Storm Dynamics Control Sedimentation and Shelf‐Bay‐Marsh Sediment Exchange Along the Louisiana Coast

• Published in: Geophysical research letters 2024-11, Vol.51 (22), p.n/a
• Main Authors: Georgiou, Ioannis Y., FitzGerald, Duncan M., Sakib, Md Mohiuddin, Messina, Francesca, Kulp, Mark A., Miner, Michael D.
• Format: Article
• Language: English
• Subjects: Accretion; Coastal erosion; Exchanging; Hurricanes; Interfaces; Marshes; Nutrients; Sea currents; Sea level; Sea level changes; Sea level rise; Sediment; Sediments; Soil erosion; Storm tracks; Storms; Submergence; Water circulation; Water column; Wetlands
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL111344

Hurricanes can benefit wetland accretion by augmenting the delivery of mineral sediment, an essential process allowing marshes to offset submergence during rising sea levels. Using Hurricane Gustav (2008, Louisiana) as a control, we examined eight synthetic storms with varying characteristics (track, speed, intensity, size) to evaluate sediment exchange between the inner shelf and bay and bay‐to‐marsh interfaces. All storms showed net landward sediment exchange from the inner shelf to the bay to the marsh—storms with closer proximity, higher intensity, and slower forward speed positively correlated with net sediment exchange; storm size had little impact. Except for slow‐moving storms (½ speed of Gustav), our analyses suggest that most hurricane scenarios cause net bay erosion, because more sediment is conveyed to landward wetlands than is replenished from erosion of the inner shelf. Our results suggest that the ongoing deepening of the bay will likely worsen because of rising sea levels. Plain Language Summary Under most circumstances, hurricanes are perceived as agents of destruction that erode coastlines and destroy dwellings and infrastructure. However, for marshes and wetlands they can add much needed sediment and new sources of nutrients helping them to build vertically. As hurricanes move onshore, the accompanying large waves and currents suspend sediment into the water column followed by surge waters that carry this sediment onto wetlands. We have modeled this process using category 2 Hurricane Gustav that struck near Terrebonne Bay on the central Louisiana coast in 2008. By changing various hurricane characteristics, we find that in addition to the importance of storm track, forward speed and intensity cause the greatest net sediment exchange from inner shelf to landward bay and from bay to adjacent wetlands. Moreover, under most conditions a deficit of sediment replenishing bays will lead to their deepening and ultimately less sediment transferred to wetlands, hastening their demise. Key Points Hurricane modeling indicates forward speed and intensity dominate net sediment exchange and transport along a shelf‐bay‐marsh system As hurricane forward speed slows, more sediment is moved onshore due to longer storm duration which entrains and transports more sediment Most scenarios show inner shelf does not fully replenish sediment moved to wetlands suggesting long‐term sediment deficit and Bay deepening