Modeling Temporal Accessibility of an Urban Road Network during an Extreme Pluvial Flood Event

Abstract

This study presents a model-based framework to assess the time-varying accessibility of a roadway network on a system-wide level during extreme flood events. A regional MIKE 21 hydrodynamic model consisting of 1,912,576 computational points with mesh cell resolutions ranging from 70 to 15 m is utilized to compute regional inundation during an extreme 500-year flood scenario. This approach allows for an explicit accounting of the impact of pluvial flooding on roadway network accessibility. Accessibility conditioned on flood depth is then computed using a raster approximation of the roadway network model employing the flood-fill search method. The approach is demonstrated in the flood-prone low-gradient region of Lafayette, Louisiana, which experienced a devastating flood event in August 2016. The findings suggest that the main evacuation points enjoy a greater degree of accessibility compared to medical facilities within the urban core of the city during the flood peak. Significant improvements in network accessibility can be made by targeted mitigation of specifically flood-prone roadway segments. However, the analysis demonstrates the adverse impacts of such mitigation activities in low-gradient urban floodplain systems when implementing routine drainage compensation steps. The approach provides key insights into the role played by pluvial flooding and flood duration on network accessibility and can help inform emergency response and transportation systems planning and design efforts.