Prior to approving a project or program, FSA must consider whether that project or program will cause adverse effects to areas known as floodplains. Specifically, those areas referred to as 100-year floodplains must be evaluated. An area is determined to be a 100-year floodplain if it has a one percent chance of being flooded within a 100-year period. Some of the actions that may cause adverse effects to a floodplain include building construction, drainage, dams, and irrigation diversion structures.
National Flood Insurance Program - FEMA