Need some regulatory guidance
Need some regulatory guidance
(OP)
Hello, all. One of my clients, a local municipality, is in the process of developing a new floodplain management ordinance. They have requested that we provide them with some recommendations as to best practices within Zone A riverine floodplains. They want to include in the ordinance a rule pertaining to floodway preservation and approximation within Zone A. I have several years of experience in floodplain management and modeling myself, but I have never run into a regulation or ordinance with guidelines for approximating the floodway in a Zone A. In that situation, I'd normally recommend that a HEC-RAS model and LOMR be performed.
I've heard general rules of thumb such as "5x the top width of the stream," etc., but this seems awfully general given the asymetrical nature of a floodway and the fact that its size doesn't necessarily relate to the size of the channel.
Can anyone point me towards any REGULATORY (preferably Federal, but state or local examples will be appreciated as well) guidance that speaks to floodway preservation within a Zone A floodplain?
Thanks in advance!
I've heard general rules of thumb such as "5x the top width of the stream," etc., but this seems awfully general given the asymetrical nature of a floodway and the fact that its size doesn't necessarily relate to the size of the channel.
Can anyone point me towards any REGULATORY (preferably Federal, but state or local examples will be appreciated as well) guidance that speaks to floodway preservation within a Zone A floodplain?
Thanks in advance!





RE: Need some regulatory guidance
RE: Need some regulatory guidance
Your client could be referring to "floodway" as a general term for "channel," but their reference to Zone A makes me think that they probably were thinking on a regulatory basis.
Is it possible that your client is interested in floodplain approximations in Zone A? If so, I have heard rumors, but never verified, that some people used to map Zone A floodplains based on Water Surface Elevations determined using Manning's Equation/basic Normal Depth calculations. I guess this could be a rough estimation (very rough), but again, I never fully bought or confirmed this.
If it's okay, I would like to add to djstrick's question by asking how the Zone A floodplains shown on FIRM maps were/are delineated.
RE: Need some regulatory guidance
Froude, what you mentioned about my client being interested in floodplain approximations is exactly what I'm after. They want to include an item in a new ordinance for preserving a "floodway" within Zone A should any development occur in such a floodplain. I'm just curious if anyone out there has seen any examples along these lines. For instance, another municipality in the state requires that 5x the top width of the stream be preserved on either side of the stream. I have no idea how they arrived at the "5x the top width" stipulation, but again, I was just curious if anyone new of any regulatory guidance on this.
RE: Need some regulatory guidance
It's a FEMA document entitled "Managing Floodplain Development in Approximate Zone A Areas"
http://www.fema.gov/library/viewRecord.do?id=2215
RE: Need some regulatory guidance
djstrick - could your client be confusing floodplain with floodway? I get that, on occaision, from some of the reviewers on our projects. I typically inform them of the difference.
RE: Need some regulatory guidance
Not specifically related to floodplains, but maybe that is what your township is looking to accomplish?