Property Protection Measures
There are several things you can do to protect yourself and your property.
The first and most important property protection measure is the purchase of flood insurance.
Temporary Property Protection Measures
Temporary / emergency measures include relocating your possessions to the highest floor or placing sandbags or similar barriers between floodwaters and your structure. (Note: Sandbags should not be stacked directly against the outer walls of a structure, since, when wet, the bags may create added pressure on the foundation.)
Permanent Property Protection Measures
A more permanent means of protecting your structure (known as retrofitting) would be elevation of a flood prone residential structure above the Base Flood Elevation (BFE) so that floodwaters do not reach any damageable area or floodproofing of a commercial structure to make the structure water tight below the Base Flood Elevation (BFE).
Information about floodproofing can be found at: http://www.fema.gov/plan/prevent/floodplain/nfipkeywords/floodproofing.shtm