Levees and Maps
First, go read Bloggledygook’s post, We are all environmentalists now. He has some excellent thoughts and links to a discussion of the levees on NPR. His post also tipped me to the relief map below, showing elevations in New Orleans, foot-by-foot. Extraordinary detail.
Just for discussion sake, since New Orleans has been “destroyed,” and you were going to re-build it on a smaller footprint, what areas would you include in “Nova New Orleans?”
Take another look at the brown, higher elevations. Note that these closely follow the Mississippi River.
Where I live, rivers flow in valleys — erosion and gravity and all that. Perhaps Newton’s “Theory” of Gravitation doesn’t apply down South; after all, “it’s only a theory.” Actually, it still does, but historic, natural Mississippi behaved differently. The river flowed through a nearly flat delta plain; it flowed very slowly; it flooded every spring; and it carried a huge weight of sediment, “The Big Muddy.”
Every year, the Mississippi left sediment on its banks and built up its natural levees, resulting in something like the cross-section below. Note that even the floor of the river is higher than the surrounding plains.
But, since gravity has not been suspended, eventually a break-through flood would have occurred. In some particularly strong flood year, the Mississippi would have burst through its natural levees, sought out a new, lower course to the Gulf, and left the old rivercourse high and dry, a ridge snaking across the plain. That would have been the New Orleans area today, absent the flood control and navigation structures of the Army Corps of Engineers. (More on this later. See Atchafalya River.)
Here’s another map of the New Orleans area levees. Shown is a section of the map illustrating that “height isn’t everything” when it comes to levees. Fronted by five miles of marshland, a 12.5-foot levee offers the same hurricane surge protection as a 22-foot seawall. As the Louisiana marshes sink below sea level, existing levees essentially become seawalls.
On a Google-Street where you live
The world as you’ve never seen it before
Why the levees broke
Corps Finishes Pumping Out New Orleans
We’re very strongly biased towards the actual facts