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Louisiana - Have elevations changed?

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Vernon Martin

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I'm looking at a lidar contour map for a waterfront site in Houma. This contour map is from 2003 and indicates elevations up to 10 feet above sea level.

Google Earth is indicating maximum elevations of 3 feet, and the photos seem consistent with Google. I'm trying to reconcile the discrepancy. Is it possible that elevations changed after Katrina?
 

Non Sequitur

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I don't practice in Houma but I know in New Orleans the corp did update/change elevations after Katrina. From the little I do know about Lafourche Parish, I don't think elevations changed 7ft.

Here's their website, the planning dept may be able to help.

http://www.lafourchegov.org/lafourchegov/AboutLafourche.aspx
 

Terrel L. Shields

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Duh... New Orleans was offshore 3000 years ago. The whole delta is sinking and not so slowly either. The Mississippi River moved there because the silt built up around Port Morgan area and shifted the river about 2500 years ago. Now Port Morgan and surrounding area is sinking and the Mississippi wants to move back, leaving New Orleans to sink below the waves. Sooner or later the Basin will not be able to keep it from doing exactly that.
 

Lee in L.A.

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I read they're requiring new homes to be built on high stilts. Soon may require higher stilts. Doesn't sound like the best plan. :shrug:
 

Mountain Man

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And you thought CA was the sinking state. LA is losing ground faster than the FL condo market!
 

c w d

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I'm looking at a lidar contour map for a waterfront site in Houma. This contour map is from 2003 and indicates elevations up to 10 feet above sea level.

Google Earth is indicating maximum elevations of 3 feet, and the photos seem consistent with Google. I'm trying to reconcile the discrepancy. Is it possible that elevations changed after Katrina?

Do not rely on Google Earth. They identify my house 5 houses down the street from where it is. Do you really think you should rely on it for something as technical as elevation data?
 

Non Sequitur

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I read they're requiring new homes to be built on high stilts. Soon may require higher stilts. Doesn't sound like the best plan. :shrug:
Don't believe everything you read.
 

Restrain

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I used to live in Pasadena, Tx, which fronts on the Gulf. The elevation had falled 10' and part of Baytown sunk into the Bay. Literally. At high tide, the water would sweep through the streets.

The bottom line is, along the Gulf Coast, especially Louisiana to Eastern Texas, the area is subsiding. Just the way it's been.
 

Vernon Martin

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Thanks, non sequitur and everyone else. I was just wondering if it was conceivable that the elevation could have declined up to 7 feet in 5 years.

About Google Earth, I understand how it is off in placing addresses, just like every other mapping software. Does anyone know how accurate their measurement of elevation above sea level is? Up until now I've always trusted it.
 

Pat Butler

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Most programs like Google Earth probably use digital elevation model (DEM) data from USGS. It's not too good because you have the resolution of the acquired data itself as well as the resolution of the sweep of the satellite receiver to contend with. I believe the sweep of the Space Shuttle acquired data was around 30 meters. The elevations in between each 30 mtr. segment would be interpolated.

It's enough for large scale map making, but not good enough for flood work.

http://en.wikipedia.org/wiki/Digital_elevation_model
 
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