Land Area Changes in Coastal Louisiana after the 2005 Hurricanes: Overview

The U.S. Geological Survey (USGS) assessed changes in land and water area in coastal Louisiana within two months of Hurricanes Katrina and Rita (Aug. 29 and Sept. 24, 2005, respectively) by using Landsat Thematic Mapper (TM) satellite imagery. Land-water conditions before the storms were represented using imagery acquired between October 13 and November 7, 2004. A series of seven Landsat TM scenes acquired between October 16 and October 25, 2005, provided a snapshot of land-water area changes after the storms. The map presents a basic analysis of net changes from 2004 to 2005.

Comparison of the 2004 and 2005 imagery showed a total increase in water area of 777 km², but this measurement includes 215 km² of flooded lands consisting of flooded burned marsh and flooded agricultural and developed areas occurring after the hurricanes. Adjusting for these flooded lands, the estimated increase in water area (and decrease in land) is 562 km². The new water area occurring after the hurricanes contains: (1) land losses that may be permanent, caused by direct removal of wetlands by storm surge, and (2) transitory water area increases caused by the following: (a) remnant flooding of marsh and impounded areas, including agricultural and developed areas, (b) removal of floating and submerged aquatic vegetation, (c) scouring of marsh vegetation, and (d) water level variations caused by normal tidal and meteorological variation between images.

The purpose of this analysis was to provide preliminary information on land area changes shortly after Hurricanes Katrina and Rita and to serve as a regional baseline for monitoring wetland recovery following the 2005 hurricane season. Estimation of permanent losses cannot be made until several growing seasons have passed and the transitory impacts of the hurricanes are minimized.