Ah yes, Professor Burns has entered the chat. Thanks for imparting that wisdom Burnsie!
Regardless of flooding, part of the reason you evacuate (beyond death and destruction) is the lack of ability to provide basic services, food, water, gas, electricity for extended periods of time for large populations. Nobody needs to drown to have storm related misery, riots, death and destruction. As someone supplying emergency services equipment and support during my day job, I can tell you the disaster services industry is in a huge pickle right now and is lacking equipment because the gov't just sucked it all up for Afghan camps in the last 96 hours. I have personally supplied Quantico, Goodfellow AFB, Fort Bliss and Fort Dix this week.
These folks wont be getting much FEMA help I can assure you of that.