Resilience-Based Optimization of Rehabilitation Planning under Budget Constraints: Developing a Risk-Oriented Decision Model considering Supply Security

Abstract

Ensuring a reliable, long-term supply of drinking water is a significant challenge for municipal water utilities, particularly given strict budget constraints and challenging topographic conditions. This thesis aims to develop a transferable, risk-oriented optimization model for rehabilitating municipal water supply networks. The model evaluates renewal needs and financial sustainability. Through lifespan simulations, the model prioritizes specific pipeline sections using a risk-based, multi-criteria framework. This model is based on the concept of localized risk, which is defined as a function of structural failure probability and the resulting socioeconomic and physical consequences. The relevant evaluation criteria, including asset age, material generations, empirical damage rates, operating pressure, and traffic loads, are defined based on the technical guidelines of (DVGW e.V. W 403, 2025) and scientific literature. The Analytic Hierarchy Process (AHP) is systematically applied to determine the objective weighting of these conflicting criteria. Furthermore, this systematic approach establishes a mathematically reliable ratio of conditions to consequences, thereby eliminating qualitative biases. Based on the evaluated criteria, a risk index is derived to enable detailed prioritization of pipeline sections. Additionally, the model incorporates resilience indicators and consumer criticality metrics to account for the impact of potential pipeline failures on populations and infrastructure that are most vulnerable. The developed evaluation model was applied and validated using a real pipeline network in a Stadtwerke Freudenstadt case study. This application demonstrates that combining multi-criteria, risk-based prioritization with strategic rehabilitation planning under fixed financial constraints establishes a consistent, transparent, and structured basis for municipal decision-making. Furthermore, the model transforms local boundary conditions into a methodology that can be applied to other water utilities. The model provides a robust foundation for short-, medium-, and long-term rehabilitation planning.