Predicting Compound Coastal Flooding in Embayment-Backed Urban Catchments: Seawall and Storm Drain Implications

Urban coastal flooding is a global humanitarian and socioeconomic hazard. Rising sea levels will increase the likelihood of hydrologic events interacting with high marine water levels. These compound events may, in turn, nonlinearly interact with urban infrastructure, potentially resulting in more extreme coastal flooding events. Here, an integrated Delft3D-FM based numerical modeling framework is used to concomitantly resolve multi-source flood processes (i.e., high marine water levels, precipitation) and infrastructure (e.g., seawalls, storm drains). Hydrodynamic model results are validated with embayment pressure sensor data and photographic observations from historical events. The impact of tide and precipitation phasing are examined. Multiple storm drain characterizations are presented and evaluated. Results show seawall and storm drain infrastructure is fundamental to accurately resolving spatial and temporal flood dynamics. Importantly, coastal management strategies such as raising seawall elevations to mitigate tidal flooding may exacerbate precipitation-based flooding in low-lying urban regions.