Spatial heterogeneity of urban pluvial flooding and its mitigation

Urban flooding has become a growing threat to human society worldwide. Urban flood hazards have occurred more frequently, resulting in a growing population exposed to flood hazards and increasing flood damage to human communities. Thus, there is an urgent need to develop an urban pluvial flooding risk framework that can be used to evaluate the impacts of the flood and to provide helpful guidance on flood mitigation. The first chapter is a general introduction of this dissertation. It also reviews the existing studies related to physical and social factors affecting urban pluvial flooding. The research gaps are highlighted, and the aim of this dissertation is described. There is a lack of studies on investigating the spatial heterogeneity of the risk factors of urban pluvial flooding and their interplay impacts, and discussing how these may affect the urban flood mitigation strategies. The second chapter investigates the spatial relationship between the urban pluvial flood locations and the controlling factors through a case study in the City of Cincinnati. Three controlling factors are investigated, including precipitation, impervious area and topography. Two comparisons are conducted, one is depression-based which utilizes the random sampling method and the other comparison analysis is flooded-location-based. The results show that topography and precipitation are more important in the prediction of urban pluvial flooding risk than impervious areas. There is spatial heterogeneity of the three controlling factors as well as their interplay impacts. The third chapter develops an integrated approach for assessing urban pluvial flooding risk by combining two components, physical exposure and social vulnerability at catchment level. An exposure index (EI), a social vulnerability index (SoVI) and a composite pluvial flood risk index (PFRI) are developed. The results demonstrate the spatial heterogeneity of exposure and social vulnerability of urban pluvial flood, as well as the composite pluvial flooding risk across the study area. The impacts of different combinations of exposure and social vulnerability on urban pluvial flood can provide helpful insights in formulating tailored strategies in mitigating urban pluvial flood risk. The fourth chapter is focused on the mitigation of urban pluvial flood. In this chapter, a Storm Water Management Model (SWMM) is developed to compare the impacts of detention basins and their retrofits, and low impact development practices on erosive flows and urban flooding in two urbanized subcatchments under different return period storm events, including 1-year, 2-year, 5-year, 50-year, and 100-year. The results show that detention basin and detention basin retrofits are more effective in reducing peak flow and delaying peak time. The integration of detention basin retrofits and LID practice can contribute to 70.61% to 94.07% peak flow reductions in the designated storms. The last chapter discusses major findings and conclusions from the three studies conducted in this dissertation. This dissertation reveals the spatial heterogeneity of the physical and social factors affecting urban pluvial flooding and investigates the performances of different stormwater management practices on urban flooding.