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 a urban flood, based 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 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 storage of runoff 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 runoff volume stored within the block. Finally, the flood risk to pedestrians, which is both velocity and flow depth related, increases locally when considering the conveyance and storage within the city block.

Publications and communications

• Mejía-Morales, M., Paquier, A., Proust, S. and Mignot, E. (2019), «Experimental and numerical modelling of the influence of street block flow exchanges during urban floods», soumis à SimHydro 2019, 12-14 juin 2019, Sophia Antipolis, France.
• Mejía-Morales, M., Paquier, A., Proust, S. and Mignot, E. (2019), « Influence of the building block structure on the flow pattern along a flooded street », soumis au 38th IAHR World Congress, 1-6 septembre 2019, Panama City, Panama.
• Mejía-Morales, M., Paquier, A., Proust, S. and Mignot, E. Article en préparation intitulée : «Physical water processes during urban floods considering a porous building block: a laboratory investigation », en préparation pour Journal of Hydraulic Research.

Cite the thesis

Miguel Angel Mejía Morales. Influence of the flow exchanges between streets and a city block during urban floods : Laboratory experiments under steady and unsteady flow conditions. Fluid mechanics [physics.class-ph]. Université de Lyon, 2022. English. ⟨NNT : 2022LYSEI042⟩. ⟨tel-03938972⟩

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