Screening vulnerabilities in water supply networks : risk analysis of infrastructure systems

The extreme importance of critical infrastructures to modern society is widely known. Recognizing that society cannot afford the costs associated with absolute protection, it is necessary to prioritize the vulnerabilities in these infrastructures. This Thesis presents a methodology for the identification and prioritization of vulnerabilities in a water supply system. Existing methods are mostly based either on an adaptation of the minimal-cut-set concept or rely on experts to do this. We suggest that for complex systems a systematic scenario-based approach is possible. We argue that the infrastructure system's capacity constraints both on the production resources and on the carrying network need to be considered in this approach. We model the infrastructure as a network, making use of its natural hierarchical structure to aggregate users into groups. We create one scenario for each system's element, seeking to understand its related vulnerability. For any given scenario, we employ short path algorithms to evaluate the supply level to each user considering the capacity of the paths connecting it to the resources. We then proceed to compute the disutility of each scenario using multiattribute utility theory. The impact of losing service to a given number of users is evaluated using a value tree that reflects the perceptions and values of the decision maker and the relevant stakeholders. These results are provided to the decision maker for use in risk management. The methodology is illustrated through the presentation of the analysis conducted on the water supply network of a 250,000 inhabitants city. Keywords: Risk Assessment, Infrastructure, Vulnerability, Water Supply