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Abstract

It remains a challenge to accurately model the runoff behavior in urban areas with a complex topography. The question to be addressed is how varying the urban spatial configurations can quantitatively influence the overland flow response in relation to the hydrodynamic variables. We use a 2D shallow water model to indicate the influence of changing spatial urban factors (such as the orientation of streets and buildings, and adding sidewalks) in small idealized (synthetic) urban catchments with a size of 267.5m*267.5m during a single pluvial flood event. We differentiate between: i) the two-way main street with of 14-m width with sidewalks, and ii) side streets of 10m width. We then define novel spatially integrated indicators over the domain to analyze quantitatively runoff variables in correlation with the urban features. Additionally, local hotspot flood maps were created to assess risk. The modelling results showed that, with respect to the flow velocities in small-scale urban catchments, the main street layout is the dominant urban factor, followed by the side street widths, which were decisively determined by the geometry of the sidewalks. The comparison with real flood risk thresholds shows that the lower part of the main road is the most sensitive to flood risk in the domain. Spatially integrated indicators of the flow variables are showing low sensitivity to the spatial urban features. Our findings offer a new important perspective on the development of urban flood risk assessment, and provide a better understanding of the spatiotemporal rainfall-runoff generation in a small urban catchment.