Urban flooding modelling: role of geometric distortion in scale models and influence of urban forms

Urban flood risk is increasing worldwide as a result of environmental changes such as more frequent hydro-climatic extremes and due to rapid urbanization. Accurate and reliable tools are critically needed for managing this risk and enhancing flood resilience. Such tools rely on numerical models for computing flood hazard and flood risk. However, the accuracy and applicability of these models still remain hampered by a lack of suitable validation data. Data generated from laboratory experiments is a valuable complement to field observations for validating these flood risk management tools. Through a comprehensive review of the 45+ available experimental studies of urban flooding, a few gaps in current experimental knowledge of urban flooding were identified.
Firstly, laboratory studies of urban flooding often use geometrically distorted scale models due to the multi-scale nature of these specific flow pattern The possible bias induced by geometric distortion has never been thoroughly investigated with dedicated laboratory experiments. To address this issue, we firstly carried out a preliminary assessment of these biases based on the reanalysis of two recent experimental datasets related to urban flooding. Then, combining two-dimensional numerical modelling and dedicated laboratory experiments, we provided a first systematic quantification of this bias in the case of a synthetic urban layout, involving models at three horizontal scales, models for different geometries and various flooding conditions. The results indicate the direction and magnitude of the bias induced by geometric distortion for a broad range of flow cases, which is valuable for offsetting these effects in practical laboratory studies of urban flooding.
Secondly, water-sensitive urban design is an integral part of flood risk management. Based on numerical modelling, we investigated the influence of various urban forms on flood severity at an urban block scale in the case of long-duration urban flooding. The upstream flow depths, downstream discharge partition and flow exchange through the urban forms were examined. Moreover, the computational model was verified against laboratory observations, which constitute a novel valuable dataset for the validation of other urban flooding models.