Designing resilient infrastructure systems will require collaborative efforts by engineers and social scientists.
Urban societies depend heavily on the proper functioning of infrastructure systems such as electric power, potable water, and transportation networks. Normally invisible, this reliance becomes painfully evident when infrastructure systems fail during disasters. Moreover, because of the network properties of infrastructure, damage in one location can disrupt service in an extensive geographic area. The societal disruption caused by infrastructure failures is therefore disproportionately high in relation to actual physical damage.
Engineers have long tried to design infrastructure to withstand extreme forces, but recently they have begun to address the need for urban infrastructure systems that are resilient to disasters (e.g., NIST, 2008). Conceptually, resilience entails three interrelated dimensions: lower probabilities of failure; less-severe negative consequences when failures do occur; and faster recovery from failures (Bruneau et al., 2003). The emphasis on consequences and recovery suggests that improving the resilience of infrastructure systems is not only a technical problem, but it also has societal dimensions.
The consequences of recent disasters have demonstrated that urban infrastructure systems in the United States and other developed countries (not to mention in developing regions of the world) remain highly vulnerable. Moreover, infrastructure failure is often a primary cause of economic and human losses in disasters. Consider, for example, the consequences of infrastructure failures caused by wind, storm surges, and levee failures in New Orleans during Hurricane Katrina. Table 1 provides a few other examples to illustrate the frequency and range of infrastructure failures in disasters.
Because infrastructure failures are clearly a primary cause of disruptions in disasters, strategies for improving the disaster resilience of communities must focus on improving infrastructure resilience. Yet few standards or guidelines have been developed for this, partly because of the complexity of the problem (American Lifelines Alliance, 2006).
Research on Infrastructure in Disasters
Much of the early work on infrastructure in disasters was on understanding the mechanics of how components of infrastructure systems (e.g., bridge piers, buried pipes, electric power transformers, and other substation equipment) perform when subjected to extreme forces or conditions. This basic understanding was then extended to the performance of component assemblages (e.g., bridges, pipeline networks, substations). Studies ranged from field work to laboratory simulations with scale models and computer-based analyses.
As a result of these studies, new engineering designs, materials, and retrofitting strategies were developed to improve the ability of infrastructure elements to withstand natural hazards. New technologies were also developed, such as sensors for monitoring structural health and detecting damage and real-time system controls.
While these remain active areas of inquiry, new research themes have emerged to address some of the complexities of infrastructures, which include societal as well as technical issues. How, for instance, will the failure of one bridge affect businesses throughout the urban area that rely on the transportation system? How will the failure of one infrastructure system disrupt other infrastructure systems? How can repairs following a disaster be planned so they minimize social and economic losses? Such questions have prompted research that is, by necessity, interdisciplinary.
Challenges of Interdisciplinary Research
Interdisciplinary inquiry is inherently difficult for many reasons, ranging from intellectual issues, such as differences in communication and attitudes, to organizational issues, such as funding mechanisms and academic structures. Interdisciplinary research at the intersection of engineering and the social sciences is especially challenging (NRC, 2006).
One basic hurdle has been different disciplinary concepts of the term “infrastructure.” To structural engineers, for example, infrastructure comprises constructed elements, such as pipes and bridges, described in terms of materials and design properties that condition their responses to physical forces. To economists, infrastructure—often referred to as “public capital"—comprises an input to economic production measured in dollars (e.g., Munnell, 1992) and often quantified at the state or national level. These fundamental differences reflect different ways of conceptualizing and measuring infrastructure.
Overcoming these challenges has required more collaborative, interdisciplinary research than in past engineering studies. It has also required researchers to pay greater attention to issues of time, space, and context. These trends are illustrated below in an example from the field of earthquake engineering.
Water Systems in a Los Angeles-Area Earthquake
The Los Angeles Department of Water and Power (LADWP), the largest municipal utility in the United States, provides potable water to 3.9 million people through 11,700 kilometers of infrastructure in one of the most seismically active regions of the country. Over the last several years, researchers affiliated with the Multidisciplinary Center for Earthquake Engineering Research (MCEER), a research center funded by the National Science Foundation, have been studying the potential consequences of major earthquakes on the LADWP water system. Highlights of three of these studies1 illustrate some key challenges and breakthroughs.
