Post on 18-Dec-2021
NRDAR Injured species’ needs assessment
Target areas
Target actions
Selection and Implementation
: Bird Restoration Planning
Breton Island: 1989
Breton Island: 2012
Major hurricanes impacting Breton since 1989 • Andrew 1994 • Georges 1998 • Ivan 2004 • Katrina 2005 • Rita 2005 • Gustav 2008 • Ike 2008
Loss of island area
~27 acres/yr loss
Island retreat 2014 lidar shoreline overlain on 2008 DOQQ imagery
~28 ft/yr past century 750 ft after Hurricane Katrina
Seafloor change
Accretion - Erosion 1920 to 2007
Breton Is.
erosion
erosion
deposition
deposition
MRGO ship channel
Data from the Louisiana Barrier Island Comprehensive Monitoring Project
Identifying resources for barrier island restoration
Chandeleur Is.
2011 oil-spill mitigation sand berm
Dredge pit
• Sufficient quantities of compatible sediments must be identified
• The sediments must be in close proximity to the restoration site
• The borrow site cannot be too close to the island platform to affect wave dynamics and sediment processes
Beach restoration
Dune restoration
Marsh restoration
Conceptual construction design
• Not a lot of sandy material off of the island platform
Identifying resources for barrier island restoration
• Regardless of source modeling is necessary to evaluate impact of sediment removal on wave climate at the island
A. Buried distributary channels
B. Offshore shoals
C. Terminal spit deposits similar to Hewes Point
• An estimated 3 million cubic yards of sand is needed
A. MRGO and natural inlet Ebb-tidal delta
• Potential sites indclude:
Identifying resources for barrier island restoration (potential offshore shoal deposits)
Offshore shoal
NOAA Bathymetry (~1922)
Breton Island
1987 vibracore
Identifying resources for barrier island restoration (potential offshore shoal deposits)
Offshore shoal
NOAA Bathymetry (~1922) Pre – 1778 Nautical Chart
Breton Is. Breton Island
• Does Breton Island predate the Chandeleur Islands? • What are the geologic and morphologic relationships between the two systems?
Identifying resources for barrier island restoration (potential offshore shoal deposits)
• Offshore geophysical investigation (August, 2014) Swath bathymetry Sidescan soar High-resolution sub-bottom seismic profiling • Ground-truth with 20-foot sediment cores (September / October, 2014)
Example seismic subbottom profile
Proposed survey tracklines
Modeling impact of dredge pits on wave refraction
Dredge pit scenarios Wave refraction modeling (SWAN)
Geophysical characterization of the barrier island system
• Nearshore investigation (July, 2014) Swath bathymetry (> 1m wd) Single-beam bathymetry High-resolution sub-bottom seismic profiling Sediment grab samples • Provide updated/baseline elevation data for models and restoration design. • Sediment budget and processes • Comparison to historical (bathymetric change, sediment change)
Breton Is.
Gosier shoal
Curlew shoal