Water Resources Policy and Practice Issues Exposed by Katrina (2009)

The Interagency Performance Evaluation Task Force (IPET) was established by the Chief of Engineers of the U. S. Army Corps of Engineers to determine the facts concerning the performance of the New Orleans Hurricane Protection System (HPS) in response to Hurricane Katrina. The Task Force conducted in-depth analyses that: (1) defined the surge and wave levels resulting from the storm, (2) determined the forces experienced by the HPS, (3) characterized the design, as-built, and as-maintained character of the HPS, (4) determined the most likely causes and mechanisms for observed behavior (failure and success), (5) characterized the extent and consequences of flooding (including the influence of the pumping stations), and (6) performed a risk and reliability assessment of both the pre-Katrina and post-Katrina HPS. Over 300 individuals from more than 50 organizations have contributed to IPET. Those organizations included 25 universities, 23 private sector firms, and 10 government agencies. There were many individuals from the Corps of Engineers embedded in the IPET teams to provide direct two-way exchanges of information and ideas. This was essential to the literally real-time transfer of information and findings to the repair and rebuilding process. The IPET Web site (https://IPET.wes.army.mil) is the primary venue for documenting and providing the IPET analysis and results. It contains over 4,300 documents dealing with the design and construction of the HPS, as well as the 9 Volume IPET Final Report, Performance Evaluation of the New Orleans and Southeast Louisiana Hurricane Protection System. The IPET analysis and results were peer reviewed by the American Society of Civil Engineers External Review Panel and the National Research Council Committee on New Orleans Regional Hurricane Protection Projects. IPET was primarily an engineering-based forensic analysis of what happened and why during Katrina. Yet, this in-depth engineering analysis both exposed and reinforced a number of serious water resources policy and practice issues that contributed to the disaster experienced in New Orleans. The issues identified are summarized below using the five fundamental areas of the IPET investigation. The System: During the IPET analysis, the basis for the design, construction, and operation of the HPS was examined in detail to understand the character and capability of the structures that comprised the HPS when Katrina struck. One of the most significant issues was the long time frame between inception and completion. The system in place before Katrina was compromised by a long series of decisions driven by competing priorities, incremental decision making and piecemeal funding. Also, within the 50-year tenure of the HPS, changes occurred in the basic hazard that defined the design criteria and errors were discovered in the assumptions made for the basic geodetic and water level data used in the design process. Deliberate decisions were made not to halt construction and change the structures to accommodate these factors. Some sections of the HPS, particularly on the West Bank, were not completed when Katrina struck and the many pumping stations that are crucial to keeping New Orleans dry from rainfall and ground water were not part of the HPS and not intended to operate during large hurricanes. The HPS could not and did not perform as a system because of these and other factors. If risk reduction measures are to be put in place they must be designed, constructed, and maintained as systems. The promise or perception of a system when it does not exist is perhaps more dangerous than no system at all. As a nation we lack clear standards for planning, design, and development of major public infrastructure for water resources. New knowledge is often too slow to be incorporated into engineering guidance, and we too often optimize based on immediate cost and accept short-term gains instead of long-term solutions. This is a national cultural malady that can only be reversed if the public demands a change in policy. Life-cycle solutions are important to our future, and we can only get there through the election cycle. The Storm: Figure 1 is a NOAA satellite image of Katrina prior to landfall and showing the enormous physical size of the storm. Katrina generated the highest surge ever experienced on the North American Continent. It was a 400-year event based on its surge generation capability and overwhelmed most of the structures on the east side of New Orleans and to the south. High performance computer models using high resolution computational grids were necessary to reproduce the surge and wave conditions experienced by the levees and floodwalls. While a Category 3 (on a 1-5 scale) storm according to the Saffir-Simpson Scale, Katrina demonstrated that intensity alone (based on central pressure) is not an adequate predictor of the severity of a hurricane. Katrina also demonstrated that central pressure, the typical criteria used, is alone not an appropriate estimator of the frequency of occurrence of hurricanes. It is the joint probability of central pressure, physical size (radius), forward speed, and track that better describe the probability of experiencing different surge levels. Hurricane Katrina was both an intense and physically large storm (Figure 1) making the Saffir–Simpson rating of Category III a poor predictor of the surge it generated, the largest ever to hit North America. Very sophisticated modeling was necessary to re-create the surge and wave conditions produced by Katrina to enable forensic analysis of levee and floodwall performance. There is much more to learn. If we as a nation hope to manage risk from the most severe