Learn more about elevated roads and bridges above flood risk.
About elevated roads and bridges
In order to maintain dry access to roads and bridges during flood events, local governments may choose to elevate this infrastructure above a certain flood level. Low-lying roads are at risk of flooding which blocks possible escape routes. Bridges can impede the flow of water causing the water to back up and flood surrounding areas. Road crossings should have sufficient bridge openings and adequate culvert capacity so that roads do not disrupt drainage patterns. Roadways drainage systems must be updated accordingly when they are elevated. Local entities have to be sure that roads are graded accordingly and the system is upgraded accordingly. It is also important to routinely maintain roadways and waterways because debris can build up along bridges which adversely affects water flow and can lead to damage of surrounding structures and roadways.
Road raising project to combat flooding in Miami Beach, Florida
Get above base flood elevation
Authorities typically try to raise roadways and bridges above the local base flood elevation (BFE). The base flood elevation (BFE) determines the height that equipment should be raised above. A property’s BFE can be found through searching for one’s local county FEMA flood insurance rating map (FIRM). Construction, reconstruction, and repair of roads and bridges should take drainage and elevation into account but also stabilization and armoring of vulnerable road shoulders and embankments.
The image above shows a road that has been flooded during a storm.
An example of one city that is raising roads to combat flooding is Miami Beach in Florida. Miami Beach is raising its roads by two feet at a cost of roughly $2 million per block. Raising roads above sea level can help drain water and reduce tidal flooding. In order to make sure that higher roads don’t channel flood waters to homes and stores at lower elevations, cities often use stormwater pumps to remove this excess water. Miami Beach’s $400 million project intends to install 80 pump stations throughout the city along with raising streets. The project specifically targets roads on Miami Beach’s low-lying western edge to be rebuilt higher above sea level and future sea level rise.
Flood risk reduction projects
Information on Flood Factor comes from the First Street Foundation Flood Model. Elevated roads are one of the 40 different types of flood risk reduction projects, known as adaptation, that this model considers when calculating and validating flood projections.
The Adaptation Team continues to collect information on the flood infrastructure that exists across the country to make sure the Flood Model includes as many adaptation projects as possible. If you know of any projects that are not shown today, please help the team by submitting this flood protection project user input form. The adaptation database contains 23,000 features today. We know there are more projects to include and value your input!