Zero Rise Analysis - for existing building

[RocketRed]

I must be missing something (maybe a portion of my brain).

We have been working with a client in a Zone X flood with a historic flood depth about 30" above finished floor. Our scope of work was to design the stop-log system for the door openings. Simple work, we have done this lots of times.

The overall project is just a renovation to an existing service station ~2100 square feet. Footprint of the building remains the same, they are just doing updates and renovations and tripped the requirement for floodproof design due to cost of renovation vs property value. All of that is normal.

Today the client called me and asked us to do a Zero Rise Analysis and accompanying certification. I said, "Has the footprint changed?" and the answer was no the plans haven't changed since you did your work. So I called the building official to ask what I was missing. His answer was "The building is going to be more waterproof than it was prior to the renovation so our opinion is it could raise the flood level. It is your job to prove that it won't."

I figure this client must have really pissed the building department off, or is this a thing and I just haven't heard about it before? Somehow I am going to guess at the waterproofedness (haha) before and after renovation.

Have a laugh or offer advice (technical, social, or psychological) please and thank you.

 

[fel3]

Wow! A 2100 sq-ft building in a flood plain goes from slowiy (I assume) leaking water to the inside to VERY slowly leaking water to the inside and the building department thinks the difference is worth worrying about. By inspection, it's not (which you obviously know). I suspect the calculated difference in the flood plane elevations from this substantial change is out in the 8th or 9th decimal place. If you end up doing the calculations, be sure to include all of the decimal places before you round off for the final result of ZERO change. That way you can pawn them without them being the wiser.

I haven't dealt with this particular brand of stupidity, but I have dealt with similar.
- I was once asked by the City of F_____ to calculate the differential hydrology for a proposed 7'x7' prefab metal building on a 40-acre petroleum tank farm and prove that this building would not have a detrimental effect on the adjacent properties. The building was to be constructed inside a curb island with a dirt interior and would be located 125 feet from the street and 350 feet from the nearest property line. The curb island by itself had enough volume between dirt and top of curb to contain the additional runoff from the building, but that didn't matter to the City of F_____.
- This same building would house a printer. After a tanker truck was filled, the driver would walk over and tear the manifest off the printer. The only other people who would ever go into this building were tank farm staff and perhaps a repairmen, all of whom would have to be fully ambulatory to do their job. So, of course the City of F_____ required full ADA compliance, including a wheel chair ramp. Think of all the wheelchair-bound big rig truck drivers. The ADA compliance cost more than the building.
- At the same site, the City of F_____ Development Department requested structural calculations for a City of F_____ Public Works Department standard 48-inch-diameter manhole that I was using in a non-traffic area as a tiny wetwell for a tiny submersible nuisance water/drainage pump. The fact that the City of F_____ has thousands of such manholes in heavily trafficed streets at depths far exceeding mine did not matter to them. So, instead of doing the calculation they wanted, I calculated the theoretical maximum depth for this type of manhole (I got the idea from a story one of my early mentors told me about doing the same thing in a similar circumstance). You can find an updated version of this calculation here:

https://www.ptcusercommunity.com/docs/DOC-4735

I have more stories, but that's enough for now.



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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[beej67]

I imagine this is just a checklist issue.

I had to do something similar recently, for an existing teardown-rebuild of a residential building in Zone X. The new building was the same footprint as the old one, and the builder basically rebuilt the home so that the only thing on the 'ground' floor was the garage and a store room, so the FFE would be above the BFE. The county floodplain manager was a pretty reasonable guy, also, whom I'd worked with before. The county's position was basically, "it's on the checklist, therefore we need something for the file." So I got the HEC-RAS model, cut a section through the footprint, added the old house, and used that as my "corrected effective" model. Then saved it again as my proposed model and showed them the data was the same. They said thanks and stuck it in the file.

When it comes to government, you have to remember who you're dealing with at the ground level. Once someone lands a government job, that job is basically for life. The only possible way they can be fired is making a wrong decision, so as long as they make no decision, they have infinite job security. Which can frustrate us in private practice, but if you take a step back and look at it objectively, it's hard to blame them.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[nkrigPE]

I had a similar instance on a project where a business owner wanted to build and elevated deck over a lake area that is dry about 99% of the time. The surface area of the lake area is about 90 acres and has a storage volume of 500 acre feet.

I had to document the water surface rise cause by 8 12"x12" columns placed in this lake area to prove that none of the adjacent structures would be inundated. Huge waste of time for what should have been a common sense decision.