Hurricanes Katrina and Rita transformed some 100 square miles of marsh to open water in southeastern Louisiana, according to preliminary estimates by USGS based on an analysis of Landsat satellite data from September and October. Future observations of Landsat imagery over the upcoming year will allow scientists at the USGS National Wetlands Research Center (NWRC) in Baton Rouge and Lafayette, La., to determine how much of the loss is permanent and how the marsh recovers. Although this early analysis of wetlands does not take into account some marsh recovery, indications are that much of the loss may be permanent. Some of the new areas of open water will likely become new lakes.
Most of the loss east of the Mississippi River is attributed to the effects of Hurricane Katrina’s storm surge, although Hurricane Rita’s surge appears to have rearranged some of the wrack, or marsh debris, left behind by Hurricane Katrina in the upper Breton Sound area. Substantial marsh loss, primarily from Katrina, occurred east of the Mississippi River in St. Bernard and Plaquemines parishes. Approximately 39 square miles of marsh around the upper and central portions of Breton Sound were converted to open water by ripping of the marsh or by marsh submergence. Follow-up imagery and aerial photography will be used to determine if some of the submerged marshes reemerge over time.
To perform satellite analysis, USGS scientists in Louisiana used remote sensing technologies and GIS. They compared land and water areas identified by using Landsat 5 Thematic Mapper satellite imagery. Landsat data from November 11, 2004 were compared to data acquired on September 7, 2005, September 16, 2005, October 9, 2005, October 18, 2005, and October 25, 2005 to identify potential wetland loss. The imagery was collected by the USGS National Center for Earth Resources Observation and Science in Sioux Falls, S.D.