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Fieldwork

USGS Scientists Investigate New Orleans Levees Broken by Hurricane Katrina


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The storm surges produced by Hurricane Katrina on August 29, 2005, breached the levees protecting New Orleans in numerous places, flooding approximately 75 percent of the metropolitan area. Most of the levee failures were caused by overtopping, as the storm surge rose over the top of a levee and scoured out the base of the landward embankment or floodwall. Three major and costly breaches appear to have been caused by failure of the soils underlying the levees or failure of the earthen levee embankments themselves; in several places, levee foundations failed when water levels were below the tops of the levees. Transitions between levees of differing heights or materials proved to be weak points in the flood-protection system; a significant number of levee washouts occurred, for example, where the weaker of two adjacent materials was at a lower elevation.

Map showing locations of places and levee breaches discussed in article.
Above: Locations of places and levee breaches discussed in article. Three of the four main protected units that make up the New Orleans flood-protection system are labeled: the New Orleans East Bank section, the New Orleans East section, and the Ninth Ward and St. Bernard Parish section. A fourth protected unit, southeast of this map, is a thin, protected strip along the Mississippi River heading southward from St. Bernard Parish to the river mouth. Blue hatching indicates pre-Katrina wetlands. Pink shading shows estimated maximum extent of urban flooding; blue shading shows areas still flooded on September 28, 2005. Modified from figure 1.4 in the joint NSF-ASCE 17 MB PDF report available at URL http://hsgac.senate.gov/_files/Katrina/Preliminary_Report.pdf. [larger version]

In the aftermath of the flooding of New Orleans, the U.S. Army Corps of Engineers requested an external review of the levees' performance by teams of engineers and scientists sponsored by the National Science Foundation (NSF) and the American Society of Civil Engineers (ASCE). Various teams worked in New Orleans from September 28 through October 15, 2005—a time chosen by balancing the need to gather ephemeral data against the need to avoid interfering with emergency operations. On numerous occasions, team units arrived and investigated sites only hours before vital information was buried by ongoing emergency repairs.

Two U.S. Geological Survey (USGS) scientists, research civil engineer Robert Kayen and Mendenhall Postdoctoral Fellow Brian Collins, both of the USGS Western Coastal and Marine Geology Team (WCMG), were asked to join as investigators on the NSF-sponsored team. They were in New Orleans from October 9 to 14, using a ground-based terrestrial laser-mapping system to conduct detailed surveys of the levee breaches. Gathering information about the magnitude and geometry of structural and soil deformation is paramount for analyzing how and why the levees failed.

Sites where Kayen and Collins conducted lidar (light detection and ranging) surveys.
Above: Sites where Kayen and Collins conducted lidar (light detection and ranging) surveys. The background image shows estimated floodwater depths on September 2, 2005, superimposed on a Landsat satellite image. Darkest blue indicates deepest water (greater than 11.5 ft). For more information, visit URL http://eros.usgs.gov/katrina/science.html and click on "Topography-Based Analysis of Hurricane Katrina Inundation of New Orleans." [larger version]

Lidar-survey site number Location Number of lidar scans
1 17th Street Canal 20
2 London Ave. Canal, North on east side 29 with Site 3
3 London Ave. Canal, North on west side 29 with Site 2
4 IHNC East Side, South Breach 9th ward 13
5 IHNC East Side, North Breach 9th ward 14
6 Lakeside Airport Levee Transition Breach 14 with Site 7
7 Lakeside Airport Levee I-Wall 14 with Site 6
8 Structural Distressed I-Wall at Container Wharf 20
9 Incipient Earth Levee failure 14
10 Entergy Plant I-Wall Scour 20
Above: Sites where Kayen and Collins surveyed levees. ("I-wall" refers to concrete floodwall with a cross section roughly similar to an "I," as opposed to "T-wall," which has the cross section of an inverted "T.")