hazards, we need to learn how to work with, rather than control, nature. Research is needed to better define the actual role of natural environments in managing surge and waves; rules of thumb are just too inaccurate. Given the challenges of continued sea level rise and subsidence and the potential for more intense storms, the art of building and sustaining the natural environment is especially important. The vulnerability of natural features to large storms is a particular challenge if we are to rely on them for long-term risk reduction. The Performance: Katrina damaged over 200 of the 350 miles of floodwalls and levees surrounding New Orleans and southeast Louisiana. There were 50 major breaches that resulted in approximately 80 percent of New Orleans being flooded. Four of the breaches occurred at water levels below the design criteria, all involving I-walls (levees with imbedded concrete capped sheet piles that rose above the levee). All of the remaining breaches occurred as the result of overtopping of the structures and subsequent erosion of the constituent or supporting materials. Ironically, the four floodwall failures that did not involve overtopping resulted in up to half of the floodwaters that entered New Orleans. Levees performed well until overtopping and those constructed of clay withstood overtopping without catastrophic breaching. The levees constructed of materials less resistant to erosion did not perform well when overtopped (Figure 2.). View of Gulf Inter-coastal Water Way levee being overtopped during Katrina. This levee constructed of quality clay was resilient to overtopping and did not fail. Levees constructed of more erodable sandy materials and capped with clay did not perform nearly as well. Beyond the failure of the four I-wall sections (three on the outfall canals and one within the Inner Harbor Navigation Canal), it was the lack of resilience that stands out as a major factor in the ultimate flooding and losses. If no catastrophic breaching had occurred, the flooding and losses would have been significantly reduced, perhaps by half. Structures must be designed to be resilient to overtopping and to prevent catastrophic breaching. Such capability would not only have dramatically reduced the losses in New Orleans but also dramatically eased the burdens of recovery. Man-made measures alone cannot sufficiently reduce risk for vulnerable areas such as New Orleans. Natural processes and attributes such as marshes, mangroves, and barrier islands need to be integral to a systems strategy for risk reduction. In combination with traditional structures and aggressive emergency management planning and execution, an enhanced natural environment can be a significant component to a sustainable and effective long-term strategy to deal with the dynamics of climate, systems and demographics. Consequences: The consequences of Katrina were staggering. Over 1600 fatalities occurred. 75 percent of the fatalities were people over 65 years of age; many of them were not self-mobile and were unable to evacuate. There was over $20 billion in direct property losses, 78 percent of which was associated with residential losses. People were living in the areas most prone to flooding, but then most of New Orleans is prone to flooding. There was another $10 billion in public property losses and indirect economic losses that dwarf property damage. Beyond the fatalities, perhaps the most severe losses with respect to recovery were social and cultural. Most of the neighborhoods that made up New Orleans were decimated, losing their population, social services, and social fabric. Risk is increasing significantly along the nation's coastlines, in part because natural hazards such as hurricanes appear to be more severe, but even more so because increasing numbers of people and property are being allowed to reside in harm's way. There is little that governments or individuals can do about the changing hazard, but there is much that can be done to manage risk by reducing exposure to the hazard. The simplest approach in principle is managing land use to avoid placing more people and property in areas vulnerable to hazards. While simple in principle, the dichotomy of land-use authorities between levels of government, the lack of adequate risk reduction standards, and the dependence on continued development has made this the correct path seldom taken. Many individuals are drawn into this web by ignorance or lack of clear information. Risk: The risk of loss of life and property in New Orleans prior to Katrina was both high and unknown. There had not been any attempt to quantify risk for hurricanes for any major metropolitan area. Risk had been used for major site-based critical infrastructure such as dams and power plants, but geographically distributed hurricane protection systems such as that in New Orleans, or major expanses of levees such as those that occur along many rivers, were not addressed. The result was a situation where the current hazard was not well understood or quantified and the performance of the structures in place was not tested or quantified. The potential consequences of major flooding were not completely undefined in that a major emergency response exercise was conducted in New Orleans not long before Katrina involving a hypothetical hurricane not unlike Katrina (named Pam). The response exercise in fact estimated much higher loss of life than occurred in Katrina. The risk assessment involved defining a future hazard using joint probability methods that modeled over 150 hypothetical hurricanes with a wide range of characteristics, many having surge generation capabilities equal to and beyond that of Katrina. The surge and wave conditions generated by these storms were used as input