Flood Risk Assessment and Increased Flood Resilience for Civil Infrastructure in Coastal Regions Under Changing Climate

Coastal regions are increasingly vulnerable to flooding impacts due to growing populations, urbanization, climate change, and relative sea level rise (SLR). Individual flood mechanisms, namely excess rainfall and coastal storm surge, can cause widespread flooding in these low-lying, densely populated, and highly developed regions. These two flood mechanisms often occur concurrently during extreme weather events, which can greatly exacerbate the severity of flooding. However, the combined effect of both excess rainfall and coastal storm surge flooding mechanisms are not often considered in modeling-based flood risk assessments. To enhance the resilience of civil infrastructure in coastal regions to increasing flood risk, this dissertation aims to advance the understanding, modeling, and prediction of coastal flooding caused by both excess rainfall and coast storm surge. This goal is achieved through three studies with increasing modeling detail and complexity. The case study areas are located in the Hampton Roads region of Virginia, an area particularly vulnerable to increasing flood risk due to climate change and SLR. The first study focuses on assessing flood risk of civil infrastructure, bridges and culverts in particular, over the coastal plain region of Hampton Roads. The study proposes a Geographic Information System (GIS) based screening method that is able to estimate overtopping risk across a large collection of bridges using a simplified modeling approach. The second study focuses on a small urban catchment in Norfolk, VA to investigate compound flood risk from excess rainfall and coastal storm surge using a detailed, hydrodynamic urban flood model. The objective is to enhance the understanding of the interaction between excess rainfall and coastal storm surge in a coastal urban catchment. The third study builds from the second by expanding the modeling domain to a near city-scale model while maintaining the hydrodynamic modeling detail. This study explores how changing rainfall and SLR due to climate change may impact compound flood risk in coastal urban environments. Key research findings resulting from this research are as follows. i) The low-cost flood assessment screening tool could be used to assist decision makers in updating the Waterway Adequacy field in the National Bridge Inventory (NBI), which indicates the overtopping risk of bridges. ii) The hydrodynamic modeling method allows for identifying portions of the floodplain with different dominate flooding mechanisms (rainfall vs. storm tide), providing valuable information for targeting flood mitigation strategies. iii) While pluvial flooding driven by rainfall is the dominate factor in interrupting transportation networks in Norfolk under current climate conditions, by 2070 projected SLR will cause tidal flooding to far exceed the impacts of rainfall-driven flooding within Norfolk. Collectively, these insights and methodologies for flood risk in urban coastal environments could be applied to other regions facing similar flooding challenges now or in coming decades to best target mitigation strategies aimed at creating more flood resilient civil infrastructures systems.