Semester of Graduation
Spring 2022
Degree
Master of Oceanography and Coastal Sciences (SOCS)
Department
Oceanography and Coastal Studies
Document Type
Thesis
Abstract
Louisiana’s Coastal Protection and Restoration Authority has been using dredged sand from onshore and offshore sites for barrier island restoration and beach nourishment projects. Caminada dredge pit (CDP) located on eastern Ship Shoal in inner Louisiana shelf underwent two increments in 2014 and 2016, with material used to restore Caminada Headland and nearby areas. Multiple pits in East Terrebonne borrow areas (ET) right next to CDP were then used for East Timbalier Island and other barrier islands near Terrebonne Bay. ET1, north of CDP, was dredged in 2020, and ET2, west of CDP, was dredged in 2020 and 2021 used two dredging methods, cutter suctions dredge (cutter) and trailing suction hopper dredge (hopper). To understand how these dredge pits evolve over time, multiple surveys were conducted using a suite of geophysical tools including bathymetry, sidescan sonar, and subbottom CHIRP, and sediment samples were collected for grain size analysis.
Despite of lack of nearby muddy sea floor, sidescan and grain size data both show that low reflectivity areas inside CDP became larger over time, indicating continuing supply from suspended mud. Bathymetric results reveal approximately 20 m to 60 m of horizontal outward pit wall migrations over 3-5 years. Due to additional stripping, northwest walls of CDP experienced larger outward migrations and wall collapses than southern and eastern walls of CDP. Although these migrations are far less than 305 m (1000 ft) setback buffer distance currently being used, monitoring is strongly recommended in future years to ensure that the long-term impact of dredging to oil pipelines is well understood. Subbottom data show decreasing pit wall slopes over time and degassing over patchy low reflectivity areas in pit bottom. Based on newly collected data, previously unseen sand waves and ripples were discovered on sidescan sonar data near ET1 and CDP. Arc-chord rugosity analysis revealed that dredging from hoppers created a rugosity value higher than cutters. This created rough, chaotic and segmented surface and is likely to impact the benthic environment recovery.
Recommended Citation
Gartelman, Adam M., "SEDIMENTATION PROCESSES IN A DREDGE PIT AND SURROUNDING ENVIRONMENT IN NORTHERN GULF OF MEXICO" (2022). LSU Master's Theses. 5558.
https://repository.lsu.edu/gradschool_theses/5558
Committee Chair
Kehui Xu
DOI
10.31390/gradschool_theses.5558