Floodplain questions
Floodplain questions
(OP)
We want to extend a buiding addition into a "Zone A" 100 yr floodplain. I'm hearing conflicting information from FEMA and others, and would like to get it clarified. Zone A is determined by approximate methods and does Not have a Base Flood Elev(BFE) or a defined Floodway. We know we have to do an engineering study.
1.) Will this be a Flood Insurance Study(F.I.S.) or Hydrology & Hydraulic study(H&H)?
2.) Will they define a new Floodway or Will they do a Pre and Post const. H&H and limit the rise in elevation to 0' or 1.0'?
3.) If we fill in the flood fringe do we have to excavate the same volume so we do Not reduce the storage volume?
4.) If they define a Floodway, can we have the engineer shift it slightly to the other side of the stream(Floodways are Not symmetric about streams) to miss our building?
1.) Will this be a Flood Insurance Study(F.I.S.) or Hydrology & Hydraulic study(H&H)?
2.) Will they define a new Floodway or Will they do a Pre and Post const. H&H and limit the rise in elevation to 0' or 1.0'?
3.) If we fill in the flood fringe do we have to excavate the same volume so we do Not reduce the storage volume?
4.) If they define a Floodway, can we have the engineer shift it slightly to the other side of the stream(Floodways are Not symmetric about streams) to miss our building?
RE: Floodplain questions
2) They will probably expect you to define the floodway
3)No, you don't have compensate for lost storage in the floodway fringe
4)Yes, you can define the floodway in any one of 5 acceptable ways.
Your engineer should know these things. Find one with good experience in this area of practice and good relations with your local FEMA reps.
good luck
RE: Floodplain questions
If you can get a Project number assigned, you can talk to the FEMA staff member assigned to it and expedite the process of understanding what is needed.
RE: Floodplain questions
2. No, floodways are part of the FIS study and are not changed for new developments. Also a small building addition is too small to affect 99% of the FIS studies. If no floodways are shown, don't worry about it.
3.Normally FEMA and local jurisdictions require the flood plain storage volume to remain unchanged with new construction and will require an excavation from the floodplain equal to the volume of the building within the flood plain.
4. Floodways are normally only revised when the FIS study is revised as it is a major project.
You will probably also need a LOMR ( letter of map revision ) from FEMA. Discuss this with your professional enineeer.
RE: Floodplain questions
good luck
RE: Floodplain questions
We consulted the guidelines for undertaking Flood Insurance Rate Maps when coming up with this methodology.
HEC-RAS is free software, available for download off the US Corps of Engineers website. Their Hydraulic Reference Manual is essential reading if this is your first model.
RE: Floodplain questions
If there is an FIS, this is the basic information and you will (as noted correctly) need to evaluate whether you are in the FEMA floodway and what the Base ELevations are. FIS report can be purchased on line, and you can obtain the electronic models thru FEMA, otherwise you will need to go to Michael Baker (They are helpful once you get to them). You will need to obtian the effective model, and then create a duplicate effective model. You will also need to then perform a FLoodway analysis to determine encroachments based on the surcharges.
Some of the FEMA language is very specific and the Fed Regs are quoted line and verse by them. Essential that you get an engineer EXPERIENCED with FEMA, not just running HECRAS. There are several publications on the FEMA website that explain the process and how they manage there floodplains and Zone A's. It is essential to obtain this information ...
Good luck.