The next big one

Natural History, Dec, 2005 by Vincent A. Ettari, Shea Penland

I happened to pick up the February 2005 issue, and as I read Shea Penland's article, "Taming the River to Let In the Sea," I was amazed by its timeliness and accuracy. Six months after its publication, Mr. Penland's dire predictions--that a big storm could wipe out New Orleans's defenses--came true.

Mr. Penland points to the compression, and consequent subsidence, of the delta plain as a critical factor in the increasing vulnerability of New Orleans to flooding. As a structural and site engineer, I am intrigued that as recently as the 1930s, levees were being built on self-compressing silt, a poor foundation for such a critical defense system. Dams, sea walls, and levees must be founded on firm base material, preferably bedrock.

Now I am concerned that the levees are not being rebuilt according to proper engineering standards. The breaches in the levees are being closed with material that, once again, rests on self-compressing silt.

Vincent A. Ettari

Shrub Oak, New York

SHEA PENLAND REPLIES: New Orleans and southeastern Louisiana underwent unprecedented devastation and extreme changes to their coasts as a result of hurricanes Katrina and Rita. And the impacts of these storms on the Mississippi River delta are still being uncovered. The barrier islands are massively eroded, and chunks of marsh litter the coast.

What can we learn from these storms? People must learn to coexist with our coasts, live in practical areas, and, where feasible, build the necessary defenses to stormproof our society. To minimize future storm risks, coastal restoration and the rebuilding of the hurricane protection system must be integrated.