital outline of the structure or area under investigation.  Perhaps Utah has a similar system in place.

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Utah a bit different than Kansas (been there!).  Mountains in the middle of a desert.

I probably need to learn how to do these.  Looking more at the FEMA site it looks like one would need to take cross sections along the channel and run the hydraulics to get the depth (BFE).  I can't think of it right now but there is government website out there where you can locate a point on a stream and it will figure out the drainage area and give you the max flow for different storm periods.

So Yeah, I could probably do all this but it is going to cost them money for sure.  You'd also need FEMA to accept your calculations.  Still not sure I want the liability.

I referred the caller to one of the larger engineering companies.  I even called them to ask about it.  Guy told be they do them BUT it's EXPENSIVE.  Caller already has his foundation (basement) cast before the county shut it down and told him he couldn't have a basement.  He'll probably pay!

I think I may call a FEMA flood specialist and get more up to speed on exactly what needs to be done.  How much work does it really take?

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I was told that you leave the BFE blank and FEMA will fill this in when reviewiug the LOMA app  for ZONE A  no BFE

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Ive not heard of FEMA calculating a BFE in a Zone A, unless perhaps a remap is pending. I'm a PE and I usually have the LS shoot the LOMA form info and gather 2-3 stream cross sections in order to compute the BFE with a USGS regression 100yr flow. Then FEMA reviews the whole package for approval or denial.

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I hire an engineer, it's expensive but when you may be paying hundreds of dollars a month for flood insurance it's a small price to pay. I've had some very happy clients that can't write the check for the service fast enough.

I've been told FEMA will give you the BFE for a zone A, never can get them to do it however.

If you think about it how can they? Who does the cross-sections?

I know how they get elevations in a zone Ae, I've talked to the people who ran cross-sections for that and I know how the topo info was generated.

Never found anyone who ran cross-sections in a Zone A for FEMA.

You have to have good data to get a good number for a BFE, if it's some rough DEM file being used then that BFE isn't going to be very accurate.

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We do a few Zone A LOMA's each year and in Maine we have a Best Available Data website that is run by our Department of Agriculture, Conservation, and Forestry that contains approximate BFE's for most Zone A flood sources. 

We submit the rough BFE if found, a topo map of the area around structure down to the flood source, and whatever other information we think may be helpful. Even if there is no BFE available we have had them approved just from filling out the LOMA paperwork and providing a detailed topo of the immediate area.


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