Infrastructure is interconnected, interdependent, and Complex. Infrastructure systems have complex connections and interdependencies that can lead to cascading failures. In many cases, infrastructure systems depend upon services provided by other infrastructure. For example, if the electricity supply is disrupted, then water supplies may be affected since pumps and treatment plants require electricity. If gasoline stations and oil pipelines depend upon the power grid for electricity, then transportation services may be disrupted. Second-order effects can also occur. For example, if electricity supply failure occurs and affects water supplies, then agriculture will be affected and eventually, banking and finance will have an effect. Figure 7.2.1 illustrates some of the interdependencies among six infrastructure services.
Geographic proximity can also result in infrastructure interdependencies. All the infrastructure on a flood plain may be vulnerable to a flood event. Similarly, an earthquake can disrupt multitude of infrastructure systems, including bridges, buildings, pipelines, electricity transmission lines, fiber optic cables, ports, and roadways.
Of course, infrastructure managers may be responsible for only one particular type of infrastructure. For example, a building manager usually relies upon the power grid for electricity, the local water supply utility for water, a telecommunications company for telephone and internet, and suppliers for a variety of resources. However, a building manager can estimate the likelihood and consequences of disruptions. Moreover, planning ahead can reduce the consequences of disruptions. Backup power systems for essential services (such as lighting) or back up communications capability can be installed in the building.
Modern communications and information technology has become pervasive in the provision of infrastructure services. Note that supervisory control and data acquisition (SCADA) and communications has the most occurrences among the interdependencies shown in Figure 7.1.3. Telecommunications companies need to be ready for rapid response to restore services in the event of disruptions to avoid cascading effects.