September 2, 2005

A centimeter a year...

It's good to keep in mind that Louisiana's current problems are actually manifestations of deeper problems. They've "built their house upon the sand," but sand moves, and needs to be replenished...

....As long as people could control floods, they could do business. But, as people learned too late, the landscape of South Louisiana depends on floods: it is made of loose Mississippi River silt, and the ground subsides as this silt consolidates. Only regular floods of muddy water can replenish the sediment and keep the landscape above water. But flood control projects channel the river's nourishing sediment to the end of the birdfoot delta and out into the deep water of the Gulf of Mexico....

....Abby Sallenger, a scientist with the United States Geological Survey who has studied the Louisiana landscape for years, sees the results of this bargain when he makes his regular flights over the Gulf Coast or goes by boat to one of the string of sandy barrier islands that line the state's coast.

The islands are the region's first line of defense against hurricane waves and storm surges. Marshes, which can normally absorb storm water, are its second.

But, starved of sediment, the islands have shrunk significantly in recent decades. And though the rate of the marshes' loss has slowed somewhat, they are still disappearing, "almost changing before your eyes," as Dr. Sallenger put it in a telephone interview from his office in St. Petersburg, Fla. "Grassland turns into open water, ponds turn into lakes."

Without the fine sediment that nourishes marshes and the coarser sediment that feeds eroding barrier islands, "the entire delta region is sinking," he said. In effect, he said, it is suffering a rise in sea level of about a centimeter - about a third of an inch - a year, 10 times the average rate globally...

From the NYT, (Thanks to Orrin). And thanks NYT. If I complain a lot about the New York Times, it's because It's I'm appalled to see one of the world's greatest newspapers sink into partisan hackery. But they still provide a ton of good information.

This is, by the way, similar to the problems of many areas where beaches are shrinking, Beaches need a constant infusion of sand, because sand is always slipping away into deeper water, where the waves can no longer push it up onto the beach. The sand comes down the rivers and streams and flood courses. Build dams, build flood-control projects, turn creeks into storm-drains...and you stop the flow of sand.

Marshes, beaches...they are hard for us to understand. We want to build walls to "protect" them, and to give them clear boundaries. Firm them up. Clarify them. But their nature is the opposite of clarity. They are very real, yet at the same time so formless you can't pin them down or measure them.

I often walk on the local beach, and I'm amazed at how it changes. Sometimes narrow and meager, other times (Winter? More sand from winter rains?) so wide it's a bit of a hike to get to the water. One day covered with thousands of smooth stones, another day not a stone to be seen...

Posted by John Weidner at September 2, 2005 9:21 PM
Weblog by John Weidner