Note: 21st-century readers may be appalled at the thought that New Orleans was flooded and rebuilt enough times in coming centuries for there to be a "Third Orleans." You'll be happy to know that Third Orleans wasn't even built on Earth, much less at the mouth of the Mississippi river.

It did however flood, and it did so impressively. The simultaneous combination of earthquake, tsunami, thixatropic collapse, and cyclonic megastorm had never been seen before, and turned the Pato del Fuego delta into a tidal super-soup, which failed to flood clean because the course of the Pato del Fuego river shifted sharply as a result.

It went down in history as one of the greatest small-scale failures of planetary engineering, and that's without taking the zombies into account.

The lesson to be learned here: Don't store large quantities of experimental, moisture-activated, emergency-resuscitation nanobots in cities on floodplains.