Modeling Potential Physical Damage
The first study, conducted by geotechnical engineers, developed a model of potential physical damage to the LADWP network (Romero et al., 2009). Geographic information system (GIS) technology was used to visualize the spatial dimensions of seismic ground waves, peak ground deformation, fault rupture, soil liquefaction, and landslides, as well as the network itself. The model, the Graphical Iterative Response Analysis for Flow Following Earthquake (GIRAFFE), assesses damage to network components (pipes, tanks, reservoirs, etc.) and performs hydraulic modeling of water flows through the damaged network. GIRAFFE also estimates serviceability—defined as the ratio of post-earthquake to pre-earthquake water flow—for each service area.
In 2008, results for one hypothetical event, a Mw 7.8 earthquake on the southern San Andreas Fault, were used as part of the largest emergency preparedness exercise in U.S. history. In that scenario, overall water serviceability 24 hours after the earthquake was estimated to be as low as 34 percent (after reserves in storage tanks had been depleted). LADWP has now adopted GIRAFFE, trained its personnel to use it, and is applying the results in its system decision making.
Modeling the Post-Earthquake Damage-Repair Process
In a related study, systems engineers modeled the damage-repair process to estimate the duration of water outages (Brink et al., 2009). A discrete-event simulation model was developed that mimics the actual post-earthquake restoration process, including the movements of repair crews over time and their activities, which are subject to personnel and material constraints. Data were derived from extensive consultations with LADWP engineering staff.
The restoration model was then run in tandem with the GIRAFFE damage and water-flow model to simulate serviceability in 12-hour increments as repairs were made over time and space; uncertainties were handled through multiple discrete simulations. The results showed substantial variations in how restoration might proceed, and LADWP concluded the restoration model would be helpful in planning for resource allocations following a disaster.
Modeling the Effects of Water Outages on Businesses
Urban planners used the models described above and other MCEER engineering studies to investigate the consequences of water outages, including impacts on the economy (Chang et al., 2008). For example, an agent-based simulation model accounts for how different types of businesses would be affected by water outages. Inputs include water serviceability ratios and restoration times based on the studies described above, as well as characteristics of businesses per se. Data were derived from surveys of impacts on businesses in previous disasters. Impacts from water outages were estimated in the context of other types of earthquake-related disruptions, specifically damage to buildings and power outages. Results for a Mw 6.9 Verdugo Fault scenario indicated that water outages could account for an estimated $467 million in direct business losses, or about 1.5 percent of the estimated total economic losses.
Critical Factors in Interdisciplinary Studies
The studies described above have demonstrated the feasibility and promise of interdisciplinary research on infrastructure resilience for developing the capability of modeling post-disaster losses and recoveries over time. Based on the experience of developing GIRAFFE, the restoration model, and other models, we have identified factors that promote interdisciplinary research in this area:
• GIS technology helps bridge disparate datasets and models by providing a common platform for information sharing and data integration.
• The concept of infrastructure “services” is critical for linking physical damage to societal impacts. This concept, which differs from both the traditional engineering concept of infrastructure and the traditional economic concept of infrastructure, reflects an intermediate representation that connects them.
• A research center approach makes it possible to address the entire scope of a complex problem through the coordinated efforts of a multidisciplinary team, convened and sustained over several years. This coordination is necessary to identifying critical gaps in knowledge, involving appropriate researchers, and overcoming disciplinary barriers.
• Collaboration with the end user, that is, with LADWP, the infrastructure organization itself, is essential. LADWP engineers contributed in important ways to framing questions, developing data, and ultimately, to applying outcomes to decision-making.
Without all of these factors in place, this interdisciplinary research could not have been conceived or conducted.
Challenges on the Horizon
Where is the current frontier in research on infrastructure resilience to disasters? In this author’s opinion, much remains to be understood and addressed about the performance of engineered elements and systems. In addition, the nexus between engineering and social sciences has just begun to be explored through interdisciplinary research, and many important questions remain to be answered. In this context, three new challenges have been gaining attention.
