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To Determine the Base Flood Elevation on an Urban Area

To Determine the Base Flood Elevation on an Urban Area

To Determine the Base Flood Elevation on an Urban Area

The firm I work with has acquired the task of determining a BFE for a section of a coastal city which up to this point has been in Zone A of the FEMA flood maps.
I was thinking of approaching this task using the EPA SWMM but am at a loss on where to begin.
How vast does my model have to be, where do I start obtaining the data, etc.

I have Hydrology experience using the NRCS (SCS Method) TR-55 for comparison of Pre & Post Runoff and volume conditions, but the derivation of an actual Storm Water Model, is a first for this Engineer.

Anyone out there kind enough to provide guidance or a step by step procedure to follow ?

Any input or help is greatly appreciated.



RE: To Determine the Base Flood Elevation on an Urban Area

First, review your scope of work that is in the contract; I presume it should contain level of effort needed to perform the analysis and what shall be included (Hydrology & limits of mapping). From there establish your plan to develop the H&H needed to map the base flood. I would recommend a FEMA Search first to determine what has been determined for the Zone A flood zone and then determine the validity of that data. Then local H&H Studies or your own hydrology based on your specific scope of work.

Step by Step for H&H:
Hydrology: Mapping/Topo, Soils, Land Use, Methodology
Hydraulics: Mapping/Topo/Survey, Hydraulic Method, Consider storm surge????
Documents: Prepare Technical Support Data Notebook in accordance with your local requirements

Real general; but, I do not know your scope. Hope this helps.

RE: To Determine the Base Flood Elevation on an Urban Area


I recommend contacting FEMA to get information on what modeling they will accept for this study. SCS method is not typically the first (or second) choice for establishing flow in FEMA flood studies. For hydraulics, HEC-RAS has been the preferred method for establishing water surfaces in channels. When you add the fact that you are dealing with a coastal city, coastal flooding can certainly play a factor. Coastal flooding has entirely different modeling vs. storm runoff models. You may want to consult with a firm who has experience with FEMA studies.

RE: To Determine the Base Flood Elevation on an Urban Area

Thanks for the Posts guys, finally getting back to this. On my way to do some research.

Thanks for the input.

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