Kayen and Collins arrived on the only United Airlines flight into New Orleans on October 9 and stayed in what appeared to be the only available hotel near the Mississippi River. The roof of their rental vehicle, a Nissan Pathfinder, served as a platform for the terrestrial laser-mapping instrument. They used a global-positioning-system (GPS) unit to navigate around the city, which was overwhelmed with flooded sections, downed trees and powerlines, and windblown and waterborne debris. Each day they drove on whatever surface allowed them get to a levee break—both sides of the road, sidewalks, lawns. In some areas, especially in the Lower Ninth Ward, the debris was so thick that they were unable to drive to their destination and had to carry in gear on foot.

Tripod-mounted lidar (light detection and ranging) unit at the 17th Street Canal breach (survey site 1). Diagram showing how overtopping caused levee breaches.
Above Left: Tripod-mounted lidar (light detection and ranging) unit at the 17th Street Canal breach (survey site 1). Brian Collins mans a pushcart containing a laptop computer and other electronics connected to the lidar unit. Photograph by Robert Kayen. [larger version]

Above Right: Diagram showing how overtopping caused levee breaches. The levee in the diagram is composed of concrete surrounding a corrugated steel "sheetpile," so called because it serves as a piling when driven into the underlying earthen embankment. Water overtopping the floodwall eroded the soil embankment on the landward side, undermining the wall and causing it to fail. In other areas, water seeped below the sheetpile and weakened the embankment, causing failure even at water levels below the height of the floodwall. Modified from a Wall Street Journal graphic based on the 17 MB PDF NSF-ASCE report available at URL http://hsgac.senate.gov/_files/Katrina/Preliminary_Report.pdf.

"Both Brian and I are familiar with post-event [earthquake] damage, but the devastation of Hurricane Katrina was so unusually severe and affected so much of urban New Orleans that we were taken aback by the magnitude of this natural and manmade catastrophe, and the absence of all services and people," said Kayen. "By analogy, imagine the impact of 50 to 80 percent of the San Francisco Bay area rendered uninhabitable by some event. That was the state of New Orleans as we worked."

The two researchers used laser-mapping techniques they developed in their WCMG studies of coastal-seacliff erosion and earthquake ground deformation to capture the surface evidence of levee deformation and distress at 10 sites in the greater New Orleans area. To do this, they brought to the field area a new terrestrial tripod-mounted laser-mapping tool to perform lidar (light detection and ranging) data collection. The terrestrial lidar method consists of sending and collecting laser pulses from the surface of objects to build a data set of three-dimensional coordinates. The USGS laser-scanning system can measure the location of as many as 8,000 surface points in 1 second. Thus, within a few minutes, an entire surface can be imaged efficiently, producing a data set that contains several million position points. The data sets from collected scans are typically transformed into virtual three-dimensional surfaces so that cross sections can be generated and volumetric calculations can be performed.

The objective of the laser-scanning effort in New Orleans was to obtain precise measurements of the ground surface in order to map

  • soil displacements at each levee site,
  • the nonuniformity of levee heights,
  • the depth of erosion where scour occurred, and
  • distress in structures that were on the verge of failure when floodwaters receded.

Overtopping was most severe on the east side of the flood-protection system, as the waters of Lake Borgne were driven west toward New Orleans, and also farther to the south, along the lower reaches of the Mississippi River. Significant overtopping and erosion caused numerous breaches in these areas. The magnitude of overtopping was less severe along the Inner Harbor Navigation Canal (IHNC, also called the "Industrial Canal") and along the western part of the Mississippi River Gulf Outlet (MRGO) channel, but overtopping in these areas nevertheless caused erosion and levee failures. Although field observations suggest that little or no overtopping occurred along most of the levees fronting Lake Pontchartrain, evidence of minor overtopping or wave splashover was observed in several places. A breach in the levee system occurred at the northwest corner of the New Orleans East protected area, near Lakefront Airport, at a complex transition between levee segments of varying heights and materials. It appears that many of the levees breached by overtopping might have performed better if conceptually simple details, such as scour protection on the land side, had been added during or after original design and construction.