to a reliability analysis to estimate the probability of breaching and overtopping of the structures protecting each of 27 drainage areas within New Orleans. This analysis was accomplished for both the pre-Katrina and post-Katrina HPS structures as well as the structures intended for the 100-year risk reduction system under construction. The reliability analysis provided basic information on the probability of flooding of different depths across the city. Combining this information with the population and property distributions in the city allowed estimates to be made of the risk of loss of life and loss of property. This information forms a new basis for the public and public officials to understand their vulnerability to flooding and associated losses. While risk continues to be high in New Orleans, some significant improvements have resulted from the work to date. The surge gates and pumps added to the outfall canals along Lake Pontchartrain have demonstrated their value as recently as Hurricanes Gustav and Ike. Similarly, stronger and higher levees along the east side of the city and stronger floodwalls within the city have reduced the potential for catastrophic breaching. The risk maps for the new system under construction, however, demonstrate that much more can be done and needs to be done to reduce the risk for New Orleans. Understanding risk is a powerful tool in helping both individuals and government agencies to make consistent and conscientious decisions concerning natural hazard risk management. The ability to quantify risk for large geographical areas and complex engineered systems is just emerging through the work in New Orleans and a similar effort is ongoing in central California. Figure 3 is an IPET flood depth-frequencey map for New Orleans prior to Katrina. Coupled with estimates of losses from these flood depths, it allows estimation of risk of loss of life and loss of property. Risk provides a much richer body of knowledge to understand and manage vulnerability to hazards as well as providing a clear common picture of the situation to all. Risk methods for regional infrastructure, if fully developed, will not only allow assessment of multiple hazards, but also allow collective consideration of life safety, direct and indirect economics, and social-cultural issues, enabling customization of solutions to situations. But the evolution and application of risk to support decision making must be enabled by policy which currently does not exist. Maps showing system-wide vulnerability to flooding such as the one above are critical to understanding risk and making decisions about how to manage risk. Coupled with estimates of potential loss of life and property, they provide a strong scientific basis for decisions to manage both sides of the risk equation, reducing the threat of flooding and reducing the extent of losses. First and foremost, the United States lacks a coherent and comprehensive strategy for water resources. Levels of protection are marginal with respect to levels of risk. Investments too often are local in scope, short-term in nature, cost-benefit based, and focused on taming, rather than working with, natural processes. Integrating risk reduction with other critical functions such as water quality, sustainability and commerce remain an idealistic goal. It is time for a new national emphasis on holistic water policy where public safety is a mandatory component. Second, our current policy and practice do not deal well with change. We must be more anticipatory and adaptive as changes occur in the hazard, the system, or the potential consequences. All of these factors changed dramatically over the life of the hurricane protection projects in New Orleans with little capability for appropriate response. This is another symptom of short-term rather than long-term sustainable strategies, policies, and practices for addressing a major life safety need. Change is inevitable, whether it is climate-induced changes in storm character and frequency, the evolution of structures and systems intended to deal with hazards, or population and property growth in vulnerable areas. Change must be a routine part of any analysis. Equally important, we must have the political will to anticipate and manage change to include continuous monitoring and updating structures and emergency response capabilities. Third, the 100-year de facto standard is far too risky for the continued vitality of our economy that is highly dependent on the viability of public infrastructure and the continuity of the economy. In fact, it has effectively generated a large volume of infrastructure that resides just outside this boundary that we all know has considerable uncertainty associated with it. The structure or people sitting within the 100-year floodplain are about as vulnerable to flooding and losses as those sitting within the 100-year zone. The nation must go to more comprehensive risk-based standards that provide longer term solutions that combine benefits of both built and natural measures. Risk measures also will allow consideration of life safety, environmental, and social/cultural goals along with economics in making critical infrastructure investment decisions. Dr. Lewis E. (Ed) Link is a Senior Research Engineer and member of the faculty of the Department of Civil and Environmental Engineering, University of Maryland. In that position he has been serving as the Director, Interagency Performance Evaluation Task Force, leading the forensic analysis of hurricane Katrina in New Orleans. He spent 34 years as a member of the U. S. Army Corps of Engineers culminating as the Director of Research and Development and Principal Scientific Advisor to the Chief of Engineers. He can be reached at elink@umd.edu.