Urban floods

Problematic issue

During floods in urbanized areas, flow is generally concentrated in streets, but lateral exchanges with building areas and vertical exchanges with the stormwater/wastewater network can modify flows locally. To fill the gap in understanding these exchange processes and assess their influence on the estimation of flood risk in streets and built-up areas, experiments are carried out on a model representing an urban district.

Scientific issues

  • What is the influence of porosity in the building (opening area / total wall area) on flow depths and velocities under steady flow conditions?
  • What is the influence, for a given porosity value, of the spatial distribution of this porosity on the waterways, and in fine, on the flow depths and velocities under steady flow conditions?
  • What is the influence of the land use of a building area on flow depths and velocities dans in streets and in the building area under unsteady flow conditions?
  •  What is the influence of vertical flow exchanges between streets and  the sewerage/stormwater network on flow depths and velocities in streets under steady flow conditions? (1) when the network overflows into the streets; (2) when the network drains part of the flows into the streets.

Methodology

The urban flood processes are studied on a physical model called ‘MURI‘ ( Modèle Urbain pour l’Étude du Risque d’Inondation =  Urban Model for the Study of Flood Risk) that was built in 2017.  MURI is a platform of 5.4 m x 3.8 m, which can be tilted from 0 to 5% in the longitudinal and transverse directions. MURI is supplied with water by 3 inlet tanks, and is also equipped with 3 outlet tanks and 6 inlet/outlet side tanks. The current geometry studied consists in 3 longitudinal streets and 3 transverse streets defining 16 rectangular urban blocks. The platform is also equipped, at the lower level, with pipes that model the sewage system and can be vertically connected with the streets.

MURI model (from left to right, and top to bottom): current geometry with 3 longitudinal streets and 3 transverse streets; the three upstream inlet tanks; flow in a cross-road with two inflows with Q= 4.5 L/s each (experiments of Ms student Cécile Lalanne, 2017)

PhDs, post-doctorates, and masters

  • PhD Thesis of Tariq Chibane (2015-2020), «Hydrodynamic modelling of flows during urban floods: interplay between surface runoff and sewerage network». Co-directors: S. Benmamar (ENPA, Alger); A. Paquier.
  • PhD Thesis of Miguel Mejia-Morales (2018-2021), «Influence of street / building block flow exchanges during urban floods». Supervisors: S. Proust (co-director), A. Paquier, et E. Mignot (co-director), INSA.
  • Master (2018) of Miguel Meija. ‘Experimental flow studies in a city neighbourhood’.
  • Master (2017) of Cécile Lalanne. ‘Étude expérimentale d’écoulements dans un quartier de ville’.

Research projects

  • Projet ANR DEUFI -DEtailing Urban Flood Impact- (2019-2022)
  • Projet PHC Tassili (2016-2019) “Diagnostics d’aléa inondation par ruissellement adaptés au contexte algérien, au service d’une stratégie de prévention”

Partners

  • ANR DEUFI: RiverLy; G-Eau; LMFA; Icube; Artelia; Cerema; GRED; Univ. Liège (Belgium); KICT (Korea).
  • PhD Miguel Mejia-Morales: RiverLy; LMFA.
  • PhD Tariq Chibane: RiverLy; ENPA (Algérie).

Example of experimental results

  • Influence of street / building block flow exchanges during urban floods» (PhD Thesis of Miguel Mejia-Morales)

Top left: building block with 12 openings. Bottom left and right: surface velocities computed using Fudaa-LSPIV (Large Scale Partical Image Velocimetry) for a block with 12 openings and 4 openings. The flow was seeded with saw dust at the water surface.

Example of numerical modelling

Numerical simulation  of the depth-averaged velocites using the 2D code Rubar 20 (developed by Irstea).

Publications

  • Mejia Morales, M. A., S. Proust, E. Mignot and A. Paquier (2019). Influence of the urban block structure on the flow pattern along a flooded street. E-proceedings of the 38th IAHR World Congress. September 1-6, 2019, Panama City, Panama.  doi:10.3850/38WC092019-1487
  • Mejia Morales, M.A. (2018). Experimental flow studies in a city neighborhood. Master 2, Ense3, Grenoble INP. 53 p.
  • Lalanne, C. (2017). Étude expérimentale d?écoulements dans un quartier de ville. Master 1 de Mécanique des Fluides (MF2A), C.M.I Université Pierre et Marie Curie, Paris. 51 p.