clarifying barriers

feedback from dk indicates some earlier posts may have shed more mud than light on what new orleans needs most, so let me try to make it clear.

the reason h.katrina hit NO as hard as it did is that the mississippi delta wetland has eroded so much—currently, at a rate of 20-30 sq mi per year—that it is now mostly open water. the barrier islands are gone too.

since land slows the windspeed of cyclonic storms, the wetlands and islands gave the city a natural shield.

part of the erosion is a result of waterways dug by oil drillers and the army engineers corps, but—paradoxically—most of it is because of levees meant to prevent river flooding.

the delta was built of silt left behind by countless prehistoric floods. before the levees got as long and high as they now are, the mississippi spilled over its banks often enough to deposit sufficient silt to replenish eroded land.

nowadays—except for relatively rare occasions when the river rises above levees or flood walls—some of that silt stays on the river bottom, and the rest gets shot out into the gulf of mexico, the same place rain washes soil from the delta.

the only way to prevent major storms from doing the kind of damage we've just seen—and it will happen again otherwise—is to rebuild the wetlands and barrier islands. it ought to be the first priority of the $200B+ reconstruction effort.

the cost has been estimated at 14-16 gigabucks [that's giga with a B].

cheap.