Historical Shoreline Changes and Barrier Island Land Loss along Louisiana's Gulf Shoreline: 1800's – 2005

The Louisiana Coastal Zone is losing land at rates of up to 100 km2/yr, resulting in drastic changes to shoreline position, geometry, and configuration. In order to: 1) establish a baseline dataset for future restoration efforts, 2) define the character and patterns of historical shoreline change, and 3) quantify the rates of linear shoreline retreat, a comprehensive shoreline change analysis of the entire Louisiana Gulf shoreline was undertaken. This study documents historical rate and range of Louisiana Gulf shoreline change for the period from 1855 to 2005 and provides a comprehensive quantification of shoreline evolution trends along Louisiana's Gulf shoreline. Using historical maps, satellite imagery, and aerial photography, patterns and rates of shoreline change were documented for 4 time periods: 1855-2005 (historical term), 1920's-2005 (long term), 1996-2005 (short term), and 2004-2005 (near term). The high-water line was used as the official shoreline and was interpreted and determined on the aerial photography and satellite imagery according to the location of the wet and dry-beach contact or the high-water debris line. Measurements of shoreline movement and change were taken along transects perpendicular to an offshore baseline spaced at 50 meter intervals alongshore. The average historical rate of shoreline change is -2.7 m/yr. The average long-term rate of shoreline change is -4.2 m/yr. During the last decade, shoreline change rates have accelerated to -8.2 m/yr. The impacts of Hurricanes Katrina and Rita in 2005 accelerated the near-term rate of erosion to -57.8 m/yr. The highest rates of erosion due to the 2005 storm impacts were found along the Mississippi River delta barrier islands of Isle Derniers, Timbaliers, and Chandeleur Islands with some sectors undergoing over 182 meters of landward retreat. Beach nourishment, dune construction, and backbarrier marsh creation projects were the only areas where shoreline retreat was not detected in this study.