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U.S. Department of the Interior
U.S. Geological Survey
National Wetlands Research Center
700 Cajundome Blvd.
Lafayette, LA 70506

Contact: Gabrielle Boudreaux Bodin
Phone: 337-266-8655
Fax: 337-266-8541
For Release: May 29, 2008



Little Coastal Land Recovery After Hurricanes Katrina and Rita, Says New Report

The Louisiana coast is not recovering most of the land lost to Hurricanes Katrina and Rita in 2005, says a new study.

Immediately after the storms, Louisiana lost 217 square miles of coastal land to open water. That’s an area roughly the size of Chicago or a little larger than New Orleans. By the end of 2006 only an estimated 19 square miles of land had been recovered, according to a new report by the U.S. Geological Survey.

Coastal lands, mostly marshes, became open water through various ways. Some were partially or completely destroyed by the force of the wind-driven surge of water. Some were flooded or submerged. And some collapsed after the hurricane because their vegetation died from the effects of the salt water of the surge.

“More time will be required to evaluate the permanent loss from the hurricanes,” said John Barras, senior author and USGS geographer at the National Wetlands Research Center in Lafayette, La.

These findings are published in a new historical analysis of land and water changes from 1956 to 2006. The study provides a refinement of prior USGS historical trend analyses and underscores that extreme weather events like hurricanes can have significant long-term impacts.

“The scientific significance of this report is that its method to predict land trends over time is more reliable than those used in previous studies because more data sets are used,” said Scott Wilson, branch chief of spatial analysis at the center. Scientists acquire data from satellite imagery that is put into computer form using geographic information systems. Analysis involves using both spatial technology and statistical methods such as linear regression to interpret the data.

Previous USGS studies used only four land-water data sets to estimate and project trends. The current study uses 10 land-water data sets from 1985 to 2006 to estimate and project current trends. The new study also uses time consistent data sets acquired within a few months of each other and representing same season conditions. Prior USGS studies used hybrid data sets created by merging or piecing together data acquired in different years.

The hurricanes of 2005 caused immediate new land loss on a coast that had already been experiencing loss since 1956. The impacts of recent hurricanes suggest that such storms can contribute to land loss, ranging in scale from specific localities to entire hydrologic basins and can cause the formation of permanent ponds of varying size.

The USGS urges caution when interpreting area changes since some of the land loss can be temporary, particularly when comparing changes over just a few years. Several years may be necessary before the long-term effects of recent hurricanes on coastal land loss are known. The new study found that land area estimates vary over short time periods and that areas undergoing loss or gain may fluctuate over the short term before permanently converting to open water or to land.

The area of the study is coastwide and these results do not directly apply on smaller scales, such as hydrologic basins or even to smaller areas. These results do, however, demonstrate that the immediate impacts of extreme storms can alter the long-term, time-averaged trends of landscape change. Distinguishing permanent from temporary land loss may require several years of observation, thus limiting reliable long-term projections, given the possibility of future storm hitting the coast.

Gregory Smith, director of the USGS center, said “This study will be useful, not only for the scientific community, but all agencies and citizens involved in restoration.” The USGS center has been studying wetland change since the 1970s.

This latest study appears in the USGS Scientific Investigations Map 3019, which has three parts. A map depicts the historical land-water area changes. A pamphlet provides the methods used and an explanation of the study. A slideshow presentation contains additional images and graphics. They are available at http://pubs.usgs.gov/sim/3019.


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