BFE determination in Flood Zone A

[MikeT]

Hello.

I have been asked to determine a BFE for an el. cert for a site in Zone A. Generally what is the procedure for this and
how complicated/time consuming is it? This is unchartered territory for me, so looking for guidance. I have determined
on site elevations.

Thanks.

[David Kendall]

Research the adjoiners

[MikeT]

Ok, how do you that? I didn't see any specific info. when you pull up the FIRM on the website (i.e. LOMR, revisions, etc.)

[PLS7393]

Mike,
Contact FEMA, as they are very helpful whenever I have a question.
Do your research in the MT-1 Technical Guidance.

[TIB]

I wouldn't try to determine BFE. Your local CityCounty has an individual appointed to act as Floodplain Manager. Ask them for BFE. It is their duty to provide info. Especially if they have enacted some sort of flood ordinance in the area. Then you can check community determined in B-10

[David Kendall]

Ok, how do you that? I didn't see any specific info. when you pull up the FIRM on the website (i.e. LOMR, revisions, etc.)

Look at other developments in a similar situation to yours along the same flood source. Find the newest one with the highest value. Get the parcel number and go ask the building department how they got their permit. Then you do what they did.

If you are unfortunate enough to be the first one on the block then you will probably need an engineer and it may be cost prohibitive.

County floodplain manager is a good place to start if you can figure out who it is and get her on the phone.

First I would look on the FEMA website for other LOMAs in the area that have been successful. Ask around and find out who their surveyor or engineer was and talk to them

[MikeT]

Thanks all for the info. I will see what LOMA s are in the area, if any. I contacted the SCVWD (Santa Clara Valley Water District). They control the creek channel where the Zone A lies. I'm hoping they did a flood study and came up with BFE determinations.

The other option I have is proving the new structure will be in Zone X. Zone X covers the majority of the lot. It appears only a small part is in Zone A.

I'm wondering if I will have to do a LOMA which requires an El Cert which requires a BFE. So then we're back to square one.

[MikeT]

TIB, I will also try to contact the floodplain manager.

[Mr. Smith]

Mike, you may need to contact a Civil Engineer to calculate flows, you can provide
cross sections for the calculations but calculating water flows is Civil Engineering.

Brian

[LS_8750]

We did one last year where we showed a building was above or at the same elevation as a nearby bridge over the floodplain.
If A is above, and down stream B (the subject building) is at or above A, then B is outside of the floodplain.

[Jim Frame]

If A is above, and down stream B (the subject building) is at or above A, then B is outside of the floodplain.

This raises an interesting question: Does applying simple logic like this constitute the practice of engineering as defined in the PE Act, or can a licensed land surveyor sign off on an Elevation Certificate using such logic?

[David Kendall]

If A is above, and down stream B (the subject building) is at or above A, then B is outside of the floodplain.

This raises an interesting question: Does applying simple logic like this constitute the practice of engineering as defined in the PE Act, or can a licensed land surveyor sign off on an Elevation Certificate using such logic?

As it turned out there was no elevation certificate required. The MT-1 form was submitted along with a couple of supporting survey exhibits (partial topo survey with spot elevations and no boundary)

FEMA took care of the logical analysis and revised the structure (residence) out of the floodplain.

The fee was $0 as well so what have you got to lose by trying? I informed the client that it was a gamble and we could lose but we didn’t. His flood insurance bill vanished a month later and I expect that he ultimately received a refund of prior payments

[MikeT]

City is saying best option is to prove new structure will be outside of flood zone. Will have to superimpose flood zone boundary on a site plan. I'm not sure why they asked for an el. cert in the first place. It's clear from looking at FIRM online that zone boundary is away from proposed structure area.

[William Magee]

Sorta the same problem. The zone A boundary is a guesstimation only and more often then not does not reflect the true limit of the 100-yr flood plain. For Zone A, it is not a survey problem or one achieved by superimposing the guesstimated boundary drawn on a FIRM.

In order to "prove" the new structure will be outside of the boundary for a Zone A region requires accurate topology, an understanding of hydraulics and hydrology, and the proper license to do the necessary analysis. Anything less is incomplete.

[MikeT]

Understood. I believe the floodplain manager is SCVWD and they haven't provided any information in that area as far as BFEs, flood studies, etc.

[David Kendall]

In order to "prove" the new structure will be outside of the boundary for a Zone A region requires accurate topology, an understanding of hydraulics and hydrology, and the proper license to do the necessary analysis. Anything less is incomplete.

If it's above a mapped elevation (unspecified but determined in a practical manner) then it could be a simple question of elevation. The whole system is actuarial hocus pocus anyway, don't overthink it

[William Magee]

Many eons back, I learned to not "underthink" anything to do with flood determinations. A competing survey firm had an oops and ended up settling by agreeing to pay a homeowner's flood insurance for 30 years.

I forget who said: "We learn from our mistakes. We profit by learning from other's mistakes".

[bruce hall]

"a fool may learn from his own mistakes, the wise man learns from the mistakes of others."

who knows

[David Kendall]

“Fools say that they learn by experience. I prefer to profit by others experience.”
― Otto von Bismarck

(Sounds like Magee - maybe he is German?)

“You don't learn to walk by following rules. You learn by doing, and by falling over.”
― Richard Branson

“Failure is instructive. The person who really thinks learns quite as much from his failures as from his successes.”
― John Dewey

My personal favorite:

“It's Impossible to Learn to Plow by Reading Books“
— Richard Linklater

Take your pick

[dedkad]

My personal favorite:

“It's Impossible to Learn to Plow by Reading Books“
— Richard Linklater

Absolutely true. YouTube is a much better source for that kind of thing :)

[mpallamary]

Hot off the press:

https://www.washingtonpost.com/outlook/ ... 271ec26f48

[Jim Frame]

Mike, WaPo has a paywall that I'm not willing to buy my way through on spec. Can you summarize the article, or at least allude to its subject?

Thanks!

[LA Stevens]

Jim,

I turned off add blocker just for that article and was able to read it. The article is meant for a lay person.

[subman]

I am both a licensed surveyor and licensed civil engineer. My opinion is you must be a licensed civil engineer to determine the BFE for a Zone A (undetermined) since you are applying the principals of hydrology and hydraulics to the topographical features of the upstream and downstream cross sections to establish a water surface profile for the subject building. Just my opinion...

[Jim Frame]

My opinion is you must be a licensed civil engineer to determine the BFE for a Zone A (undetermined) since you are applying the principals of hydrology and hydraulics to the topographical features of the upstream and downstream cross sections to establish a water surface profile for the subject building.

FEMA allows determination of a BFE by "simplified methods" for use in establishing minimum floor elevations for individual sites. Those methods don't require engineering analysis, they're more of an interpolation approach and thus can be employed by land surveyors. However, the BFE thus established isn't allowed for use in flood insurance rating.

See https://www.fema.gov/media-library-data ... rm_zna.pdf for more information.