Hurricane Katrina and the Indian Ocean Tsunami are among the most serious and devastating natural disasters in recent history. They are both known worldwide for the many lives lost and the extreme property damage that resulted. Hurricane Katrina struck the Gulf Coast in 2005, primarily hitting Louisiana, Mississippi, and Alabama. Hurricane Katrina was a Category 3 hurricane when it made landfall and was the costliest hurricane in the history of the United States, causing $81.2 billion in damage. New Orleans was among the cities to be hit the hardest, as protective levees broke and much of the city flooded. Storm surge wave heights exceeded twenty feet and flooded 80% of the city. The Gulf Coast of Mississippi was equally devastated by storm surge and wave action as well as winds. The Indian Ocean, or Boxing Day, Tsunami occurred on December 26, 2004, originating off the northwest coast of Sumatra, Indonesia. Its destructive effects were felt across the Indian Ocean and all the way to the eastern coast of Africa. The tsunami resulted from a magnitude 9.2 subduction earthquake. The waves propagated from the epicenter of the earthquake and caused the most damage in Indonesia, Thailand, Sri Lanka, and India. Wave heights exceeded 10 meters and reached several kilometers inland in Thailand, as shown below by the markers placed along the coast in Phuket. It is estimated that 230,000 people were killed as a result of the tsunami, in part because of the absence of a warning system. The tsunami was especially devastating in small Asian fishing villages that were built along the coast. Not only did these disasters cause immediate destruction, but for some areas much of the devastation remains today, as shown in the image above, taken two years after the Indian Ocean Tsunami.
Hurricane Katrina and the Indian Ocean Tsunami remain pivotal events in my life due to personal experiences with the resulting devastation. I had the opportunity to visit New Orleans after Hurricane Katrina with my Computational Methods class at the University of Notre Dame to study the levee system and its failure. I was also involved in forensic engineering research that used satellite imagery and aerial photography to investigate the causes of damage to structures near the coast in Mississippi. In addition, I participated in a Research Experience for Undergraduates (REU) program, Interdisciplinary Studies in Tsunami Impacts and Mitigation (ISTIM), at the University of Notre Dame during the Summer of 2007. As part of this program, we traveled to Phuket, Thailand to see first-hand the devastation caused by the tsunami and learn how to better design and build structures to prevent future deaths and destruction from similar disasters. While the occurrence of these hazards is beyond our control, novel structural engineering approaches have the ability to reduce their consequences.
It became apparent during these site visits and research experiences that structures in these areas are affected by multiple hazards, leading to unexpected effects. For example, many structures close to the coast in the southeastern United States are not only affected by the strong winds associated with a hurricane but also the damaging effects of storm surge and waves. This can be seen in the images below, taken after Hurricane Katrina, which show complete destruction of homes due storm surge and waves (left) in close proximity to homes that suffered minor wind damage but were elevated from the storm surge (right). In addition, the Indian Ocean Tsunami showed that structures near the coast in strong seismic areas may be affected by both earthquakes and tsunamis. And finally, the 2010 Haiti Earthquake occurred in an area typically affected by hurricanes. Therefore, most structures are not vulnerable to one single hazard and managing hazards individually may not yield the most efficient and effective designs. In addition, the most extreme load conditions, two hazards acting together, may not be considered.
These and similar observations are what generated the relatively new area of multi-hazard engineering. Multi-hazard engineering aims to use available resources most effectively to design safe structures that are able to withstand a range of natural hazards. This approach involves an understanding of all of the hazards that could potentially affect a structure and the use of this knowledge to determine which aspects of the structure may be most vulnerable. Then, robust design features can be incorporated in order to enhance performance when considering individual hazards or the combined loading from several hazards. Post-disaster site visits and satellite imagery are invaluable to the determination of these robust design features. For example, the building shown below is in the region hit by the 2004 Indian Ocean Tsunami. The lower level of the structure bore the brunt of the damage. The walls perpendicular to the wave direction have been completely destroyed. The structure, however, remained standing. After the perpendicular walls were broken, the water was able to flow through the first floor diminishing the overall loads on the structure. Post-disaster photography, such as this, can help in determining better design practices for the future. Breakaway walls on the lower levels of structures in tsunami-prone regions would allow the water to flow through instead of causing a build-up in the pressure and the forces on the ocean-side wall and other foundation components.
POST-INDIAN OCEAN DAMAGE IN ACEH, SUMATRA, INDONESIA (DEPARTMENT OF DEFENSE PHOTO—MICHAEL L. BAK)
Designing low income urban housing comes with its own set of unique challenges without consideration of the multiple hazards with which the structures may be faced. A multi-hazard approach, however, can readily be incorporated into the design stages in order to ensure that the resources that are available are being used to most effectively resist the hazards. It is envisaged that a strong, multi-faceted structural system promises to mitigate damage from many hazards. Structural engineers have the unique ability to positively influence society in an important way by improving the resiliency of structures to hazards, allowing people all over the world to have access to safe structures in which to live and work, Shelters For All!
– Megan McCullough, Civil Engineering Graduate Student, NatHaz Modeling Laboratory, Department of Civil Engineering and Geological Sciences, University of Notre Dame