Assessing Urban Wetland Restoration Impacts on Local Flood Risk and Biodiversity

Thesis Abstract

Urban areas increasingly rely on restored wetlands to mitigate flood risk and conserve biodiversity amid accelerating urbanization and climate variability. Despite growing investment in restoration projects, there is limited empirical evidence linking specific restoration configurations to localized flood attenuation and biodiversity outcomes within metropolitan landscapes. This study aims to evaluate the hydrological and ecological performance of urban wetland restoration sites and to elucidate the processes by which restoration influences flood risk and biodiversity in surrounding urban catchments. The objectives are to quantify changes in peak discharge and stormwater storage capacity before and after restoration; assess alterations in local biodiversity indicators (avian, amphibian, and invertebrate assemblages, as well as plant diversity and vegetation structure); identify the sociotechnical drivers that influence restoration effectiveness; and develop a transferable framework for decision-makers to optimize restoration design for flood risk reduction and biodiversity co-benefits. The research adopts a mixed-methods design anchored in systems thinking and resilience theory, combining quantitative hydrological and ecological monitoring with qualitative stakeholder interviews. The population comprises four urban wetland restoration projects within a major metropolitan region, each characterized by different hydrogeomorphic settings and restoration scales. A quasi-experimental, stepped-wedge approach is employed, with pre-restoration baseline data collected for two years and post-restoration monitoring conducted for three years at each site, yielding a sample of 16 site-time observations. Hydrological data (stream stage, rainfall, soil moisture, infiltration rates) will be collected using automated gauges, rain gauges, and soil moisture probes, while hydrologic performance will be analyzed through paired t-tests and generalized additive models (GAMs) to detect changes in peak flow, duration of inundation, and storage volume. Biodiversity assessment will utilize standardized point counts for birds, pitfall and sweep-net sampling for invertebrates, dipnet surveys for amphibians, and vegetation surveys to quantify species richness, evenness, and structural complexity. Multivariate analyses (non-metric multidimensional scaling, PERMANOVA) will examine shifts in community composition, complemented by indicator species analyses. For the qualitative component, semi-structured interviews with municipal planners, engineers, and local residents will be thematically analyzed to identify perceived barriers and enablers of restoration effectiveness, using a framework grounded in the Social- Ecological Systems and Resilience theories. A convergent mixed-methods integration will synthesize hydrological, ecological, and social findings to derive a comprehensive impact assessment. Expected findings include statistically significant reductions in peak river discharge and enhancements in stormwater storage volumes attributable to increased surface detention and groundwater recharge at multiple sites, with GAMs indicating non-linear responses to rainfall severity. Biodiversity outcomes are anticipated to show context-dependent improvements increased resident species richness and higher habitat suitability indices in sites with emergent vegetation mosaics and improved connectivity to surrounding green space, along with measurable changes in invertebrate functional diversity. The study is expected to reveal that restoration design features—such as hydrologic connectivity, soil hydrophobicity management, and vegetation community structure—modulate the magnitude of flood attenuation and biodiversity gains. The contribution to knowledge lies in providing empirical, site-based evidence linking restoration attributes to hydraulic performance and ecological responses in urban settings, and in offering a transferable, design-oriented framework for prioritizing restoration actions under budgetary constraints and climate risk. The anticipated conclusions emphasize that urban wetland restoration can simultaneously reduce local flood risk and bolster biodiversity when designed to enhance hydrological integration and habitat heterogeneity, and that governance arrangements must align with adaptive management and community engagement. Practical recommendations include (1) adopting a hierarchical restoration design that prioritizes hydrologic connectivity at the catchment scale, (2) integrating functional vegetation mosaics to support multi-taxa biodiversity, and (3) implementing monitoring protocols combining hydrological, ecological, and social indicators to enable iterative improvements. The study would inform practitioners and policymakers on optimizing urban wetland restoration for resilience, while contributing to theoretical discourse on the links between ecosystem-based flood management and biodiversity conservation in cities.