Title
Broadening the discourse on infrastructure interdependence by modeling the "Ecology" of infrastructure systems
Author(s)
Larocca, S.;Guikema, S. D.;Cole, J.;Sanderson, E.
Published
2011
Abstract
Interdependencies among infrastructure systems arise for many reasons, including, among others, geographic proximity inducing common cause failures, direct dependence for physical flows of information, and common maintenance and repair actions. However, existing modeling of the risk and reliability of interdependent infrastructure generally deals with a limited subset of these sources of dependence, often focusing on only physical flows and geographic proximity. In this paper we show how a modeling construct recently proposed for ecological modeling can be used to give a much broader picture of dependencies between infrastructure systems and the elements of these systems and the effects of these dependencies on the reliability of interdependent infrastructure systems. This approach is based on Muir webs. Muir webs are a modeling approach first proposed for modeling complex, multi-faceted interdependence in a pre-European ecological-human community in the U.S. by Sanderson (2009). Traditional ecological network models focus on predator-prey relationships, the direct analogue to infrastructure interdependence models that focus on physical input-output dependencies. Muir webs generalize from predator-prey relationships to consider broader interactions such as dependencies on biotic but not directly consumed factors (e.g., shade for certain species of trees). They also include interdependencies due to abiotic factors (e.g., soil types, moisture levels, and climate) and due to human management of the environment (e.g., fire-maintained meadows due to agricultural practices). These factors are considered through a multi-way dependency network describing (1) what factors a given organism depends on and (2) what other organisms and factors depend on a given organism performing its role in the environment. The end result is a directed graph together with probabilities of each of the organisms being present and performing its role as a function of the needed inputs. In this paper we show how a Muir web can be used to represent and model interdependent infrastructure system reliability. The analogy is that each organism in the infrastructure Muir web is either a component of the system (e.g., a pump or valve in a water distribution system) or is a factor needed by some element(s) of the system for it to perform its intended role (e.g., stable soil, a water supply, and proper maintenance, all for a water pump). We then use this expanded representation of the dependencies and interdependencies and demonstrate how to estimate system reliability through a simulation-based approach. This new approach provides a much broader representation and understanding of infrastructure interdependencies © 2011 Taylor & Francis Group, London.
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