Composite lidar image of northern levee breach on the Inner Harbor Navigation Canal (site 5).
Above: Composite lidar image of northern levee breach on the Inner Harbor Navigation Canal (site 5). Inset photograph by Robert Kayen. [larger version]

Brian Collins scans the area around the 17th Street Canal breach (survey site 1). Lidar unit and tripod mounted to the roof of Kayen and Collins' field vehicle.
Above Left: Brian Collins scans the area around the 17th Street Canal breach (survey site 1). The lidar unit is on the roof of the survey vehicle behind Collins. Photograph by Robert Kayen. [larger version]

Above Right: Lidar unit and tripod mounted to the roof of Kayen and Collins' field vehicle. The fixed roof base allowed for leveling of the tripod and lidar instrument on sloping ground. Here the instrument is scanning scour at the base of intact floodwall at an Entergy New Orleans plant in east New Orleans (survey site 10). Photograph by Robert Kayen. [larger version]

Farther west, in the New Orleans East Bank Canal District, three levee failures occurred along the banks of the 17th Street and London Avenue Canals. Kayen and Collins observed evidence indicating that the failures occurred when water levels were below the tops of the concrete floodwalls lining the canals. These three levee failures were likely caused by failure of the foundation soils underlying the levees. Signs of an incipient failure were observed at a fourth distressed levee/floodwall segment on the London Avenue Canal, where lateral displacements, sinkholes, and sand boils all indicate that water was flowing through a weakening embankment.

Rob Kayen and lidar unit near the southern levee breach on the Inner Harbor Navigation Canal. Tripod-mounted lidar unit at the northern levee breach on the Inner Harbor Navigation Canal
Above Left: Rob Kayen and lidar unit near the southern levee breach on the Inner Harbor Navigation Canal (survey site 4). Floodwall behind Kayen is intact, but wall shows increasing damage from right to left. Breach is outside area of photograph to left. Photograph by Brian Collins. [larger version]

Above Right: Tripod-mounted lidar unit at the northern levee breach on the Inner Harbor Navigation Canal (survey site 5). The floodwall—typically, concrete sandwiched around corrugated steel (called a "sheetpile") that is driven into an earthen embankment—was flipped over when the levee was breached. Photograph by Robert Kayen. [larger version]

The levee-investigation teams pooled their findings to produce a joint NSF-ASCE report that was presented to Congress in early November, along with Congressional testimony from the NSF and ASCE team leaders. The 17 MB PDF file of the report can be downloaded from URL http://hsgac.senate.gov/_files/Katrina/Preliminary_Report.pdf.

Kayen and Collins were among the experts featured in a 10-minute television news feature about the NSF-ASCE investigation of the New Orleans levee failures after Hurricane Katrina (see Sound Waves article, USGS Scientists Featured in National News Segment on Investigating Broken Levees in New Orleans). The segment aired on October 20, 2005, on the "News Hour with Jim Lehrer," a national Public Broadcasting Service (PBS) news program. A transcript, photographs, and links to video and audio files of the television feature, called "Investigating Broken Levees," are available online at http://www.pbs.org/newshour/bb/science/july-dec05/levees_10-20.html.


Related Sound Waves Stories
USGS Scientists Featured in National News Segment on Investigating Broken Levees in New Orleans
November 2005

Related Web Sites
Hurricane Katrina Hearings
Senate Committee on Homeland Security & Government Affairs
"Investigating Broken Levees"
Public Broadcasting Service (PBS)
Hurricane Katrina Disaster Response
U.S. Geological Survey (USGS)

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in this issue: Fieldwork
cover story:
USGS Scientists Investigate New Orleans Levees

special feature:
Post-Katrina Cleanup—a Volunteer's Reflections

Offshore Impacts of Hurricane Katrina

Sediment-Toxicity Studies in Western Long Island Sound

Sea-Floor Geology Off Massachusetts Coast

Alvin Dives to Deep-Water Coral Habitats

Research Study Links Urbanization to Amphibian Decline

Outreach San Francisco Bay Floor Explored

Briefing on Coastal Research in Hawai'i

USGS Research on the Kona Coast, Hawai'i

Meetings Third International Symposium on Deep-Sea Corals

Awards Award for USGS Map Hawaii's Volcanoes Revealed

Staff USGS Citizen Soldier on the Move!

Native-Plant Landscaping in Florida

Publications New Book on Benthic Habitats and the Effects of Fishing

Dec. 2005 / Jan. 2006 Publications List


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