Recurrent Flooding Study for Tidewater Virginia – Transportation Impacts
This study makes projections for recurrent flooding in coastal Virginia, outlines the predicted impacts on transportation infrastructure, and offers planning and implementation activities to reduce risks to coastal infrastructure. The report provides an overview of available adaptation strategies for recurrent flooding, reviews their implementation around the world, and identifies specific strategies appropriate for Virginia.
Recurrent flooding is flooding that occurs repeatedly in the same area over time and in Virginia is due to sea-level rise, storm surge, and heavy rainfall with increasingly frequent storm-driven water levels that flood developed areas. The report addresses three major threats to road systems from sea-level rise including alterations to the drainage capacity, flooding of evacuation routes, and increased hydraulic pressure on tunnels.
As sea levels rise, the capacity of road drainage systems will decrease which can cause stormwater to back up, in turn causing flooding. Roads and bridges can be raised as sea level rises, however, tunnels are relatively static constructions. Tunnels are used throughout Southside Virginia to ensure navigability of channels. If tunnel entrances cannot be raised, there is danger of flooding in the tunnels and a higher water table (due to sea-level rise) results in increased hydraulic pressure on the tunnel structure (Titus 2003). Sea-level rise is also predicted to increase coastal erosion, and in coastal Virginia, many roads are adjacent to waterways.
Port facilities and boat traffic are a key part of the economic activity in Virginia and navigation is important to coastal Virginia. Although sea-level rise will make channels deeper, allowing access to deeper draft vessels, it will also reduce clearance under bridges. Other transportation infrastructure at risk in Virginia includes airports and railroads. For example, Reagan National Airport (located in Arlington, VA) has runways immediately adjacent to tidal waters, which are at risk from storm surge flooding and from Potomac River flooding.
The strategies for recurrent flooding discussed fall into three broad categories of management/retreat, accommodation, and protection. The most common adaptive approach in coastal Virginia currently is accommodation, which includes raising buildings and roads, establishing evacuation routes and warning systems, and creating or enhancing stormwater systems.
For accommodation, the report discusses the option of raising roads above predicted flood levels. The study summarizes the pros of cons of raising roads, in which the cost and difficulty of the project depend entirely upon the type and setting of the road that needs to be raised. In rural areas, where drainage systems are typically ditches, raising the road may be as easy as adding an extra lift of pavement. In more developed areas, with smaller lots and interconnected storm sewer systems, elevating roads becomes costly and more complicated because adequate drainage from both the road and the adjacent properties has to be designed into the project.
Many localities in Virginia have considered some type of adaptation strategy to address flooding. Northern Neck and Middle Peninsula localities considered elevating road surfaces and raising structures as the primary adaptation strategies. These localities tend to have populations that are relatively spread out and roads with little associated infrastructure (e.g. stormwater drainage systems). The Regional Emergency Management Technical Advisory Committee localities of Hampton Roads considered a wide variety of adaptations, including (in order of popularity): raising structures, relocating people, elevating road surfaces and sea walls, and pumping stations/dams/levees.
The findings in this study are based on data and analyses from agencies at the local, state, and federal levels, as well as from non-governmental organizations and regional authorities such as the Chesapeake Bay Program. A comprehensive list of strategies used in other vulnerable areas around the U.S. and world, including New Orleans, the Netherlands, the United Kingdom, Japan, and other smaller Pacific islands was also reviewed. This report was called for by a joint resolution of Virginia’s House and Senate in 2012. The authors of the report from the Virginia Institute of Marine Science presented the 135 page document to legislators for consideration during the General Assembly’s 2013 session.
This Adaptation Clearinghouse entry was prepared with support from the Federal Highway Administration. This entry was last updated on February 3, 2015.
Publication Date: January 14, 2013
Authors or Affiliated Users:
- Molly Mitchell
- Carl Hershner
- Julie Herman
- Dan Schatt
- Pam Mason
- Emily Eggington
- Hampton Roads Planning District Commission
- Virginia Institute of Marine Science (VIMS)
- Policy analysis/recommendations