You should look at the current FEMA FIRM Map.
Just google "am I in flood zone" and put int the Convo's address.
It shows that most of the area at/near the Convo is in a Flood Zone.
There's no question that,in the past,there have been structures built in flood zones.
But,regulations regarding this type of construction, have gotten a lot more restrictive over time.
Speaking for NJ ,where I do my designs,if you want to build in a Flood Zone there are restrictions on placing fill,not increasing runoff by providing what is known as "storm water management" and "treating" run off to remove things like Suspended Solids.
Basically,your project can't have any impact on properties "downstream".
These things can be addressed,but they increase,significantly,construction costs and long term maintenance.