Uncertainty in risk analysis of urban pluvial flooding: a case study

The interest in urban flood risk is growing steadily over the last decades. Still, in the Netherlands no data is available to quantify urban flood risk. In this paper an estimation of urban flood frequencies is made in a detailed analysis of an urban catchment. Calculation results from a theoretical model are compared with data from a complaint register. The analysis in the case study shows that insufficient system maintenance condition is an important potential cause of urban flooding. The estimated flood frequency caused by severe rainfall is 4 events in 7 years or 0.6 per year, while the flood frequency caused by maintenance problems is 13 in 4 years or 3.3 per year. This includes 2 flood events that are caused by heavy rainfall and 11 events that are related to maintenance problems. The number of locations that suffer flooding caused by severe rainfall is more than 3 or 4 per event, while the number of locations that suffer flooding caused by maintenance problems is not more than 2 per event. It is expected that these numbers are representative for the rest of the Netherlands. Further research and data collection will very this assumption.