Operational response model for physically attacked water networks using NSGA-II

Homeland security challenges civil engineers to develop solutions to protect critical infrastructure systems from intentional attacks. The water infrastructure system is one of eight critical infrastructures defined in the report by the President's Commission on Critical Infrastructure Protection (PDD 1998). This paper offers a model for an operational response strategy to mitigate consequences of intentional physical attacks on the water infrastructure system. An intentional physical attack occurs when a water infrastructure facility is nonfunctional because of physical destruction of the facility by individuals or groups with malicious intentions. Three indices are presented in this paper to measure the consequences of intentional physical attacks: (a) the degree of the disruption of critical infrastructure services, (b) economic loss, and (c) the number of people affected. Then, a multiobjective genetic algorithm is used to find solutions to affect minimum consequences among these indicators. Evaluation of the model using two water infrastructure networks indicates that the genetic algorithms can successfully identify Pareto-optimal solutions to reduce the negative consequences of different attack scenarios. These solutions represent a pool of strategies to be incorporated in emergency plans. In addition, the modified nondominated sorting genetic algorithms (NSGA-II) developed in this study can significantly improve the quality of the solution early in the evolution process. This can be very critical when the time available to obtain mitigation plans is very limited.