Hydrodynamics of long-duration urban floods: experiments and numerical modelling

Abstract

Abstract. Flood risk in urbanized areas raises increasing concerns as a result of demographic and climate changes. Hydraulic modelling is a key component of urban flood risk analysis; yet, detailed validation data are still lacking for comprehensively validating hydraulic modelling of inundation flow in urbanized floodplains. In this study, we present an experimental model of inundation flow in a typical European urban district and we compare the experimental observations with predictions by a 2-D shallow-water numerical model. The experimental set-up is 5 m × 5 m and involves seven streets in each direction, leading to 49 intersections. For a wide range of inflow discharges, the partition of the measured outflow discharges at the different street outlets was found to remain virtually constant. The observations also suggest that the street widths have a significant influence on the discharge partition between the different streets' outlets. The profiles of water depths along the streets are mainly influenced by the complex flow processes at the intersections, while bottom roughness plays a small part. The numerical model reproduces most of the observed flow features satisfactorily. Using a turbulence model was shown to modify the length of the recirculations in the streets, but not to alter significantly the discharge partition. The main limitation of the numerical model results from the Cartesian grid used, which can be overcome by using a porosity-based formulation of the shallow-water equations. The upscaling of the experimental observations to the field is also discussed.

Formation, breaching and flood consequences of a landslide dam near Bujumbura, Burundi

“…This model has been extensively validated and applied for simulating flow induced by dam and dike breaching Roger et al, 2009) as well as for conducting flood risk analysis (Arrault et al, 2016;Beckers et al, 2013;Bruwier et al, 2015;Detrembleur et al, 2015;Ernst et al, 2010).…”

Urban and rural flood forecasting

“…The HLM was used to get streamflow boundary conditions for the local model created in XPSWMM. Instead of focusing on a single street or block (Arrault et al, 2016), this study uses the necessary detail to analyze how flooding propagates in a whole urban district.…”

“…With an increase in model resolution, the number of grid cells increased by square Schubert & Sanders, 2012; G. P. Smith, Wasko, & Miller, 2012;Syme, 2008). There are a few experimental studies on the flow behavior in urban areas both focusing on a single street intersection and those that analyze the entire flow field in an urban area (Arrault et al, 2016;Dottori & Todini, 2013). Numerous methods have been devised to represent the influence of buildings on flood flow behavior in either account for the effect of buildings by physically including them in the topography or by introducing additional head loss in the model computational gird points at the building footprints.…”

“…The XPSWWM 2D landuse types used in the Manchester model The Manning's roughness (n) describes how the sheet flow moves over the gridded surface. There are difficulties for estimating the roughness parameters which vary significantly in space, particularly in floodplains(Arrault et al, 2016). The typical range of values for the Manning's roughness values are listed below(Engineering, 2016;Janses & SCE, 2016).…”

“…The 2D overland flow was calculated by solving the dynamic wave version of the SWE. Flows in urban areas are supercritical with high Froude numbers which usually require smaller timesteps(Arrault et al, 2016;Dottori & Todini, 2013). The flow is subject to viscous effects of the frictional surfaces.…”