R&D highlights edition 2019

PROJECTS Flood risk 12 P luvial flood risks in urban areas are a worldwide concern because of ongoing urbanisation and the increased frequency of extreme rainfall events as a result of climate change. Numerical models of rainfall run-off, urban drainage and sewer overflow help to estimate the probability and extent of floods in the urban environment. A hydrologic/ hydraulic model of the urban drainage system and the surface flow embedded in a probabilistic framework can generate a set of flood maps for a range of recurrence periods in order to establish a basis for risk-based flood mitigation, spatial planning and prioritisation of measures. A key component in these risk studies is the rainfall model input. Existing approaches to rainfall input for risk studies suffer from various drawbacks: some involve long computing times; others make crude assumptions that result in doubts about the validity of the outcomes. Deltares has developed a new method for deriving a set of rainfall events that produces realistic rainfall patterns with minimal computing time, giving it the edge over alternative methods. The method was tested on a realistic case – urban drainage and flood risk in the city of Florence, Italy – in collaboration with the precipitation expert group of the University of Florence. The results, which showed that the method works well, were presented at the UrbanRain18 conference in Pontresina, Switzerland. The next step will be to publish the method in a peer-reviewed journal and to start using it in Deltares projects on urban drainage. Contact: Joost Beckers, Joost.Beckers@deltares.nl t +31 (0)6 1218 4327 A NOVEL APPROACH FOR DESIGN RAINFALL IN URBAN DRAINAGE STUDIES