California Surveyors Forums

Has anybody challenged the location of the Floodway boundary line on one of these latest FIRMs?

The location of this line calls into question the buildability of a client's parcel, since it is vacant and located along the edge of the floodway line.

Any ideas other than a detailed hydrologic and hydraulic study?

Cheers.

This particular vacant lot sits right in the middle of a fully developed subdivision near the edge of the floodway boundary line.

It seems worth while to challenge the location of the floodway boundary line. If I can demonstrate the floodway boundary line to be in a different location, favorable to my client, then he is in the clear.

Otherwise, I will need to perform a substantial H&H study, including the topographic survey and floodway boundary line determination, to help this guy build on the parcel.

Would raising the grade enable the parcel to be built upon? I know that works in flood plains, but I don't know about floodways.

All the time. If you can demonstrate that the lot/structure is not flood prone or can be modified, process a LOMR or CLOMR.

See:

http://www.fema.gov/plan/prevent/floodp ... /lomr.shtm

http://www.fema.gov/plan/prevent/floodp ... clomr.shtm

I respectfully disaggree that this is more an engineering discussion than a surveying discussion, but luckily, Clark is both a PE and a PLS. This is an opportunity for Land Surveyors to work with Engineers to determine the best solution for the client, and to protect the public. For a PLS unfamiliar with FEMA processes, this could be an opportunity to provide the land surveying expertise with which they are competent, and (gasp) to learn from a PE with FEMA experience.

Actually, this discussion brings up some interesting things that surveyors might want to be familiar with, if not already.

We all get our base flood elevation (BFE) for elevation certificates from scaling the FIRMs, or better, interpolating between FIRM cross sections and cross section data in the Flood Insurance Study (FIS).

If you topo a cross section of the floodway at a given point, or at a given cross section on the FIRM, and then plot the cross section and input the BFE for that location, then you can compare the actual cross sectional area against the data from the FIS. This comparison will tell you just how reliable the BFE and floodway boundaries are on the FIRM. If the measured cross sectional area is greater than that from the FIS, then the floodway can likely be reduced, or the BFE can be reduced, or both.

But, requesting an adjustment to the floodway boundary or the BFE triggers the full blown hydrologic and hydraulic study. But this little task can help to justify the cost of the study.

It looks like I'll be taken some time away from the field on this one. But those H&H studies are fun.

Thanks for all your input folks.

Cheers.