Life-cycle cost analysis and resilience consideration for coupled grey infrastructure and low-impact development practices

Recent studies have suggested that coupling grey infrastructure (GREI) with low-impact development may be a promising approach to urban stormwater management. However, comprehensive assessment of the hydrological resilience of such a coupled-system is challenging, and this limits planning and implementation. In this paper the authors developed an innovative approach to measure and optimise life cycle costs for layouts with different levels of decentralisation under the constraint of hydrological reliability, and assess their technology-based and operational resilience. The authors found that coupled solutions implemented in a high-density catchment are economically competitive compared with conventional GREI. Based on the findings of risk scenario modeling, the coupled-systems show better technology-based resilience to extreme weather, except during extreme storms (rainfall of 50-year recurrence interval with 24-hr storm duration). Regarding operational resilience (versus structural failure), coupled-systems incorporating source control and pathway drainage with higher redundancy are more robust than GREI-only system. Decentralisation with optimised layouts does not significantly improve system resilience. This methodology could be a helpful decision-making tool in developing strategies to manage stormwater runoff for better hydrological resilience in high-density urban catchments.