FEMA culvert freeboard requirements 1

[SLOCivil]

FEMA requires 3 feet of freeboard for levees, but is their a freeboard requirement for culverts? A developer wants to build adjacent to a creek that goes underground through a culvert for 50 feet. If, for example, the hydraulic analysis shows the water surface elevation at the upstream end of culvert is at elevation of 100 feet, at what elevation must the finish floors be? This is not a levee situation. The effective map shows this area as an A zone, so we are having the developer do the hydraulic analysis to determine a BFE.

 

[froude]

SLOCivil,

According to FEMA/NFIP the FF has to be at or above BFE (based on FIS flows or similar). That is just the minimum requirement. I don't believe that there is a requirement for culvert freeboard. Most local municipalities (in my area, anyway) enforce stricter measures (i.e. FF anywhere from 1 to 2 feet above fully developed water surface and 1+ foot of freeboard at culverts).

 

[SLOCivil]

We do have stricter requirements for buildings in the floodplain (BFE +2') but we will be asking the developer to process a LOMR if the culvert can contain the 100-year flow. This will remove the proposed building from the floodplain, so our ordinance will no longer apply. We do not have any municipal requirements or engineering standards regarding culvert freeboard design. I would have thought that FEMA would have something to say about freeboard at culvert inlets, since they require 3 feet of freeboard for levees and want an additional one foot of freeboard on the levee at the entrance to hydraulic structures such as bridges and culverts. But it appears that without a levee, FEMA is silent on freeboard requirements for culverts.

 

[froude]

Yes, I believe all of what you said is correct. It may be that the levees end up having such a big impact on overall flood risk and flood insurance that FEMA has incentive to regulate those more stringently. Plus it could be a game of numbers - there are probably exponentially more culverts that get designed than levees. If FEMA began regulating culvert freeboard, then that would require municipalities to spend a lot more money to increase their designs.

 

[Rye1]

FEMA is silent on culvert freeboards...which is correct. The NFIP regulations are specific and have been upheld in the courts. It is the local jurisdiction's authority to require or not to require freeboard requirements.

In an unnumbered A zone as you have described, I would believe that requiring the FFE to be 2 feet above the calculated BFE should be sufficient. Before the first shovel full of dirt is turned, the developer will have to have a building permit. To receive a building permit in our region the developer must either have an approved "no-rise" or a CLOMR. A LOMR isn't always the answer.

Robert Billings

http://www.newrivereng.com