Inside Report for February 26, 2008

• By AMY WOLD
• Advocate staff writer
• Published: Feb 26, 2008 - Page: 7B

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Because much of the land in south Louisiana is sinking, measuring land elevations is like trying to catch a moving target.

That means engineers — the same ones who design roads, levees and other structures — have relied on benchmarks that don’t reflect true elevation.

This isn’t new information.

Back in 2001, the National Oceanic and Atmospheric Administration sent a report to Congress that basically said south Louisiana’s benchmarks were unreliable.

South Louisiana’s land is sinking for many reasons, and scientists don’t agree on the culprits.

Some of the published research cites the following possible reasons:

• Compaction of the recent sediment that makes up south Louisiana.
• Active faults throughout the coast that add to sinking of land.
• An overall downward push of delta sediments.
• Oil, gas and groundwater extraction that removes underground pressure, resulting in subsidence that equalizes that pressure.

In one sense, it matters that coastal scientists understand the real reason land sinks in Louisiana, because that reason will direct how coastal restoration continues.

In another sense, it doesn’t matter why land is sinking. What does matter is how much and if that sinking can be measured accurately.

“We’ve basically been building blind for many years,” Roy Dokka, executive director of the LSU Center for GeoInformatics, said during a January presentation at the state Department of Transportation and Development.

After hurricanes Katrina and Rita, the Legislature asked the LSU Center for GeoInformatics to take another measurement of levee and floodwall elevations.

In order to do that, Dokka and his team set up reference stations — about 50 — across the state. Using those sites, a Global Positioning System was used to get real-time measurements, Dokka said.

A cell phone and GPS equipment can get the real elevation anywhere in south Louisiana in about three minutes, he said.

“This is the best way to make sure we have good elevations,” Dokka said.