Exploring Infiltration Effects on Coastal Urban Flooding: Insights from Nuisance to Extreme Events Using 2d Hydrodynamic Modeling and Crowdsourced Flood Reports

Abstract

AbstractCoastal urban flooding presents significant challenges due to the complex interactions between surface runoff, storm tides, and drainage systems. A common assumption in urban flood models is that infiltration is not a dominate process and can, therefore, be ignored in the model. While this may be an appropriate assumption for extreme weather events, it may not be appropriate for nuisance flooding events that are becoming more frequent in many coastal communities due to seal level rise and changing rainfall patterns. This study aims to assess the impact of incorporating infiltration processes into an urban flood model by evaluating flood extent under 1-, 10-, 50-, and 100-years return periods. Specifically, we performed our test case over an urban coastal watershed in Norfolk, Virginia using a detailed 1D/2D hydrodynamic model. For the evaluation of the model, we incorporated community-sourced inputs from residents and drivers collected through data portal application and a mobile navigation platform. Our findings are: (1) infiltration losses reduced the flooded areas by 33% during the 1 year return period and by 12%, 9%, and 5% during 10-, 50-, and 100-years return periods respectively (2) significant variability in water depth was observed, with nearly a 20 cm difference between full and zero saturation conditions during the nuisance flooding event on a selected street in the Park Place neighborhood; (3) while less intense storms did not achieve full soil saturation, thereby reducing flood risks, extreme events rapidly overwhelmed infiltration capacity, leading to increased surface runoff and inundation; and (4) crowdsourced flood reports showed that the model accurately predicted flood locations, with 88% of community reports and 89% of driver reports aligning with simulated inundation maps. These findings highlight the importance of incorporating infiltration processes in flood risk assessments, particularly for nuisance events, and underscore the value of using crowdsourced data to enhance urban flood modeling.

Keywords: Coastal flooding, Nuisance Flooding, Extreme Flooding, Infiltration Losses, Hydrodynamic Modeling, Crowdsourced Flood Report.