Well, "building" engineering design issue maybe. But you're not really solving an engineering design issue by using fill in the flood plain to raise a building out of the 500' year flood, you're filling the flood plain and pushing more water to your downstream neighbors to deal with. You haven't solved the problem of flooding, you've just passed it on and made it worse.
Actually,no.
My post only dealt the fact that you can put a building in Flood Zone,without it flooding.
I didn't want to bore people with the "mechanics" of doing this.
But,since you brought it up.
Building in Flood Zone,when done properly, will not adversely impact downstream properties.In fact it will actually make their situation better.
I can only speak about New Jersey.
In what are known as Fluvial (non tidal) Flood Zones, we have what is known as "Zero Net Fill".
That means that,for every cubic yard of fill we place in a Flood Zone for a building,parking lot etc.,we have to remove an equal volume of material.
Its called a "Net Fill Compensation Area",the design of which must be approved by the State.
In addition to "Zero Net Fill",we also have to provide a drainage system that reduces,by up to 50% ,the volume of existing runoff.
Again, the design of this has to be approved by the State
So,from a runoff volume perspective,a project like this not only doesn't make flooding worse for people downstream,it makes it better.
For projects that are 1 acre or more,the design must include a Water Quality System.
This system has to remove 80% of the "Total Suspended Solids" from surface runoff.
So,not only is there less runoff,its cleaner.
We also,depending on soil conditions, put some of the runoff back into the ground,to recharge aquifers.
We must also prepare an "Operation and Maintenance Manual".
The Operation and Maintenance Manual must be approved by the engineer for the town where the site is located.
The Manual must have signed log sheets confirming that the system is maintained.
The signed sheets must be kept on site and are reviewed by the Municipality.