Infrastructure resiliency is the capability to restore infrastructure to its original state after a disruption occurs. Improved resiliency can be achieved with planning for disruptions and having resources available to respond to disruptions. Figure 7.3.1 illustrates the various time periods. Prior to an incident or disaster, preparations can be made. At the time of an incident, the infrastructure performance degrades, especially as failures propagate through associated components. In extreme cases, the infrastructure performance may degrade to closure (so I would equal zero in Figure 7.3.1). A recovery period ensues until the infrastructure returns to normal performance.
Table 7.3.1 lists some strategies to improve resiliency along with technical, organizational, social and economic examples. The strategies are:
- Robustness may refer to facility design and construction but also includes good planning for emergencies and rehearsals.
- Redundancy includes strategies such as back-up power and lifeline resources such as food and water.
- Resourcefulness involves the resources that can be mobilized in response to an event.
- Rapidity is the speed at which restoration can occur.
Table 7.3.1: Technical, Organization, Social and Economic Dimensions of Infrastructure Resiliency. Source: O’Rourke, 2007. Redrawn and altered by Authors
|Robustness||Appropriate building codes and construction procedures||Emergency operations planning and practice||Degree of community preparedness||Regional economic diversification for supply|
|Redundancy||Capacity for technical substitutions||Alternative sites for managing emergency operations||Availability of Housing options for disaster victims||Investment in backup systems|
|Resourcefulness||Availability of equipment and materials for response||Capacity to improvise and innovate||Capacity to address lifeline needs||Capacity to improvise|
|Rapidity||Restoration time||Reduced Reaction Time||Time to restore lifeline services||Time to regain capacity|
As an example of resiliency planning, consider an electricity utility. The utility can insure redundancy in transmission lines and power generation sources. Individual facilities can be design and built to withstand significant stresses. With major storms forecast, crews with equipment and supplies can be pre-positioned to respond to any outages rapidly. While the utility may still see disruptions, all of these activities will improve the resiliency of the utility.
Another example is planning for evacuation effectively. Figure 7.3.2 shows a 2005 evacuation of Houston due to forecast hurricane. During this evacuation, roadway lanes in to the city have been reversed to increase the available capacity. Unfortunately, the traffic volumes resulted in major traffic jams. Improved entry controls onto the highway could eliminate this type of jam.
Climate change and sea level rise are two factors that are increasing the importance of infrastructure resiliency. As average sea level increases, the likelihood of flooding increases. A variety of new strategies may be required, as with the response to Hurricane Sandy that flooded portions of the New York subway system.
Finally, the use of scenario analysis (as described in Chapter 6) may be useful for planning. A regular session to consider possible risks, preparedness, and documentation of procedures can be extremely useful.