HEC-RAS model procurement

You need a hydraulic engineer to obtain the HEC-RAS model of the site...they would have to make a request to FEMA for the model (there is a fee for FEMA to search their library and provide this)...half the time, despite being an AE zone they can't find the model, in which case I will usually look to the State governing body for the latest model they might have in their records (usually the State department of environmental quality...(whoever issues floodplain permits)). Worse case scenario is that you are creating the hec-ras from scratch...but you have to set your boundary conditions per the information in the Flood Insurance Study (FIS). If there is an existing model then you have to establish duplicate effective, corrected effective, existing conditions and proposed conditions. Bottom line you have to show that your proposed project will have zero impact on the base flood elevation (BFE = 100-year). If the bottom chord of the bridge is above the BFE, then you should "generally" be ok. The issue will be where your abutments are located within the floodplain/floodway. You aren't permitted to build anything in the floodway...you MIGHT be able to construct in the floodway but would have to redo the mapping (Letter of Map Revision (LOMR)...actually best to do a Conditional LOMR (CLOMR) where you get pre-approval prior to construction...but then will have to follow-up with a LOMR once built). Redoing the mapping is a HUGE expense and also can take a VERY long time to get done. I just had a LOMR become final in May after 2.5 years of back and forth with FEMA. Anyhow, avoiding the mapping effort would mean to set your abutments outside the floodway (which is the cross-hatch area on the National Flood Hazard Layer (i.e. FEMA maps)). Any hydraulic engineer that does these type of analysis should know what needs to be done to model your proposed bridge. Look for a consultant with a water resource group and key word is hec-ras.

Good Luck!

Jennifer Morreale P.E., M.ASCE

Project Engineer

Hubbell Roth & Clark

Detroit MI