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4: National Hazards, Risk, and Resilience Assessment Program: Hurricanes

Thomas C. Michot, Christopher J. Wells, Paul C. Chadwick

U.S. Geological Survey, National Wetlands Research Center, Lafayette, Louisiana

Hurricane Katrina made landfall in southeast Louisiana on August 29, 2005, and Hurricane Rita made landfall in southwest Louisiana on September 24, 2005. United States Geological Survey (USGS) scientists flew aerial surveys to assess damages to natural resources and to lands owned and managed by the U.S. Department of the Interior and other agencies. Flights were made on eight dates from August 27 through October 4, including one pre-Katrina, three post-Katrina, and four post-Rita surveys. The total geographic area covered by all flights extended from Galveston, Tex., to Gulf Shores, Ala., and from the Gulf of Mexico shoreline inland 5 to 75 mi (8-121 km). Scientists flew 5,003 mi (8,050 km; 64.4 flight hours), recorded 657 observations on hurricane impacts, and took 3,856 high-resolution digital oblique photographs. Each observation and photograph was georeferenced as to spatial coordinates and marked with a time stamp, using a DOI aircraft that is specially configured to collect and integrate spatial, videographic, photographic, and audio data. Impacts to barrier island habitats were severe, especially at the Chandeleur Islands, which were reduced in land area by roughly 50 percent. Barrier islands and shorelines west of the Mississippi River were impacted to a lesser degree, similar to recent storm effects. Marsh impacts varied but were greatest in Saint Bernard and Cameron parishes where much emergent vegetation was scoured or killed. Forested wetlands were impacted heavily, especially in the Pearl River basin and on the cheniers of southwest Louisiana. These data were provided and made available to other scientists as well as to land managers and the general public through being served on the NWRC web site, press realeases, distribution of CD/DVD to managers/partners, and publication of a peer-reviewed scientific article.

Thomas W. Doyle, U.S. Geological Survey, National Wetlands Research Center, Lafayette, Louisiana

HURASIM is a spatial simulation model of hurricane structure and circulation for reconstructing chronologies of estimated windforce and vectors of past hurricanes. The model uses historical tracking and meteorological data of dated North Atlantic tropical storms from 1851 to present. The model generates a matrix of storm characteristics (i.e., quadrant, windspeed, and direction) within discrete spatial units and time intervals specified by the user for any specific storm or set of storms. HURASIM recreates the spatial structure of past hurricanes based on a tangential wind function, inflow angle offset, forward speed, and radius of maximum winds. Data input for the model includes tracking information of storm position, latitude and longitude, every six hours or less and maximum sustained wind speed. HURASIM model output from Hurricane Andrew (1992) was correlated with field data to construct data tables of damage probabilities by site and species and to determine critical windspeeds and vectors of tree mortality and injury. HURASIM has also been applied to reconstruct probable windfields of past hurricanes for remote field locations and correlated with tree ring growth patterns and direction of leaning trees and downed logs. HURASIM is also used to construct landscape templates of past hurricane activity that are linked with landscape simulation models of coastal habitat for predicting effects of climate past and future on the growth and succession of important wetland communities.

Contact Information: Tom Doyle, U.S. Geological Survey, National Wetlands Research Center, 700 Cajundome Blvd., Lafayette, Louisiana 70506; phone: 337-266-8647; fax: 337-266-8586; email: doylet@usgs.gov

K. Van Wilson1, D. Phil Turnipseed2, James E. Hathorn3, Dean Tyler4, Jason Stoker4, and Robert R. Mason, Jr.2

1 U.S. Geological Survey, Mississippi Water Science Center, Jackson, Mississippi
2 U.S. Geological Survey, Office of Surface Water, Reston, Virginia
3 U.S. Army Corps of Engineers, Mobile District, Mobile, Alabama
4 U.S. Geological Survey Earth Resources Observation and Science (EROS), Sioux Falls, South Dakota

In the months that followed the Hurricane Katrina devastation in the Central Gulf of Mexico region of the United States, the U.S. Geological Survey (USGS), in cooperation with the U.S. Army Corps of Engineers (USACE), developed an Internet Map Server (IMS) that enables a user to determine flood depths above the North American Vertical Datum of 1988 (NAVD88) for the Hurricane Katrina maximum storm tide in the affected states.

The server includes a comprehensive geospatial information system allowing free access to many digital layers and GIS tools for this region which includes:

• Pre-Katrina Light Detection and Ranging (LiDAR) digital elevation model (DEM) with 1/9th arc-second (3-meter) grid resolution served as the base for the mapping furnished by USGS; FEMA; USACE; Baldwin and Mobile Counties, Alabama; and others;
• GIS layer with 842 high-water marks (HWMs) that were used to generate the maximum storm tide surface;
• Katrina Maximum Storm Tide Surface generated from the HWMs for areas outside of the New Orleans, Louisiana, levees to approximate the maximum storm tide that approached the levees;
• Cultural boundaries;
• Hydrography;
• Transportation;
• Orthoimagery;
• Land cover/use;
• Elevation Query Tool; and
• Elevation Profile Comparison Tool

The seamless DEM across the coastal areas of Alabama, Mississippi, and Louisiana was created from LiDAR data that were obtained from multiple sources and were collected independently in various file formats, projections, and levels of processing. The task of producing a seamless DEM, used as the map base for projecting the Katrina maximum storm tide in the affected coastal region, required extensive research, coordination, and revision.

