The Value of Global Fiducial Imagery for Monitoring and Assessing Multi-Decadal Shoreline Change on the U.S. Atlantic and Gulf Coasts 669255

Abstract:

The USGS National Civil Applications Center analyzed Global Fiducials Library (GFL) imagery time-series spanning several decades to assess changes in two hurricane-impacted barrier island systems: Fire Island, NY, and East Timbalier Island, LA. Following decades of little change, Fire Island was breached by Hurricane Sandy in late October 2012. Since then the breach has widened; a flood-tide delta has formed and grown in Long Island Sound; and the shoreline has been reshaped differentially on either side of the breach. The area is of interest to local planning authorities who developed options for managing the shoreline contingent on the size and location of the breach.

East Timbalier Island was breached by Hurricane Andrew in August 1992. Since then, the island has undergone several cycles of wash-overs, vegetation removal, breaching, and erosion with northward sediment movement. Despite partial restoration of the island between 1998 and 2000, each cycle increased the distance between the island and the mainland to the east, reducing sediment supply from the east and lessening the protection that adjacent coastal lands receive from the barrier island during storms. East Timbalier Island split into three pieces by mid-June of 2020 following tropical storm Cristobal, and absent remediation efforts, the sediment comprising the remnant pieces of East Timbalier Island is likely to rapidly erode.

GFL imagery provides valuable, objective, long-term data for the sites, which allows changes to be measured against a baseline. GFL imagery of both Fire Island and East Timbalier Island was available before and after the key breaching events. The two barrier islands are in dynamic environments with variables including elevation profile of the barrier and foreshore slope; net long-shore sediment transport; tidal range; wave height; frequency of storms; vegetation type and amount; sediment size and supply, and local net sea-level changes. The decades-long baseline provided by GFL imagery allows for periodic reassessment of the relative importance of these and other factors as new data becomes available. The value of GFL imagery is enhanced when combined with commercial and government imagery (e.g. Landsat, Sentinel) which possess a complementary range of temporal, spatial, and spectral resolution.