Advanced porosity-based models to assess the influence of urban layouts on inundation flows and impact of urban evolution on flood damage

摘要

Worldwide, flood risk is expected to increase over the 21st century due to the combined effect of climate and land use changes. However, while the impact of climate change on future flood risk was extensively studied, the effects of urbanization remain unclear. The goal of this PhD thesis is to contribute to a better understanding of the influence of future urban development on changes in inundation flows as well as on the related damage.First, an original porosity-based model was developed, which enables efficient computation of urban flooding. It uses anisotropic porosity parameters to reproduce the influence of subgrid-scale obstacles on the flow. An original merging technique was implemented to optimize the computational efficiency in the presence of low values of the storage porosity parameter. Compared to a standard inundation model, the developed model enables speedup factors of the order of 100, while keeping the error on the flow variables at a few percent.Second, we systematically investigated how the layout of buildings located in floodplains influences the inundation characteristics for a long-duration flood scenario. The anisotropic porosity-based model was used to compute the flow variables for 2,000 alternative urban patterns. Correlations between the computed water depths and the urban characteristics reveal which features of the layout of buildings influences most the severity of urban flooding. In particular, the results suggest how the hydraulic effect of new urban development can be effectively mitigated by a suitable location of the buildings preserving a higher flow conveyance at the district-scale. This result provides guidance for more flood-proof urban developments.Finally, we evaluated the evolution of future flood damage as a result of urbanization along all the main rivers in the Walloon region, Belgium. The study was conducted at the regional level using detailed hydraulic results (resolution of 2 to 5 m). Despite high uncertainties in the considered urbanization scenarios, involving both urban expansion and densification, robust conclusions could be drawn, such as the overwhelming influence of banning new developments in flood-prone areas compared to the other tested facets of urban planning policy.