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Fieldwork

Assessing the Resilience of a Vital Barrier-Island Chain—Chandeleur and Breton Islands, Louisiana


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The Chandeleur and Breton Islands make up a north-south-trending island chain, remnants of the St. Bernard Delta that occupied the area 2,000 years ago. The ancient delta was deposited by the Mississippi River, and its remnants lie northeast of the modern river delta. Since abandonment, the St. Bernard Delta, including the islands and the adjacent Breton Sound, has undergone erosion and subsidence.

Map showing the Chandeleur Islands, Breton Island, and Breton Sound.
Above: Chandeleur Islands, Breton Island, and Breton Sound. The Chandeleur and Breton Islands constitute Breton National Wildlife Refuge.

In 1904, the island chain became the Nation's second wildlife refuge, Breton National Wildlife Refuge (URL http://www.fws.gov/breton/), when President Theodore Roosevelt learned of disruption to the nesting habits of migrant birds and pushed to protect the flora and fauna of the islands from human intervention. The islands have been home to wildlife, a lighthouse station (destroyed by Hurricane Katrina), a quarantine station, a small fishing village, and even an oil-production facility.

Over the years, the islands not only provided sanctuary for the endangered and threatened wildlife species that seasonally inhabit them, but also protected the mainland, wetlands, and population centers, such as New Orleans, from countless tropical storms and everyday wave activity. Erosion and subsidence, however, along with the increasing strength and frequency of hurricanes and storms, have negatively impacted the islands. Since the 1880s, the documented impacts of severe weather on the islands have illustrated a constant state of dynamic change as the islands respond to hurricanes and other natural processes. These events have caused breaches that fragment the islands. In 2005, Hurricanes Katrina and Rita turned the fragmented and fragile islands into splinters of marsh and a mosaic of submerged shoals, destroying the integrity of the island chain and reducing its area by 85 percent.

photos of the Chandeleur lighthouse Shoreline-change map of the Chandeleur Islands after the 2005 hurricane season.
Above left: Chandeleur lighthouse (red frame; first lit in 1896) at the north end of the Chandeleur chain. Arrows point to a radio tower. Post-Rita sidescan-sonar and bathymetric surveys found no trace of debris from the lighthouse. Photographs compiled by Karen Westphall, Louisiana State University. [larger version]

Above right: Shoreline-change map of the Chandeleur Islands after the 2005 hurricane season. Land areas shown in green from a 2004 survey were obliterated by the 2005 hurricanes, leaving only the land areas shown in brown above water by the end of the season. Modified (type enlarged) from a Barrier Island Comprehensive Monitoring Program (BICM) Interim Product of 2006 by UNO-PIES, USGS, LDNR, and the U.S. Army Corps of Engineers. [larger version]

In 2006, the USGS collaborated with the University of New Orleans (UNO)'s Pontchartrain Institute of Environmental Studies (PIES)—with partnership and support from the Louisiana Coastal Area (LCA) Ecosystem Restoration Science and Technology Program of the Louisiana Department of Natural Resources (LDNR)—to provide a new set of post-Katrina baseline bathymetric and topographic data and maps for all the sandy shorelines in Louisiana. During 2006, the first year of this 2-year project, the scientific partners conducted extensive surveys of the northern part of the Chandeleur island chain to produce a data set needed to evaluate shoreline change. Such baseline data sets will be used to measure island response to future events. The 2006 survey was featured in Sound Waves, August 2006 (URL http://soundwaves.usgs.gov/2006/08/).

The Chandeleur Islands. The houseboat Pelican, one of the base stations for operations, is visible between patches of marsh.
Above: The Chandeleur Islands. The houseboat Pelican, one of the base stations for operations, is visible between patches of marsh. View southward; photograph by Mike Miner, UNO. [larger version]

In 2007, the same team of scientists expanded its collaborators, gaining an additional partner, the U.S. Fish and Wildlife Service (FWS). The team also expanded the scope of work to include the southern part of Breton National Wildlife Refuge. As the refuge manager, the FWS has the task of making restoration-management decisions, when feasible, to protect endangered wildlife struggling to recover from Hurricane Katrina and restore decimated land. To accomplish this task and the expanded project goals, the scientists collected additional bathymetric and topographic data along the south half of the island chain and investigated the subsurface geology through geophysical surveys and subbottom sediment sampling. These data will be entered into models to predict the future of the island chain under various restoration scenarios.

The team is focusing on three critical questions posed under the expanded project, titled "Predicting the Resilience of the Chandeleur Island Chain as a Function of Restoration Options":

  • Can the islands be restored, and is it feasible in the long and short term to restore and rehabilitate parts of Breton National Wildlife Refuge?
  • How much benefit will restoration provide to struggling habitats, or will the islands rebuild themselves naturally?
  • Is there a point of no return for the Chandeleur and Breton Islands; are they ultimately going to disappear completely?

