Morphodynamics and Sedimentation of Dredge Pits for Barrier Island Restoration

Abstract:

Global sea level rise, subsidence, decreasing river sediment supply and other factors have caused rapid land loss in many low-elevation coastal areas around the world in recent decades. Coastal restoration projects have become increasingly popular in the northern Gulf of Mexico due to high relative sea level rise rate and many vulnerable coastal lines. Both sandy shoals and paleo river channels have been used for the restoration of coastal barrier islands to protect and restore coastal systems. This study is focused on the morphodynamics, sedimentation, and geotechnical properties of several paleo-river dredge pits for barrier island restoration in Louisiana shelf. Raccoon Island dredge pit in central Louisiana shelf and Peveto Channel pit in western Louisiana shelf are two only known pits with 100% infilling after sand excavation and high sedimentation rates of 0.2-1.0 m/year. They provide a unique opportunity to study the “entire” life cycle of dredge pit infilling and very high temporal resolution of sedimentation. Both historical and new coring and geophysical methods from above two pits as well as Sandy Point pit in east Louisiana shelf were used to study the morphological change and quantify sediment accumulation rates. Vibra-cores and multi-cores were used to study grain size, radionuclide, organic matter, and lithological properties (e.g., compressibility, permeability, shear strength). Sub-bottom profiling, sidescan, and bathymetric data were utilized to quantify infilling rates, morphological evolution, pit slope stability, and impact to seafloor infrastructure. Our results help scientific community and decision makers to better understand the coastal processes and manage valuable sediment resources in coastal area.