February 25, 2003
NEW ORLEANS -- The high wooden porch slants toward the street. The twin steps are cracked. So is the plastered support between them.
"My wife and I, we'll lie in bed and notice a new crack every couple weeks," said Stalios Leres, who rents one side of the aging two-family house.
Southern Louisiana is sinking -- houses, cemeteries, roads and all.
While most of North America rests on bedrock, New Orleans and the surrounding area are built on Mississippi River silt. And the silt is slowly settling and compacting because of gravity.
The settling has been going on for ages, but the surface really began dropping fast during the 20th century because of man's doing: The levees built to keep the Mississippi within its banks all but stopped the floods that used to lay down new layers of soil over the land.
Moreover, the human effects of the sinking are greater than ever simply because more people are living here.
Houses not built on deep pilings are tipping and cracking. So are streets, often rupturing water mains and sewer lines beneath them. Along parts of the coast, the ground is now under water, and some yards have become marshland.
The situation is so dire that some highways might be unable to serve as evacuation routes while a hurricane is approaching, the National Geodetic Survey recently warned. The roads themselves could be awash.
Among the solutions that have been floated: spreading fertilizer to stimulate the growth of plants, which trap soil and add to the dirt when they die. Also: digging a deep trench to divert the Mississippi River and its silt, or building pipelines to spread silt across the landscape.
But those solutions would work only on undeveloped land, not property that has been built over.
"Say your neighborhood's 8 feet below sea level," said University of New Orleans geologist Shea Penland. "Are you going to say the government wants to cover your house in mud to raise the level?"
For lack of a better solution, houses have to be jacked up and stabilized one at a time. Some house levelers use a technique called "mudjacking" -- drilling holes in the foundation, then pumping in a mixture of mud and cement under pressure to raise and level part of a building.
The sinking has run anywhere from 6 to 20 inches over the past 20 years, said Roy Dokka, a professor at Louisiana State University's Center for Geoinformatics. Penland disputed that, saying those figures apply only to the highways where the measurements were taken, not to southern Louisiana as a whole. The marshlands are sinking much more slowly, he said.
Whatever the case, there is "a huge trend of sinking throughout Louisiana, making it the hotspot of the country in terms of this kind of phenomenon," said geologist Stephen Leatherman of Florida International University.
Part of the problem is silt is finer than sand and compresses more easily.
In southern Louisiana, pilings often must be sunk 30 feet or more to get to sand dense enough to stabilize the buildings they bear. In Metairie and Kenner, just west of the city, a large building might need pilings up to 100 feet deep.