To answer these questions, the team spent summer 2007 completing the survey of the southern Chandeleurs to provide information on the processes that change the extent of the islands and shoals. The team is continuing to monitor short- and long-term habitat change and island evolution. Shoreline change is monitored by using lidar (light detection and ranging) and aerial photography, comparing images collected every 3 to 4 months to a baseline survey and to prestorm images (for more information on the lidar and aerial-photography efforts, please contact Abby Sallenger at asallenger@usgs.gov).

trackline map representing the collaboration of four teams that operated simultaneously to collect bathymetry Phil McCarty and Mike Brown tighten the vibrating head to the aluminum core before beginning to vibracore in shallow water off the Chandeleur Islands on the research vessel Greenhead
Above left: Trackline map representing the collaboration of four teams that operated simultaneously to collect bathymetry in 2006 (gray lines) and 2007 (red lines). In addition, Chirp subbottom data, sidescan-sonar data, and interferometric swath bathymetry were collected on the gulf side of the islands (dense grids), and Chirp subbottom data on the Breton Sound side of the islands. Sediment cores were collected in 2007 (yellow circles) around the northern islands, and additional cores and grab samples (not shown) nearshore. Survey lines laid over a National Oceanic and Atmospheric Administration (NOAA) bathymetric chart, with the 2005 (post-Katrina) land area superimposed (green). [larger version]

Above right: Phil McCarty and Mike Brown (UNO) tighten the vibrating head to the aluminum core before beginning to vibracore in shallow water off the Chandeleur Islands on the research vessel Greenhead. Photograph by Dallon Weathers, UNO. [larger version]

In June 2007, USGS and UNO scientists collected bathymetric data off the southern Chandeleur Islands, Breton Island, and the west Louisiana coastline as part of the Barrier Island Comprehensive Monitoring (BICM) program with LDNR. Teams from USGS offices in St. Petersburg, Florida (Jim Flocks, Dana Wiese, and Rich Young on the research vessel G.K. Gilbert), and Woods Hole, Massachusetts (Dave Twichell, Chuck Worley, Emile Bergeron, Bill Danforth, and Wayne Baldwin on the research vessel Acadiana), collaborated to collect high-resolution geophysical and bathymetric data (including Chirp subbottom data, sidescan-sonar data, and interferometric swath bathymetry). Shallow-water bathymetric data were collected simultaneously by teams from the USGS office in St. Petersburg (Nancy Dewitt, BJ Reynolds, and Dawn Lavoie) and from UNO (Mark Kulp, Jeff Motti, Dallon Weathers, Mike Miner, Phil McCarty, and Mike Brown). The 2007 bathymetric surveys are currently being processed and will be integrated with data from the 2006 surveys to develop a landmark database of sea-floor and subbottom information. The bathymetric data will allow the team to assess sediment budgets, including sediment-transport, sediment-distribution, and erosional patterns for the islands, and the integrated data will be used in models to project future trends for the islands.

USGS crew on the research vessel G.K. Gilbert collect a 20-ft sediment core Phil McCarty and Mike Brown tighten the vibrating head to the aluminum core before beginning to vibracore in shallow water off the Chandeleur Islands
Above left: USGS crew on the research vessel G.K. Gilbert collect a 20-ft sediment core, using a Rossfelder electric vibracore system and hydraulic crane. [larger version]

Above right: Sunset at the vessel Southern 6, home base for all the bathymetric and shallow-water seismic surveys during summer 2007. Photograph by Mike Miner, UNO. [larger version]

Data from the geophysical surveys conducted in 2006 were used to develop a coring strategy to ground-truth the data and provide textural classification of the sediments that make up the geologic framework of Breton National Wildlife Refuge. In 2007, teams from the USGS office in St. Petersburg (Nick Ferina, Chandra Dreher, Jordan Stanford, and Keith Ludwig on the Gilbert) collected vibracores in the waters surrounding the islands, while a team from UNO-PIES (McCarty and Brown) collected shallow-water and marsh vibracores. Concurrently, another team—Ioannis Georgiou, Jeff Motti, and Dallon Weathers (UNO) and colleague Duncan FitzGerald (Boston University)—collected grab samples of sediment on the shoreface, in the surf zone, and in the backbarrier of the Chandeleurs, as well as in tidal inlets. Data from the samples will be used to develop simulation tools and models to document and forecast the recovery processes taking place since the 2005 hurricanes. Sample data will also be used in regional wave and storm-surge models to characterize island response to intermediate-magnitude storms and to provide estimates of sediment-transport rates. The scientific data collected during these efforts will provide the FWS with information on the stability and fate of the islands and help the agency make sound management decisions.

The USGS and its partners are integrating all data types to provide the short-term data needed for the next step, which is modeling the data to predict island response to future events. The near-term goal of the cooperative effort is to determine how or whether the islands will recover naturally, to estimate the magnitude of effort required to push the islands toward recovery, and to ascertain what a sustainable "recovery cure" might be.


Related Sound Waves Stories
Measuring Hurricane Impact—USGS Scientists Map the Louisiana Coastline
August 2006
Before-and-After Aerial Photographs Show Coastal Impacts of Hurricane Katrina
September 2005

Related Web Sites
Coastal Change Hazards: Hurricanes and Extreme Storms
USGS (U.S. Geological Survey)
Breton National Wildlife Refuge
U.S. Fish and Wildlife Service

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in this issue:

Fieldwork
cover story:
Ocean-Bottom Seismometers Monitor Earthquake Swarms

Assessing Resilience of the Chandeleur and Breton Islands

Outreach Earth Science Day in Menlo Park, CA

Meetings USGS Emeritus Scientist Leads Field Trip

Awards Abby Sallenger Wins USGS Shoemaker Award for Lifetime Achievement in Communication

American Fisheries Society Honors Biologist Walter R. Courtenay

Renee Taksue Recognized by AGU for Excellence in Refereeing

Staff USGS Director Mark Myers Visits the Florida Integrated Science Center

Publications

New Book Includes USGS Sea-Floor Data

December Publications List


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