Floodplain Management consists primarily of assessing flood risk for structures prior to construction.
State and Federal construction projects are subject to an extensive engineering review that includes hydrologic analysis and environmental impact. This also applies to large commercial projects.
Local construction that falls within a floodplain is regulated by local government using Federal Emergency Management Agency (FEMA) and United States Environmental Protection Agency (EPA) standards. This protects watersheds, wetlands, and rivers from sedimentation, and chemical or biological pollution (EPA). And it prevents property losses to citizens that could be significant in the event of a flood (FEMA).