Sedimentation Processes and Morphological Changes in a Dredge Pit and Surrounding Environment on Ship Shoal in the Northern Gulf of Mexico

The use of dredged material from continental shelves and estuaries for degraded barrier islands has become a common practice worldwide. South Pelto block on eastern Ship Shoal (SS) off the coast of Louisiana has been dredged for high-quality sand resources, including Caminada Dredge Pit (CDP) and multiple pits in East Timbalier borrow areas (ET) adjacent to CDP. To understand how these dredge pits change and sediments infill over time, multiple surveys were conducted, including bathymetry, sidescan sonar, subbottom CHIRP, and sediment samples were collected for grain size analysis. Although there is no nearby muddy sediment, sidescan and grain size data both show low-reflectivity areas inside CDP became larger over time, indicating continual supply from suspended mud. Subbottom data show decreasing pit wall slopes over time and degassing over patchy low reflectivity areas on the pit bottom. Arc-chord rugosity analysis was performed with emphasis applied to ET to examine the difference between cutter and hopper dredge techniques. It was revealed that dredging from the hopper created a higher rugosity value than the cutter, leading to a shorter recovery time for the benthic environment. Bathymetric results reveal approximately 20 m to 60 m of horizontal outward pit wall migrations over 3 -5 years. Hurricanes Marco, Zeta, and Ida as well as Tropical Storm Claudette passed the study site (within 50 Km) during the study period which increased wind-wave energies sufficiently to develop new sand ripples discovered on sidescan sonar data near ET and CDP. By integrating various datasets and investigating the effects of tropical cyclones on a dredged area in SS, this study contributes valuable insights that fill existing knowledge gaps and enhance decision-making for future management strategies.