Assessing the Impact of Green Infrastructure on Urban Flood Mitigation Efficiency

Thesis Abstract

Rapid urbanization and increasingly frequent extreme weather events have intensified the challenge of managing urban floods, prompting a critical need to evaluate the effectiveness of sustainable flood mitigation strategies such as green infrastructure (GI). This study aims to systematically assess the impact of green infrastructure on the efficiency of urban flood mitigation, specifically targeting the extent to which GI measures reduce flood volume, peak discharge, and infrastructure strain during storm events. The research adopts a mixed-methods approach, integrating quantitative hydrological data analysis with qualitative assessments of community perceptions, to provide a comprehensive understanding of GI's role in flood mitigation. The primary research design is structured around an observational field study complemented by spatial analysis. The population comprises urban areas within the metropolitan region of Porto, Portugal, characterized by significant recent implementations of green infrastructure projects, including bioswales, rain gardens, permeable pavements, and green roofs. A stratified random sampling technique selects ten neighborhoods based on the density and age of GI installations, with a total sample size of 150 households and 10 designated monitoring sites for hydrological data collection. Data are collected through an array of instruments hydrological sensors measuring runoff and flood parameters, GIS mapping tools for spatial analysis, and structured questionnaires and interviews to gather residents' perceptions and behavioral responses. The validity and reliability of data collection instruments are enhanced through pilot testing and calibration against historical flood data. Data analysis employs multiple regression analysis to quantify the relationship between GI features and flood peak reduction, while ANOVA tests examine differences across varying types and scales of GI interventions. Thematic analysis is used to interpret qualitative data from residents' perceptions, and a conceptual framework grounded in the Water Sensitive Urban Design (WSUD) theory and the Resilience Theory guides the analytical approach. The combined analysis aims to elucidate the contribution of various GI components to flood mitigation, considering contextual factors such as land use, community engagement, and maintenance practices. Expected findings suggest that green infrastructure significantly improves flood mitigation efficiency, evidenced by reductions in peak flow rates by up to 35%, and decreased flood volumes by approximately 25% in neighborhoods with integrated GI systems. The study also anticipates revealing disparities in effectiveness based on the type, scale, and maintenance of GI, with community engagement emerging as a pivotal factor in sustaining operational performance. Additionally, the qualitative component is expected to highlight residents' increased awareness and adaptive behaviors linked to GI implementation, fostering a culture of resilience. This research contributes to the existing body of knowledge by providing empirical evidence of how specific green infrastructure measures influence flood dynamics in an urban context, offering a nuanced understanding that informs policy and design standards. It advances the application of integrated assessment frameworks in urban flood management, emphasizing the importance of community participation and spatial planning in optimizing GI effectiveness. The main conclusion underscores the potential of green infrastructure as a cornerstone of sustainable urban flood management strategies. Recommendations include prioritizing the integration of diverse GI types in urban planning, establishing maintenance protocols, and fostering community involvement to enhance resilience against flood risks. Finally, the study advocates for further longitudinal research to evaluate the long-term performance and climate adaptability of green infrastructure, thereby contributing to resilient urban ecosystems amid the increasing challenges posed by climate change.