There are places along the Mississippi River (e.g. New Orleans) where many people live in areas that would normally be flooded, were it not for levees or other flood control works. Many more places in the U.S. are dependent on levees to protect them from routine seasonal flooding. As many as 1,000 died when the Great Flood of 1927 broke Mississippi River levees. Levees are often poorly protected against deliberate damage, with possible catastrophic casualties. But whether the "trigger" is a terrorist, a hurricane, earthquake, bad engineering, or climate-related global sea level rise, the outcome could be the same. The most effective solutions to such problems may not be building bigger levees or posting armed guards on levees, but removing the underlying hazard. That might mean raising land forms, resettling populations, controlling new settlement and growth, etc.
What are the flood plains in your area? Are there flood control or levee districts? How well are the levees and flood works in your area engineered and maintained? How are they funded? You can probably find more information from the U.S. Army Corps of Engineers Division or District office in your area. Do levees in your area meet the standards of FEMA's National Flood Insurance Program? Are improvements fundable under the Corps of Engineers' Levee Rehabilitation Program or the Natural Resources Conservation Service (NRCS) Emergency Watershed Protection (EWP) Program?