Using Rain-on-Grid Hydrodynamic Models and Planning-Level Cost Estimates to Prioritize the Creation of “Resilient Routes”

Recent extreme flooding events in the southeastern United States have revealed serious vulnerabilities across the country’s transportation networks and highlighted the urgent need for upgrades. Flood damage has been widespread and addressing all the vulnerable areas would be cost prohibitive. We propose a methodology that combines rain-on-grid (ROG) hydraulic model output with planning-level cost estimates to quickly evaluate potential routes based on the cost to upgrade to a given return period (e.g., 100 years). The continuous water surface elevation (WSE) output from the ROG model allows for analysis of the entire network for both pluvial and fluvial flood risk. Model simulated WSEs were compared at each bridge and culvert and to each 15-m segment of road length. Costs from previous road projects were used to estimate the cost of upsizing bridges and culverts to no longer overtop and raising road segments above the predicted flooding WSE. Road costs included road embankment fill, paving, curbs, traffic control, marking, and shoulder armoring. Estimated costs were summed for each return period. The costs for upgrading each potential route can be compared across a range of return periods. This approach allows planners to quickly identify critical routes that are already safely passible during extreme events or routes that would likely require the least investment to become “resilient” routes. It also helps to reveal areas where overtopping may create significant risks for motorists and pedestrians. This prioritization approach can substantially reduce the number of corridors that should be considered for more detailed analysis and costing.