Quantitative fault tree analysis for urban water infrastructure flooding

Flooding in urban areas can be caused by heavy rainfall, improper planning or component failures. Few studies have addressed quantitative contributions of different causes to urban flood probability. In this article, we apply probabilistic fault tree analysis for the first time to assess the probability of urban flooding as a result of a range of causes. We rank the causes according to their relative contributions. To quantify the occurrence of flood incidents for individual causes we use data from municipal call centres complemented with rainfall data and hydrodynamic model simulations. Results show that component failures and human errors contribute more to flood probability than sewer overloading by heavy rainfall. This applies not only to flooding in public areas but also to flooding in buildings. Fault tree analysis has proved useful in identifying relative contributions of failure mechanisms and providing quantitative data for risk management.