Raymond B. Seed, University of California, Berkeley "SGER: Hurricane Katrina and Lessons for Responding and Repairing Catastrophic Levee Failures Applicable to Other Similarly Threatened Areas in the U.S."
The potential for hurricane-induced catastrophic failure of the levees and subsequent flooding of New Orleans had long been foreseen by technical experts. However, New Orleans is not the only region in the United States in which this type of catastrophic hazard exists, but goes largely unaddressed. A stunningly similar situation exists in California with regard to potentially catastrophic seismic risk associated with the fragile labyrinth of levees that pass two-thirds of California's vital fresh water safely through the key node in the State's extensive water distribution system. The city of Sacramento is currently the largest metropolitan area with the lowest level of levee flood protection in North America. Additional critical levee systems provide flood protection throughout the Mississippi and Ohio River basins, as well as in the Charleston area, and in other regions of the U.S.
There are key lessons of vital importance to be learned from the performance of the New Orleans levee systems, and the emergency repair and pumping to dewater the inundated areas. Although there is considerable experience in the emergency repair of isolated breaks, the New Orleans disaster represents an unprecedented instance in which military assets were made available for assisting in emergency repairs. This event provides the first opportunity to quantitatively assess the value and impact of such operations as opposed to more traditional use of barges to dump rock and dredged fill, or land-borne transport and equipment to carry and place new fill soils. The degree of scour erosion at the various levees breaks will be investigated and compared to placement rates of oversized helicopter-borne "sand bags." The team will investigate issues related to contracting and difficulties in the field placement of material. Additional elements include the seepage as well as settlement and subsidence of the emergency repaired sections. Long term performance of the hurried repairs is an important element of the problem, as is the degree to which permanent repairs will be affected by the presence of the unorthodox emergency levee "patches." Other issues that will be investigated include the degree to which wind driven waves eroded the back faces of the flooded levees, the degree of erosion and damage caused in non-breached levee sections due to partial and wave-driven overtopping, and the levee configurations and crest and upper face protection details, and their interaction with surge-driven water levels and wind-driven waves. Another set of issues that will be studied are the levee designs and configurations, and their overall performances in this event. Many critical levees did not fail, and these represent important lessons as well. The design basis and decision process that led to the current levee configurations are also key elements that will be investigated.
It is vital to absorb these lessons from the engineers and personnel who performed and oversaw the repairs, and that these lessons be effectively transmitted to levee repair experts, emergency planners, and risk assessment experts in other regions. These lessons can improve speed and efficiency and thus are invaluable in planning the response to large (catastrophic) emergencies. The interdisciplinary team benefits from the synergistic efforts and/or funding from the American Society of Civil Engineers and the California Department of Water Resources. The team members are diverse and include nationally recognized levee experts and outstanding experience in the field of natural disasters. The investigation of the performance of the New Orleans area levees in the aftermath of the Hurricane Katrina will provide vital information for the future performance of critical protective levee systems throughout large areas of the U.S.
