Experimental and Numerical Modelling of the Influence of Street-Block Flow Exchanges During Urban Floods

During urban floods, the flow is generally concentrated in streets, but lateral exchanges with building blocks can alter locally the flow pattern. These blocks include buildings, courtyards, parking lots, gardens, into which water enters through different openings, such as windows, doors, gates, fences, etc. In order to study these exchange processes and their influence on flow depth and velocity in the streets during flood events, experiments were conducted on a devoted physical model termed MURI (Urban Model for the study of Inundation Risk), at Irstea Lyon-Villeurbanne centre, France. A 2D numerical model was also used to simulate the experiments, using a constant eddy viscosity and then an eddy viscosity in relation to the flow depth. The present study focusses on two geometric configurations. The first one consists of a straight street flanked by two lateral cavities, and the second one a straight street flanked by one-side opening. These flows are compared to a reference configuration under quasi-uniform flow conditions (without openings). The results obtained with the numerical model are consistent with the experiments, mainly in terms of flow depths. The experiments and simulations show that a detailed description of the building blocks is required if the flow pattern is estimated locally.