RAPID: Hurricane-induced Shelf Sediment Transport and Deposition after Hurricane Ida in 2021

Louisiana State University, Baton Rouge LA

Investigators

Abstract

Hurricane Ida was a very destructive Category 4 storm that made landfall at Elmer’s Island and Caminada Headlands, Louisiana on 29 August 2021, bringing storm surge and waves of 13 feet, not seen since Hurricane Katrina. The importance of the role of these large storms on shelf sediment transport and the effect of these events on coastal change has become apparent in recent years. With improvements in instrumentation and technology, more field studies have been conducted to measure sediment transport processes on offshore continental shelves during storm events. However, due to the unpredictability of storm paths and the difficulties and expense in obtaining measurements, there is still a lack of field data. During this project, samples will be obtained in two dredge pits, which are used to replenish beaches after these storms, to test the overarching hypothesis that hurricanes play a major role in redistributing sediment on the continental shelf and likely produce massive sediment deposition in dredge pits and extensive mass wasting of the dredge pit walls. Dredge pits may be a sustainable resource for this sand in Louisiana, but their efficacy as sediment traps requires an understanding of their long-term evolution and marine processes along the continental shelf. Data collection is time-sensitive because of the goal of capturing the post-hurricane sediment on the continental shelf and within the two dredge pits. The project supports the training of undergraduate and graduate students at sea. While it is readily known that continental shelves can be energetic environments, there is a lack of marine observational data for sediment transport and deposition that occurs during and immediately after major hurricanes. In particular, the sediment fluxes of bed and suspended loads can increase one to two orders of magnitude during hurricanes. However, these deposits may be obliterated by subsequent events. Dredge pits serve as excellent recorders of post-hurricane sediment deposition and can provide natural capture basins on continental shelves that record these major events. This project will result in a post-hurricane quantification of sediment transport and stratigraphy of the South Pelto and Sandy Point dredge pits as well as multiple stations east and west of Hurricane Ida along the 10-m isobath on the inner Louisiana shelf. A comparison will be made between the pre- and post-hurricane conditions by leveraging historical data over the past seven years (2014 to 2021). Hurricane conditions often cause mass wasting and submarine landslides in coastal environments, which pose a hazard to existing critical infrastructure on the continental shelf, such as renewable wind energy and telecommunication infrastructure. It is also likely that Hurricane Ida triggered dredge pit wall collapse and outward migration, possibly posing a major hazard to hurricane-impacted platforms and pipelines in the vicinity. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.