THE FLUVIAL-MARINE TRANSITION IN SPACE AND TIME - USING GLOBAL FIDUCIALS HIGH RESOLUTION IMAGERY, LANDSAT, AND AERIAL PHOTOGRAPHY TO MONITOR SIX DECADES OF CHANGE AT EAST TIMBALIER ISLAND, LOUISIANA: 1953 - 2019

Between 2000 and 2010, the U.S. Geological Survey National Civil Applications Center monitored dramatic changes at East Timbalier, a barrier island located on the west side of the Mississippi River Delta (Thomas et. al, 2011), using ~ 1 m resolution Global Fiducials Library (GFL) imagery derived from US National Imagery Systems. New research expands this study both retrospectively and prospectively using declassified imagery collected in 1962 and 1972; Landsat imagery collected since 1972; aerial photography collected since 1953; and 1992-2019 GFL imagery.

Since 2000, the island has lost over 87% of its area, with parts migrating hundreds of meters north. After Hurricane Andrew breached the island in several places in August 1992, erosion and land loss increased. Since then, the island has undergone a cycle of washovers, vegetation removal, breaching, and erosion with sediment transport to the north. Imagery shows three such cycles between 1992 and 2017, despite partial restoration of the island between 1998 and 2000. Each cycle increases the distance between the island and the mainland to the east, reducing the protection that Timbalier Bay and adjacent coastal lands receive from the barrier island.

Since 2017, the island has decreased in width by ~ 50%, area by 40%, and the number and size of washovers have increased. Erosion occurs primarily on the Gulf-facing side of the island and is most severe on the east end. Additionally, much of the vegetation on the south side of the island has been eroded or buried by sand during washovers.

The main drivers in this cycle are northward and westward sediment-transporting currents, and storm waves and surges. Other factors may include regional subsidence of the Mississippi River Delta area, locally augmented by more-rapid subsidence related to oil extraction; regional sediment starvation resulting from Mississippi River flood control projects; and local sediment starvation due to construction of a nearby jetty.

Absent implementation of restoration efforts, East Timbalier will continue to experience severe land loss, potentially impacting petroleum-related infrastructure on the north side of the island.

East Timbalier Island is one of > 500 GFL locations worldwide. As shown, GFL data provides an untapped resource for assessing a wide range of dynamic Earth surface processes.