Part of Breton National Wildlife Refuge, the Chandeleur Islands are a barrier island arc located ~120 km east of New Orleans, LA and ~50 km south of Biloxi, MS. The islands help regulate the salinity in Chandeleur Sound by balancing freshwater discharged from the Mississippi River with saltwater from the Gulf of America and provide habitat for threatened and endangered terrestrial and aquatic species. Maintaining these critical ecological functions and the economic activities they support has been challenged by the degradation of the barrier island chain due to relative sea level rise, decreasing natural sediment supply, and tropical cyclones, making restoring this coastal system a priority for the state of Louisiana.

The U.S. Geological Survey has been measuring island elevations and extent for almost 20 years to understand how the Chandeleur Islands are changing, how quickly, and the natural and human processes driving these changes. The observations capture the state of the islands after Hurricane Katrina, the impacts of the construction and evolution of the oil spill-mitigation sand berm, and the effects of several tropical cyclones since 2011. Integrating satellite and lidar remote sensing with boat-based geophysics, we quantify spatial and temporal changes on the islands and in surrounding submerged areas from 2006 to 2023.

During this time, the islands have experienced several cycles of degradation and rebuilding driven by tropical cyclones and sediment supply. Observations show that the addition of sediment from the constructed sand berm likely facilitated post-Katrina island re-emergence at the northern end of the island chain. The observations also show that tropical cyclones passing close to the islands drive sediments into the submerged portion of the system, whereas distant tropical systems and quiescent periods result in increased alongshore sediment transport to shallow water areas supporting island re-emergence. In the submerged portion of the system, we find that the gulf-side shoreface is eroding, suggesting that island re-emergence and sound-side increases in elevation are driven by both natural and human-mediated processes. Further, annual variations in accumulation around a 2010 borrow site at the northern portion of the study area reflect the variable influence of tropical cyclones and emplaced sediment availability. Altogether, these observations can shape our expectations of how the Chandeleurs may respond to future tropical cyclones and planned coastal restoration activities.