Risk analysis of combined rainwater detention and pumping systems

Storm sewer systems (SSSs) are complex, with many hydraulic, mechanical and electrical components which may fail during natural extreme events, changing environmental conditions (including urban development), or simply due to poor maintenance. System complexity and management are important and still debated concepts within the framework of SSS risk analysis. A new probabilistic model for a conceptualized urban SSS, including a storage unit (SU) and a pumping station (PS), shows how single-component risk analysis can be extended to complex SSSs and demonstrates the combined effect of key design parameters (SU volume, detention time, prescribed outflow discharge) and management strategy on the overall SSS risk of failure. The risk of failure evaluated in a typical case study, demonstrates that economic restrictions leading to the loss of reliability of PS elements and the lack of redundant mechanical elements represent a major threat to SSSs and suggests a new risk-based definition of 'extended' SU.