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.

Anchoring tools to communities: insights into perceptions of flood informational tools from a flood-prone community in Louisiana, USA

“…A 500-year flood was used as an example of an extreme event that could impact the community. These simulations were developed for the drainage basins surrounding Lafayette Parish using a MIKE 21 two-dimensional hydrodynamic model (Miller, 2022). The model was based on a high resolution, LiDAR-based Digital Elevation Model (DEM) dataset.…”

“…Given the drivability raster map for a given timestep, network accessibility to the following two example target points were calculated from all other points on the network: a medical center in southwest Lafayette, and the United States Interstate Highway 10 (I-10) west interchange (I-10 being a primary hurricane evacuation route). Accessibility was calculated using the D8-flood fill algorithm detailed in Miller (2022). A target point was considered to be accessible from a source point on the network if there was a continuous path (including diagonal connections) from the source to the target (Figure 4).…”