Check out this link at Wetlands Watch.

Info like:

Substantial Structural Changes
If your property is located in a floodplain, substantial structural changes in the form of damages or improvements can affect your flood insurance rates and whether you are required to bring the structure up to code. “Damages” are any structural damage caused by an event like a storm or fire. “Improvements” are any changes that the property owner makes to improve or expand the structure, such as putting on an addition.