Hydraulic Vulnerability of Elementary Urban Cell

During urban storms, the overloading of a sewer system or a riverbank overflow produces flows that are routed by the road infrastructure and causes flooding of adjacent built-up areas. The evaluation of the damage inflicted in these built-up areas requires the determination of important hydraulic parameters of the inundation, such as the maximum water depth or the inundation duration. For each independent hydraulic urban cell, these parameters depend upon its intrinsic hydraulic properties (perviousness and storage capacity) and on the characteristics of the flood outside the cell. This paper proposes a quantitative formulation of the concept of cell hydraulic vulnerability based on the cellʹs hydraulic properties and on the basic characteristics of the flood (peak flow and time to peak). This study is based on observations made in three districts of Ouagadougou, Burkina Faso, and on a 23-year record of rainfall events in this region. The hydraulic vulnerability is discussed according to the district hydraulic properties and to the flood event characteristics. The developed methodology could be used in principle in every city where built-up areas are highly subpartitioned into walled properties.