Effect of urban neighbourhood layout on the flood intrusion rate of residential buildings and associated risk for pedestrians

Urban neighbourhood layouts affect the flood intrusion rate towards residential buildings through various kinds of damaged openings (doors, windows, gates and shafts) and the associated risk for pedestrians within the urban building complex and ultimately the safety of indoor and outdoor pedestrians in urban flooding events. This study adopts computational fluid dynamics (CFD) to quantify the flood intrusion discharge towards residential buildings and evaluate the flood hazard rating of pedestrians within urban areas of divergent configurations in conjunction with a laboratory flume experiment regarding the stability/instability behaviour of a dummy model that represents a human body in a quasi-natural state. Five types of urban building layouts with three different building densities under three various floodwater conditions, including a determinant type A (see the graphic abstract hereafter), a point group type B, an enclosed type C, a hybrid type D and a new hybrid type E, are examined. The results show that the determinant type A and hybrid type D have a similar trend in terms of the flood intrusion discharge distributions towards each row of buildings and discharge variation with respect to urban building spacing, whereas other urban layouts exhibit different characteristics. Strong floodwater leads to an increased flood risk for pedestrians both outdoors and even indoors within various urban configurations: pedestrians are the most prone to toppling instability on the streets, in turn, behind the building and within the interior of the building. For both determinant type A and hybrid type D, the more pedestrians lie behind the building approaching the upstream, the safer the pedestrians become, while for point group type B, enclosed type C and new hybrid type E, the trend is reversed. The experimental results also offer a novel valuable dataset for the validation of other urban flooding numerical models. This study could be referred to by local authorities and stakeholders to take effective measures to improve the safety of pedestrians and mitigate flood risk in the context of urban planning and urban flood emergency management, such as strengthening flood-resilient urban facility designs and devising optimal routines for emergent evacuation of outdoor pedestrians.