An article written in 2001 on ScientificAmerican.com states that New Orleans could get hit by a hurricane and flooded in 20ft of water.

A major hurricane could swamp New Orleans under 20 feet of water, killing thousands. Human activities along the Mississippi River have dramatically increased the risk, and now only massive reengineering of southeastern Louisiana can save the city

So my question is with hindsight if there was a select few that could have foreseen what has happened, why wasn’t any extra defence barriers erected or any training of evacuation procedures put into place?