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Résumé
The increasing occurrence of urban flooding in recent years demands a more accurate flood hazard assessment (flow depth and velocity) and the associated risk to property and people. This assessment must be based on a detailed understanding of the hydrodynamic processes, particularly on a local scale (at street or at city block).
In this context, the aim of the thesis work was to study the lateral flow exchanges between a city block and streets during an urban flood, relying on laboratory experiments. The latter were carried out under steady and unsteady flow conditions. The investigation area was limited to a single city block and its adjacent streets, considering the mechanisms that affect the capability of the city block to convey and store floodwaters. Three key issues were then addressed to quantify the influence on flow depth, velocity and discharge in the streets and within the city block : (i) by varying the magnitude of the conveyance porosity of the block ; (ii) by varying the distribution of the conveyance porosity of the block ; and (iii) by varying the storage capacity of the city block. Firstly, it was found that in the streets surrounding the block, the velocity and flow depth can vary significantly when considering the conveyance and floodwater storage in the block. Within the block, the most impacted flow parameter is the number and size of horizontal secondary flow cells. Secondly, it was found that the inflow hydrograph unsteadiness has a strong influence on the flood flow characteristics, as well as on the floodwater volume stored within the block. Finally, the flood hazard to pedestrians, which is both velocity and flow depth related, increases locally when considering the conveyance and storage within the city block.