The first challenge is interdependencies—understanding and addressing how failures in one infrastructure system lead to failures in another. Loss of electric power, for example, commonly leads to disruptions in water, transportation, and health care systems, among others (McDaniels et al., 2007). There are several types of interdependencies: physical linkages (e.g., pump stations in water delivery systems that require electricity); cyber linkages (e.g., computerized system controls that rely on telecommunications); geographic linkages (e.g., pipelines located on transportation bridges); and “logical” linkages (e.g., infrastructure elements related through economic markets driven by human decision-making) (Rinaldi et al., 2001).
The technical understanding of these interdependencies is still in its early stages, and many infrastructure organizations have been reluctant to share information about their vulnerabilities for security reasons. Nevertheless, an understanding of infrastructure interdependencies is critical for cities deciding on strategic investments in infrastructure improvements that will have the greatest payoff in terms of resilience.
The second new challenge is multi-hazards. Because infrastructure systems are vulnerable to multiple stressors (e.g., wind, ice, flood, earthquake, terrorism, deterioration), it is important to find solutions and support decisions that consider them in that context. Synergies in risk-reduction technologies may reduce the costs of pre-disaster retrofitting and post-disaster repairs. Methods are also needed to assess how the deterioration of infrastructure over time affects disaster risk.
The third challenge, sustainability, is the consideration of infrastructure resilience in a long-term environmental context. It can be argued that disaster resilience is an inherent characteristic of sustainability. On one level, designing and building infrastructure that is able to withstand disasters will reduce their negative environmental impact, such as debris from damaged structures, spills of hazardous materials and other contaminants, and the carbon footprint of reconstruction activities. Infrastructure designers should, therefore, include such life-cycle environmental impacts in their decision-making (Guikema, 2009).
On another level, because infrastructures are long-lived, infrastructure resilience will require the capacity to meet demands that may change drastically over their life cycles. Such changes may include urban growth and increases in populations. Climate change will also be important, for example, through rising sea levels that redefine coastlines and through changes in the occurrence probabilities of hazardous events, including hurricanes, extreme rainfalls, droughts, temperature extremes, landslides, and floods. Climate change will not only put coastal infrastructure, such as port and harbor facilities, at risk. In many cities, climate change will also stress water supplies, wastewater treatment facilities, and transportation systems (Infrastructure Canada, 2006).
In addition, infrastructure systems themselves have substantial effects on the environment. For example, building flood-control levees, paradoxically, encourages development in hazardous floodplains. Thus the vulnerability of New Orleans to Hurricane Katrina was partly attributable to decisions, such as levee construction, that were made over a period of many decades to protect against relatively frequent storms, but that increased the city’s vulnerability to very large, albeit rare, catastrophic storms (Kates et al., 2006).
In addition, the capacity of Louisiana’s coastal wetlands to help buffer wind and storm surges was substantially degraded over decades by the construction of levees, shipping channels, oil and gas industry facilities, and other infrastructures (e.g., Kousky and Zeckhauser, 2006). Some have suggested that flood protection should not only comprise building levees, but should also be designed to encourage marsh restoration (Guikema, 2009). Others have proposed the decommissioning of existing infrastructures—such as the selective dismantling of dams and levees—along with ecosystem restoration as an approach to addressing the problems of aging infrastructure and the ecological degradation it has caused (Doyle et al., 2008).
Still others have pointed out that compact city designs intended to promote sustainability (e.g., to promote energy efficiency and reduce emissions of greenhouse gases) may actually undermine disaster resilience by putting more people in high-density developments located in floodplains and other hazardous locations (Berke et al., 2009).
How can infrastructure systems be designed to both reduce risk and support more sustainable cities? How can infrastructure systems be designed for disaster resilience—for today, as well as for the future? These questions may be the most difficult, and the most important, to answer. Addressing them will require interdisciplinary research that spans the distances between engineering fields and between engineering and the social sciences.
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1 The MCEER-LADWP research program also involved other studies (not described here) that analyzed regional seismicity, modeled performance of the electric power transmission system, and investigated forms of business resilience and resilient behaviors.