Assessment of Mud-Capped Dredge Pit Evolution Offshore Louisiana: Implications to Sand Excavation and Coastal Restoration
Kehui Xu1,2, MIke D Miner3, Samuel J Bentley4, Chunyan Li1, Jeffrey Obelcz5 and Meg Cathlin O'Connor6, (1)Louisiana State University, Department of Oceanography and Coastal Sciences, Baton Rouge, LA, United States, (2)Louisiana State University, Coastal Studies Institute, Baton Rouge, LA, United States, (3)U.S Department of Interior, Bureau of Ocean Energy Management, New Orleans, LA, United States, (4)Louisiana State University, Baton Rouge, LA, United States, (5)Coastal Studies Institute, Baton Rouge, LA, United States, (6)Louisiana State University, Geology and Geophysics, Baton Rouge, LA, United States
Abstract:
The shelf offshore Louisiana is characterized by a dominantly muddy seafloor with a paucity of restoration-quality sand proximal to shore. Discrete sand deposits associated with ancient rivers that incised the shelf during lower sea-level positions occur close to shore. These shelf channel sands have been targeted for coastal restoration projects resulting in significant cost savings over more distal deposits. Several recent projects targeted shelf paleo-fluvial deposits comprising relatively deep (10 m) channel sands underlying a muddy overburden. Because of contrasting characteristics of cohesive mud vs. non-cohesive sand and potential modern fluvial mud supply from the Mississippi and Atchafalaya Rivers, long term pit evolution is poorly understood relative to their more common sand-only counterparts. Alterations to seafloor topography from dredging shelf sediment resources can potentially affect oil and gas infrastructure or other resources of concern (i.e. historic shipwrecks) located proximal to dredge pits. Site-specific data required to make accurate predictions and empirical measurements to test and validate predictive models were only available for Peveto Channel offshore Holly Beach, Louisiana. Here we present new geophysical and geological data (bathymetry, sidescan, subbottom, and radionuclide of sediment cores) and physical oceanographic observations (hydrodynamics and sediment dynamics) collected at Raccoon Island (dredged in 2013) dredge pit in Louisiana. These field data collections along with pre-existing data provide a time-series to capture evolution at Raccoon Island post-excavation. Conceptual morphological models will be developed for dredge pit evolution and testing effectiveness of setback buffers protecting pipelines, habitats, and cultural resources. Our results will increase decision making ability regarding safety and protecting environmental and cultural resources, and better management of valuable sand resources.
