Shoreline and Wetland Change Assessment

Shoreline changes document subaerial dynamics of the land-water boundary in response to various coastal processes, particularly those associated with storm events. Applied Coastal personnel specialize in quantification and interpretation of historical trends in shoreline position, bathymetry, and wetland area relative to dominant coastal processes. Innovative strategies have been developed to take advantage of state-of-technology advances in surveying, image analysis and interpretation, and geographic information systems (GIS), combined with a comprehensive and detailed understanding of the processes impacting coastal geomorphic change. Topographic and hydrographic surveys of coastal and nearshore environments provide a direct source of data for quantifying system response. Applied Coastal personnel analyze these data to evaluate coastal change trends at various locations along the U.S. coast in relation to normal incident coastal processes, storm impacts, relative sea-level change, and human modifications of the coast.

The Barrier Island Comprehensive Monitoring Program (BICM) provides integrated, comprehensive data on Louisiana shorelines, aiding in planning, design, maintenance, and evaluation of restoration projects. The primary goal of this BICM-Phase 2 effort was to revise and update existing BICM historical shoreline change data for coastal Louisiana from the mid-1800s to 2015. Backbarrier shorelines for the 1998, 2004, 2005, 2008, 2012, and 2015 periods also were digitized for establishing geomorphic polygons for habitat change analysis within the broader BICM program. Coastal structure locations were digitized for all epochs as well. Once shorelines were compiled and attributed, the Digital Shoreline Analysis System (DSAS version 4.3) was used to quantify changes in shoreline position for six epochs: 1) 1880s to 1930s, 2) 1930s to 1950s, 3) 1950s to 1998, 4) 1998 to 2015, 5) 2004 to 2012, and 6) 1880s to 2015. Shoreline change analysis was completed for nine geomorphic regions and 83 shoreline reaches by establishing region-specific baselines and shore-perpendicular transects at 50-m (164-ft) longshore intervals.

Although shoreline change variability is large for all geomorphic regions, regional changes isolate areas of large and chronic loss that have been the primary focus of shoreline restoration. Mean shoreline position change for the entire coast of Louisiana varied between -9.5 and -13.5 ft/yr. Most vulnerable geomorphic regions include the Eastern Chenier Plain, Early Lafourche Delta, Late Lafourche Delta, Modern Delta, and Chandeleur Islands. As expected, primarily protected shorelines of the Acadiana Bays, Atchafalaya and Wax Lake Deltas, and Pontchartrain Basin regions recorded relatively small mean shoreline recession rates. For open-Gulf shorelines, mean shoreline change varied between -10.5 and ‑21.7 ft/yr. These regions absorb the greatest impact from storms, thereby requiring greatest potential for shoreline restoration to provide protection to interior shorelines. For semi-protected coastal areas, a smaller range in mean shoreline recession was documented (5.8 to 8.6 ft/yr). Further, variability in shoreline change rates was much lower in semi-protected coastal areas away from the direct impact of open-Gulf waves and currents.