The 842 HWMs used to generate the IMS representing the Katrina maximum storm tide were processed and filtered from more than 1,500 HWMs that were flagged, surveyed, and documented by teams representing the Federal Emergency Management Agency (FEMA), USGS, USACE, and others. The maximum storm tide elevations of about 29 feet were documented near Bay St. Louis, Mississippi, confirming that Katrina was more than 4 feet greater than storm tide caused in 1969 by Hurricane Camille (highest previously known storm tide to inundate the region).

The Website is available to the public at http://gisdata.usgs.gov/website/gulf/

Contact Information: K. Van Wilson, U.S. Geological Survey, Mississippi Water Science Center, 308 South Airport Road, Jackson, Mississippi 39208, phone: 601-933-2922, fax: 601-933-2901, email: kvwilson@usgs.gov

Jim Flocks1, Dawn Lavoie2, David Twichell3, Mike Miner4

1 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida
2 U.S. Geological Survey, New Orleans, Louisiana
3 Woods Hole Science Center, Woods Hole, Massachusetts
4 University of New Orleans (UNO), New Orleans, Louisiana

The barrier islands of the Northern Gulf of Mexico provide habitat for a variety of flora and fauna, a platform for human infrastructure and recreation, and protection of interior wetlands and mainland populations from storm activity. The Chandeleur Islands of Louisiana and Gulf Islands National Seashore (GUIS) of Mississippi are preserved natural environments that are vital assets to the entire Gulf Coast. The islands formed between 6,000 and 4,000 years ago in response to decelerating sea-level rise and wave-directed transport of sediments from existing geologic formations. The development of barrier islands is a finite process, and the conditions that initiated these islands have been reduced or no longer exist. A diminishing amount of sediments available to build and maintain the islands is being scavenged by storms and reworked by prevailing wave climate to support the shorelines, with a net loss of island area. This natural process is being exacerbated by human alteration of the islands and adjacent inlets, continued sea level rise, subsidence, and increased storm activity. In 2005, hurricane Katrina overtopped the islands with up to 10-m of storm surge and caused significant erosion of sediment from the shoreface and protective dune systems. This combination of natural longevity, human alteration and the impact of a devastating 100-year storm brings into question what the future configuration of the barrier islands will be, what protective function they will provide for the mainland wetlands and human population centers, and whether they can continue to provide the same level of functional habitat for nesting birds and other wildlife.

Beginning in 2006, the U.S. Geological Survey in collaboration with federal (National Park Service, U.S. Army Corps of Engineers, Fish and Wildlife Service, Minerals Management Service) and state agencies (Louisiana Department of Natural Resources, Pontchartrain Institute of Environmental Science, Mississippi Minerals Research Institute) began an assessment of the topography, bathymetry and stratigraphy of the barrier islands. Understanding the geologic processes that influence the islands is crucial in determining their stability and fate. Collection of high-resolution scientific data is the first step in answering the questions about the future configuration of the islands, and identifying resources useful for island restoration. Initial assessment of the information collected around the Chandeleur and GUIS barrier islands reveals direct relationships between subsurface features and island configuration, and identifies potential sources of suitable material for island restoration. Examples of the initial studies conducted around the islands, and the methodologies developed by the U.S. Geological Survey and collaborators for collection, processing, analysis and distribution of scientific information around the barrier islands of the Northern Gulf of Mexico, is presented.

Contact Information: James Flocks, U.S. Geological Survey, Florida Integrated Science Center, Coastal and Watershed Studies Team, 600 4th Street South, St. Petersburg, FL 33701; phone: 727-803-8747; email: jflocks@usgs.gov

David Twichell1, Elizabeth Pendleton1, Wayne Baldwin1, and James Flocks2

1 U.S. Geological Survey, Woods Hole Science Center, Woods Hole, Massachusetts
2 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida

The Chandeleur Islands lie on the eastern side of the modern Mississippi Delta, near the edge of the St. Bernard delta complex of the Mississippi River. The St. Bernard Delta was active from about 4,000-2,000 yr BP; presently it is undergoing subsidence and erosion. Erosion of this delta complex produces different surficial expressions controlled by differences in the shallow stratigraphy. A detailed bathymetric, geophysical and sampling survey of the inner shelf offshore of the Chandeleur Islands reveals two distinct populations of shallow depressions: subcircular and linear. Subcircular depressions are concentrated in 9-12 m water depths, and have 7-340 m diameters, steep edges, and 0.5-1.5 m relief. Sidescan sonar imagery shows that the floors of some subcircular depressions are smooth, others are interrupted by small arcuate scarps, and others have vent-like structures in them. Seismic profiles and cores show that subcircular depressions are concentrated in areas where delta-front deposits are exposed on the sea floor, and occasional seismic blanking in these areas indicates that gas is present. Vibracores taken through delta-front deposits are composed of clayey silts interrupted by thin sand beds. Linear depressions occur in 3-15 m water depths, and have 600-3000 m lengths, widths less than 550 m, and relief less than 1.5 m. Seismic profiles and cores show that linear depressions occur in areas where sandy distributary channel deposits are exposed on the sea floor. This difference in erosional signature suggests that distributary channel deposits respond differently than delta-front deposits to present oceanographic conditions. The linear depressions may form in sandy distributary channel deposits due to their being more vulnerable to scour by waves and coastal currents than the surrounding delta-front deposits where collapse due to liquefaction or gas discharge may dominate.

Contact Information: Dave Twichell, U.S. Geological Survey, Woods Hole Science Center, 384 Woods Hole Rd, Woods Hole, MA 02543; phone: 508 457 2266; email: dtwichell@usgs.gov